2 @c This is part of the GNU Emacs Lisp Reference Manual.
3 @c Copyright (C) 1990-1995, 1998-2015 Free Software Foundation, Inc.
4 @c See the file elisp.texi for copying conditions.
8 This chapter describes a number of features related to the display
9 that Emacs presents to the user.
12 * Refresh Screen:: Clearing the screen and redrawing everything on it.
13 * Forcing Redisplay:: Forcing redisplay.
14 * Truncation:: Folding or wrapping long text lines.
15 * The Echo Area:: Displaying messages at the bottom of the screen.
16 * Warnings:: Displaying warning messages for the user.
17 * Invisible Text:: Hiding part of the buffer text.
18 * Selective Display:: Hiding part of the buffer text (the old way).
19 * Temporary Displays:: Displays that go away automatically.
20 * Overlays:: Use overlays to highlight parts of the buffer.
21 * Size of Displayed Text:: How large displayed text is.
22 * Line Height:: Controlling the height of lines.
23 * Faces:: A face defines a graphics style for text characters:
25 * Fringes:: Controlling window fringes.
26 * Scroll Bars:: Controlling scroll bars.
27 * Window Dividers:: Separating windows visually.
28 * Display Property:: Enabling special display features.
29 * Images:: Displaying images in Emacs buffers.
30 * Buttons:: Adding clickable buttons to Emacs buffers.
31 * Abstract Display:: Emacs's Widget for Object Collections.
32 * Blinking:: How Emacs shows the matching open parenthesis.
33 * Character Display:: How Emacs displays individual characters.
34 * Beeping:: Audible signal to the user.
35 * Window Systems:: Which window system is being used.
36 * Bidirectional Display:: Display of bidirectional scripts, such as
41 @section Refreshing the Screen
42 @cindex refresh the screen
43 @cindex screen refresh
45 The function @code{redraw-frame} clears and redisplays the entire
46 contents of a given frame (@pxref{Frames}). This is useful if the
49 @defun redraw-frame frame
50 This function clears and redisplays frame @var{frame}.
53 Even more powerful is @code{redraw-display}:
55 @deffn Command redraw-display
56 This function clears and redisplays all visible frames.
59 In Emacs, processing user input takes priority over redisplay. If
60 you call these functions when input is available, they don't redisplay
61 immediately, but the requested redisplay does happen
62 eventually---after all the input has been processed.
64 On text terminals, suspending and resuming Emacs normally also
65 refreshes the screen. Some terminal emulators record separate
66 contents for display-oriented programs such as Emacs and for ordinary
67 sequential display. If you are using such a terminal, you might want
68 to inhibit the redisplay on resumption.
70 @defopt no-redraw-on-reenter
71 @cindex suspend (cf. @code{no-redraw-on-reenter})
72 @cindex resume (cf. @code{no-redraw-on-reenter})
73 This variable controls whether Emacs redraws the entire screen after it
74 has been suspended and resumed. Non-@code{nil} means there is no need
75 to redraw, @code{nil} means redrawing is needed. The default is @code{nil}.
78 @node Forcing Redisplay
79 @section Forcing Redisplay
80 @cindex forcing redisplay
82 Emacs normally tries to redisplay the screen whenever it waits for
83 input. With the following function, you can request an immediate
84 attempt to redisplay, in the middle of Lisp code, without actually
87 @defun redisplay &optional force
88 This function tries immediately to redisplay. The optional argument
89 @var{force}, if non-@code{nil}, forces the redisplay to be performed,
90 instead of being preempted, even if input is pending and the variable
91 @code{redisplay-dont-pause} is @code{nil} (see below). If
92 @code{redisplay-dont-pause} is non-@code{nil} (the default), this
93 function redisplays in any case, i.e., @var{force} does nothing.
95 The function returns @code{t} if it actually tried to redisplay, and
96 @code{nil} otherwise. A value of @code{t} does not mean that
97 redisplay proceeded to completion; it could have been preempted by
101 @defvar redisplay-dont-pause
102 If this variable is @code{nil}, arriving input events preempt
103 redisplay; Emacs avoids starting a redisplay, and stops any redisplay
104 that is in progress, until the input has been processed. In
105 particular, @code{(redisplay)} returns @code{nil} without actually
106 redisplaying, if there is pending input.
108 The default value is @code{t}, which means that pending input does not
112 @defvar redisplay-preemption-period
113 If @code{redisplay-dont-pause} is @code{nil}, this variable specifies
114 how many seconds Emacs waits between checks for new input during
115 redisplay; if input arrives during this interval, redisplay stops and
116 the input is processed. The default value is 0.1; if the value is
117 @code{nil}, Emacs does not check for input during redisplay.
119 This variable has no effect when @code{redisplay-dont-pause} is
120 non-@code{nil} (the default).
123 @defvar pre-redisplay-function
124 A function run just before redisplay. It is called with one argument,
125 the set of windows to redisplay.
128 Although @code{redisplay} tries immediately to redisplay, it does
129 not change how Emacs decides which parts of its frame(s) to redisplay.
130 By contrast, the following function adds certain windows to the
131 pending redisplay work (as if their contents had completely changed),
132 but does not immediately try to perform redisplay.
134 @defun force-window-update &optional object
135 This function forces some or all windows to be updated the next time
136 Emacs does a redisplay. If @var{object} is a window, that window is
137 to be updated. If @var{object} is a buffer or buffer name, all
138 windows displaying that buffer are to be updated. If @var{object} is
139 @code{nil} (or omitted), all windows are to be updated.
141 This function does not do a redisplay immediately; Emacs does that as
142 it waits for input, or when the function @code{redisplay} is called.
147 @cindex line wrapping
148 @cindex line truncation
149 @cindex continuation lines
150 @cindex @samp{$} in display
151 @cindex @samp{\} in display
153 When a line of text extends beyond the right edge of a window, Emacs
154 can @dfn{continue} the line (make it ``wrap'' to the next screen
155 line), or @dfn{truncate} the line (limit it to one screen line). The
156 additional screen lines used to display a long text line are called
157 @dfn{continuation} lines. Continuation is not the same as filling;
158 continuation happens on the screen only, not in the buffer contents,
159 and it breaks a line precisely at the right margin, not at a word
160 boundary. @xref{Filling}.
162 On a graphical display, tiny arrow images in the window fringes
163 indicate truncated and continued lines (@pxref{Fringes}). On a text
164 terminal, a @samp{$} in the rightmost column of the window indicates
165 truncation; a @samp{\} on the rightmost column indicates a line that
166 ``wraps''. (The display table can specify alternate characters to use
167 for this; @pxref{Display Tables}).
169 @defopt truncate-lines
170 If this buffer-local variable is non-@code{nil}, lines that extend
171 beyond the right edge of the window are truncated; otherwise, they are
172 continued. As a special exception, the variable
173 @code{truncate-partial-width-windows} takes precedence in
174 @dfn{partial-width} windows (i.e., windows that do not occupy the
178 @defopt truncate-partial-width-windows
179 @cindex partial-width windows
180 This variable controls line truncation in @dfn{partial-width} windows.
181 A partial-width window is one that does not occupy the entire frame
182 width (@pxref{Splitting Windows}). If the value is @code{nil}, line
183 truncation is determined by the variable @code{truncate-lines} (see
184 above). If the value is an integer @var{n}, lines are truncated if
185 the partial-width window has fewer than @var{n} columns, regardless of
186 the value of @code{truncate-lines}; if the partial-width window has
187 @var{n} or more columns, line truncation is determined by
188 @code{truncate-lines}. For any other non-@code{nil} value, lines are
189 truncated in every partial-width window, regardless of the value of
190 @code{truncate-lines}.
193 When horizontal scrolling (@pxref{Horizontal Scrolling}) is in use in
194 a window, that forces truncation.
197 If this buffer-local variable is non-@code{nil}, it defines a
198 @dfn{wrap prefix} which Emacs displays at the start of every
199 continuation line. (If lines are truncated, @code{wrap-prefix} is
200 never used.) Its value may be a string or an image (@pxref{Other
201 Display Specs}), or a stretch of whitespace such as specified by the
202 @code{:width} or @code{:align-to} display properties (@pxref{Specified
203 Space}). The value is interpreted in the same way as a @code{display}
204 text property. @xref{Display Property}.
206 A wrap prefix may also be specified for regions of text, using the
207 @code{wrap-prefix} text or overlay property. This takes precedence
208 over the @code{wrap-prefix} variable. @xref{Special Properties}.
212 If this buffer-local variable is non-@code{nil}, it defines a
213 @dfn{line prefix} which Emacs displays at the start of every
214 non-continuation line. Its value may be a string or an image
215 (@pxref{Other Display Specs}), or a stretch of whitespace such as
216 specified by the @code{:width} or @code{:align-to} display properties
217 (@pxref{Specified Space}). The value is interpreted in the same way
218 as a @code{display} text property. @xref{Display Property}.
220 A line prefix may also be specified for regions of text using the
221 @code{line-prefix} text or overlay property. This takes precedence
222 over the @code{line-prefix} variable. @xref{Special Properties}.
226 If your buffer contains only very short lines, you might find it
227 advisable to set @code{cache-long-scans} to @code{nil}.
229 @defvar cache-long-scans
230 If this variable is non-@code{nil} (the default), various indentation
231 and motion functions, and Emacs redisplay, cache the results of
232 scanning the buffer, and consult the cache to avoid rescanning regions
233 of the buffer unless they are modified.
235 Turning off the cache speeds up processing of short lines somewhat.
237 This variable is automatically buffer-local in every buffer.
242 @section The Echo Area
243 @cindex error display
246 @c FIXME: Why not use @xref{Minibuffers} directly? --xfq
247 The @dfn{echo area} is used for displaying error messages
248 (@pxref{Errors}), for messages made with the @code{message} primitive,
249 and for echoing keystrokes. It is not the same as the minibuffer,
250 despite the fact that the minibuffer appears (when active) in the same
251 place on the screen as the echo area. @xref{Minibuffer,, The
252 Minibuffer, emacs, The GNU Emacs Manual}.
254 Apart from the functions documented in this section, you can print
255 Lisp objects to the echo area by specifying @code{t} as the output
256 stream. @xref{Output Streams}.
259 * Displaying Messages:: Explicitly displaying text in the echo area.
260 * Progress:: Informing user about progress of a long operation.
261 * Logging Messages:: Echo area messages are logged for the user.
262 * Echo Area Customization:: Controlling the echo area.
265 @node Displaying Messages
266 @subsection Displaying Messages in the Echo Area
267 @cindex display message in echo area
269 This section describes the standard functions for displaying
270 messages in the echo area.
272 @defun message format-string &rest arguments
273 This function displays a message in the echo area.
274 @var{format-string} is a format string, and @var{arguments} are the
275 objects for its format specifications, like in the @code{format}
276 function (@pxref{Formatting Strings}). The resulting formatted string
277 is displayed in the echo area; if it contains @code{face} text
278 properties, it is displayed with the specified faces (@pxref{Faces}).
279 The string is also added to the @file{*Messages*} buffer, but without
280 text properties (@pxref{Logging Messages}).
282 In batch mode, the message is printed to the standard error stream,
283 followed by a newline.
285 If @var{format-string} is @code{nil} or the empty string,
286 @code{message} clears the echo area; if the echo area has been
287 expanded automatically, this brings it back to its normal size. If
288 the minibuffer is active, this brings the minibuffer contents back
289 onto the screen immediately.
293 (message "Minibuffer depth is %d."
295 @print{} Minibuffer depth is 0.
296 @result{} "Minibuffer depth is 0."
300 ---------- Echo Area ----------
301 Minibuffer depth is 0.
302 ---------- Echo Area ----------
306 To automatically display a message in the echo area or in a pop-buffer,
307 depending on its size, use @code{display-message-or-buffer} (see below).
310 @defmac with-temp-message message &rest body
311 This construct displays a message in the echo area temporarily, during
312 the execution of @var{body}. It displays @var{message}, executes
313 @var{body}, then returns the value of the last body form while restoring
314 the previous echo area contents.
317 @defun message-or-box format-string &rest arguments
318 This function displays a message like @code{message}, but may display it
319 in a dialog box instead of the echo area. If this function is called in
320 a command that was invoked using the mouse---more precisely, if
321 @code{last-nonmenu-event} (@pxref{Command Loop Info}) is either
322 @code{nil} or a list---then it uses a dialog box or pop-up menu to
323 display the message. Otherwise, it uses the echo area. (This is the
324 same criterion that @code{y-or-n-p} uses to make a similar decision; see
325 @ref{Yes-or-No Queries}.)
327 You can force use of the mouse or of the echo area by binding
328 @code{last-nonmenu-event} to a suitable value around the call.
331 @defun message-box format-string &rest arguments
333 This function displays a message like @code{message}, but uses a dialog
334 box (or a pop-up menu) whenever that is possible. If it is impossible
335 to use a dialog box or pop-up menu, because the terminal does not
336 support them, then @code{message-box} uses the echo area, like
340 @defun display-message-or-buffer message &optional buffer-name not-this-window frame
341 This function displays the message @var{message}, which may be either a
342 string or a buffer. If it is shorter than the maximum height of the
343 echo area, as defined by @code{max-mini-window-height}, it is displayed
344 in the echo area, using @code{message}. Otherwise,
345 @code{display-buffer} is used to show it in a pop-up buffer.
347 Returns either the string shown in the echo area, or when a pop-up
348 buffer is used, the window used to display it.
350 If @var{message} is a string, then the optional argument
351 @var{buffer-name} is the name of the buffer used to display it when a
352 pop-up buffer is used, defaulting to @file{*Message*}. In the case
353 where @var{message} is a string and displayed in the echo area, it is
354 not specified whether the contents are inserted into the buffer anyway.
356 The optional arguments @var{not-this-window} and @var{frame} are as for
357 @code{display-buffer}, and only used if a buffer is displayed.
360 @defun current-message
361 This function returns the message currently being displayed in the
362 echo area, or @code{nil} if there is none.
366 @subsection Reporting Operation Progress
367 @cindex progress reporting
369 When an operation can take a while to finish, you should inform the
370 user about the progress it makes. This way the user can estimate
371 remaining time and clearly see that Emacs is busy working, not hung.
372 A convenient way to do this is to use a @dfn{progress reporter}.
374 Here is a working example that does nothing useful:
377 (let ((progress-reporter
378 (make-progress-reporter "Collecting mana for Emacs..."
382 (progress-reporter-update progress-reporter k))
383 (progress-reporter-done progress-reporter))
386 @defun make-progress-reporter message &optional min-value max-value current-value min-change min-time
387 This function creates and returns a progress reporter object, which
388 you will use as an argument for the other functions listed below. The
389 idea is to precompute as much data as possible to make progress
392 When this progress reporter is subsequently used, it will display
393 @var{message} in the echo area, followed by progress percentage.
394 @var{message} is treated as a simple string. If you need it to depend
395 on a filename, for instance, use @code{format} before calling this
398 The arguments @var{min-value} and @var{max-value} should be numbers
399 standing for the starting and final states of the operation. For
400 instance, an operation that ``scans'' a buffer should set these to the
401 results of @code{point-min} and @code{point-max} correspondingly.
402 @var{max-value} should be greater than @var{min-value}.
404 Alternatively, you can set @var{min-value} and @var{max-value} to
405 @code{nil}. In that case, the progress reporter does not report
406 process percentages; it instead displays a ``spinner'' that rotates a
407 notch each time you update the progress reporter.
409 If @var{min-value} and @var{max-value} are numbers, you can give the
410 argument @var{current-value} a numerical value specifying the initial
411 progress; if omitted, this defaults to @var{min-value}.
413 The remaining arguments control the rate of echo area updates. The
414 progress reporter will wait for at least @var{min-change} more
415 percents of the operation to be completed before printing next
416 message; the default is one percent. @var{min-time} specifies the
417 minimum time in seconds to pass between successive prints; the default
418 is 0.2 seconds. (On some operating systems, the progress reporter may
419 handle fractions of seconds with varying precision).
421 This function calls @code{progress-reporter-update}, so the first
422 message is printed immediately.
425 @defun progress-reporter-update reporter &optional value
426 This function does the main work of reporting progress of your
427 operation. It displays the message of @var{reporter}, followed by
428 progress percentage determined by @var{value}. If percentage is zero,
429 or close enough according to the @var{min-change} and @var{min-time}
430 arguments, then it is omitted from the output.
432 @var{reporter} must be the result of a call to
433 @code{make-progress-reporter}. @var{value} specifies the current
434 state of your operation and must be between @var{min-value} and
435 @var{max-value} (inclusive) as passed to
436 @code{make-progress-reporter}. For instance, if you scan a buffer,
437 then @var{value} should be the result of a call to @code{point}.
439 This function respects @var{min-change} and @var{min-time} as passed
440 to @code{make-progress-reporter} and so does not output new messages
441 on every invocation. It is thus very fast and normally you should not
442 try to reduce the number of calls to it: resulting overhead will most
443 likely negate your effort.
446 @defun progress-reporter-force-update reporter &optional value new-message
447 This function is similar to @code{progress-reporter-update} except
448 that it prints a message in the echo area unconditionally.
450 The first two arguments have the same meaning as for
451 @code{progress-reporter-update}. Optional @var{new-message} allows
452 you to change the message of the @var{reporter}. Since this function
453 always updates the echo area, such a change will be immediately
454 presented to the user.
457 @defun progress-reporter-done reporter
458 This function should be called when the operation is finished. It
459 prints the message of @var{reporter} followed by word ``done'' in the
462 You should always call this function and not hope for
463 @code{progress-reporter-update} to print ``100%''. Firstly, it may
464 never print it, there are many good reasons for this not to happen.
465 Secondly, ``done'' is more explicit.
468 @defmac dotimes-with-progress-reporter (var count [result]) message body@dots{}
469 This is a convenience macro that works the same way as @code{dotimes}
470 does, but also reports loop progress using the functions described
471 above. It allows you to save some typing.
473 You can rewrite the example in the beginning of this node using
477 (dotimes-with-progress-reporter
479 "Collecting some mana for Emacs..."
484 @node Logging Messages
485 @subsection Logging Messages in @file{*Messages*}
486 @cindex logging echo-area messages
488 Almost all the messages displayed in the echo area are also recorded
489 in the @file{*Messages*} buffer so that the user can refer back to
490 them. This includes all the messages that are output with
491 @code{message}. By default, this buffer is read-only and uses the major
492 mode @code{messages-buffer-mode}. Nothing prevents the user from
493 killing the @file{*Messages*} buffer, but the next display of a message
494 recreates it. Any Lisp code that needs to access the
495 @file{*Messages*} buffer directly and wants to ensure that it exists
496 should use the function @code{messages-buffer}.
498 @defun messages-buffer
499 This function returns the @file{*Messages*} buffer. If it does not
500 exist, it creates it, and switches it to @code{messages-buffer-mode}.
503 @defopt message-log-max
504 This variable specifies how many lines to keep in the @file{*Messages*}
505 buffer. The value @code{t} means there is no limit on how many lines to
506 keep. The value @code{nil} disables message logging entirely. Here's
507 how to display a message and prevent it from being logged:
510 (let (message-log-max)
515 To make @file{*Messages*} more convenient for the user, the logging
516 facility combines successive identical messages. It also combines
517 successive related messages for the sake of two cases: question
518 followed by answer, and a series of progress messages.
520 A ``question followed by an answer'' means two messages like the
521 ones produced by @code{y-or-n-p}: the first is @samp{@var{question}},
522 and the second is @samp{@var{question}...@var{answer}}. The first
523 message conveys no additional information beyond what's in the second,
524 so logging the second message discards the first from the log.
526 A ``series of progress messages'' means successive messages like
527 those produced by @code{make-progress-reporter}. They have the form
528 @samp{@var{base}...@var{how-far}}, where @var{base} is the same each
529 time, while @var{how-far} varies. Logging each message in the series
530 discards the previous one, provided they are consecutive.
532 The functions @code{make-progress-reporter} and @code{y-or-n-p}
533 don't have to do anything special to activate the message log
534 combination feature. It operates whenever two consecutive messages
535 are logged that share a common prefix ending in @samp{...}.
537 @node Echo Area Customization
538 @subsection Echo Area Customization
539 @cindex echo area customization
541 These variables control details of how the echo area works.
543 @defvar cursor-in-echo-area
544 This variable controls where the cursor appears when a message is
545 displayed in the echo area. If it is non-@code{nil}, then the cursor
546 appears at the end of the message. Otherwise, the cursor appears at
547 point---not in the echo area at all.
549 The value is normally @code{nil}; Lisp programs bind it to @code{t}
550 for brief periods of time.
553 @defvar echo-area-clear-hook
554 This normal hook is run whenever the echo area is cleared---either by
555 @code{(message nil)} or for any other reason.
558 @defopt echo-keystrokes
559 This variable determines how much time should elapse before command
560 characters echo. Its value must be a number, and specifies the
561 number of seconds to wait before echoing. If the user types a prefix
562 key (such as @kbd{C-x}) and then delays this many seconds before
563 continuing, the prefix key is echoed in the echo area. (Once echoing
564 begins in a key sequence, all subsequent characters in the same key
565 sequence are echoed immediately.)
567 If the value is zero, then command input is not echoed.
570 @defvar message-truncate-lines
571 Normally, displaying a long message resizes the echo area to display
572 the entire message. But if the variable @code{message-truncate-lines}
573 is non-@code{nil}, the echo area does not resize, and the message is
577 The variable @code{max-mini-window-height}, which specifies the
578 maximum height for resizing minibuffer windows, also applies to the
579 echo area (which is really a special use of the minibuffer window;
580 @pxref{Minibuffer Misc}).
583 @section Reporting Warnings
586 @dfn{Warnings} are a facility for a program to inform the user of a
587 possible problem, but continue running.
590 * Warning Basics:: Warnings concepts and functions to report them.
591 * Warning Variables:: Variables programs bind to customize their warnings.
592 * Warning Options:: Variables users set to control display of warnings.
593 * Delayed Warnings:: Deferring a warning until the end of a command.
597 @subsection Warning Basics
598 @cindex severity level
600 Every warning has a textual message, which explains the problem for
601 the user, and a @dfn{severity level} which is a symbol. Here are the
602 possible severity levels, in order of decreasing severity, and their
607 A problem that will seriously impair Emacs operation soon
608 if you do not attend to it promptly.
610 A report of data or circumstances that are inherently wrong.
612 A report of data or circumstances that are not inherently wrong, but
613 raise suspicion of a possible problem.
615 A report of information that may be useful if you are debugging.
618 When your program encounters invalid input data, it can either
619 signal a Lisp error by calling @code{error} or @code{signal} or report
620 a warning with severity @code{:error}. Signaling a Lisp error is the
621 easiest thing to do, but it means the program cannot continue
622 processing. If you want to take the trouble to implement a way to
623 continue processing despite the bad data, then reporting a warning of
624 severity @code{:error} is the right way to inform the user of the
625 problem. For instance, the Emacs Lisp byte compiler can report an
626 error that way and continue compiling other functions. (If the
627 program signals a Lisp error and then handles it with
628 @code{condition-case}, the user won't see the error message; it could
629 show the message to the user by reporting it as a warning.)
631 @c FIXME: Why use "(bytecomp)" instead of "'bytecomp" or simply
632 @c "bytecomp" here? The parens are part of warning-type-format but
633 @c not part of the warning type. --xfq
635 Each warning has a @dfn{warning type} to classify it. The type is a
636 list of symbols. The first symbol should be the custom group that you
637 use for the program's user options. For example, byte compiler
638 warnings use the warning type @code{(bytecomp)}. You can also
639 subcategorize the warnings, if you wish, by using more symbols in the
642 @defun display-warning type message &optional level buffer-name
643 This function reports a warning, using @var{message} as the message
644 and @var{type} as the warning type. @var{level} should be the
645 severity level, with @code{:warning} being the default.
647 @var{buffer-name}, if non-@code{nil}, specifies the name of the buffer
648 for logging the warning. By default, it is @file{*Warnings*}.
651 @defun lwarn type level message &rest args
652 This function reports a warning using the value of @code{(format
653 @var{message} @var{args}...)} as the message in the @file{*Warnings*}
654 buffer. In other respects it is equivalent to @code{display-warning}.
657 @defun warn message &rest args
658 This function reports a warning using the value of @code{(format
659 @var{message} @var{args}...)} as the message, @code{(emacs)} as the
660 type, and @code{:warning} as the severity level. It exists for
661 compatibility only; we recommend not using it, because you should
662 specify a specific warning type.
665 @node Warning Variables
666 @subsection Warning Variables
667 @cindex warning variables
669 Programs can customize how their warnings appear by binding
670 the variables described in this section.
672 @defvar warning-levels
673 This list defines the meaning and severity order of the warning
674 severity levels. Each element defines one severity level,
675 and they are arranged in order of decreasing severity.
677 Each element has the form @code{(@var{level} @var{string}
678 @var{function})}, where @var{level} is the severity level it defines.
679 @var{string} specifies the textual description of this level.
680 @var{string} should use @samp{%s} to specify where to put the warning
681 type information, or it can omit the @samp{%s} so as not to include
684 The optional @var{function}, if non-@code{nil}, is a function to call
685 with no arguments, to get the user's attention.
687 Normally you should not change the value of this variable.
690 @defvar warning-prefix-function
691 If non-@code{nil}, the value is a function to generate prefix text for
692 warnings. Programs can bind the variable to a suitable function.
693 @code{display-warning} calls this function with the warnings buffer
694 current, and the function can insert text in it. That text becomes
695 the beginning of the warning message.
697 The function is called with two arguments, the severity level and its
698 entry in @code{warning-levels}. It should return a list to use as the
699 entry (this value need not be an actual member of
700 @code{warning-levels}). By constructing this value, the function can
701 change the severity of the warning, or specify different handling for
702 a given severity level.
704 If the variable's value is @code{nil} then there is no function
708 @defvar warning-series
709 Programs can bind this variable to @code{t} to say that the next
710 warning should begin a series. When several warnings form a series,
711 that means to leave point on the first warning of the series, rather
712 than keep moving it for each warning so that it appears on the last one.
713 The series ends when the local binding is unbound and
714 @code{warning-series} becomes @code{nil} again.
716 The value can also be a symbol with a function definition. That is
717 equivalent to @code{t}, except that the next warning will also call
718 the function with no arguments with the warnings buffer current. The
719 function can insert text which will serve as a header for the series
722 Once a series has begun, the value is a marker which points to the
723 buffer position in the warnings buffer of the start of the series.
725 The variable's normal value is @code{nil}, which means to handle
726 each warning separately.
729 @defvar warning-fill-prefix
730 When this variable is non-@code{nil}, it specifies a fill prefix to
731 use for filling each warning's text.
734 @defvar warning-type-format
735 This variable specifies the format for displaying the warning type
736 in the warning message. The result of formatting the type this way
737 gets included in the message under the control of the string in the
738 entry in @code{warning-levels}. The default value is @code{" (%s)"}.
739 If you bind it to @code{""} then the warning type won't appear at
743 @node Warning Options
744 @subsection Warning Options
745 @cindex warning options
747 These variables are used by users to control what happens
748 when a Lisp program reports a warning.
750 @defopt warning-minimum-level
751 This user option specifies the minimum severity level that should be
752 shown immediately to the user. The default is @code{:warning}, which
753 means to immediately display all warnings except @code{:debug}
757 @defopt warning-minimum-log-level
758 This user option specifies the minimum severity level that should be
759 logged in the warnings buffer. The default is @code{:warning}, which
760 means to log all warnings except @code{:debug} warnings.
763 @defopt warning-suppress-types
764 This list specifies which warning types should not be displayed
765 immediately for the user. Each element of the list should be a list
766 of symbols. If its elements match the first elements in a warning
767 type, then that warning is not displayed immediately.
770 @defopt warning-suppress-log-types
771 This list specifies which warning types should not be logged in the
772 warnings buffer. Each element of the list should be a list of
773 symbols. If it matches the first few elements in a warning type, then
774 that warning is not logged.
777 @node Delayed Warnings
778 @subsection Delayed Warnings
779 @cindex delayed warnings
781 Sometimes, you may wish to avoid showing a warning while a command is
782 running, and only show it only after the end of the command. You can
783 use the variable @code{delayed-warnings-list} for this.
785 @defvar delayed-warnings-list
786 The value of this variable is a list of warnings to be displayed after
787 the current command has finished. Each element must be a list
790 (@var{type} @var{message} [@var{level} [@var{buffer-name}]])
794 with the same form, and the same meanings, as the argument list of
795 @code{display-warning} (@pxref{Warning Basics}). Immediately after
796 running @code{post-command-hook} (@pxref{Command Overview}), the Emacs
797 command loop displays all the warnings specified by this variable,
798 then resets it to @code{nil}.
801 Programs which need to further customize the delayed warnings
802 mechanism can change the variable @code{delayed-warnings-hook}:
804 @defvar delayed-warnings-hook
805 This is a normal hook which is run by the Emacs command loop, after
806 @code{post-command-hook}, in order to to process and display delayed
809 Its default value is a list of two functions:
812 (collapse-delayed-warnings display-delayed-warnings)
815 @findex collapse-delayed-warnings
816 @findex display-delayed-warnings
818 The function @code{collapse-delayed-warnings} removes repeated entries
819 from @code{delayed-warnings-list}. The function
820 @code{display-delayed-warnings} calls @code{display-warning} on each
821 of the entries in @code{delayed-warnings-list}, in turn, and then sets
822 @code{delayed-warnings-list} to @code{nil}.
826 @section Invisible Text
828 @cindex invisible text
829 You can make characters @dfn{invisible}, so that they do not appear on
830 the screen, with the @code{invisible} property. This can be either a
831 text property (@pxref{Text Properties}) or an overlay property
832 (@pxref{Overlays}). Cursor motion also partly ignores these
833 characters; if the command loop finds that point is inside a range of
834 invisible text after a command, it relocates point to the other side
837 In the simplest case, any non-@code{nil} @code{invisible} property makes
838 a character invisible. This is the default case---if you don't alter
839 the default value of @code{buffer-invisibility-spec}, this is how the
840 @code{invisible} property works. You should normally use @code{t}
841 as the value of the @code{invisible} property if you don't plan
842 to set @code{buffer-invisibility-spec} yourself.
844 More generally, you can use the variable @code{buffer-invisibility-spec}
845 to control which values of the @code{invisible} property make text
846 invisible. This permits you to classify the text into different subsets
847 in advance, by giving them different @code{invisible} values, and
848 subsequently make various subsets visible or invisible by changing the
849 value of @code{buffer-invisibility-spec}.
851 Controlling visibility with @code{buffer-invisibility-spec} is
852 especially useful in a program to display the list of entries in a
853 database. It permits the implementation of convenient filtering
854 commands to view just a part of the entries in the database. Setting
855 this variable is very fast, much faster than scanning all the text in
856 the buffer looking for properties to change.
858 @defvar buffer-invisibility-spec
859 This variable specifies which kinds of @code{invisible} properties
860 actually make a character invisible. Setting this variable makes it
865 A character is invisible if its @code{invisible} property is
866 non-@code{nil}. This is the default.
869 Each element of the list specifies a criterion for invisibility; if a
870 character's @code{invisible} property fits any one of these criteria,
871 the character is invisible. The list can have two kinds of elements:
875 A character is invisible if its @code{invisible} property value is
876 @var{atom} or if it is a list with @var{atom} as a member; comparison
877 is done with @code{eq}.
879 @item (@var{atom} . t)
880 A character is invisible if its @code{invisible} property value is
881 @var{atom} or if it is a list with @var{atom} as a member; comparison
882 is done with @code{eq}. Moreover, a sequence of such characters
883 displays as an ellipsis.
888 Two functions are specifically provided for adding elements to
889 @code{buffer-invisibility-spec} and removing elements from it.
891 @defun add-to-invisibility-spec element
892 This function adds the element @var{element} to
893 @code{buffer-invisibility-spec}. If @code{buffer-invisibility-spec}
894 was @code{t}, it changes to a list, @code{(t)}, so that text whose
895 @code{invisible} property is @code{t} remains invisible.
898 @defun remove-from-invisibility-spec element
899 This removes the element @var{element} from
900 @code{buffer-invisibility-spec}. This does nothing if @var{element}
904 A convention for use of @code{buffer-invisibility-spec} is that a
905 major mode should use the mode's own name as an element of
906 @code{buffer-invisibility-spec} and as the value of the
907 @code{invisible} property:
910 ;; @r{If you want to display an ellipsis:}
911 (add-to-invisibility-spec '(my-symbol . t))
912 ;; @r{If you don't want ellipsis:}
913 (add-to-invisibility-spec 'my-symbol)
915 (overlay-put (make-overlay beginning end)
916 'invisible 'my-symbol)
918 ;; @r{When done with the invisibility:}
919 (remove-from-invisibility-spec '(my-symbol . t))
920 ;; @r{Or respectively:}
921 (remove-from-invisibility-spec 'my-symbol)
924 You can check for invisibility using the following function:
926 @defun invisible-p pos-or-prop
927 If @var{pos-or-prop} is a marker or number, this function returns a
928 non-@code{nil} value if the text at that position is invisible.
930 If @var{pos-or-prop} is any other kind of Lisp object, that is taken
931 to mean a possible value of the @code{invisible} text or overlay
932 property. In that case, this function returns a non-@code{nil} value
933 if that value would cause text to become invisible, based on the
934 current value of @code{buffer-invisibility-spec}.
937 @vindex line-move-ignore-invisible
938 Ordinarily, functions that operate on text or move point do not care
939 whether the text is invisible, they process invisible characters and
940 visible characters alike. The user-level line motion commands,
941 such as @code{next-line}, @code{previous-line}, ignore invisible
942 newlines if @code{line-move-ignore-invisible} is non-@code{nil} (the
943 default), i.e., behave like these invisible newlines didn't exist in
944 the buffer, but only because they are explicitly programmed to do so.
946 If a command ends with point inside or at the boundary of
947 invisible text, the main editing loop relocates point to one of the
948 two ends of the invisible text. Emacs chooses the direction of
949 relocation so that it is the same as the overall movement direction of
950 the command; if in doubt, it prefers a position where an inserted char
951 would not inherit the @code{invisible} property. Additionally, if the
952 text is not replaced by an ellipsis and the command only moved within
953 the invisible text, then point is moved one extra character so as to
954 try and reflect the command's movement by a visible movement of the
957 Thus, if the command moved point back to an invisible range (with the usual
958 stickiness), Emacs moves point back to the beginning of that range. If the
959 command moved point forward into an invisible range, Emacs moves point forward
960 to the first visible character that follows the invisible text and then forward
963 These @dfn{adjustments} of point that ended up in the middle of
964 invisible text can be disabled by setting @code{disable-point-adjustment}
965 to a non-@code{nil} value. @xref{Adjusting Point}.
967 Incremental search can make invisible overlays visible temporarily
968 and/or permanently when a match includes invisible text. To enable
969 this, the overlay should have a non-@code{nil}
970 @code{isearch-open-invisible} property. The property value should be a
971 function to be called with the overlay as an argument. This function
972 should make the overlay visible permanently; it is used when the match
973 overlaps the overlay on exit from the search.
975 During the search, such overlays are made temporarily visible by
976 temporarily modifying their invisible and intangible properties. If you
977 want this to be done differently for a certain overlay, give it an
978 @code{isearch-open-invisible-temporary} property which is a function.
979 The function is called with two arguments: the first is the overlay, and
980 the second is @code{nil} to make the overlay visible, or @code{t} to
981 make it invisible again.
983 @node Selective Display
984 @section Selective Display
985 @c @cindex selective display Duplicates selective-display
987 @dfn{Selective display} refers to a pair of related features for
988 hiding certain lines on the screen.
990 @cindex explicit selective display
991 The first variant, explicit selective display, was designed for use in a Lisp
992 program: it controls which lines are hidden by altering the text. This kind of
993 hiding is now obsolete; instead you can get the same effect with the
994 @code{invisible} property (@pxref{Invisible Text}).
996 In the second variant, the choice of lines to hide is made
997 automatically based on indentation. This variant is designed to be a
1000 The way you control explicit selective display is by replacing a
1001 newline (control-j) with a carriage return (control-m). The text that
1002 was formerly a line following that newline is now hidden. Strictly
1003 speaking, it is temporarily no longer a line at all, since only
1004 newlines can separate lines; it is now part of the previous line.
1006 Selective display does not directly affect editing commands. For
1007 example, @kbd{C-f} (@code{forward-char}) moves point unhesitatingly
1008 into hidden text. However, the replacement of newline characters with
1009 carriage return characters affects some editing commands. For
1010 example, @code{next-line} skips hidden lines, since it searches only
1011 for newlines. Modes that use selective display can also define
1012 commands that take account of the newlines, or that control which
1013 parts of the text are hidden.
1015 When you write a selectively displayed buffer into a file, all the
1016 control-m's are output as newlines. This means that when you next read
1017 in the file, it looks OK, with nothing hidden. The selective display
1018 effect is seen only within Emacs.
1020 @defvar selective-display
1021 This buffer-local variable enables selective display. This means that
1022 lines, or portions of lines, may be made hidden.
1026 If the value of @code{selective-display} is @code{t}, then the character
1027 control-m marks the start of hidden text; the control-m, and the rest
1028 of the line following it, are not displayed. This is explicit selective
1032 If the value of @code{selective-display} is a positive integer, then
1033 lines that start with more than that many columns of indentation are not
1037 When some portion of a buffer is hidden, the vertical movement
1038 commands operate as if that portion did not exist, allowing a single
1039 @code{next-line} command to skip any number of hidden lines.
1040 However, character movement commands (such as @code{forward-char}) do
1041 not skip the hidden portion, and it is possible (if tricky) to insert
1042 or delete text in an hidden portion.
1044 In the examples below, we show the @emph{display appearance} of the
1045 buffer @code{foo}, which changes with the value of
1046 @code{selective-display}. The @emph{contents} of the buffer do not
1051 (setq selective-display nil)
1054 ---------- Buffer: foo ----------
1061 ---------- Buffer: foo ----------
1065 (setq selective-display 2)
1068 ---------- Buffer: foo ----------
1073 ---------- Buffer: foo ----------
1078 @defopt selective-display-ellipses
1079 If this buffer-local variable is non-@code{nil}, then Emacs displays
1080 @samp{@dots{}} at the end of a line that is followed by hidden text.
1081 This example is a continuation of the previous one.
1085 (setq selective-display-ellipses t)
1088 ---------- Buffer: foo ----------
1093 ---------- Buffer: foo ----------
1097 You can use a display table to substitute other text for the ellipsis
1098 (@samp{@dots{}}). @xref{Display Tables}.
1101 @node Temporary Displays
1102 @section Temporary Displays
1103 @cindex temporary display
1104 @cindex temporary buffer display
1106 Temporary displays are used by Lisp programs to put output into a
1107 buffer and then present it to the user for perusal rather than for
1108 editing. Many help commands use this feature.
1110 @defmac with-output-to-temp-buffer buffer-name body@dots{}
1111 This function executes the forms in @var{body} while arranging to insert
1112 any output they print into the buffer named @var{buffer-name}, which is
1113 first created if necessary, and put into Help mode. (See the similar
1114 form @code{with-temp-buffer-window} below.) Finally, the buffer is
1115 displayed in some window, but that window is not selected.
1117 If the forms in @var{body} do not change the major mode in the output
1118 buffer, so that it is still Help mode at the end of their execution,
1119 then @code{with-output-to-temp-buffer} makes this buffer read-only at
1120 the end, and also scans it for function and variable names to make them
1121 into clickable cross-references. @xref{Docstring hyperlinks, , Tips for
1122 Documentation Strings}, in particular the item on hyperlinks in
1123 documentation strings, for more details.
1125 The string @var{buffer-name} specifies the temporary buffer, which need
1126 not already exist. The argument must be a string, not a buffer. The
1127 buffer is erased initially (with no questions asked), and it is marked
1128 as unmodified after @code{with-output-to-temp-buffer} exits.
1130 @code{with-output-to-temp-buffer} binds @code{standard-output} to the
1131 temporary buffer, then it evaluates the forms in @var{body}. Output
1132 using the Lisp output functions within @var{body} goes by default to
1133 that buffer (but screen display and messages in the echo area, although
1134 they are ``output'' in the general sense of the word, are not affected).
1135 @xref{Output Functions}.
1137 Several hooks are available for customizing the behavior
1138 of this construct; they are listed below.
1140 The value of the last form in @var{body} is returned.
1144 ---------- Buffer: foo ----------
1145 This is the contents of foo.
1146 ---------- Buffer: foo ----------
1150 (with-output-to-temp-buffer "foo"
1152 (print standard-output))
1153 @result{} #<buffer foo>
1155 ---------- Buffer: foo ----------
1161 ---------- Buffer: foo ----------
1166 @defopt temp-buffer-show-function
1167 If this variable is non-@code{nil}, @code{with-output-to-temp-buffer}
1168 calls it as a function to do the job of displaying a help buffer. The
1169 function gets one argument, which is the buffer it should display.
1171 It is a good idea for this function to run @code{temp-buffer-show-hook}
1172 just as @code{with-output-to-temp-buffer} normally would, inside of
1173 @code{save-selected-window} and with the chosen window and buffer
1177 @defvar temp-buffer-setup-hook
1178 This normal hook is run by @code{with-output-to-temp-buffer} before
1179 evaluating @var{body}. When the hook runs, the temporary buffer is
1180 current. This hook is normally set up with a function to put the
1181 buffer in Help mode.
1184 @defvar temp-buffer-show-hook
1185 This normal hook is run by @code{with-output-to-temp-buffer} after
1186 displaying the temporary buffer. When the hook runs, the temporary buffer
1187 is current, and the window it was displayed in is selected.
1190 @defmac with-temp-buffer-window buffer-or-name action quit-function body@dots{}
1191 This macro is similar to @code{with-output-to-temp-buffer}. Like that
1192 construct, it executes @var{body} while arranging to insert any output
1193 it prints into the buffer named @var{buffer-or-name} and displays that
1194 buffer in some window. Unlike @code{with-output-to-temp-buffer},
1195 however, it does not automatically switch that buffer to Help mode.
1197 The argument @var{buffer-or-name} specifies the temporary buffer. It
1198 can be either a buffer, which must already exist, or a string, in which
1199 case a buffer of that name is created, if necessary. The buffer is
1200 marked as unmodified and read-only when @code{with-temp-buffer-window}
1203 This macro does not call @code{temp-buffer-show-function}. Rather, it
1204 passes the @var{action} argument to @code{display-buffer}
1205 (@pxref{Choosing Window}) in order to display the buffer.
1207 The value of the last form in @var{body} is returned, unless the
1208 argument @var{quit-function} is specified. In that case, it is called
1209 with two arguments: the window showing the buffer and the result of
1210 @var{body}. The final return value is then whatever @var{quit-function}
1213 @vindex temp-buffer-window-setup-hook
1214 @vindex temp-buffer-window-show-hook
1215 This macro uses the normal hooks @code{temp-buffer-window-setup-hook}
1216 and @code{temp-buffer-window-show-hook} in place of the analogous hooks
1217 run by @code{with-output-to-temp-buffer}.
1220 The two constructs described next are mostly identical to
1221 @code{with-temp-buffer-window} but differ from it as specified:
1223 @defmac with-current-buffer-window buffer-or-name action quit-function &rest body
1224 This macro is like @code{with-temp-buffer-window} but unlike that makes
1225 the buffer specified by @var{buffer-or-name} current for running
1229 @defmac with-displayed-buffer-window buffer-or-name action quit-function &rest body
1230 This macro is like @code{with-current-buffer-window} but unlike that
1231 displays the buffer specified by @var{buffer-or-name} @emph{before}
1235 A window showing a temporary buffer can be fit to the size of that
1236 buffer using the following mode:
1238 @defopt temp-buffer-resize-mode
1239 When this minor mode is enabled, windows showing a temporary buffer are
1240 automatically resized to fit their buffer's contents.
1242 A window is resized if and only if it has been specially created for the
1243 buffer. In particular, windows that have shown another buffer before
1244 are not resized. By default, this mode uses @code{fit-window-to-buffer}
1245 (@pxref{Resizing Windows}) for resizing. You can specify a different
1246 function by customizing the options @code{temp-buffer-max-height} and
1247 @code{temp-buffer-max-width} below.
1250 @defopt temp-buffer-max-height
1251 This option specifies the maximum height (in lines) of a window
1252 displaying a temporary buffer when @code{temp-buffer-resize-mode} is
1253 enabled. It can also be a function to be called to choose the height
1254 for such a buffer. It gets one argument, the buffer, and should return
1255 a positive integer. At the time the function is called, the window to
1256 be resized is selected.
1259 @defopt temp-buffer-max-width
1260 This option specifies the maximum width of a window (in columns)
1261 displaying a temporary buffer when @code{temp-buffer-resize-mode} is
1262 enabled. It can also be a function to be called to choose the width for
1263 such a buffer. It gets one argument, the buffer, and should return a
1264 positive integer. At the time the function is called, the window to be
1265 resized is selected.
1268 The following function uses the current buffer for temporal display:
1270 @defun momentary-string-display string position &optional char message
1271 This function momentarily displays @var{string} in the current buffer at
1272 @var{position}. It has no effect on the undo list or on the buffer's
1273 modification status.
1275 The momentary display remains until the next input event. If the next
1276 input event is @var{char}, @code{momentary-string-display} ignores it
1277 and returns. Otherwise, that event remains buffered for subsequent use
1278 as input. Thus, typing @var{char} will simply remove the string from
1279 the display, while typing (say) @kbd{C-f} will remove the string from
1280 the display and later (presumably) move point forward. The argument
1281 @var{char} is a space by default.
1283 The return value of @code{momentary-string-display} is not meaningful.
1285 If the string @var{string} does not contain control characters, you can
1286 do the same job in a more general way by creating (and then subsequently
1287 deleting) an overlay with a @code{before-string} property.
1288 @xref{Overlay Properties}.
1290 If @var{message} is non-@code{nil}, it is displayed in the echo area
1291 while @var{string} is displayed in the buffer. If it is @code{nil}, a
1292 default message says to type @var{char} to continue.
1294 In this example, point is initially located at the beginning of the
1299 ---------- Buffer: foo ----------
1300 This is the contents of foo.
1301 @point{}Second line.
1302 ---------- Buffer: foo ----------
1306 (momentary-string-display
1307 "**** Important Message! ****"
1309 "Type RET when done reading")
1314 ---------- Buffer: foo ----------
1315 This is the contents of foo.
1316 **** Important Message! ****Second line.
1317 ---------- Buffer: foo ----------
1319 ---------- Echo Area ----------
1320 Type RET when done reading
1321 ---------- Echo Area ----------
1329 @c FIXME: mention intervals in this section?
1331 You can use @dfn{overlays} to alter the appearance of a buffer's text on
1332 the screen, for the sake of presentation features. An overlay is an
1333 object that belongs to a particular buffer, and has a specified
1334 beginning and end. It also has properties that you can examine and set;
1335 these affect the display of the text within the overlay.
1337 @cindex scalability of overlays
1338 The visual effect of an overlay is the same as of the corresponding
1339 text property (@pxref{Text Properties}). However, due to a different
1340 implementation, overlays generally don't scale well (many operations
1341 take a time that is proportional to the number of overlays in the
1342 buffer). If you need to affect the visual appearance of many portions
1343 in the buffer, we recommend using text properties.
1345 An overlay uses markers to record its beginning and end; thus,
1346 editing the text of the buffer adjusts the beginning and end of each
1347 overlay so that it stays with the text. When you create the overlay,
1348 you can specify whether text inserted at the beginning should be
1349 inside the overlay or outside, and likewise for the end of the overlay.
1352 * Managing Overlays:: Creating and moving overlays.
1353 * Overlay Properties:: How to read and set properties.
1354 What properties do to the screen display.
1355 * Finding Overlays:: Searching for overlays.
1358 @node Managing Overlays
1359 @subsection Managing Overlays
1360 @cindex managing overlays
1361 @cindex overlays, managing
1363 This section describes the functions to create, delete and move
1364 overlays, and to examine their contents. Overlay changes are not
1365 recorded in the buffer's undo list, since the overlays are not
1366 part of the buffer's contents.
1368 @defun overlayp object
1369 This function returns @code{t} if @var{object} is an overlay.
1372 @defun make-overlay start end &optional buffer front-advance rear-advance
1373 This function creates and returns an overlay that belongs to
1374 @var{buffer} and ranges from @var{start} to @var{end}. Both @var{start}
1375 and @var{end} must specify buffer positions; they may be integers or
1376 markers. If @var{buffer} is omitted, the overlay is created in the
1379 The arguments @var{front-advance} and @var{rear-advance} specify the
1380 marker insertion type for the start of the overlay and for the end of
1381 the overlay, respectively. @xref{Marker Insertion Types}. If they
1382 are both @code{nil}, the default, then the overlay extends to include
1383 any text inserted at the beginning, but not text inserted at the end.
1384 If @var{front-advance} is non-@code{nil}, text inserted at the
1385 beginning of the overlay is excluded from the overlay. If
1386 @var{rear-advance} is non-@code{nil}, text inserted at the end of the
1387 overlay is included in the overlay.
1390 @defun overlay-start overlay
1391 This function returns the position at which @var{overlay} starts,
1395 @defun overlay-end overlay
1396 This function returns the position at which @var{overlay} ends,
1400 @defun overlay-buffer overlay
1401 This function returns the buffer that @var{overlay} belongs to. It
1402 returns @code{nil} if @var{overlay} has been deleted.
1405 @defun delete-overlay overlay
1406 This function deletes @var{overlay}. The overlay continues to exist as
1407 a Lisp object, and its property list is unchanged, but it ceases to be
1408 attached to the buffer it belonged to, and ceases to have any effect on
1411 A deleted overlay is not permanently disconnected. You can give it a
1412 position in a buffer again by calling @code{move-overlay}.
1415 @defun move-overlay overlay start end &optional buffer
1416 This function moves @var{overlay} to @var{buffer}, and places its bounds
1417 at @var{start} and @var{end}. Both arguments @var{start} and @var{end}
1418 must specify buffer positions; they may be integers or markers.
1420 If @var{buffer} is omitted, @var{overlay} stays in the same buffer it
1421 was already associated with; if @var{overlay} was deleted, it goes into
1424 The return value is @var{overlay}.
1426 This is the only valid way to change the endpoints of an overlay. Do
1427 not try modifying the markers in the overlay by hand, as that fails to
1428 update other vital data structures and can cause some overlays to be
1432 @defun remove-overlays &optional start end name value
1433 This function removes all the overlays between @var{start} and
1434 @var{end} whose property @var{name} has the value @var{value}. It can
1435 move the endpoints of the overlays in the region, or split them.
1437 If @var{name} is omitted or @code{nil}, it means to delete all overlays in
1438 the specified region. If @var{start} and/or @var{end} are omitted or
1439 @code{nil}, that means the beginning and end of the buffer respectively.
1440 Therefore, @code{(remove-overlays)} removes all the overlays in the
1444 @defun copy-overlay overlay
1445 This function returns a copy of @var{overlay}. The copy has the same
1446 endpoints and properties as @var{overlay}. However, the marker
1447 insertion type for the start of the overlay and for the end of the
1448 overlay are set to their default values (@pxref{Marker Insertion
1452 Here are some examples:
1455 ;; @r{Create an overlay.}
1456 (setq foo (make-overlay 1 10))
1457 @result{} #<overlay from 1 to 10 in display.texi>
1462 (overlay-buffer foo)
1463 @result{} #<buffer display.texi>
1464 ;; @r{Give it a property we can check later.}
1465 (overlay-put foo 'happy t)
1467 ;; @r{Verify the property is present.}
1468 (overlay-get foo 'happy)
1470 ;; @r{Move the overlay.}
1471 (move-overlay foo 5 20)
1472 @result{} #<overlay from 5 to 20 in display.texi>
1477 ;; @r{Delete the overlay.}
1478 (delete-overlay foo)
1480 ;; @r{Verify it is deleted.}
1482 @result{} #<overlay in no buffer>
1483 ;; @r{A deleted overlay has no position.}
1488 (overlay-buffer foo)
1490 ;; @r{Undelete the overlay.}
1491 (move-overlay foo 1 20)
1492 @result{} #<overlay from 1 to 20 in display.texi>
1493 ;; @r{Verify the results.}
1498 (overlay-buffer foo)
1499 @result{} #<buffer display.texi>
1500 ;; @r{Moving and deleting the overlay does not change its properties.}
1501 (overlay-get foo 'happy)
1505 Emacs stores the overlays of each buffer in two lists, divided
1506 around an arbitrary ``center position''. One list extends backwards
1507 through the buffer from that center position, and the other extends
1508 forwards from that center position. The center position can be anywhere
1511 @defun overlay-recenter pos
1512 This function recenters the overlays of the current buffer around
1513 position @var{pos}. That makes overlay lookup faster for positions
1514 near @var{pos}, but slower for positions far away from @var{pos}.
1517 A loop that scans the buffer forwards, creating overlays, can run
1518 faster if you do @code{(overlay-recenter (point-max))} first.
1520 @node Overlay Properties
1521 @subsection Overlay Properties
1522 @cindex overlay properties
1524 Overlay properties are like text properties in that the properties that
1525 alter how a character is displayed can come from either source. But in
1526 most respects they are different. @xref{Text Properties}, for comparison.
1528 Text properties are considered a part of the text; overlays and
1529 their properties are specifically considered not to be part of the
1530 text. Thus, copying text between various buffers and strings
1531 preserves text properties, but does not try to preserve overlays.
1532 Changing a buffer's text properties marks the buffer as modified,
1533 while moving an overlay or changing its properties does not. Unlike
1534 text property changes, overlay property changes are not recorded in
1535 the buffer's undo list.
1537 Since more than one overlay can specify a property value for the
1538 same character, Emacs lets you specify a priority value of each
1539 overlay. In case two overlays have the same priority value, and one
1540 is nested in the other, then the inner one will have priority over the
1541 outer one. If neither is nested in the other then you should not make
1542 assumptions about which overlay will prevail.
1544 These functions read and set the properties of an overlay:
1546 @defun overlay-get overlay prop
1547 This function returns the value of property @var{prop} recorded in
1548 @var{overlay}, if any. If @var{overlay} does not record any value for
1549 that property, but it does have a @code{category} property which is a
1550 symbol, that symbol's @var{prop} property is used. Otherwise, the value
1554 @defun overlay-put overlay prop value
1555 This function sets the value of property @var{prop} recorded in
1556 @var{overlay} to @var{value}. It returns @var{value}.
1559 @defun overlay-properties overlay
1560 This returns a copy of the property list of @var{overlay}.
1563 See also the function @code{get-char-property} which checks both
1564 overlay properties and text properties for a given character.
1565 @xref{Examining Properties}.
1567 Many overlay properties have special meanings; here is a table
1572 @kindex priority @r{(overlay property)}
1573 This property's value determines the priority of the overlay.
1574 If you want to specify a priority value, use either @code{nil}
1575 (or zero), or a positive integer. Any other value has undefined behavior.
1577 The priority matters when two or more overlays cover the same
1578 character and both specify the same property; the one whose
1579 @code{priority} value is larger overrides the other. For the
1580 @code{face} property, the higher priority overlay's value does not
1581 completely override the other value; instead, its face attributes
1582 override the face attributes of the lower priority @code{face}
1585 Currently, all overlays take priority over text properties.
1587 Note that Emacs sometimes uses non-numeric priority values for some of
1588 its internal overlays, so do not try to do arithmetic on the
1589 priority of an overlay (unless it is one that you created). If you
1590 need to put overlays in priority order, use the @var{sorted} argument
1591 of @code{overlays-at}. @xref{Finding Overlays}.
1594 @kindex window @r{(overlay property)}
1595 If the @code{window} property is non-@code{nil}, then the overlay
1596 applies only on that window.
1599 @kindex category @r{(overlay property)}
1600 If an overlay has a @code{category} property, we call it the
1601 @dfn{category} of the overlay. It should be a symbol. The properties
1602 of the symbol serve as defaults for the properties of the overlay.
1605 @kindex face @r{(overlay property)}
1606 This property controls the appearance of the text (@pxref{Faces}).
1607 The value of the property can be the following:
1611 A face name (a symbol or string).
1614 An anonymous face: a property list of the form @code{(@var{keyword}
1615 @var{value} @dots{})}, where each @var{keyword} is a face attribute
1616 name and @var{value} is a value for that attribute.
1619 A list of faces. Each list element should be either a face name or an
1620 anonymous face. This specifies a face which is an aggregate of the
1621 attributes of each of the listed faces. Faces occurring earlier in
1622 the list have higher priority.
1625 A cons cell of the form @code{(foreground-color . @var{color-name})}
1626 or @code{(background-color . @var{color-name})}. This specifies the
1627 foreground or background color, similar to @code{(:foreground
1628 @var{color-name})} or @code{(:background @var{color-name})}. This
1629 form is supported for backward compatibility only, and should be
1634 @kindex mouse-face @r{(overlay property)}
1635 This property is used instead of @code{face} when the mouse is within
1636 the range of the overlay. However, Emacs ignores all face attributes
1637 from this property that alter the text size (e.g., @code{:height},
1638 @code{:weight}, and @code{:slant}). Those attributes are always the
1639 same as in the unhighlighted text.
1642 @kindex display @r{(overlay property)}
1643 This property activates various features that change the
1644 way text is displayed. For example, it can make text appear taller
1645 or shorter, higher or lower, wider or narrower, or replaced with an image.
1646 @xref{Display Property}.
1649 @kindex help-echo @r{(overlay property)}
1650 If an overlay has a @code{help-echo} property, then when you move the
1651 mouse onto the text in the overlay, Emacs displays a help string in the
1652 echo area, or in the tooltip window. For details see @ref{Text
1656 @kindex field @r{(overlay property)}
1657 @c Copied from Special Properties.
1658 Consecutive characters with the same @code{field} property constitute a
1659 @emph{field}. Some motion functions including @code{forward-word} and
1660 @code{beginning-of-line} stop moving at a field boundary.
1663 @item modification-hooks
1664 @kindex modification-hooks @r{(overlay property)}
1665 This property's value is a list of functions to be called if any
1666 character within the overlay is changed or if text is inserted strictly
1669 The hook functions are called both before and after each change.
1670 If the functions save the information they receive, and compare notes
1671 between calls, they can determine exactly what change has been made
1674 When called before a change, each function receives four arguments: the
1675 overlay, @code{nil}, and the beginning and end of the text range to be
1678 When called after a change, each function receives five arguments: the
1679 overlay, @code{t}, the beginning and end of the text range just
1680 modified, and the length of the pre-change text replaced by that range.
1681 (For an insertion, the pre-change length is zero; for a deletion, that
1682 length is the number of characters deleted, and the post-change
1683 beginning and end are equal.)
1685 If these functions modify the buffer, they should bind
1686 @code{inhibit-modification-hooks} to @code{t} around doing so, to
1687 avoid confusing the internal mechanism that calls these hooks.
1689 Text properties also support the @code{modification-hooks} property,
1690 but the details are somewhat different (@pxref{Special Properties}).
1692 @item insert-in-front-hooks
1693 @kindex insert-in-front-hooks @r{(overlay property)}
1694 This property's value is a list of functions to be called before and
1695 after inserting text right at the beginning of the overlay. The calling
1696 conventions are the same as for the @code{modification-hooks} functions.
1698 @item insert-behind-hooks
1699 @kindex insert-behind-hooks @r{(overlay property)}
1700 This property's value is a list of functions to be called before and
1701 after inserting text right at the end of the overlay. The calling
1702 conventions are the same as for the @code{modification-hooks} functions.
1705 @kindex invisible @r{(overlay property)}
1706 The @code{invisible} property can make the text in the overlay
1707 invisible, which means that it does not appear on the screen.
1708 @xref{Invisible Text}, for details.
1711 @kindex intangible @r{(overlay property)}
1712 The @code{intangible} property on an overlay works just like the
1713 @code{intangible} text property. @xref{Special Properties}, for details.
1715 @item isearch-open-invisible
1716 This property tells incremental search how to make an invisible overlay
1717 visible, permanently, if the final match overlaps it. @xref{Invisible
1720 @item isearch-open-invisible-temporary
1721 This property tells incremental search how to make an invisible overlay
1722 visible, temporarily, during the search. @xref{Invisible Text}.
1725 @kindex before-string @r{(overlay property)}
1726 This property's value is a string to add to the display at the beginning
1727 of the overlay. The string does not appear in the buffer in any
1728 sense---only on the screen.
1731 @kindex after-string @r{(overlay property)}
1732 This property's value is a string to add to the display at the end of
1733 the overlay. The string does not appear in the buffer in any
1734 sense---only on the screen.
1737 This property specifies a display spec to prepend to each
1738 non-continuation line at display-time. @xref{Truncation}.
1741 This property specifies a display spec to prepend to each continuation
1742 line at display-time. @xref{Truncation}.
1745 @kindex evaporate @r{(overlay property)}
1746 If this property is non-@code{nil}, the overlay is deleted automatically
1747 if it becomes empty (i.e., if its length becomes zero). If you give
1748 an empty overlay a non-@code{nil} @code{evaporate} property, that deletes
1752 @cindex keymap of character (and overlays)
1753 @kindex keymap @r{(overlay property)}
1754 If this property is non-@code{nil}, it specifies a keymap for a portion of the
1755 text. This keymap is used when the character after point is within the
1756 overlay, and takes precedence over most other keymaps. @xref{Active Keymaps}.
1759 @kindex local-map @r{(overlay property)}
1760 The @code{local-map} property is similar to @code{keymap} but replaces the
1761 buffer's local map rather than augmenting existing keymaps. This also means it
1762 has lower precedence than minor mode keymaps.
1765 The @code{keymap} and @code{local-map} properties do not affect a
1766 string displayed by the @code{before-string}, @code{after-string}, or
1767 @code{display} properties. This is only relevant for mouse clicks and
1768 other mouse events that fall on the string, since point is never on
1769 the string. To bind special mouse events for the string, assign it a
1770 @code{keymap} or @code{local-map} text property. @xref{Special
1773 @node Finding Overlays
1774 @subsection Searching for Overlays
1775 @cindex searching for overlays
1776 @cindex overlays, searching for
1778 @defun overlays-at pos &optional sorted
1779 This function returns a list of all the overlays that cover the character at
1780 position @var{pos} in the current buffer. If @var{sorted} is non-@code{nil},
1781 the list is in decreasing order of priority, otherwise it is in no particular
1782 order. An overlay contains position @var{pos} if it begins at or before
1783 @var{pos}, and ends after @var{pos}.
1785 To illustrate usage, here is a Lisp function that returns a list of the
1786 overlays that specify property @var{prop} for the character at point:
1789 (defun find-overlays-specifying (prop)
1790 (let ((overlays (overlays-at (point)))
1793 (let ((overlay (car overlays)))
1794 (if (overlay-get overlay prop)
1795 (setq found (cons overlay found))))
1796 (setq overlays (cdr overlays)))
1801 @defun overlays-in beg end
1802 This function returns a list of the overlays that overlap the region
1803 @var{beg} through @var{end}. ``Overlap'' means that at least one
1804 character is contained within the overlay and also contained within the
1805 specified region; however, empty overlays are included in the result if
1806 they are located at @var{beg}, strictly between @var{beg} and @var{end},
1807 or at @var{end} when @var{end} denotes the position at the end of the
1811 @defun next-overlay-change pos
1812 This function returns the buffer position of the next beginning or end
1813 of an overlay, after @var{pos}. If there is none, it returns
1817 @defun previous-overlay-change pos
1818 This function returns the buffer position of the previous beginning or
1819 end of an overlay, before @var{pos}. If there is none, it returns
1823 As an example, here's a simplified (and inefficient) version of the
1824 primitive function @code{next-single-char-property-change}
1825 (@pxref{Property Search}). It searches forward from position
1826 @var{pos} for the next position where the value of a given property
1827 @code{prop}, as obtained from either overlays or text properties,
1831 (defun next-single-char-property-change (position prop)
1833 (goto-char position)
1834 (let ((propval (get-char-property (point) prop)))
1835 (while (and (not (eobp))
1836 (eq (get-char-property (point) prop) propval))
1837 (goto-char (min (next-overlay-change (point))
1838 (next-single-property-change (point) prop)))))
1842 @node Size of Displayed Text
1843 @section Size of Displayed Text
1844 @cindex size of text on display
1845 @cindex character width on display
1847 Since not all characters have the same width, these functions let you
1848 check the width of a character. @xref{Primitive Indent}, and
1849 @ref{Screen Lines}, for related functions.
1851 @defun char-width char
1852 This function returns the width in columns of the character
1853 @var{char}, if it were displayed in the current buffer (i.e., taking
1854 into account the buffer's display table, if any; @pxref{Display
1855 Tables}). The width of a tab character is usually @code{tab-width}
1856 (@pxref{Usual Display}).
1859 @defun string-width string
1860 This function returns the width in columns of the string @var{string},
1861 if it were displayed in the current buffer and the selected window.
1864 @defun truncate-string-to-width string width &optional start-column padding ellipsis
1865 This function returns the part of @var{string} that fits within
1866 @var{width} columns, as a new string.
1868 If @var{string} does not reach @var{width}, then the result ends where
1869 @var{string} ends. If one multi-column character in @var{string}
1870 extends across the column @var{width}, that character is not included in
1871 the result. Thus, the result can fall short of @var{width} but cannot
1874 The optional argument @var{start-column} specifies the starting column.
1875 If this is non-@code{nil}, then the first @var{start-column} columns of
1876 the string are omitted from the value. If one multi-column character in
1877 @var{string} extends across the column @var{start-column}, that
1878 character is not included.
1880 The optional argument @var{padding}, if non-@code{nil}, is a padding
1881 character added at the beginning and end of the result string, to extend
1882 it to exactly @var{width} columns. The padding character is used at the
1883 end of the result if it falls short of @var{width}. It is also used at
1884 the beginning of the result if one multi-column character in
1885 @var{string} extends across the column @var{start-column}.
1887 If @var{ellipsis} is non-@code{nil}, it should be a string which will
1888 replace the end of @var{string} (including any padding) if it extends
1889 beyond @var{width}, unless the display width of @var{string} is equal
1890 to or less than the display width of @var{ellipsis}. If
1891 @var{ellipsis} is non-@code{nil} and not a string, it stands for
1895 (truncate-string-to-width "\tab\t" 12 4)
1897 (truncate-string-to-width "\tab\t" 12 4 ?\s)
1902 The following function returns the size in pixels of text as if it were
1903 displayed in a given window. This function is used by
1904 @code{fit-window-to-buffer} (@pxref{Resizing Windows}) and
1905 @code{fit-frame-to-buffer} (@pxref{Size and Position}) to make a window
1906 exactly as large as the text it contains.
1908 @defun window-text-pixel-size &optional window from to x-limit y-limit mode-and-header-line
1909 This function returns the size of the text of @var{window}'s buffer in
1910 pixels. @var{window} must be a live window and defaults to the selected
1911 one. The return value is a cons of the maximum pixel-width of any text
1912 line and the maximum pixel-height of all text lines.
1914 The optional argument @var{from}, if non-@code{nil}, specifies the first
1915 text position to consider and defaults to the minimum accessible
1916 position of the buffer. If @var{from} is @code{t}, it uses the minimum
1917 accessible position that is not a newline character. The optional
1918 argument @var{to}, if non-@code{nil}, specifies the last text position
1919 to consider and defaults to the maximum accessible position of the
1920 buffer. If @var{to} is @code{t}, it uses the maximum accessible
1921 position that is not a newline character.
1923 The optional argument @var{x-limit}, if non-@code{nil}, specifies the
1924 maximum pixel-width that can be returned. @var{x-limit} @code{nil} or
1925 omitted, means to use the pixel-width of @var{window}'s body
1926 (@pxref{Window Sizes}); this is useful when the caller does not intend
1927 to change the width of @var{window}. Otherwise, the caller should
1928 specify here the maximum width @var{window}'s body may assume. Text
1929 whose x-coordinate is beyond @var{x-limit} is ignored. Since
1930 calculating the width of long lines can take some time, it's always a
1931 good idea to make this argument as small as needed; in particular, if
1932 the buffer might contain long lines that will be truncated anyway.
1934 The optional argument @var{y-limit}, if non-@code{nil}, specifies the
1935 maximum pixel-height that can be returned. Text lines whose
1936 y-coordinate is beyond @var{y-limit} are ignored. Since calculating the
1937 pixel-height of a large buffer can take some time, it makes sense to
1938 specify this argument; in particular, if the caller does not know the
1941 The optional argument @var{mode-and-header-line} @code{nil} or omitted
1942 means to not include the height of the mode- or header-line of
1943 @var{window} in the return value. If it is either the symbol
1944 @code{mode-line} or @code{header-line}, include only the height of that
1945 line, if present, in the return value. If it is @code{t}, include the
1946 height of both, if present, in the return value.
1951 @section Line Height
1953 @cindex height of a line
1955 The total height of each display line consists of the height of the
1956 contents of the line, plus optional additional vertical line spacing
1957 above or below the display line.
1959 The height of the line contents is the maximum height of any
1960 character or image on that display line, including the final newline
1961 if there is one. (A display line that is continued doesn't include a
1962 final newline.) That is the default line height, if you do nothing to
1963 specify a greater height. (In the most common case, this equals the
1964 height of the default frame font.)
1966 There are several ways to explicitly specify a larger line height,
1967 either by specifying an absolute height for the display line, or by
1968 specifying vertical space. However, no matter what you specify, the
1969 actual line height can never be less than the default.
1971 @kindex line-height @r{(text property)}
1972 A newline can have a @code{line-height} text or overlay property
1973 that controls the total height of the display line ending in that
1976 If the property value is @code{t}, the newline character has no
1977 effect on the displayed height of the line---the visible contents
1978 alone determine the height. This is useful for tiling small images
1979 (or image slices) without adding blank areas between the images.
1981 If the property value is a list of the form @code{(@var{height}
1982 @var{total})}, that adds extra space @emph{below} the display line.
1983 First Emacs uses @var{height} as a height spec to control extra space
1984 @emph{above} the line; then it adds enough space @emph{below} the line
1985 to bring the total line height up to @var{total}. In this case, the
1986 other ways to specify the line spacing are ignored.
1989 Any other kind of property value is a height spec, which translates
1990 into a number---the specified line height. There are several ways to
1991 write a height spec; here's how each of them translates into a number:
1995 If the height spec is a positive integer, the height value is that integer.
1997 If the height spec is a float, @var{float}, the numeric height value
1998 is @var{float} times the frame's default line height.
1999 @item (@var{face} . @var{ratio})
2000 If the height spec is a cons of the format shown, the numeric height
2001 is @var{ratio} times the height of face @var{face}. @var{ratio} can
2002 be any type of number, or @code{nil} which means a ratio of 1.
2003 If @var{face} is @code{t}, it refers to the current face.
2004 @item (nil . @var{ratio})
2005 If the height spec is a cons of the format shown, the numeric height
2006 is @var{ratio} times the height of the contents of the line.
2009 Thus, any valid height spec determines the height in pixels, one way
2010 or another. If the line contents' height is less than that, Emacs
2011 adds extra vertical space above the line to achieve the specified
2014 If you don't specify the @code{line-height} property, the line's
2015 height consists of the contents' height plus the line spacing.
2016 There are several ways to specify the line spacing for different
2017 parts of Emacs text.
2019 On graphical terminals, you can specify the line spacing for all
2020 lines in a frame, using the @code{line-spacing} frame parameter
2021 (@pxref{Layout Parameters}). However, if the default value of
2022 @code{line-spacing} is non-@code{nil}, it overrides the
2023 frame's @code{line-spacing} parameter. An integer specifies the
2024 number of pixels put below lines. A floating-point number specifies
2025 the spacing relative to the frame's default line height.
2027 @vindex line-spacing
2028 You can specify the line spacing for all lines in a buffer via the
2029 buffer-local @code{line-spacing} variable. An integer specifies
2030 the number of pixels put below lines. A floating-point number
2031 specifies the spacing relative to the default frame line height. This
2032 overrides line spacings specified for the frame.
2034 @kindex line-spacing @r{(text property)}
2035 Finally, a newline can have a @code{line-spacing} text or overlay
2036 property that overrides the default frame line spacing and the buffer
2037 local @code{line-spacing} variable, for the display line ending in
2040 One way or another, these mechanisms specify a Lisp value for the
2041 spacing of each line. The value is a height spec, and it translates
2042 into a Lisp value as described above. However, in this case the
2043 numeric height value specifies the line spacing, rather than the line
2046 On text terminals, the line spacing cannot be altered.
2052 A @dfn{face} is a collection of graphical attributes for displaying
2053 text: font, foreground color, background color, optional underlining,
2054 etc. Faces control how Emacs displays text in buffers, as well as
2055 other parts of the frame such as the mode line.
2057 @cindex anonymous face
2058 One way to represent a face is as a property list of attributes,
2059 like @code{(:foreground "red" :weight bold)}. Such a list is called
2060 an @dfn{anonymous face}. For example, you can assign an anonymous
2061 face as the value of the @code{face} text property, and Emacs will
2062 display the underlying text with the specified attributes.
2063 @xref{Special Properties}.
2066 More commonly, a face is referred to via a @dfn{face name}: a Lisp
2067 symbol associated with a set of face attributes@footnote{For backward
2068 compatibility, you can also use a string to specify a face name; that
2069 is equivalent to a Lisp symbol with the same name.}. Named faces are
2070 defined using the @code{defface} macro (@pxref{Defining Faces}).
2071 Emacs comes with several standard named faces (@pxref{Basic Faces}).
2073 Many parts of Emacs required named faces, and do not accept
2074 anonymous faces. These include the functions documented in
2075 @ref{Attribute Functions}, and the variable @code{font-lock-keywords}
2076 (@pxref{Search-based Fontification}). Unless otherwise stated, we
2077 will use the term @dfn{face} to refer only to named faces.
2080 This function returns a non-@code{nil} value if @var{object} is a
2081 named face: a Lisp symbol or string which serves as a face name.
2082 Otherwise, it returns @code{nil}.
2086 * Face Attributes:: What is in a face?
2087 * Defining Faces:: How to define a face.
2088 * Attribute Functions:: Functions to examine and set face attributes.
2089 * Displaying Faces:: How Emacs combines the faces specified for a character.
2090 * Face Remapping:: Remapping faces to alternative definitions.
2091 * Face Functions:: How to define and examine faces.
2092 * Auto Faces:: Hook for automatic face assignment.
2093 * Basic Faces:: Faces that are defined by default.
2094 * Font Selection:: Finding the best available font for a face.
2095 * Font Lookup:: Looking up the names of available fonts
2096 and information about them.
2097 * Fontsets:: A fontset is a collection of fonts
2098 that handle a range of character sets.
2099 * Low-Level Font:: Lisp representation for character display fonts.
2102 @node Face Attributes
2103 @subsection Face Attributes
2104 @cindex face attributes
2106 @dfn{Face attributes} determine the visual appearance of a face.
2107 The following table lists all the face attributes, their possible
2108 values, and their effects.
2110 Apart from the values given below, each face attribute can have the
2111 value @code{unspecified}. This special value means that the face
2112 doesn't specify that attribute directly. An @code{unspecified}
2113 attribute tells Emacs to refer instead to a parent face (see the
2114 description @code{:inherit} attribute below); or, failing that, to an
2115 underlying face (@pxref{Displaying Faces}). The @code{default} face
2116 must specify all attributes.
2118 Some of these attributes are meaningful only on certain kinds of
2119 displays. If your display cannot handle a certain attribute, the
2120 attribute is ignored.
2124 Font family or fontset (a string). @xref{Fonts,,, emacs, The GNU
2125 Emacs Manual}, for more information about font families. The function
2126 @code{font-family-list} (see below) returns a list of available family
2127 names. @xref{Fontsets}, for information about fontsets.
2130 The name of the @dfn{font foundry} for the font family specified by
2131 the @code{:family} attribute (a string). @xref{Fonts,,, emacs, The
2135 Relative character width. This should be one of the symbols
2136 @code{ultra-condensed}, @code{extra-condensed}, @code{condensed},
2137 @code{semi-condensed}, @code{normal}, @code{semi-expanded},
2138 @code{expanded}, @code{extra-expanded}, or @code{ultra-expanded}.
2141 The height of the font. In the simplest case, this is an integer in
2142 units of 1/10 point.
2144 The value can also be floating point or a function, which
2145 specifies the height relative to an @dfn{underlying face}
2146 (@pxref{Displaying Faces}). A floating-point value
2147 specifies the amount by which to scale the height of the
2148 underlying face. A function value is called
2149 with one argument, the height of the underlying face, and returns the
2150 height of the new face. If the function is passed an integer
2151 argument, it must return an integer.
2153 The height of the default face must be specified using an integer;
2154 floating point and function values are not allowed.
2157 Font weight---one of the symbols (from densest to faintest)
2158 @code{ultra-bold}, @code{extra-bold}, @code{bold}, @code{semi-bold},
2159 @code{normal}, @code{semi-light}, @code{light}, @code{extra-light}, or
2160 @code{ultra-light}. On text terminals which support
2161 variable-brightness text, any weight greater than normal is displayed
2162 as extra bright, and any weight less than normal is displayed as
2167 Font slant---one of the symbols @code{italic}, @code{oblique},
2168 @code{normal}, @code{reverse-italic}, or @code{reverse-oblique}. On
2169 text terminals that support variable-brightness text, slanted text is
2170 displayed as half-bright.
2173 Foreground color, a string. The value can be a system-defined color
2174 name, or a hexadecimal color specification. @xref{Color Names}. On
2175 black-and-white displays, certain shades of gray are implemented by
2178 @item :distant-foreground
2179 Alternative foreground color, a string. This is like @code{:foreground}
2180 but the color is only used as a foreground when the background color is
2181 near to the foreground that would have been used. This is useful for
2182 example when marking text (i.e. the region face). If the text has a foreground
2183 that is visible with the region face, that foreground is used.
2184 If the foreground is near the region face background,
2185 @code{:distant-foreground} is used instead so the text is readable.
2188 Background color, a string. The value can be a system-defined color
2189 name, or a hexadecimal color specification. @xref{Color Names}.
2191 @cindex underlined text
2193 Whether or not characters should be underlined, and in what
2194 way. The possible values of the @code{:underline} attribute are:
2201 Underline with the foreground color of the face.
2204 Underline in color @var{color}, a string specifying a color.
2206 @item @code{(:color @var{color} :style @var{style})}
2207 @var{color} is either a string, or the symbol @code{foreground-color},
2208 meaning the foreground color of the face. Omitting the attribute
2209 @code{:color} means to use the foreground color of the face.
2210 @var{style} should be a symbol @code{line} or @code{wave}, meaning to
2211 use a straight or wavy line. Omitting the attribute @code{:style}
2212 means to use a straight line.
2215 @cindex overlined text
2217 Whether or not characters should be overlined, and in what color.
2218 If the value is @code{t}, overlining uses the foreground color of the
2219 face. If the value is a string, overlining uses that color. The
2220 value @code{nil} means do not overline.
2222 @cindex strike-through text
2223 @item :strike-through
2224 Whether or not characters should be strike-through, and in what
2225 color. The value is used like that of @code{:overline}.
2230 Whether or not a box should be drawn around characters, its color, the
2231 width of the box lines, and 3D appearance. Here are the possible
2232 values of the @code{:box} attribute, and what they mean:
2239 Draw a box with lines of width 1, in the foreground color.
2242 Draw a box with lines of width 1, in color @var{color}.
2244 @item @code{(:line-width @var{width} :color @var{color} :style @var{style})}
2245 This way you can explicitly specify all aspects of the box. The value
2246 @var{width} specifies the width of the lines to draw; it defaults to
2247 1. A negative width @var{-n} means to draw a line of width @var{n}
2248 that occupies the space of the underlying text, thus avoiding any
2249 increase in the character height or width.
2251 The value @var{color} specifies the color to draw with. The default is
2252 the foreground color of the face for simple boxes, and the background
2253 color of the face for 3D boxes.
2255 The value @var{style} specifies whether to draw a 3D box. If it is
2256 @code{released-button}, the box looks like a 3D button that is not being
2257 pressed. If it is @code{pressed-button}, the box looks like a 3D button
2258 that is being pressed. If it is @code{nil} or omitted, a plain 2D box
2262 @item :inverse-video
2263 Whether or not characters should be displayed in inverse video. The
2264 value should be @code{t} (yes) or @code{nil} (no).
2267 The background stipple, a bitmap.
2269 The value can be a string; that should be the name of a file containing
2270 external-format X bitmap data. The file is found in the directories
2271 listed in the variable @code{x-bitmap-file-path}.
2273 Alternatively, the value can specify the bitmap directly, with a list
2274 of the form @code{(@var{width} @var{height} @var{data})}. Here,
2275 @var{width} and @var{height} specify the size in pixels, and
2276 @var{data} is a string containing the raw bits of the bitmap, row by
2277 row. Each row occupies @math{(@var{width} + 7) / 8} consecutive bytes
2278 in the string (which should be a unibyte string for best results).
2279 This means that each row always occupies at least one whole byte.
2281 If the value is @code{nil}, that means use no stipple pattern.
2283 Normally you do not need to set the stipple attribute, because it is
2284 used automatically to handle certain shades of gray.
2287 The font used to display the face. Its value should be a font object.
2288 @xref{Low-Level Font}, for information about font objects, font specs,
2291 When specifying this attribute using @code{set-face-attribute}
2292 (@pxref{Attribute Functions}), you may also supply a font spec, a font
2293 entity, or a string. Emacs converts such values to an appropriate
2294 font object, and stores that font object as the actual attribute
2295 value. If you specify a string, the contents of the string should be
2296 a font name (@pxref{Fonts,,, emacs, The GNU Emacs Manual}); if the
2297 font name is an XLFD containing wildcards, Emacs chooses the first
2298 font matching those wildcards. Specifying this attribute also changes
2299 the values of the @code{:family}, @code{:foundry}, @code{:width},
2300 @code{:height}, @code{:weight}, and @code{:slant} attributes.
2302 @cindex inheritance, for faces
2304 The name of a face from which to inherit attributes, or a list of face
2305 names. Attributes from inherited faces are merged into the face like
2306 an underlying face would be, with higher priority than underlying
2307 faces (@pxref{Displaying Faces}). If a list of faces is used,
2308 attributes from faces earlier in the list override those from later
2312 @defun font-family-list &optional frame
2313 This function returns a list of available font family names. The
2314 optional argument @var{frame} specifies the frame on which the text is
2315 to be displayed; if it is @code{nil}, the selected frame is used.
2318 @defopt underline-minimum-offset
2319 This variable specifies the minimum distance between the baseline and
2320 the underline, in pixels, when displaying underlined text.
2323 @defopt x-bitmap-file-path
2324 This variable specifies a list of directories for searching
2325 for bitmap files, for the @code{:stipple} attribute.
2328 @defun bitmap-spec-p object
2329 This returns @code{t} if @var{object} is a valid bitmap specification,
2330 suitable for use with @code{:stipple} (see above). It returns
2331 @code{nil} otherwise.
2334 @node Defining Faces
2335 @subsection Defining Faces
2336 @cindex defining faces
2339 The usual way to define a face is through the @code{defface} macro.
2340 This macro associates a face name (a symbol) with a default @dfn{face
2341 spec}. A face spec is a construct which specifies what attributes a
2342 face should have on any given terminal; for example, a face spec might
2343 specify one foreground color on high-color terminals, and a different
2344 foreground color on low-color terminals.
2346 People are sometimes tempted to create a variable whose value is a
2347 face name. In the vast majority of cases, this is not necessary; the
2348 usual procedure is to define a face with @code{defface}, and then use
2351 @defmac defface face spec doc [keyword value]@dots{}
2352 This macro declares @var{face} as a named face whose default face spec
2353 is given by @var{spec}. You should not quote the symbol @var{face},
2354 and it should not end in @samp{-face} (that would be redundant). The
2355 argument @var{doc} is a documentation string for the face. The
2356 additional @var{keyword} arguments have the same meanings as in
2357 @code{defgroup} and @code{defcustom} (@pxref{Common Keywords}).
2359 If @var{face} already has a default face spec, this macro does
2362 The default face spec determines @var{face}'s appearance when no
2363 customizations are in effect (@pxref{Customization}). If @var{face}
2364 has already been customized (via Custom themes or via customizations
2365 read from the init file), its appearance is determined by the custom
2366 face spec(s), which override the default face spec @var{spec}.
2367 However, if the customizations are subsequently removed, the
2368 appearance of @var{face} will again be determined by its default face
2371 As an exception, if you evaluate a @code{defface} form with
2372 @kbd{C-M-x} in Emacs Lisp mode (@code{eval-defun}), a special feature
2373 of @code{eval-defun} overrides any custom face specs on the face,
2374 causing the face to reflect exactly what the @code{defface} says.
2376 The @var{spec} argument is a @dfn{face spec}, which states how the
2377 face should appear on different kinds of terminals. It should be an
2378 alist whose elements each have the form
2381 (@var{display} . @var{plist})
2385 @var{display} specifies a class of terminals (see below). @var{plist}
2386 is a property list of face attributes and their values, specifying how
2387 the face appears on such terminals. For backward compatibility, you
2388 can also write an element as @code{(@var{display} @var{plist})}.
2390 The @var{display} part of an element of @var{spec} determines which
2391 terminals the element matches. If more than one element of @var{spec}
2392 matches a given terminal, the first element that matches is the one
2393 used for that terminal. There are three possibilities for
2397 @item @code{default}
2398 This element of @var{spec} doesn't match any terminal; instead, it
2399 specifies defaults that apply to all terminals. This element, if
2400 used, must be the first element of @var{spec}. Each of the following
2401 elements can override any or all of these defaults.
2404 This element of @var{spec} matches all terminals. Therefore, any
2405 subsequent elements of @var{spec} are never used. Normally @code{t}
2406 is used in the last (or only) element of @var{spec}.
2409 If @var{display} is a list, each element should have the form
2410 @code{(@var{characteristic} @var{value}@dots{})}. Here
2411 @var{characteristic} specifies a way of classifying terminals, and the
2412 @var{value}s are possible classifications which @var{display} should
2413 apply to. Here are the possible values of @var{characteristic}:
2417 The kind of window system the terminal uses---either @code{graphic}
2418 (any graphics-capable display), @code{x}, @code{pc} (for the MS-DOS
2419 console), @code{w32} (for MS Windows 9X/NT/2K/XP), or @code{tty} (a
2420 non-graphics-capable display). @xref{Window Systems, window-system}.
2423 What kinds of colors the terminal supports---either @code{color},
2424 @code{grayscale}, or @code{mono}.
2427 The kind of background---either @code{light} or @code{dark}.
2430 An integer that represents the minimum number of colors the terminal
2431 should support. This matches a terminal if its
2432 @code{display-color-cells} value is at least the specified integer.
2435 Whether or not the terminal can display the face attributes given in
2436 @var{value}@dots{} (@pxref{Face Attributes}). @xref{Display Face
2437 Attribute Testing}, for more information on exactly how this testing
2441 If an element of @var{display} specifies more than one @var{value} for
2442 a given @var{characteristic}, any of those values is acceptable. If
2443 @var{display} has more than one element, each element should specify a
2444 different @var{characteristic}; then @emph{each} characteristic of the
2445 terminal must match one of the @var{value}s specified for it in
2450 For example, here's the definition of the standard face
2455 '((((class color) (min-colors 88) (background light))
2456 :background "darkseagreen2")
2457 (((class color) (min-colors 88) (background dark))
2458 :background "darkolivegreen")
2459 (((class color) (min-colors 16) (background light))
2460 :background "darkseagreen2")
2461 (((class color) (min-colors 16) (background dark))
2462 :background "darkolivegreen")
2463 (((class color) (min-colors 8))
2464 :background "green" :foreground "black")
2465 (t :inverse-video t))
2466 "Basic face for highlighting."
2467 :group 'basic-faces)
2470 Internally, Emacs stores each face's default spec in its
2471 @code{face-defface-spec} symbol property (@pxref{Symbol Properties}).
2472 The @code{saved-face} property stores any face spec saved by the user
2473 using the customization buffer; the @code{customized-face} property
2474 stores the face spec customized for the current session, but not
2475 saved; and the @code{theme-face} property stores an alist associating
2476 the active customization settings and Custom themes with the face
2477 specs for that face. The face's documentation string is stored in the
2478 @code{face-documentation} property.
2480 Normally, a face is declared just once, using @code{defface}, and
2481 any further changes to its appearance are applied using the Customize
2482 framework (e.g., via the Customize user interface or via the
2483 @code{custom-set-faces} function; @pxref{Applying Customizations}), or
2484 by face remapping (@pxref{Face Remapping}). In the rare event that
2485 you need to change a face spec directly from Lisp, you can use the
2486 @code{face-spec-set} function.
2488 @defun face-spec-set face spec &optional spec-type
2489 This function applies @var{spec} as a face spec for @code{face}.
2490 @var{spec} should be a face spec, as described in the above
2491 documentation for @code{defface}.
2493 This function also defines @var{face} as a valid face name if it is
2494 not already one, and (re)calculates its attributes on existing frames.
2496 @cindex override spec @r{(for a face)}
2497 The argument @var{spec-type} determines which spec to set. If it is
2498 @code{nil} or @code{face-override-spec}, this function sets the
2499 @dfn{override spec}, which overrides over all other face specs on
2500 @var{face}. If it is @code{customized-face} or @code{saved-face},
2501 this function sets the customized spec or the saved custom spec. If
2502 it is @code{face-defface-spec}, this function sets the default face
2503 spec (the same one set by @code{defface}). If it is @code{reset},
2504 this function clears out all customization specs and override specs
2505 from @var{face} (in this case, the value of @var{spec} is ignored).
2506 Any other value of @var{spec-type} is reserved for internal use.
2509 @node Attribute Functions
2510 @subsection Face Attribute Functions
2511 @cindex face attributes, access and modification
2513 This section describes functions for directly accessing and
2514 modifying the attributes of a named face.
2516 @defun face-attribute face attribute &optional frame inherit
2517 This function returns the value of the @var{attribute} attribute for
2518 @var{face} on @var{frame}.
2520 If @var{frame} is @code{nil}, that means the selected frame
2521 (@pxref{Input Focus}). If @var{frame} is @code{t}, this function
2522 returns the value of the specified attribute for newly-created frames
2523 (this is normally @code{unspecified}, unless you have specified some
2524 value using @code{set-face-attribute}; see below).
2526 If @var{inherit} is @code{nil}, only attributes directly defined by
2527 @var{face} are considered, so the return value may be
2528 @code{unspecified}, or a relative value. If @var{inherit} is
2529 non-@code{nil}, @var{face}'s definition of @var{attribute} is merged
2530 with the faces specified by its @code{:inherit} attribute; however the
2531 return value may still be @code{unspecified} or relative. If
2532 @var{inherit} is a face or a list of faces, then the result is further
2533 merged with that face (or faces), until it becomes specified and
2536 To ensure that the return value is always specified and absolute, use
2537 a value of @code{default} for @var{inherit}; this will resolve any
2538 unspecified or relative values by merging with the @code{default} face
2539 (which is always completely specified).
2544 (face-attribute 'bold :weight)
2549 @c FIXME: Add an index for "relative face attribute", maybe here? --xfq
2550 @defun face-attribute-relative-p attribute value
2551 This function returns non-@code{nil} if @var{value}, when used as the
2552 value of the face attribute @var{attribute}, is relative. This means
2553 it would modify, rather than completely override, any value that comes
2554 from a subsequent face in the face list or that is inherited from
2557 @code{unspecified} is a relative value for all attributes. For
2558 @code{:height}, floating point and function values are also relative.
2563 (face-attribute-relative-p :height 2.0)
2568 @defun face-all-attributes face &optional frame
2569 This function returns an alist of attributes of @var{face}. The
2570 elements of the result are name-value pairs of the form
2571 @w{@code{(@var{attr-name} . @var{attr-value})}}. Optional argument
2572 @var{frame} specifies the frame whose definition of @var{face} to
2573 return; if omitted or @code{nil}, the returned value describes the
2574 default attributes of @var{face} for newly created frames.
2577 @defun merge-face-attribute attribute value1 value2
2578 If @var{value1} is a relative value for the face attribute
2579 @var{attribute}, returns it merged with the underlying value
2580 @var{value2}; otherwise, if @var{value1} is an absolute value for the
2581 face attribute @var{attribute}, returns @var{value1} unchanged.
2584 Normally, Emacs uses the face specs of each face to automatically
2585 calculate its attributes on each frame (@pxref{Defining Faces}). The
2586 function @code{set-face-attribute} can override this calculation by
2587 directly assigning attributes to a face, either on a specific frame or
2588 for all frames. This function is mostly intended for internal usage.
2590 @defun set-face-attribute face frame &rest arguments
2591 This function sets one or more attributes of @var{face} for
2592 @var{frame}. The attributes specifies in this way override the face
2593 spec(s) belonging to @var{face}.
2595 The extra arguments @var{arguments} specify the attributes to set, and
2596 the values for them. They should consist of alternating attribute
2597 names (such as @code{:family} or @code{:underline}) and values. Thus,
2600 (set-face-attribute 'foo nil :weight 'bold :slant 'italic)
2604 sets the attribute @code{:weight} to @code{bold} and the attribute
2605 @code{:slant} to @code{italic}.
2608 If @var{frame} is @code{t}, this function sets the default attributes
2609 for newly created frames. If @var{frame} is @code{nil}, this function
2610 sets the attributes for all existing frames, as well as for newly
2614 The following commands and functions mostly provide compatibility
2615 with old versions of Emacs. They work by calling
2616 @code{set-face-attribute}. Values of @code{t} and @code{nil} for
2617 their @var{frame} argument are handled just like
2618 @code{set-face-attribute} and @code{face-attribute}. The commands
2619 read their arguments using the minibuffer, if called interactively.
2621 @deffn Command set-face-foreground face color &optional frame
2622 @deffnx Command set-face-background face color &optional frame
2623 These set the @code{:foreground} attribute (or @code{:background}
2624 attribute, respectively) of @var{face} to @var{color}.
2627 @deffn Command set-face-stipple face pattern &optional frame
2628 This sets the @code{:stipple} attribute of @var{face} to
2632 @deffn Command set-face-font face font &optional frame
2633 This sets the @code{:font} attribute of @var{face} to @var{font}.
2636 @defun set-face-bold face bold-p &optional frame
2637 This sets the @code{:weight} attribute of @var{face} to @var{normal}
2638 if @var{bold-p} is @code{nil}, and to @var{bold} otherwise.
2641 @defun set-face-italic face italic-p &optional frame
2642 This sets the @code{:slant} attribute of @var{face} to @var{normal} if
2643 @var{italic-p} is @code{nil}, and to @var{italic} otherwise.
2646 @defun set-face-underline face underline &optional frame
2647 This sets the @code{:underline} attribute of @var{face} to
2651 @defun set-face-inverse-video face inverse-video-p &optional frame
2652 This sets the @code{:inverse-video} attribute of @var{face} to
2653 @var{inverse-video-p}.
2656 @deffn Command invert-face face &optional frame
2657 This swaps the foreground and background colors of face @var{face}.
2660 The following functions examine the attributes of a face. They
2661 mostly provide compatibility with old versions of Emacs. If you don't
2662 specify @var{frame}, they refer to the selected frame; @code{t} refers
2663 to the default data for new frames. They return @code{unspecified} if
2664 the face doesn't define any value for that attribute. If
2665 @var{inherit} is @code{nil}, only an attribute directly defined by the
2666 face is returned. If @var{inherit} is non-@code{nil}, any faces
2667 specified by its @code{:inherit} attribute are considered as well, and
2668 if @var{inherit} is a face or a list of faces, then they are also
2669 considered, until a specified attribute is found. To ensure that the
2670 return value is always specified, use a value of @code{default} for
2673 @defun face-font face &optional frame
2674 This function returns the name of the font of face @var{face}.
2677 @defun face-foreground face &optional frame inherit
2678 @defunx face-background face &optional frame inherit
2679 These functions return the foreground color (or background color,
2680 respectively) of face @var{face}, as a string.
2683 @defun face-stipple face &optional frame inherit
2684 This function returns the name of the background stipple pattern of face
2685 @var{face}, or @code{nil} if it doesn't have one.
2688 @defun face-bold-p face &optional frame inherit
2689 This function returns a non-@code{nil} value if the @code{:weight}
2690 attribute of @var{face} is bolder than normal (i.e., one of
2691 @code{semi-bold}, @code{bold}, @code{extra-bold}, or
2692 @code{ultra-bold}). Otherwise, it returns @code{nil}.
2695 @defun face-italic-p face &optional frame inherit
2696 This function returns a non-@code{nil} value if the @code{:slant}
2697 attribute of @var{face} is @code{italic} or @code{oblique}, and
2698 @code{nil} otherwise.
2701 @defun face-underline-p face &optional frame inherit
2702 This function returns non-@code{nil} if face @var{face} specifies
2703 a non-@code{nil} @code{:underline} attribute.
2706 @defun face-inverse-video-p face &optional frame inherit
2707 This function returns non-@code{nil} if face @var{face} specifies
2708 a non-@code{nil} @code{:inverse-video} attribute.
2711 @node Displaying Faces
2712 @subsection Displaying Faces
2713 @cindex displaying faces
2714 @cindex face merging
2716 When Emacs displays a given piece of text, the visual appearance of
2717 the text may be determined by faces drawn from different sources. If
2718 these various sources together specify more than one face for a
2719 particular character, Emacs merges the attributes of the various
2720 faces. Here is the order in which Emacs merges the faces, from
2721 highest to lowest priority:
2725 If the text consists of a special glyph, the glyph can specify a
2726 particular face. @xref{Glyphs}.
2729 If the text lies within an active region, Emacs highlights it using
2730 the @code{region} face. @xref{Standard Faces,,, emacs, The GNU Emacs
2734 If the text lies within an overlay with a non-@code{nil} @code{face}
2735 property, Emacs applies the face(s) specified by that property. If
2736 the overlay has a @code{mouse-face} property and the mouse is ``near
2737 enough'' to the overlay, Emacs applies the face or face attributes
2738 specified by the @code{mouse-face} property instead. @xref{Overlay
2741 When multiple overlays cover one character, an overlay with higher
2742 priority overrides those with lower priority. @xref{Overlays}.
2745 If the text contains a @code{face} or @code{mouse-face} property,
2746 Emacs applies the specified faces and face attributes. @xref{Special
2747 Properties}. (This is how Font Lock mode faces are applied.
2748 @xref{Font Lock Mode}.)
2751 If the text lies within the mode line of the selected window, Emacs
2752 applies the @code{mode-line} face. For the mode line of a
2753 non-selected window, Emacs applies the @code{mode-line-inactive} face.
2754 For a header line, Emacs applies the @code{header-line} face.
2757 If any given attribute has not been specified during the preceding
2758 steps, Emacs applies the attribute of the @code{default} face.
2761 At each stage, if a face has a valid @code{:inherit} attribute,
2762 Emacs treats any attribute with an @code{unspecified} value as having
2763 the corresponding value drawn from the parent face(s). @pxref{Face
2764 Attributes}. Note that the parent face(s) may also leave the
2765 attribute unspecified; in that case, the attribute remains unspecified
2766 at the next level of face merging.
2768 @node Face Remapping
2769 @subsection Face Remapping
2770 @cindex face remapping
2772 The variable @code{face-remapping-alist} is used for buffer-local or
2773 global changes in the appearance of a face. For instance, it is used
2774 to implement the @code{text-scale-adjust} command (@pxref{Text
2775 Scale,,, emacs, The GNU Emacs Manual}).
2777 @defvar face-remapping-alist
2778 The value of this variable is an alist whose elements have the form
2779 @code{(@var{face} . @var{remapping})}. This causes Emacs to display
2780 any text having the face @var{face} with @var{remapping}, rather than
2781 the ordinary definition of @var{face}.
2783 @var{remapping} may be any face spec suitable for a @code{face} text
2784 property: either a face (i.e., a face name or a property list of
2785 attribute/value pairs), or a list of faces. For details, see the
2786 description of the @code{face} text property in @ref{Special
2787 Properties}. @var{remapping} serves as the complete specification for
2788 the remapped face---it replaces the normal definition of @var{face},
2789 instead of modifying it.
2791 If @code{face-remapping-alist} is buffer-local, its local value takes
2792 effect only within that buffer.
2794 Note: face remapping is non-recursive. If @var{remapping} references
2795 the same face name @var{face}, either directly or via the
2796 @code{:inherit} attribute of some other face in @var{remapping}, that
2797 reference uses the normal definition of @var{face}. For instance, if
2798 the @code{mode-line} face is remapped using this entry in
2799 @code{face-remapping-alist}:
2802 (mode-line italic mode-line)
2806 then the new definition of the @code{mode-line} face inherits from the
2807 @code{italic} face, and the @emph{normal} (non-remapped) definition of
2808 @code{mode-line} face.
2811 @cindex relative remapping, faces
2812 @cindex base remapping, faces
2813 The following functions implement a higher-level interface to
2814 @code{face-remapping-alist}. Most Lisp code should use these
2815 functions instead of setting @code{face-remapping-alist} directly, to
2816 avoid trampling on remappings applied elsewhere. These functions are
2817 intended for buffer-local remappings, so they all make
2818 @code{face-remapping-alist} buffer-local as a side-effect. They manage
2819 @code{face-remapping-alist} entries of the form
2822 (@var{face} @var{relative-spec-1} @var{relative-spec-2} @var{...} @var{base-spec})
2826 where, as explained above, each of the @var{relative-spec-N} and
2827 @var{base-spec} is either a face name, or a property list of
2828 attribute/value pairs. Each of the @dfn{relative remapping} entries,
2829 @var{relative-spec-N}, is managed by the
2830 @code{face-remap-add-relative} and @code{face-remap-remove-relative}
2831 functions; these are intended for simple modifications like changing
2832 the text size. The @dfn{base remapping} entry, @var{base-spec}, has
2833 the lowest priority and is managed by the @code{face-remap-set-base}
2834 and @code{face-remap-reset-base} functions; it is intended for major
2835 modes to remap faces in the buffers they control.
2837 @defun face-remap-add-relative face &rest specs
2838 This function adds the face spec in @var{specs} as relative
2839 remappings for face @var{face} in the current buffer. The remaining
2840 arguments, @var{specs}, should form either a list of face names, or a
2841 property list of attribute/value pairs.
2843 The return value is a Lisp object that serves as a ``cookie''; you can
2844 pass this object as an argument to @code{face-remap-remove-relative}
2845 if you need to remove the remapping later.
2848 ;; Remap the `escape-glyph' face into a combination
2849 ;; of the `highlight' and `italic' faces:
2850 (face-remap-add-relative 'escape-glyph 'highlight 'italic)
2852 ;; Increase the size of the `default' face by 50%:
2853 (face-remap-add-relative 'default :height 1.5)
2857 @defun face-remap-remove-relative cookie
2858 This function removes a relative remapping previously added by
2859 @code{face-remap-add-relative}. @var{cookie} should be the Lisp
2860 object returned by @code{face-remap-add-relative} when the remapping
2864 @defun face-remap-set-base face &rest specs
2865 This function sets the base remapping of @var{face} in the current
2866 buffer to @var{specs}. If @var{specs} is empty, the default base
2867 remapping is restored, similar to calling @code{face-remap-reset-base}
2868 (see below); note that this is different from @var{specs} containing a
2869 single value @code{nil}, which has the opposite result (the global
2870 definition of @var{face} is ignored).
2872 This overwrites the default @var{base-spec}, which inherits the global
2873 face definition, so it is up to the caller to add such inheritance if
2877 @defun face-remap-reset-base face
2878 This function sets the base remapping of @var{face} to its default
2879 value, which inherits from @var{face}'s global definition.
2882 @node Face Functions
2883 @subsection Functions for Working with Faces
2885 Here are additional functions for creating and working with faces.
2888 This function returns a list of all defined face names.
2892 This function returns the @dfn{face number} of face @var{face}. This
2893 is a number that uniquely identifies a face at low levels within
2894 Emacs. It is seldom necessary to refer to a face by its face number.
2897 @defun face-documentation face
2898 This function returns the documentation string of face @var{face}, or
2899 @code{nil} if none was specified for it.
2902 @defun face-equal face1 face2 &optional frame
2903 This returns @code{t} if the faces @var{face1} and @var{face2} have the
2904 same attributes for display.
2907 @defun face-differs-from-default-p face &optional frame
2908 This returns non-@code{nil} if the face @var{face} displays
2909 differently from the default face.
2913 @cindex alias, for faces
2914 A @dfn{face alias} provides an equivalent name for a face. You can
2915 define a face alias by giving the alias symbol the @code{face-alias}
2916 property, with a value of the target face name. The following example
2917 makes @code{modeline} an alias for the @code{mode-line} face.
2920 (put 'modeline 'face-alias 'mode-line)
2923 @defmac define-obsolete-face-alias obsolete-face current-face when
2924 This macro defines @code{obsolete-face} as an alias for
2925 @var{current-face}, and also marks it as obsolete, indicating that it
2926 may be removed in future. @var{when} should be a string indicating
2927 when @code{obsolete-face} was made obsolete (usually a version number
2932 @subsection Automatic Face Assignment
2933 @cindex automatic face assignment
2934 @cindex faces, automatic choice
2936 This hook is used for automatically assigning faces to text in the
2937 buffer. It is part of the implementation of Jit-Lock mode, used by
2940 @defvar fontification-functions
2941 This variable holds a list of functions that are called by Emacs
2942 redisplay as needed, just before doing redisplay. They are called even
2943 when Font Lock Mode isn't enabled. When Font Lock Mode is enabled, this
2944 variable usually holds just one function, @code{jit-lock-function}.
2946 The functions are called in the order listed, with one argument, a
2947 buffer position @var{pos}. Collectively they should attempt to assign
2948 faces to the text in the current buffer starting at @var{pos}.
2950 The functions should record the faces they assign by setting the
2951 @code{face} property. They should also add a non-@code{nil}
2952 @code{fontified} property to all the text they have assigned faces to.
2953 That property tells redisplay that faces have been assigned to that text
2956 It is probably a good idea for the functions to do nothing if the
2957 character after @var{pos} already has a non-@code{nil} @code{fontified}
2958 property, but this is not required. If one function overrides the
2959 assignments made by a previous one, the properties after the last
2960 function finishes are the ones that really matter.
2962 For efficiency, we recommend writing these functions so that they
2963 usually assign faces to around 400 to 600 characters at each call.
2967 @subsection Basic Faces
2970 If your Emacs Lisp program needs to assign some faces to text, it is
2971 often a good idea to use certain existing faces or inherit from them,
2972 rather than defining entirely new faces. This way, if other users
2973 have customized the basic faces to give Emacs a certain look, your
2974 program will ``fit in'' without additional customization.
2976 Some of the basic faces defined in Emacs are listed below. In
2977 addition to these, you might want to make use of the Font Lock faces
2978 for syntactic highlighting, if highlighting is not already handled by
2979 Font Lock mode, or if some Font Lock faces are not in use.
2980 @xref{Faces for Font Lock}.
2984 The default face, whose attributes are all specified. All other faces
2985 implicitly inherit from it: any unspecified attribute defaults to the
2986 attribute on this face (@pxref{Face Attributes}).
2993 @itemx variable-pitch
2994 These have the attributes indicated by their names (e.g., @code{bold}
2995 has a bold @code{:weight} attribute), with all other attributes
2996 unspecified (and so given by @code{default}).
2999 For ``dimmed out'' text. For example, it is used for the ignored
3000 part of a filename in the minibuffer (@pxref{Minibuffer File,,
3001 Minibuffers for File Names, emacs, The GNU Emacs Manual}).
3005 For clickable text buttons that send the user to a different
3006 buffer or ``location''.
3009 For stretches of text that should temporarily stand out. For example,
3010 it is commonly assigned to the @code{mouse-face} property for cursor
3011 highlighting (@pxref{Special Properties}).
3014 For text matching a search command.
3019 For text concerning errors, warnings, or successes. For example,
3020 these are used for messages in @file{*Compilation*} buffers.
3023 @node Font Selection
3024 @subsection Font Selection
3025 @cindex font selection
3026 @cindex selecting a font
3028 Before Emacs can draw a character on a graphical display, it must
3029 select a @dfn{font} for that character@footnote{In this context, the
3030 term @dfn{font} has nothing to do with Font Lock (@pxref{Font Lock
3031 Mode}).}. @xref{Fonts,,, emacs, The GNU Emacs Manual}. Normally,
3032 Emacs automatically chooses a font based on the faces assigned to that
3033 character---specifically, the face attributes @code{:family},
3034 @code{:weight}, @code{:slant}, and @code{:width} (@pxref{Face
3035 Attributes}). The choice of font also depends on the character to be
3036 displayed; some fonts can only display a limited set of characters.
3037 If no available font exactly fits the requirements, Emacs looks for
3038 the @dfn{closest matching font}. The variables in this section
3039 control how Emacs makes this selection.
3041 @defopt face-font-family-alternatives
3042 If a given family is specified but does not exist, this variable
3043 specifies alternative font families to try. Each element should have
3047 (@var{family} @var{alternate-families}@dots{})
3050 If @var{family} is specified but not available, Emacs will try the other
3051 families given in @var{alternate-families}, one by one, until it finds a
3052 family that does exist.
3055 @defopt face-font-selection-order
3056 If there is no font that exactly matches all desired face attributes
3057 (@code{:width}, @code{:height}, @code{:weight}, and @code{:slant}),
3058 this variable specifies the order in which these attributes should be
3059 considered when selecting the closest matching font. The value should
3060 be a list containing those four attribute symbols, in order of
3061 decreasing importance. The default is @code{(:width :height :weight
3064 Font selection first finds the best available matches for the first
3065 attribute in the list; then, among the fonts which are best in that
3066 way, it searches for the best matches in the second attribute, and so
3069 The attributes @code{:weight} and @code{:width} have symbolic values in
3070 a range centered around @code{normal}. Matches that are more extreme
3071 (farther from @code{normal}) are somewhat preferred to matches that are
3072 less extreme (closer to @code{normal}); this is designed to ensure that
3073 non-normal faces contrast with normal ones, whenever possible.
3075 One example of a case where this variable makes a difference is when the
3076 default font has no italic equivalent. With the default ordering, the
3077 @code{italic} face will use a non-italic font that is similar to the
3078 default one. But if you put @code{:slant} before @code{:height}, the
3079 @code{italic} face will use an italic font, even if its height is not
3083 @defopt face-font-registry-alternatives
3084 This variable lets you specify alternative font registries to try, if a
3085 given registry is specified and doesn't exist. Each element should have
3089 (@var{registry} @var{alternate-registries}@dots{})
3092 If @var{registry} is specified but not available, Emacs will try the
3093 other registries given in @var{alternate-registries}, one by one,
3094 until it finds a registry that does exist.
3097 @cindex scalable fonts
3098 Emacs can make use of scalable fonts, but by default it does not use
3101 @defopt scalable-fonts-allowed
3102 This variable controls which scalable fonts to use. A value of
3103 @code{nil}, the default, means do not use scalable fonts. @code{t}
3104 means to use any scalable font that seems appropriate for the text.
3106 Otherwise, the value must be a list of regular expressions. Then a
3107 scalable font is enabled for use if its name matches any regular
3108 expression in the list. For example,
3111 (setq scalable-fonts-allowed '("iso10646-1$"))
3115 allows the use of scalable fonts with registry @code{iso10646-1}.
3118 @defvar face-font-rescale-alist
3119 This variable specifies scaling for certain faces. Its value should
3120 be a list of elements of the form
3123 (@var{fontname-regexp} . @var{scale-factor})
3126 If @var{fontname-regexp} matches the font name that is about to be
3127 used, this says to choose a larger similar font according to the
3128 factor @var{scale-factor}. You would use this feature to normalize
3129 the font size if certain fonts are bigger or smaller than their
3130 nominal heights and widths would suggest.
3134 @subsection Looking Up Fonts
3136 @cindex looking up fonts
3138 @defun x-list-fonts name &optional reference-face frame maximum width
3139 This function returns a list of available font names that match
3140 @var{name}. @var{name} should be a string containing a font name in
3141 either the Fontconfig, GTK, or XLFD format (@pxref{Fonts,,, emacs, The
3142 GNU Emacs Manual}). Within an XLFD string, wildcard characters may be
3143 used: the @samp{*} character matches any substring, and the @samp{?}
3144 character matches any single character. Case is ignored when matching
3147 If the optional arguments @var{reference-face} and @var{frame} are
3148 specified, the returned list includes only fonts that are the same
3149 size as @var{reference-face} (a face name) currently is on the frame
3152 The optional argument @var{maximum} sets a limit on how many fonts to
3153 return. If it is non-@code{nil}, then the return value is truncated
3154 after the first @var{maximum} matching fonts. Specifying a small
3155 value for @var{maximum} can make this function much faster, in cases
3156 where many fonts match the pattern.
3158 The optional argument @var{width} specifies a desired font width. If
3159 it is non-@code{nil}, the function only returns those fonts whose
3160 characters are (on average) @var{width} times as wide as
3161 @var{reference-face}.
3164 @defun x-family-fonts &optional family frame
3165 This function returns a list describing the available fonts for family
3166 @var{family} on @var{frame}. If @var{family} is omitted or @code{nil},
3167 this list applies to all families, and therefore, it contains all
3168 available fonts. Otherwise, @var{family} must be a string; it may
3169 contain the wildcards @samp{?} and @samp{*}.
3171 The list describes the display that @var{frame} is on; if @var{frame} is
3172 omitted or @code{nil}, it applies to the selected frame's display
3173 (@pxref{Input Focus}).
3175 Each element in the list is a vector of the following form:
3178 [@var{family} @var{width} @var{point-size} @var{weight} @var{slant}
3179 @var{fixed-p} @var{full} @var{registry-and-encoding}]
3182 The first five elements correspond to face attributes; if you
3183 specify these attributes for a face, it will use this font.
3185 The last three elements give additional information about the font.
3186 @var{fixed-p} is non-@code{nil} if the font is fixed-pitch.
3187 @var{full} is the full name of the font, and
3188 @var{registry-and-encoding} is a string giving the registry and
3189 encoding of the font.
3193 @subsection Fontsets
3196 A @dfn{fontset} is a list of fonts, each assigned to a range of
3197 character codes. An individual font cannot display the whole range of
3198 characters that Emacs supports, but a fontset can. Fontsets have names,
3199 just as fonts do, and you can use a fontset name in place of a font name
3200 when you specify the ``font'' for a frame or a face. Here is
3201 information about defining a fontset under Lisp program control.
3203 @defun create-fontset-from-fontset-spec fontset-spec &optional style-variant-p noerror
3204 This function defines a new fontset according to the specification
3205 string @var{fontset-spec}. The string should have this format:
3208 @var{fontpattern}, @r{[}@var{charset}:@var{font}@r{]@dots{}}
3212 Whitespace characters before and after the commas are ignored.
3214 The first part of the string, @var{fontpattern}, should have the form of
3215 a standard X font name, except that the last two fields should be
3216 @samp{fontset-@var{alias}}.
3218 The new fontset has two names, one long and one short. The long name is
3219 @var{fontpattern} in its entirety. The short name is
3220 @samp{fontset-@var{alias}}. You can refer to the fontset by either
3221 name. If a fontset with the same name already exists, an error is
3222 signaled, unless @var{noerror} is non-@code{nil}, in which case this
3223 function does nothing.
3225 If optional argument @var{style-variant-p} is non-@code{nil}, that says
3226 to create bold, italic and bold-italic variants of the fontset as well.
3227 These variant fontsets do not have a short name, only a long one, which
3228 is made by altering @var{fontpattern} to indicate the bold and/or italic
3231 The specification string also says which fonts to use in the fontset.
3232 See below for the details.
3235 The construct @samp{@var{charset}:@var{font}} specifies which font to
3236 use (in this fontset) for one particular character set. Here,
3237 @var{charset} is the name of a character set, and @var{font} is the font
3238 to use for that character set. You can use this construct any number of
3239 times in the specification string.
3241 For the remaining character sets, those that you don't specify
3242 explicitly, Emacs chooses a font based on @var{fontpattern}: it replaces
3243 @samp{fontset-@var{alias}} with a value that names one character set.
3244 For the @acronym{ASCII} character set, @samp{fontset-@var{alias}} is replaced
3245 with @samp{ISO8859-1}.
3247 In addition, when several consecutive fields are wildcards, Emacs
3248 collapses them into a single wildcard. This is to prevent use of
3249 auto-scaled fonts. Fonts made by scaling larger fonts are not usable
3250 for editing, and scaling a smaller font is not useful because it is
3251 better to use the smaller font in its own size, which Emacs does.
3253 Thus if @var{fontpattern} is this,
3256 -*-fixed-medium-r-normal-*-24-*-*-*-*-*-fontset-24
3260 the font specification for @acronym{ASCII} characters would be this:
3263 -*-fixed-medium-r-normal-*-24-*-ISO8859-1
3267 and the font specification for Chinese GB2312 characters would be this:
3270 -*-fixed-medium-r-normal-*-24-*-gb2312*-*
3273 You may not have any Chinese font matching the above font
3274 specification. Most X distributions include only Chinese fonts that
3275 have @samp{song ti} or @samp{fangsong ti} in the @var{family} field. In
3276 such a case, @samp{Fontset-@var{n}} can be specified as below:
3279 Emacs.Fontset-0: -*-fixed-medium-r-normal-*-24-*-*-*-*-*-fontset-24,\
3280 chinese-gb2312:-*-*-medium-r-normal-*-24-*-gb2312*-*
3284 Then, the font specifications for all but Chinese GB2312 characters have
3285 @samp{fixed} in the @var{family} field, and the font specification for
3286 Chinese GB2312 characters has a wild card @samp{*} in the @var{family}
3289 @defun set-fontset-font name character font-spec &optional frame add
3290 This function modifies the existing fontset @var{name} to use the font
3291 matching with @var{font-spec} for the character @var{character}.
3293 If @var{name} is @code{nil}, this function modifies the fontset of the
3294 selected frame or that of @var{frame} if @var{frame} is not
3297 If @var{name} is @code{t}, this function modifies the default
3298 fontset, whose short name is @samp{fontset-default}.
3300 @var{character} may be a cons; @code{(@var{from} . @var{to})}, where
3301 @var{from} and @var{to} are character codepoints. In that case, use
3302 @var{font-spec} for all characters in the range @var{from} and @var{to}
3305 @var{character} may be a charset. In that case, use
3306 @var{font-spec} for all character in the charsets.
3308 @var{character} may be a script name. In that case, use
3309 @var{font-spec} for all character in the charsets.
3311 @var{font-spec} may be a cons; @code{(@var{family} . @var{registry})},
3312 where @var{family} is a family name of a font (possibly including a
3313 foundry name at the head), @var{registry} is a registry name of a font
3314 (possibly including an encoding name at the tail).
3316 @var{font-spec} may be a font name string.
3318 The optional argument @var{add}, if non-@code{nil}, specifies how to
3319 add @var{font-spec} to the font specifications previously set. If it
3320 is @code{prepend}, @var{font-spec} is prepended. If it is
3321 @code{append}, @var{font-spec} is appended. By default,
3322 @var{font-spec} overrides the previous settings.
3324 For instance, this changes the default fontset to use a font of which
3325 family name is @samp{Kochi Gothic} for all characters belonging to
3326 the charset @code{japanese-jisx0208}.
3329 (set-fontset-font t 'japanese-jisx0208
3330 (font-spec :family "Kochi Gothic"))
3334 @defun char-displayable-p char
3335 This function returns @code{t} if Emacs ought to be able to display
3336 @var{char}. More precisely, if the selected frame's fontset has a
3337 font to display the character set that @var{char} belongs to.
3339 Fontsets can specify a font on a per-character basis; when the fontset
3340 does that, this function's value may not be accurate.
3343 @node Low-Level Font
3344 @subsection Low-Level Font Representation
3345 @cindex font property
3347 Normally, it is not necessary to manipulate fonts directly. In case
3348 you need to do so, this section explains how.
3350 In Emacs Lisp, fonts are represented using three different Lisp
3351 object types: @dfn{font objects}, @dfn{font specs}, and @dfn{font
3354 @defun fontp object &optional type
3355 Return @code{t} if @var{object} is a font object, font spec, or font
3356 entity. Otherwise, return @code{nil}.
3358 The optional argument @var{type}, if non-@code{nil}, determines the
3359 exact type of Lisp object to check for. In that case, @var{type}
3360 should be one of @code{font-object}, @code{font-spec}, or
3365 A font object is a Lisp object that represents a font that Emacs has
3366 @dfn{opened}. Font objects cannot be modified in Lisp, but they can
3369 @defun font-at position &optional window string
3370 Return the font object that is being used to display the character at
3371 position @var{position} in the window @var{window}. If @var{window}
3372 is @code{nil}, it defaults to the selected window. If @var{string} is
3373 @code{nil}, @var{position} specifies a position in the current buffer;
3374 otherwise, @var{string} should be a string, and @var{position}
3375 specifies a position in that string.
3379 A font spec is a Lisp object that contains a set of specifications
3380 that can be used to find a font. More than one font may match the
3381 specifications in a font spec.
3383 @defun font-spec &rest arguments
3384 Return a new font spec using the specifications in @var{arguments},
3385 which should come in @code{property}-@code{value} pairs. The possible
3386 specifications are as follows:
3390 The font name (a string), in either XLFD, Fontconfig, or GTK format.
3391 @xref{Fonts,,, emacs, The GNU Emacs Manual}.
3398 These have the same meanings as the face attributes of the same name.
3399 @xref{Face Attributes}.
3402 The font size---either a non-negative integer that specifies the pixel
3403 size, or a floating-point number that specifies the point size.
3406 Additional typographic style information for the font, such as
3407 @samp{sans}. The value should be a string or a symbol.
3409 @cindex font registry
3411 The charset registry and encoding of the font, such as
3412 @samp{iso8859-1}. The value should be a string or a symbol.
3415 The script that the font must support (a symbol).
3418 @cindex OpenType font
3419 The font must be an OpenType font that supports these OpenType
3420 features, provided Emacs is compiled with a library, such as
3421 @samp{libotf} on GNU/Linux, that supports complex text layout for
3422 scripts which need that. The value must be a list of the form
3425 @code{(@var{script-tag} @var{langsys-tag} @var{gsub} @var{gpos})}
3428 where @var{script-tag} is the OpenType script tag symbol;
3429 @var{langsys-tag} is the OpenType language system tag symbol, or
3430 @code{nil} to use the default language system; @code{gsub} is a list
3431 of OpenType GSUB feature tag symbols, or @code{nil} if none is
3432 required; and @code{gpos} is a list of OpenType GPOS feature tag
3433 symbols, or @code{nil} if none is required. If @code{gsub} or
3434 @code{gpos} is a list, a @code{nil} element in that list means that
3435 the font must not match any of the remaining tag symbols. The
3436 @code{gpos} element may be omitted.
3440 @defun font-put font-spec property value
3441 Set the font property @var{property} in the font-spec @var{font-spec}
3446 A font entity is a reference to a font that need not be open. Its
3447 properties are intermediate between a font object and a font spec:
3448 like a font object, and unlike a font spec, it refers to a single,
3449 specific font. Unlike a font object, creating a font entity does not
3450 load the contents of that font into computer memory. Emacs may open
3451 multiple font objects of different sizes from a single font entity
3452 referring to a scalable font.
3454 @defun find-font font-spec &optional frame
3455 This function returns a font entity that best matches the font spec
3456 @var{font-spec} on frame @var{frame}. If @var{frame} is @code{nil},
3457 it defaults to the selected frame.
3460 @defun list-fonts font-spec &optional frame num prefer
3461 This function returns a list of all font entities that match the font
3462 spec @var{font-spec}.
3464 The optional argument @var{frame}, if non-@code{nil}, specifies the
3465 frame on which the fonts are to be displayed. The optional argument
3466 @var{num}, if non-@code{nil}, should be an integer that specifies the
3467 maximum length of the returned list. The optional argument
3468 @var{prefer}, if non-@code{nil}, should be another font spec, which is
3469 used to control the order of the returned list; the returned font
3470 entities are sorted in order of decreasing ``closeness'' to that font
3474 If you call @code{set-face-attribute} and pass a font spec, font
3475 entity, or font name string as the value of the @code{:font}
3476 attribute, Emacs opens the best ``matching'' font that is available
3477 for display. It then stores the corresponding font object as the
3478 actual value of the @code{:font} attribute for that face.
3480 The following functions can be used to obtain information about a
3481 font. For these functions, the @var{font} argument can be a font
3482 object, a font entity, or a font spec.
3484 @defun font-get font property
3485 This function returns the value of the font property @var{property}
3488 If @var{font} is a font spec and the font spec does not specify
3489 @var{property}, the return value is @code{nil}. If @var{font} is a
3490 font object or font entity, the value for the @var{:script} property
3491 may be a list of scripts supported by the font.
3494 @defun font-face-attributes font &optional frame
3495 This function returns a list of face attributes corresponding to
3496 @var{font}. The optional argument @var{frame} specifies the frame on
3497 which the font is to be displayed. If it is @code{nil}, the selected
3498 frame is used. The return value has the form
3501 (:family @var{family} :height @var{height} :weight @var{weight}
3502 :slant @var{slant} :width @var{width})
3505 where the values of @var{family}, @var{height}, @var{weight},
3506 @var{slant}, and @var{width} are face attribute values. Some of these
3507 key-attribute pairs may be omitted from the list if they are not
3508 specified by @var{font}.
3511 @defun font-xlfd-name font &optional fold-wildcards
3512 This function returns the XLFD (X Logical Font Descriptor), a string,
3513 matching @var{font}. @xref{Fonts,,, emacs, The GNU Emacs Manual}, for
3514 information about XLFDs. If the name is too long for an XLFD (which
3515 can contain at most 255 characters), the function returns @code{nil}.
3517 If the optional argument @var{fold-wildcards} is non-@code{nil},
3518 consecutive wildcards in the XLFD are folded into one.
3521 The following two functions return important information about a font.
3523 @defun font-info name &optional frame
3524 This function returns information about a font specified by its
3525 @var{name}, a string, as it is used on @var{frame}. If @var{frame} is
3526 omitted or @code{nil}, it defaults to the selected frame.
3528 The value returned by the function is a vector of the form
3529 @code{[@var{opened-name} @var{full-name} @var{size} @var{height}
3530 @var{baseline-offset} @var{relative-compose} @var{default-ascent}
3531 @var{max-width} @var{ascent} @var{descent} @var{space-width}
3532 @var{average-width} @var{filename} @var{capability}]}. Here's the
3533 description of each components of this vector:
3537 The name used to open the font, a string.
3540 The full name of the font, a string.
3543 The pixel size of the font.
3546 The height of the font in pixels.
3548 @item baseline-offset
3549 The offset in pixels from the @acronym{ASCII} baseline, positive
3552 @item relative-compose
3553 @itemx default-ascent
3554 Numbers controlling how to compose characters.
3558 The ascent and descent of this font. The sum of these two numbers
3559 should be equal to the value of @var{height} above.
3562 The width, in pixels, of the font's space character.
3565 The average width of the font characters. If this is zero, Emacs uses
3566 the value of @var{space-width} instead, when it calculates text layout
3570 The file name of the font as a string. This can be @code{nil} if the
3571 font back-end does not provide a way to find out the font's file name.
3574 A list whose first element is a symbol representing the font type, one
3575 of @code{x}, @code{opentype}, @code{truetype}, @code{type1},
3576 @code{pcf}, or @code{bdf}. For OpenType fonts, the list includes 2
3577 additional elements describing the @sc{gsub} and @sc{gpos} features
3578 supported by the font. Each of these elements is a list of the form
3579 @code{((@var{script} (@var{langsys} @var{feature} @dots{}) @dots{})
3580 @dots{})}, where @var{script} is a symbol representing an OpenType
3581 script tag, @var{langsys} is a symbol representing an OpenType langsys
3582 tag (or @code{nil}, which stands for the default langsys), and each
3583 @var{feature} is a symbol representing an OpenType feature tag.
3587 @defun query-font font-object
3588 This function returns information about a @var{font-object}. (This is
3589 in contrast to @code{font-info}, which takes the font name, a string,
3592 The value returned by the function is a vector of the form
3593 @code{[@var{name} @var{filename} @var{pixel-size} @var{max-width}
3594 @var{ascent} @var{descent} @var{space-width} @var{average-width}
3595 @var{capability}]}. Here's the description of each components of this
3600 The font name, a string.
3603 The file name of the font as a string. This can be @code{nil} if the
3604 font back-end does not provide a way to find out the font's file name.
3607 The pixel size of the font used to open the font.
3610 The maximum advance width of the font.
3614 The ascent and descent of this font. The sum of these two numbers
3615 gives the font height.
3618 The width, in pixels, of the font's space character.
3621 The average width of the font characters. If this is zero, Emacs uses
3622 the value of @var{space-width} instead, when it calculates text layout
3626 A list whose first element is a symbol representing the font type, one
3627 of @code{x}, @code{opentype}, @code{truetype}, @code{type1},
3628 @code{pcf}, or @code{bdf}. For OpenType fonts, the list includes 2
3629 additional elements describing the @sc{gsub} and @sc{gpos} features
3630 supported by the font. Each of these elements is a list of the form
3631 @code{((@var{script} (@var{langsys} @var{feature} @dots{}) @dots{})
3632 @dots{})}, where @var{script} is a symbol representing an OpenType
3633 script tag, @var{langsys} is a symbol representing an OpenType langsys
3634 tag (or @code{nil}, which stands for the default langsys), and each
3635 @var{feature} is a symbol representing an OpenType feature tag.
3643 On graphical displays, Emacs draws @dfn{fringes} next to each
3644 window: thin vertical strips down the sides which can display bitmaps
3645 indicating truncation, continuation, horizontal scrolling, and so on.
3648 * Fringe Size/Pos:: Specifying where to put the window fringes.
3649 * Fringe Indicators:: Displaying indicator icons in the window fringes.
3650 * Fringe Cursors:: Displaying cursors in the right fringe.
3651 * Fringe Bitmaps:: Specifying bitmaps for fringe indicators.
3652 * Customizing Bitmaps:: Specifying your own bitmaps to use in the fringes.
3653 * Overlay Arrow:: Display of an arrow to indicate position.
3656 @node Fringe Size/Pos
3657 @subsection Fringe Size and Position
3659 The following buffer-local variables control the position and width
3660 of fringes in windows showing that buffer.
3662 @defvar fringes-outside-margins
3663 The fringes normally appear between the display margins and the window
3664 text. If the value is non-@code{nil}, they appear outside the display
3665 margins. @xref{Display Margins}.
3668 @defvar left-fringe-width
3669 This variable, if non-@code{nil}, specifies the width of the left
3670 fringe in pixels. A value of @code{nil} means to use the left fringe
3671 width from the window's frame.
3674 @defvar right-fringe-width
3675 This variable, if non-@code{nil}, specifies the width of the right
3676 fringe in pixels. A value of @code{nil} means to use the right fringe
3677 width from the window's frame.
3680 Any buffer which does not specify values for these variables uses
3681 the values specified by the @code{left-fringe} and @code{right-fringe}
3682 frame parameters (@pxref{Layout Parameters}).
3684 The above variables actually take effect via the function
3685 @code{set-window-buffer} (@pxref{Buffers and Windows}), which calls
3686 @code{set-window-fringes} as a subroutine. If you change one of these
3687 variables, the fringe display is not updated in existing windows
3688 showing the buffer, unless you call @code{set-window-buffer} again in
3689 each affected window. You can also use @code{set-window-fringes} to
3690 control the fringe display in individual windows.
3692 @defun set-window-fringes window left &optional right outside-margins
3693 This function sets the fringe widths of window @var{window}.
3694 If @var{window} is @code{nil}, the selected window is used.
3696 The argument @var{left} specifies the width in pixels of the left
3697 fringe, and likewise @var{right} for the right fringe. A value of
3698 @code{nil} for either one stands for the default width. If
3699 @var{outside-margins} is non-@code{nil}, that specifies that fringes
3700 should appear outside of the display margins.
3703 @defun window-fringes &optional window
3704 This function returns information about the fringes of a window
3705 @var{window}. If @var{window} is omitted or @code{nil}, the selected
3706 window is used. The value has the form @code{(@var{left-width}
3707 @var{right-width} @var{outside-margins})}.
3711 @node Fringe Indicators
3712 @subsection Fringe Indicators
3713 @cindex fringe indicators
3714 @cindex indicators, fringe
3716 @dfn{Fringe indicators} are tiny icons displayed in the window
3717 fringe to indicate truncated or continued lines, buffer boundaries,
3720 @defopt indicate-empty-lines
3721 @cindex fringes, and empty line indication
3722 @cindex empty lines, indicating
3723 When this is non-@code{nil}, Emacs displays a special glyph in the
3724 fringe of each empty line at the end of the buffer, on graphical
3725 displays. @xref{Fringes}. This variable is automatically
3726 buffer-local in every buffer.
3729 @defopt indicate-buffer-boundaries
3730 @cindex buffer boundaries, indicating
3731 This buffer-local variable controls how the buffer boundaries and
3732 window scrolling are indicated in the window fringes.
3734 Emacs can indicate the buffer boundaries---that is, the first and last
3735 line in the buffer---with angle icons when they appear on the screen.
3736 In addition, Emacs can display an up-arrow in the fringe to show
3737 that there is text above the screen, and a down-arrow to show
3738 there is text below the screen.
3740 There are three kinds of basic values:
3744 Don't display any of these fringe icons.
3746 Display the angle icons and arrows in the left fringe.
3748 Display the angle icons and arrows in the right fringe.
3750 Display the angle icons in the left fringe
3751 and don't display the arrows.
3754 Otherwise the value should be an alist that specifies which fringe
3755 indicators to display and where. Each element of the alist should
3756 have the form @code{(@var{indicator} . @var{position})}. Here,
3757 @var{indicator} is one of @code{top}, @code{bottom}, @code{up},
3758 @code{down}, and @code{t} (which covers all the icons not yet
3759 specified), while @var{position} is one of @code{left}, @code{right}
3762 For example, @code{((top . left) (t . right))} places the top angle
3763 bitmap in left fringe, and the bottom angle bitmap as well as both
3764 arrow bitmaps in right fringe. To show the angle bitmaps in the left
3765 fringe, and no arrow bitmaps, use @code{((top . left) (bottom . left))}.
3768 @defvar fringe-indicator-alist
3769 This buffer-local variable specifies the mapping from logical fringe
3770 indicators to the actual bitmaps displayed in the window fringes. The
3771 value is an alist of elements @code{(@var{indicator}
3772 . @var{bitmaps})}, where @var{indicator} specifies a logical indicator
3773 type and @var{bitmaps} specifies the fringe bitmaps to use for that
3776 Each @var{indicator} should be one of the following symbols:
3779 @item @code{truncation}, @code{continuation}.
3780 Used for truncation and continuation lines.
3782 @item @code{up}, @code{down}, @code{top}, @code{bottom}, @code{top-bottom}
3783 Used when @code{indicate-buffer-boundaries} is non-@code{nil}:
3784 @code{up} and @code{down} indicate a buffer boundary lying above or
3785 below the window edge; @code{top} and @code{bottom} indicate the
3786 topmost and bottommost buffer text line; and @code{top-bottom}
3787 indicates where there is just one line of text in the buffer.
3789 @item @code{empty-line}
3790 Used to indicate empty lines when @code{indicate-empty-lines} is
3793 @item @code{overlay-arrow}
3794 Used for overlay arrows (@pxref{Overlay Arrow}).
3795 @c Is this used anywhere?
3796 @c @item Unknown bitmap indicator:
3800 Each @var{bitmaps} value may be a list of symbols @code{(@var{left}
3801 @var{right} [@var{left1} @var{right1}])}. The @var{left} and
3802 @var{right} symbols specify the bitmaps shown in the left and/or right
3803 fringe, for the specific indicator. @var{left1} and @var{right1} are
3804 specific to the @code{bottom} and @code{top-bottom} indicators, and
3805 are used to indicate that the last text line has no final newline.
3806 Alternatively, @var{bitmaps} may be a single symbol which is used in
3807 both left and right fringes.
3809 @xref{Fringe Bitmaps}, for a list of standard bitmap symbols and how
3810 to define your own. In addition, @code{nil} represents the empty
3811 bitmap (i.e., an indicator that is not shown).
3813 When @code{fringe-indicator-alist} has a buffer-local value, and
3814 there is no bitmap defined for a logical indicator, or the bitmap is
3815 @code{t}, the corresponding value from the default value of
3816 @code{fringe-indicator-alist} is used.
3819 @node Fringe Cursors
3820 @subsection Fringe Cursors
3821 @cindex fringe cursors
3822 @cindex cursor, fringe
3824 When a line is exactly as wide as the window, Emacs displays the
3825 cursor in the right fringe instead of using two lines. Different
3826 bitmaps are used to represent the cursor in the fringe depending on
3827 the current buffer's cursor type.
3829 @defopt overflow-newline-into-fringe
3830 If this is non-@code{nil}, lines exactly as wide as the window (not
3831 counting the final newline character) are not continued. Instead,
3832 when point is at the end of the line, the cursor appears in the right
3836 @defvar fringe-cursor-alist
3837 This variable specifies the mapping from logical cursor type to the
3838 actual fringe bitmaps displayed in the right fringe. The value is an
3839 alist where each element has the form @code{(@var{cursor-type}
3840 . @var{bitmap})}, which means to use the fringe bitmap @var{bitmap} to
3841 display cursors of type @var{cursor-type}.
3843 Each @var{cursor-type} should be one of @code{box}, @code{hollow},
3844 @code{bar}, @code{hbar}, or @code{hollow-small}. The first four have
3845 the same meanings as in the @code{cursor-type} frame parameter
3846 (@pxref{Cursor Parameters}). The @code{hollow-small} type is used
3847 instead of @code{hollow} when the normal @code{hollow-rectangle}
3848 bitmap is too tall to fit on a specific display line.
3850 Each @var{bitmap} should be a symbol specifying the fringe bitmap to
3851 be displayed for that logical cursor type.
3853 See the next subsection for details.
3856 @xref{Fringe Bitmaps}.
3859 @c FIXME: I can't find the fringes-indicator-alist variable. Maybe
3860 @c it should be fringe-indicator-alist or fringe-cursor-alist? --xfq
3861 When @code{fringe-cursor-alist} has a buffer-local value, and there is
3862 no bitmap defined for a cursor type, the corresponding value from the
3863 default value of @code{fringes-indicator-alist} is used.
3866 @node Fringe Bitmaps
3867 @subsection Fringe Bitmaps
3868 @cindex fringe bitmaps
3869 @cindex bitmaps, fringe
3871 The @dfn{fringe bitmaps} are the actual bitmaps which represent the
3872 logical fringe indicators for truncated or continued lines, buffer
3873 boundaries, overlay arrows, etc. Each bitmap is represented by a
3876 These symbols are referred to by the variables
3877 @code{fringe-indicator-alist} and @code{fringe-cursor-alist},
3878 described in the previous subsections.
3881 These symbols are referred to by the variable
3882 @code{fringe-indicator-alist}, which maps fringe indicators to bitmaps
3883 (@pxref{Fringe Indicators}), and the variable
3884 @code{fringe-cursor-alist}, which maps fringe cursors to bitmaps
3885 (@pxref{Fringe Cursors}).
3888 Lisp programs can also directly display a bitmap in the left or
3889 right fringe, by using a @code{display} property for one of the
3890 characters appearing in the line (@pxref{Other Display Specs}). Such
3891 a display specification has the form
3894 (@var{fringe} @var{bitmap} [@var{face}])
3898 @var{fringe} is either the symbol @code{left-fringe} or
3899 @code{right-fringe}. @var{bitmap} is a symbol identifying the bitmap
3900 to display. The optional @var{face} names a face whose foreground
3901 color is used to display the bitmap; this face is automatically merged
3902 with the @code{fringe} face.
3904 Here is a list of the standard fringe bitmaps defined in Emacs, and
3905 how they are currently used in Emacs (via
3906 @code{fringe-indicator-alist} and @code{fringe-cursor-alist}):
3909 @item @code{left-arrow}, @code{right-arrow}
3910 Used to indicate truncated lines.
3912 @item @code{left-curly-arrow}, @code{right-curly-arrow}
3913 Used to indicate continued lines.
3915 @item @code{right-triangle}, @code{left-triangle}
3916 The former is used by overlay arrows. The latter is unused.
3918 @item @code{up-arrow}, @code{down-arrow}, @code{top-left-angle} @code{top-right-angle}
3919 @itemx @code{bottom-left-angle}, @code{bottom-right-angle}
3920 @itemx @code{top-right-angle}, @code{top-left-angle}
3921 @itemx @code{left-bracket}, @code{right-bracket}, @code{top-right-angle}, @code{top-left-angle}
3922 Used to indicate buffer boundaries.
3924 @item @code{filled-rectangle}, @code{hollow-rectangle}
3925 @itemx @code{filled-square}, @code{hollow-square}
3926 @itemx @code{vertical-bar}, @code{horizontal-bar}
3927 Used for different types of fringe cursors.
3929 @item @code{empty-line}, @code{exclamation-mark}, @code{question-mark}, @code{exclamation-mark}
3930 Not used by core Emacs features.
3934 The next subsection describes how to define your own fringe bitmaps.
3936 @defun fringe-bitmaps-at-pos &optional pos window
3937 This function returns the fringe bitmaps of the display line
3938 containing position @var{pos} in window @var{window}. The return
3939 value has the form @code{(@var{left} @var{right} @var{ov})}, where @var{left}
3940 is the symbol for the fringe bitmap in the left fringe (or @code{nil}
3941 if no bitmap), @var{right} is similar for the right fringe, and @var{ov}
3942 is non-@code{nil} if there is an overlay arrow in the left fringe.
3944 The value is @code{nil} if @var{pos} is not visible in @var{window}.
3945 If @var{window} is @code{nil}, that stands for the selected window.
3946 If @var{pos} is @code{nil}, that stands for the value of point in
3950 @node Customizing Bitmaps
3951 @subsection Customizing Fringe Bitmaps
3952 @cindex fringe bitmaps, customizing
3954 @defun define-fringe-bitmap bitmap bits &optional height width align
3955 This function defines the symbol @var{bitmap} as a new fringe bitmap,
3956 or replaces an existing bitmap with that name.
3958 The argument @var{bits} specifies the image to use. It should be
3959 either a string or a vector of integers, where each element (an
3960 integer) corresponds to one row of the bitmap. Each bit of an integer
3961 corresponds to one pixel of the bitmap, where the low bit corresponds
3962 to the rightmost pixel of the bitmap.
3964 The height is normally the length of @var{bits}. However, you
3965 can specify a different height with non-@code{nil} @var{height}. The width
3966 is normally 8, but you can specify a different width with non-@code{nil}
3967 @var{width}. The width must be an integer between 1 and 16.
3969 The argument @var{align} specifies the positioning of the bitmap
3970 relative to the range of rows where it is used; the default is to
3971 center the bitmap. The allowed values are @code{top}, @code{center},
3974 The @var{align} argument may also be a list @code{(@var{align}
3975 @var{periodic})} where @var{align} is interpreted as described above.
3976 If @var{periodic} is non-@code{nil}, it specifies that the rows in
3977 @code{bits} should be repeated enough times to reach the specified
3981 @defun destroy-fringe-bitmap bitmap
3982 This function destroy the fringe bitmap identified by @var{bitmap}.
3983 If @var{bitmap} identifies a standard fringe bitmap, it actually
3984 restores the standard definition of that bitmap, instead of
3985 eliminating it entirely.
3988 @defun set-fringe-bitmap-face bitmap &optional face
3989 This sets the face for the fringe bitmap @var{bitmap} to @var{face}.
3990 If @var{face} is @code{nil}, it selects the @code{fringe} face. The
3991 bitmap's face controls the color to draw it in.
3993 @var{face} is merged with the @code{fringe} face, so normally
3994 @var{face} should specify only the foreground color.
3998 @subsection The Overlay Arrow
3999 @c @cindex overlay arrow Duplicates variable names
4001 The @dfn{overlay arrow} is useful for directing the user's attention
4002 to a particular line in a buffer. For example, in the modes used for
4003 interface to debuggers, the overlay arrow indicates the line of code
4004 about to be executed. This feature has nothing to do with
4005 @dfn{overlays} (@pxref{Overlays}).
4007 @defvar overlay-arrow-string
4008 This variable holds the string to display to call attention to a
4009 particular line, or @code{nil} if the arrow feature is not in use.
4010 On a graphical display the contents of the string are ignored; instead a
4011 glyph is displayed in the fringe area to the left of the display area.
4014 @defvar overlay-arrow-position
4015 This variable holds a marker that indicates where to display the overlay
4016 arrow. It should point at the beginning of a line. On a non-graphical
4017 display the arrow text
4018 appears at the beginning of that line, overlaying any text that would
4019 otherwise appear. Since the arrow is usually short, and the line
4020 usually begins with indentation, normally nothing significant is
4023 The overlay-arrow string is displayed in any given buffer if the value
4024 of @code{overlay-arrow-position} in that buffer points into that
4025 buffer. Thus, it is possible to display multiple overlay arrow strings
4026 by creating buffer-local bindings of @code{overlay-arrow-position}.
4027 However, it is usually cleaner to use
4028 @code{overlay-arrow-variable-list} to achieve this result.
4029 @c !!! overlay-arrow-position: but the overlay string may remain in the display
4030 @c of some other buffer until an update is required. This should be fixed
4034 You can do a similar job by creating an overlay with a
4035 @code{before-string} property. @xref{Overlay Properties}.
4037 You can define multiple overlay arrows via the variable
4038 @code{overlay-arrow-variable-list}.
4040 @defvar overlay-arrow-variable-list
4041 This variable's value is a list of variables, each of which specifies
4042 the position of an overlay arrow. The variable
4043 @code{overlay-arrow-position} has its normal meaning because it is on
4047 Each variable on this list can have properties
4048 @code{overlay-arrow-string} and @code{overlay-arrow-bitmap} that
4049 specify an overlay arrow string (for text terminals) or fringe bitmap
4050 (for graphical terminals) to display at the corresponding overlay
4051 arrow position. If either property is not set, the default
4052 @code{overlay-arrow-string} or @code{overlay-arrow} fringe indicator
4057 @section Scroll Bars
4060 Normally the frame parameter @code{vertical-scroll-bars} controls
4061 whether the windows in the frame have vertical scroll bars, and whether
4062 they are on the left or right. The frame parameter
4063 @code{scroll-bar-width} specifies how wide they are (@code{nil} meaning
4066 The frame parameter @code{horizontal-scroll-bars} controls whether
4067 the windows in the frame have horizontal scroll bars. The frame
4068 parameter @code{scroll-bar-height} specifies how high they are
4069 (@code{nil} meaning the default). @xref{Layout Parameters}.
4071 @vindex horizontal-scroll-bars-available-p
4072 Horizontal scroll bars are not available on all platforms. The
4073 function @code{horizontal-scroll-bars-available-p} which takes no
4074 argument returns non-@code{nil} if they are available on your system.
4076 The following three functions take as argument a live frame which
4077 defaults to the selected one.
4079 @defun frame-current-scroll-bars &optional frame
4080 This function reports the scroll bar types for frame @var{frame}. The
4081 value is a cons cell @code{(@var{vertical-type} .@:
4082 @var{horizontal-type})}, where @var{vertical-type} is either
4083 @code{left}, @code{right}, or @code{nil} (which means no vertical scroll
4084 bar.) @var{horizontal-type} is either @code{bottom} or @code{nil}
4085 (which means no horizontal scroll bar).
4088 @defun frame-scroll-bar-width &optional Lisp_Object &optional frame
4089 This function returns the width of vertical scroll bars of @var{frame}
4093 @defun frame-scroll-bar-height &optional Lisp_Object &optional frame
4094 This function returns the height of horizontal scroll bars of
4095 @var{frame} in pixels.
4098 You can override the frame specific settings for individual windows by
4099 using the following function:
4101 @defun set-window-scroll-bars window &optional width vertical-type height horizontal-type
4102 This function sets the width and/or height and the types of scroll bars
4103 for window @var{window}.
4105 @var{width} specifies the width of the vertical scroll bar in pixels
4106 (@code{nil} means use the width specified for the frame).
4107 @var{vertical-type} specifies whether to have a vertical scroll bar and,
4108 if so, where. The possible values are @code{left}, @code{right},
4109 @code{t}, which means to use the frame's default, and @code{nil} for no
4110 vertical scroll bar.
4112 @var{height} specifies the height of the horizontal scroll bar in pixels
4113 (@code{nil} means use the height specified for the frame).
4114 @var{horizontal-type} specifies whether to have a horizontal scroll bar.
4115 The possible values are @code{bottom}, @code{t}, which means to use the
4116 frame's default, and @code{nil} for no horizontal scroll bar.
4118 If @var{window} is @code{nil}, the selected window is used.
4121 The following four functions take as argument a live window which
4122 defaults to the selected one.
4124 @defun window-scroll-bars &optional window
4125 This function returns a list of the form @code{(@var{width}
4126 @var{columns} @var{vertical-type} @var{height} @var{lines}
4127 @var{horizontal-type})}.
4129 The value @var{width} is the value that was specified for the width of
4130 the vertical scroll bar (which may be @code{nil}); @var{columns} is the
4131 (possibly rounded) number of columns that the vertical scroll bar
4134 The value @var{height} is the value that was specified for the height of
4135 the horizontal scroll bar (which may be @code{nil}); @var{lines} is the
4136 (possibly rounded) number of lines that the horizontally scroll bar
4140 @defun window-current-scroll-bars &optional window
4141 This function reports the scroll bar type for window @var{window}. The
4142 value is a cons cell @code{(@var{vertical-type} .@:
4143 @var{horizontal-type})}. Unlike @code{window-scroll-bars}, this reports
4144 the scroll bar type actually used, once frame defaults and
4145 @code{scroll-bar-mode} are taken into account.
4148 @defun window-scroll-bar-width &optional window
4149 This function returns the width in pixels of @var{window}'s vertical
4153 @defun window-scroll-bar-height &optional window
4154 This function returns the height in pixels of @var{window}'s horizontal
4158 If you don't specify these values for a window with
4159 @code{set-window-scroll-bars}, the buffer-local variables
4160 @code{vertical-scroll-bar}, @code{horizontal-scroll-bar},
4161 @code{scroll-bar-width} and @code{scroll-bar-height} in the buffer being
4162 displayed control the window's scroll bars. The function
4163 @code{set-window-buffer} examines these variables. If you change them
4164 in a buffer that is already visible in a window, you can make the window
4165 take note of the new values by calling @code{set-window-buffer}
4166 specifying the same buffer that is already displayed.
4168 You can control the appearance of scroll bars for a particular buffer by
4169 setting the following variables which automatically become buffer-local
4172 @defvar vertical-scroll-bar
4173 This variable specifies the location of the vertical scroll bar. The
4174 possible values are @code{left}, @code{right}, @code{t}, which means to
4175 use the frame's default, and @code{nil} for no scroll bar.
4178 @defvar horizontal-scroll-bar
4179 This variable specifies the location of the horizontal scroll bar. The
4180 possible values are @code{bottom}, @code{t}, which means to use the
4181 frame's default, and @code{nil} for no scroll bar.
4184 @defvar scroll-bar-width
4185 This variable specifies the width of the buffer's vertical scroll bars,
4186 measured in pixels. A value of @code{nil} means to use the value
4187 specified by the frame.
4190 @defvar scroll-bar-height
4191 This variable specifies the height of the buffer's horizontal scroll
4192 bar, measured in pixels. A value of @code{nil} means to use the value
4193 specified by the frame.
4196 Finally you can toggle the display of scroll bars on all frames by
4197 customizing the variables @code{scroll-bar-mode} and
4198 @code{horizontal-scroll-bar-mode}.
4200 @defopt scroll-bar-mode
4201 This variable controls whether and where to put vertical scroll bars in
4202 all frames. The possible values are @code{nil} for no scroll bars,
4203 @code{left} to put scroll bars on the left and @code{right} to put
4204 scroll bars on the right.
4207 @defopt horizontal-scroll-bar-mode
4208 This variable controls whether to display horizontal scroll bars on all
4213 @node Window Dividers
4214 @section Window Dividers
4215 @cindex window dividers
4216 @cindex right dividers
4217 @cindex bottom dividers
4219 Window dividers are bars drawn between a frame's windows. A ``right''
4220 divider is drawn between a window and any adjacent windows on the right.
4221 Its width (thickness) is specified by the frame parameter
4222 @code{right-divider-width}. A ``bottom'' divider is drawn between a
4223 window and adjacent windows on the bottom or the echo area. Its width
4224 is specified by the frame parameter @code{bottom-divider-width}. In
4225 either case, specifying a width of zero means to not draw such dividers.
4226 @xref{Layout Parameters}.
4228 Technically, a right divider ``belongs'' to the window on its left,
4229 which means that its width contributes to the total width of that
4230 window. A bottom divider ``belongs'' to the window above it, which
4231 means that its width contributes to the total height of that window.
4232 @xref{Window Sizes}. When a window has both, a right and a bottom
4233 divider, the bottom divider ``prevails''. This means that a bottom
4234 divider is drawn over the full total width of its window while the right
4235 divider ends above the bottom divider.
4237 Dividers can be dragged with the mouse and are therefore useful for
4238 adjusting the sizes of adjacent windows with the mouse. They also serve
4239 to visually set apart adjacent windows when no scroll bars or mode lines
4240 are present. The following three faces allow to customize the
4241 appearance of dividers:
4244 @item window-divider
4245 When a divider is less than three pixels wide, it is drawn solidly with
4246 the foreground of this face. For larger dividers this face is used for
4247 the inner part only, excluding the first and last pixel.
4249 @item window-divider-first-pixel
4250 This is the face used for drawing the first pixel of a divider that is
4251 at least three pixels wide. To obtain a solid appearance, set this to
4252 the same value used for the @code{window-divider} face.
4254 @item window-divider-last-pixel
4255 This is the face used for drawing the last pixel of a divider that is at
4256 least three pixels wide. To obtain a solid appearance, set this to the
4257 same value used for the @code{window-divider} face.
4260 You can get the sizes of the dividers of a specific window with the
4261 following two functions.
4263 @defun window-right-divider-width &optional window
4264 Return the width (thickness) in pixels of @var{window}'s right divider.
4265 @var{window} must be a live window and defaults to the selected one.
4266 The return value is always zero for a rightmost window.
4269 @defun window-bottom-divider-width &optional window
4270 Return the width (thickness) in pixels of @var{window}'s bottom divider.
4271 @var{window} must be a live window and defaults to the selected one.
4272 The return value is zero for the minibuffer window or a bottommost
4273 window on a minibuffer-less frame.
4277 @node Display Property
4278 @section The @code{display} Property
4279 @cindex display specification
4280 @kindex display @r{(text property)}
4282 The @code{display} text property (or overlay property) is used to
4283 insert images into text, and to control other aspects of how text
4284 displays. The value of the @code{display} property should be a
4285 display specification, or a list or vector containing several display
4286 specifications. Display specifications in the same @code{display}
4287 property value generally apply in parallel to the text they cover.
4289 If several sources (overlays and/or a text property) specify values
4290 for the @code{display} property, only one of the values takes effect,
4291 following the rules of @code{get-char-property}. @xref{Examining
4294 The rest of this section describes several kinds of
4295 display specifications and what they mean.
4298 * Replacing Specs:: Display specs that replace the text.
4299 * Specified Space:: Displaying one space with a specified width.
4300 * Pixel Specification:: Specifying space width or height in pixels.
4301 * Other Display Specs:: Displaying an image; adjusting the height,
4302 spacing, and other properties of text.
4303 * Display Margins:: Displaying text or images to the side of the main text.
4306 @node Replacing Specs
4307 @subsection Display Specs That Replace The Text
4308 @cindex replacing display specs
4310 Some kinds of display specifications specify something to display
4311 instead of the text that has the property. These are called
4312 @dfn{replacing} display specifications. Emacs does not allow the user
4313 to interactively move point into the middle of buffer text that is
4314 replaced in this way.
4316 If a list of display specifications includes more than one replacing
4317 display specification, the first overrides the rest. Replacing
4318 display specifications make most other display specifications
4319 irrelevant, since those don't apply to the replacement.
4321 For replacing display specifications, ``the text that has the
4322 property'' means all the consecutive characters that have the same
4323 Lisp object as their @code{display} property; these characters are
4324 replaced as a single unit. If two characters have different Lisp
4325 objects as their @code{display} properties (i.e., objects which are
4326 not @code{eq}), they are handled separately.
4328 Here is an example which illustrates this point. A string serves as
4329 a replacing display specification, which replaces the text that has
4330 the property with the specified string (@pxref{Other Display Specs}).
4331 Consider the following function:
4336 (let ((string (concat "A"))
4337 (start (+ i i (point-min))))
4338 (put-text-property start (1+ start) 'display string)
4339 (put-text-property start (+ 2 start) 'display string))))
4343 This function gives each of the first ten characters in the buffer a
4344 @code{display} property which is a string @code{"A"}, but they don't
4345 all get the same string object. The first two characters get the same
4346 string object, so they are replaced with one @samp{A}; the fact that
4347 the display property was assigned in two separate calls to
4348 @code{put-text-property} is irrelevant. Similarly, the next two
4349 characters get a second string (@code{concat} creates a new string
4350 object), so they are replaced with one @samp{A}; and so on. Thus, the
4351 ten characters appear as five A's.
4353 @node Specified Space
4354 @subsection Specified Spaces
4355 @cindex spaces, specified height or width
4356 @cindex variable-width spaces
4358 To display a space of specified width and/or height, use a display
4359 specification of the form @code{(space . @var{props})}, where
4360 @var{props} is a property list (a list of alternating properties and
4361 values). You can put this property on one or more consecutive
4362 characters; a space of the specified height and width is displayed in
4363 place of @emph{all} of those characters. These are the properties you
4364 can use in @var{props} to specify the weight of the space:
4367 @item :width @var{width}
4368 If @var{width} is a number, it specifies
4369 that the space width should be @var{width} times the normal character
4370 width. @var{width} can also be a @dfn{pixel width} specification
4371 (@pxref{Pixel Specification}).
4373 @item :relative-width @var{factor}
4374 Specifies that the width of the stretch should be computed from the
4375 first character in the group of consecutive characters that have the
4376 same @code{display} property. The space width is the width of that
4377 character, multiplied by @var{factor}.
4379 @item :align-to @var{hpos}
4380 Specifies that the space should be wide enough to reach @var{hpos}.
4381 If @var{hpos} is a number, it is measured in units of the normal
4382 character width. @var{hpos} can also be a @dfn{pixel width}
4383 specification (@pxref{Pixel Specification}).
4386 You should use one and only one of the above properties. You can
4387 also specify the height of the space, with these properties:
4390 @item :height @var{height}
4391 Specifies the height of the space.
4392 If @var{height} is a number, it specifies
4393 that the space height should be @var{height} times the normal character
4394 height. The @var{height} may also be a @dfn{pixel height} specification
4395 (@pxref{Pixel Specification}).
4397 @item :relative-height @var{factor}
4398 Specifies the height of the space, multiplying the ordinary height
4399 of the text having this display specification by @var{factor}.
4401 @item :ascent @var{ascent}
4402 If the value of @var{ascent} is a non-negative number no greater than
4403 100, it specifies that @var{ascent} percent of the height of the space
4404 should be considered as the ascent of the space---that is, the part
4405 above the baseline. The ascent may also be specified in pixel units
4406 with a @dfn{pixel ascent} specification (@pxref{Pixel Specification}).
4410 Don't use both @code{:height} and @code{:relative-height} together.
4412 The @code{:width} and @code{:align-to} properties are supported on
4413 non-graphic terminals, but the other space properties in this section
4416 Note that space properties are treated as paragraph separators for
4417 the purposes of reordering bidirectional text for display.
4418 @xref{Bidirectional Display}, for the details.
4420 @node Pixel Specification
4421 @subsection Pixel Specification for Spaces
4422 @cindex spaces, pixel specification
4424 The value of the @code{:width}, @code{:align-to}, @code{:height},
4425 and @code{:ascent} properties can be a special kind of expression that
4426 is evaluated during redisplay. The result of the evaluation is used
4427 as an absolute number of pixels.
4429 The following expressions are supported:
4433 @var{expr} ::= @var{num} | (@var{num}) | @var{unit} | @var{elem} | @var{pos} | @var{image} | @var{form}
4434 @var{num} ::= @var{integer} | @var{float} | @var{symbol}
4435 @var{unit} ::= in | mm | cm | width | height
4438 @var{elem} ::= left-fringe | right-fringe | left-margin | right-margin
4440 @var{pos} ::= left | center | right
4441 @var{form} ::= (@var{num} . @var{expr}) | (@var{op} @var{expr} ...)
4446 The form @var{num} specifies a fraction of the default frame font
4447 height or width. The form @code{(@var{num})} specifies an absolute
4448 number of pixels. If @var{num} is a symbol, @var{symbol}, its
4449 buffer-local variable binding is used.
4451 The @code{in}, @code{mm}, and @code{cm} units specify the number of
4452 pixels per inch, millimeter, and centimeter, respectively. The
4453 @code{width} and @code{height} units correspond to the default width
4454 and height of the current face. An image specification @code{image}
4455 corresponds to the width or height of the image.
4457 The elements @code{left-fringe}, @code{right-fringe},
4458 @code{left-margin}, @code{right-margin}, @code{scroll-bar}, and
4459 @code{text} specify to the width of the corresponding area of the
4462 The @code{left}, @code{center}, and @code{right} positions can be
4463 used with @code{:align-to} to specify a position relative to the left
4464 edge, center, or right edge of the text area.
4466 Any of the above window elements (except @code{text}) can also be
4467 used with @code{:align-to} to specify that the position is relative to
4468 the left edge of the given area. Once the base offset for a relative
4469 position has been set (by the first occurrence of one of these
4470 symbols), further occurrences of these symbols are interpreted as the
4471 width of the specified area. For example, to align to the center of
4472 the left-margin, use
4475 :align-to (+ left-margin (0.5 . left-margin))
4478 If no specific base offset is set for alignment, it is always relative
4479 to the left edge of the text area. For example, @samp{:align-to 0} in a
4480 header-line aligns with the first text column in the text area.
4482 A value of the form @code{(@var{num} . @var{expr})} stands for the
4483 product of the values of @var{num} and @var{expr}. For example,
4484 @code{(2 . in)} specifies a width of 2 inches, while @code{(0.5 .
4485 @var{image})} specifies half the width (or height) of the specified
4488 The form @code{(+ @var{expr} ...)} adds up the value of the
4489 expressions. The form @code{(- @var{expr} ...)} negates or subtracts
4490 the value of the expressions.
4492 @node Other Display Specs
4493 @subsection Other Display Specifications
4495 Here are the other sorts of display specifications that you can use
4496 in the @code{display} text property.
4500 Display @var{string} instead of the text that has this property.
4502 Recursive display specifications are not supported---@var{string}'s
4503 @code{display} properties, if any, are not used.
4505 @item (image . @var{image-props})
4506 This kind of display specification is an image descriptor (@pxref{Images}).
4507 When used as a display specification, it means to display the image
4508 instead of the text that has the display specification.
4510 @item (slice @var{x} @var{y} @var{width} @var{height})
4511 This specification together with @code{image} specifies a @dfn{slice}
4512 (a partial area) of the image to display. The elements @var{y} and
4513 @var{x} specify the top left corner of the slice, within the image;
4514 @var{width} and @var{height} specify the width and height of the
4515 slice. Integers are numbers of pixels. A floating-point number
4516 in the range 0.0--1.0 stands for that fraction of the width or height
4517 of the entire image.
4519 @item ((margin nil) @var{string})
4520 A display specification of this form means to display @var{string}
4521 instead of the text that has the display specification, at the same
4522 position as that text. It is equivalent to using just @var{string},
4523 but it is done as a special case of marginal display (@pxref{Display
4526 @item (left-fringe @var{bitmap} @r{[}@var{face}@r{]})
4527 @itemx (right-fringe @var{bitmap} @r{[}@var{face}@r{]})
4528 This display specification on any character of a line of text causes
4529 the specified @var{bitmap} be displayed in the left or right fringes
4530 for that line, instead of the characters that have the display
4531 specification. The optional @var{face} specifies the colors to be
4532 used for the bitmap. @xref{Fringe Bitmaps}, for the details.
4534 @item (space-width @var{factor})
4535 This display specification affects all the space characters within the
4536 text that has the specification. It displays all of these spaces
4537 @var{factor} times as wide as normal. The element @var{factor} should
4538 be an integer or float. Characters other than spaces are not affected
4539 at all; in particular, this has no effect on tab characters.
4541 @item (height @var{height})
4542 This display specification makes the text taller or shorter.
4543 Here are the possibilities for @var{height}:
4546 @item @code{(+ @var{n})}
4547 @c FIXME: Add an index for "step"? --xfq
4548 This means to use a font that is @var{n} steps larger. A ``step'' is
4549 defined by the set of available fonts---specifically, those that match
4550 what was otherwise specified for this text, in all attributes except
4551 height. Each size for which a suitable font is available counts as
4552 another step. @var{n} should be an integer.
4554 @item @code{(- @var{n})}
4555 This means to use a font that is @var{n} steps smaller.
4557 @item a number, @var{factor}
4558 A number, @var{factor}, means to use a font that is @var{factor} times
4559 as tall as the default font.
4561 @item a symbol, @var{function}
4562 A symbol is a function to compute the height. It is called with the
4563 current height as argument, and should return the new height to use.
4565 @item anything else, @var{form}
4566 If the @var{height} value doesn't fit the previous possibilities, it is
4567 a form. Emacs evaluates it to get the new height, with the symbol
4568 @code{height} bound to the current specified font height.
4571 @item (raise @var{factor})
4572 This kind of display specification raises or lowers the text
4573 it applies to, relative to the baseline of the line.
4575 @var{factor} must be a number, which is interpreted as a multiple of the
4576 height of the affected text. If it is positive, that means to display
4577 the characters raised. If it is negative, that means to display them
4580 If the text also has a @code{height} display specification, that does
4581 not affect the amount of raising or lowering, which is based on the
4582 faces used for the text.
4585 @c We put all the `@code{(when ...)}' on one line to encourage
4586 @c makeinfo's end-of-sentence heuristics to DTRT. Previously, the dot
4587 @c was at eol; the info file ended up w/ two spaces rendered after it.
4588 You can make any display specification conditional. To do that,
4589 package it in another list of the form
4590 @code{(when @var{condition} . @var{spec})}.
4591 Then the specification @var{spec} applies only when
4592 @var{condition} evaluates to a non-@code{nil} value. During the
4593 evaluation, @code{object} is bound to the string or buffer having the
4594 conditional @code{display} property. @code{position} and
4595 @code{buffer-position} are bound to the position within @code{object}
4596 and the buffer position where the @code{display} property was found,
4597 respectively. Both positions can be different when @code{object} is a
4600 @node Display Margins
4601 @subsection Displaying in the Margins
4602 @cindex display margins
4603 @cindex margins, display
4605 A buffer can have blank areas called @dfn{display margins} on the
4606 left and on the right. Ordinary text never appears in these areas,
4607 but you can put things into the display margins using the
4608 @code{display} property. There is currently no way to make text or
4609 images in the margin mouse-sensitive.
4611 The way to display something in the margins is to specify it in a
4612 margin display specification in the @code{display} property of some
4613 text. This is a replacing display specification, meaning that the
4614 text you put it on does not get displayed; the margin display appears,
4615 but that text does not.
4617 A margin display specification looks like @code{((margin
4618 right-margin) @var{spec})} or @code{((margin left-margin) @var{spec})}.
4619 Here, @var{spec} is another display specification that says what to
4620 display in the margin. Typically it is a string of text to display,
4621 or an image descriptor.
4623 To display something in the margin @emph{in association with}
4624 certain buffer text, without altering or preventing the display of
4625 that text, put a @code{before-string} property on the text and put the
4626 margin display specification on the contents of the before-string.
4628 Before the display margins can display anything, you must give
4629 them a nonzero width. The usual way to do that is to set these
4632 @defvar left-margin-width
4633 This variable specifies the width of the left margin, in character
4634 cell (a.k.a.@: ``column'') units. It is buffer-local in all buffers.
4635 A value of @code{nil} means no left marginal area.
4638 @defvar right-margin-width
4639 This variable specifies the width of the right margin, in character
4640 cell units. It is buffer-local in all buffers. A value of @code{nil}
4641 means no right marginal area.
4644 Setting these variables does not immediately affect the window. These
4645 variables are checked when a new buffer is displayed in the window.
4646 Thus, you can make changes take effect by calling
4647 @code{set-window-buffer}.
4649 You can also set the margin widths immediately.
4651 @defun set-window-margins window left &optional right
4652 This function specifies the margin widths for window @var{window}, in
4653 character cell units. The argument @var{left} controls the left
4654 margin, and @var{right} controls the right margin (default @code{0}).
4657 @defun window-margins &optional window
4658 This function returns the width of the left and right margins of
4659 @var{window} as a cons cell of the form @w{@code{(@var{left}
4660 . @var{right})}}. If one of the two marginal areas does not exist,
4661 its width is returned as @code{nil}; if neither of the two margins exist,
4662 the function returns @code{(nil)}. If @var{window} is @code{nil}, the
4663 selected window is used.
4668 @cindex images in buffers
4670 To display an image in an Emacs buffer, you must first create an image
4671 descriptor, then use it as a display specifier in the @code{display}
4672 property of text that is displayed (@pxref{Display Property}).
4674 Emacs is usually able to display images when it is run on a
4675 graphical terminal. Images cannot be displayed in a text terminal, on
4676 certain graphical terminals that lack the support for this, or if
4677 Emacs is compiled without image support. You can use the function
4678 @code{display-images-p} to determine if images can in principle be
4679 displayed (@pxref{Display Feature Testing}).
4682 * Image Formats:: Supported image formats.
4683 * Image Descriptors:: How to specify an image for use in @code{:display}.
4684 * XBM Images:: Special features for XBM format.
4685 * XPM Images:: Special features for XPM format.
4686 * PostScript Images:: Special features for PostScript format.
4687 * ImageMagick Images:: Special features available through ImageMagick.
4688 * Other Image Types:: Various other formats are supported.
4689 * Defining Images:: Convenient ways to define an image for later use.
4690 * Showing Images:: Convenient ways to display an image once it is defined.
4691 * Multi-Frame Images:: Some images contain more than one frame.
4692 * Image Cache:: Internal mechanisms of image display.
4696 @subsection Image Formats
4697 @cindex image formats
4700 Emacs can display a number of different image formats. Some of
4701 these image formats are supported only if particular support libraries
4702 are installed. On some platforms, Emacs can load support libraries on
4703 demand; if so, the variable @code{dynamic-library-alist} can be used
4704 to modify the set of known names for these dynamic libraries.
4705 @xref{Dynamic Libraries}.
4707 Supported image formats (and the required support libraries) include
4708 PBM and XBM (which do not depend on support libraries and are always
4709 available), XPM (@code{libXpm}), GIF (@code{libgif} or
4710 @code{libungif}), PostScript (@code{gs}), JPEG (@code{libjpeg}), TIFF
4711 (@code{libtiff}), PNG (@code{libpng}), and SVG (@code{librsvg}).
4713 Each of these image formats is associated with an @dfn{image type
4714 symbol}. The symbols for the above formats are, respectively,
4715 @code{pbm}, @code{xbm}, @code{xpm}, @code{gif}, @code{postscript},
4716 @code{jpeg}, @code{tiff}, @code{png}, and @code{svg}.
4718 Furthermore, if you build Emacs with ImageMagick
4719 (@code{libMagickWand}) support, Emacs can display any image format
4720 that ImageMagick can. @xref{ImageMagick Images}. All images
4721 displayed via ImageMagick have type symbol @code{imagemagick}.
4724 This variable contains a list of type symbols for image formats which
4725 are potentially supported in the current configuration.
4727 ``Potentially'' means that Emacs knows about the image types, not
4728 necessarily that they can be used (for example, they could depend on
4729 unavailable dynamic libraries). To know which image types are really
4730 available, use @code{image-type-available-p}.
4733 @defun image-type-available-p type
4734 This function returns non-@code{nil} if images of type @var{type} can
4735 be loaded and displayed. @var{type} must be an image type symbol.
4737 For image types whose support libraries are statically linked, this
4738 function always returns @code{t}. For image types whose support
4739 libraries are dynamically loaded, it returns @code{t} if the library
4740 could be loaded and @code{nil} otherwise.
4743 @node Image Descriptors
4744 @subsection Image Descriptors
4745 @cindex image descriptor
4747 An @dfn{image descriptor} is a list which specifies the underlying
4748 data for an image, and how to display it. It is typically used as the
4749 value of a @code{display} overlay or text property (@pxref{Other
4750 Display Specs}); but @xref{Showing Images}, for convenient helper
4751 functions to insert images into buffers.
4753 Each image descriptor has the form @code{(image . @var{props})},
4754 where @var{props} is a property list of alternating keyword symbols
4755 and values, including at least the pair @code{:type @var{type}} that
4756 specifies the image type.
4758 The following is a list of properties that are meaningful for all
4759 image types (there are also properties which are meaningful only for
4760 certain image types, as documented in the following subsections):
4763 @item :type @var{type}
4766 @xref{Image Formats}.
4768 Every image descriptor must include this property.
4770 @item :file @var{file}
4771 This says to load the image from file @var{file}. If @var{file} is
4772 not an absolute file name, it is expanded in @code{data-directory}.
4774 @item :data @var{data}
4775 This specifies the raw image data. Each image descriptor must have
4776 either @code{:data} or @code{:file}, but not both.
4778 For most image types, the value of a @code{:data} property should be a
4779 string containing the image data. Some image types do not support
4780 @code{:data}; for some others, @code{:data} alone is not enough, so
4781 you need to use other image properties along with @code{:data}. See
4782 the following subsections for details.
4784 @item :margin @var{margin}
4785 This specifies how many pixels to add as an extra margin around the
4786 image. The value, @var{margin}, must be a non-negative number, or a
4787 pair @code{(@var{x} . @var{y})} of such numbers. If it is a pair,
4788 @var{x} specifies how many pixels to add horizontally, and @var{y}
4789 specifies how many pixels to add vertically. If @code{:margin} is not
4790 specified, the default is zero.
4792 @item :ascent @var{ascent}
4793 This specifies the amount of the image's height to use for its
4794 ascent---that is, the part above the baseline. The value,
4795 @var{ascent}, must be a number in the range 0 to 100, or the symbol
4798 If @var{ascent} is a number, that percentage of the image's height is
4799 used for its ascent.
4801 If @var{ascent} is @code{center}, the image is vertically centered
4802 around a centerline which would be the vertical centerline of text drawn
4803 at the position of the image, in the manner specified by the text
4804 properties and overlays that apply to the image.
4806 If this property is omitted, it defaults to 50.
4808 @item :relief @var{relief}
4809 This adds a shadow rectangle around the image. The value,
4810 @var{relief}, specifies the width of the shadow lines, in pixels. If
4811 @var{relief} is negative, shadows are drawn so that the image appears
4812 as a pressed button; otherwise, it appears as an unpressed button.
4814 @item :conversion @var{algorithm}
4815 This specifies a conversion algorithm that should be applied to the
4816 image before it is displayed; the value, @var{algorithm}, specifies
4822 Specifies the Laplace edge detection algorithm, which blurs out small
4823 differences in color while highlighting larger differences. People
4824 sometimes consider this useful for displaying the image for a
4825 ``disabled'' button.
4827 @item (edge-detection :matrix @var{matrix} :color-adjust @var{adjust})
4828 @cindex edge detection, images
4829 Specifies a general edge-detection algorithm. @var{matrix} must be
4830 either a nine-element list or a nine-element vector of numbers. A pixel
4831 at position @math{x/y} in the transformed image is computed from
4832 original pixels around that position. @var{matrix} specifies, for each
4833 pixel in the neighborhood of @math{x/y}, a factor with which that pixel
4834 will influence the transformed pixel; element @math{0} specifies the
4835 factor for the pixel at @math{x-1/y-1}, element @math{1} the factor for
4836 the pixel at @math{x/y-1} etc., as shown below:
4839 $$\pmatrix{x-1/y-1 & x/y-1 & x+1/y-1 \cr
4840 x-1/y & x/y & x+1/y \cr
4841 x-1/y+1& x/y+1 & x+1/y+1 \cr}$$
4846 (x-1/y-1 x/y-1 x+1/y-1
4848 x-1/y+1 x/y+1 x+1/y+1)
4852 The resulting pixel is computed from the color intensity of the color
4853 resulting from summing up the RGB values of surrounding pixels,
4854 multiplied by the specified factors, and dividing that sum by the sum
4855 of the factors' absolute values.
4857 Laplace edge-detection currently uses a matrix of
4860 $$\pmatrix{1 & 0 & 0 \cr
4873 Emboss edge-detection uses a matrix of
4876 $$\pmatrix{ 2 & -1 & 0 \cr
4890 Specifies transforming the image so that it looks ``disabled''.
4893 @item :mask @var{mask}
4894 If @var{mask} is @code{heuristic} or @code{(heuristic @var{bg})}, build
4895 a clipping mask for the image, so that the background of a frame is
4896 visible behind the image. If @var{bg} is not specified, or if @var{bg}
4897 is @code{t}, determine the background color of the image by looking at
4898 the four corners of the image, assuming the most frequently occurring
4899 color from the corners is the background color of the image. Otherwise,
4900 @var{bg} must be a list @code{(@var{red} @var{green} @var{blue})}
4901 specifying the color to assume for the background of the image.
4903 If @var{mask} is @code{nil}, remove a mask from the image, if it has
4904 one. Images in some formats include a mask which can be removed by
4905 specifying @code{:mask nil}.
4907 @item :pointer @var{shape}
4908 This specifies the pointer shape when the mouse pointer is over this
4909 image. @xref{Pointer Shape}, for available pointer shapes.
4911 @item :map @var{map}
4913 This associates an image map of @dfn{hot spots} with this image.
4915 An image map is an alist where each element has the format
4916 @code{(@var{area} @var{id} @var{plist})}. An @var{area} is specified
4917 as either a rectangle, a circle, or a polygon.
4919 A rectangle is a cons
4920 @code{(rect . ((@var{x0} . @var{y0}) . (@var{x1} . @var{y1})))}
4921 which specifies the pixel coordinates of the upper left and bottom right
4922 corners of the rectangle area.
4925 @code{(circle . ((@var{x0} . @var{y0}) . @var{r}))}
4926 which specifies the center and the radius of the circle; @var{r} may
4927 be a float or integer.
4930 @code{(poly . [@var{x0} @var{y0} @var{x1} @var{y1} ...])}
4931 where each pair in the vector describes one corner in the polygon.
4933 When the mouse pointer lies on a hot-spot area of an image, the
4934 @var{plist} of that hot-spot is consulted; if it contains a @code{help-echo}
4935 property, that defines a tool-tip for the hot-spot, and if it contains
4936 a @code{pointer} property, that defines the shape of the mouse cursor when
4937 it is on the hot-spot.
4938 @xref{Pointer Shape}, for available pointer shapes.
4940 When you click the mouse when the mouse pointer is over a hot-spot, an
4941 event is composed by combining the @var{id} of the hot-spot with the
4942 mouse event; for instance, @code{[area4 mouse-1]} if the hot-spot's
4943 @var{id} is @code{area4}.
4946 @defun image-mask-p spec &optional frame
4947 This function returns @code{t} if image @var{spec} has a mask bitmap.
4948 @var{frame} is the frame on which the image will be displayed.
4949 @var{frame} @code{nil} or omitted means to use the selected frame
4950 (@pxref{Input Focus}).
4954 @subsection XBM Images
4957 To use XBM format, specify @code{xbm} as the image type. This image
4958 format doesn't require an external library, so images of this type are
4961 Additional image properties supported for the @code{xbm} image type are:
4964 @item :foreground @var{foreground}
4965 The value, @var{foreground}, should be a string specifying the image
4966 foreground color, or @code{nil} for the default color. This color is
4967 used for each pixel in the XBM that is 1. The default is the frame's
4970 @item :background @var{background}
4971 The value, @var{background}, should be a string specifying the image
4972 background color, or @code{nil} for the default color. This color is
4973 used for each pixel in the XBM that is 0. The default is the frame's
4977 If you specify an XBM image using data within Emacs instead of an
4978 external file, use the following three properties:
4981 @item :data @var{data}
4982 The value, @var{data}, specifies the contents of the image.
4983 There are three formats you can use for @var{data}:
4987 A vector of strings or bool-vectors, each specifying one line of the
4988 image. Do specify @code{:height} and @code{:width}.
4991 A string containing the same byte sequence as an XBM file would contain.
4992 You must not specify @code{:height} and @code{:width} in this case,
4993 because omitting them is what indicates the data has the format of an
4994 XBM file. The file contents specify the height and width of the image.
4997 A string or a bool-vector containing the bits of the image (plus perhaps
4998 some extra bits at the end that will not be used). It should contain at
4999 least @var{width} * @code{height} bits. In this case, you must specify
5000 @code{:height} and @code{:width}, both to indicate that the string
5001 contains just the bits rather than a whole XBM file, and to specify the
5005 @item :width @var{width}
5006 The value, @var{width}, specifies the width of the image, in pixels.
5008 @item :height @var{height}
5009 The value, @var{height}, specifies the height of the image, in pixels.
5013 @subsection XPM Images
5016 To use XPM format, specify @code{xpm} as the image type. The
5017 additional image property @code{:color-symbols} is also meaningful with
5018 the @code{xpm} image type:
5021 @item :color-symbols @var{symbols}
5022 The value, @var{symbols}, should be an alist whose elements have the
5023 form @code{(@var{name} . @var{color})}. In each element, @var{name} is
5024 the name of a color as it appears in the image file, and @var{color}
5025 specifies the actual color to use for displaying that name.
5028 @node PostScript Images
5029 @subsection PostScript Images
5030 @cindex postscript images
5032 To use PostScript for an image, specify image type @code{postscript}.
5033 This works only if you have Ghostscript installed. You must always use
5034 these three properties:
5037 @item :pt-width @var{width}
5038 The value, @var{width}, specifies the width of the image measured in
5039 points (1/72 inch). @var{width} must be an integer.
5041 @item :pt-height @var{height}
5042 The value, @var{height}, specifies the height of the image in points
5043 (1/72 inch). @var{height} must be an integer.
5045 @item :bounding-box @var{box}
5046 The value, @var{box}, must be a list or vector of four integers, which
5047 specifying the bounding box of the PostScript image, analogous to the
5048 @samp{BoundingBox} comment found in PostScript files.
5051 %%BoundingBox: 22 171 567 738
5055 @node ImageMagick Images
5056 @subsection ImageMagick Images
5057 @cindex ImageMagick images
5058 @cindex images, support for more formats
5060 If you build Emacs with ImageMagick support, you can use the
5061 ImageMagick library to load many image formats (@pxref{File
5062 Conveniences,,, emacs, The GNU Emacs Manual}). The image type symbol
5063 for images loaded via ImageMagick is @code{imagemagick}, regardless of
5064 the actual underlying image format.
5066 @defun imagemagick-types
5067 This function returns a list of image file extensions supported by the
5068 current ImageMagick installation. Each list element is a symbol
5069 representing an internal ImageMagick name for an image type, such as
5070 @code{BMP} for @file{.bmp} images.
5073 @defopt imagemagick-enabled-types
5074 The value of this variable is a list of ImageMagick image types which
5075 Emacs may attempt to render using ImageMagick. Each list element
5076 should be one of the symbols in the list returned by
5077 @code{imagemagick-types}, or an equivalent string. Alternatively, a
5078 value of @code{t} enables ImageMagick for all possible image types.
5079 Regardless of the value of this variable,
5080 @code{imagemagick-types-inhibit} (see below) takes precedence.
5083 @defopt imagemagick-types-inhibit
5084 The value of this variable lists the ImageMagick image types which
5085 should never be rendered using ImageMagick, regardless of the value of
5086 @code{imagemagick-enabled-types}. A value of @code{t} disables
5087 ImageMagick entirely.
5090 @defvar image-format-suffixes
5091 This variable is an alist mapping image types to file name extensions.
5092 Emacs uses this in conjunction with the @code{:format} image property
5093 (see below) to give a hint to the ImageMagick library as to the type
5094 of an image. Each element has the form @code{(@var{type}
5095 @var{extension})}, where @var{type} is a symbol specifying an image
5096 content-type, and @var{extension} is a string that specifies the
5097 associated file name extension.
5100 Images loaded with ImageMagick support the following additional
5101 image descriptor properties:
5104 @item :background @var{background}
5105 @var{background}, if non-@code{nil}, should be a string specifying a
5106 color, which is used as the image's background color if the image
5107 supports transparency. If the value is @code{nil}, it defaults to the
5108 frame's background color.
5110 @item :width @var{width}, :height @var{height}
5111 The @code{:width} and @code{:height} keywords are used for scaling the
5112 image. If only one of them is specified, the other one will be
5113 calculated so as to preserve the aspect ratio. If both are specified,
5114 aspect ratio may not be preserved.
5116 @item :max-width @var{max-width}, :max-height @var{max-height}
5117 The @code{:max-width} and @code{:max-height} keywords are used for
5118 scaling if the size of the image of the image exceeds these values.
5119 If @code{:width} is set it will have precedence over @code{max-width},
5120 and if @code{:height} is set it will have precedence over
5121 @code{max-height}, but you can otherwise mix these keywords as you
5122 wish. @code{:max-width} and @code{:max-height} will always preserve
5125 @item :format @var{type}
5126 The value, @var{type}, should be a symbol specifying the type of the
5127 image data, as found in @code{image-format-suffixes}. This is used
5128 when the image does not have an associated file name, to provide a
5129 hint to ImageMagick to help it detect the image type.
5131 @item :rotation @var{angle}
5132 Specifies a rotation angle in degrees.
5134 @item :index @var{frame}
5135 @c Doesn't work: http://debbugs.gnu.org/7978
5136 @xref{Multi-Frame Images}.
5139 @node Other Image Types
5140 @subsection Other Image Types
5143 For PBM images, specify image type @code{pbm}. Color, gray-scale and
5144 monochromatic images are supported. For mono PBM images, two additional
5145 image properties are supported.
5148 @item :foreground @var{foreground}
5149 The value, @var{foreground}, should be a string specifying the image
5150 foreground color, or @code{nil} for the default color. This color is
5151 used for each pixel in the PBM that is 1. The default is the frame's
5154 @item :background @var{background}
5155 The value, @var{background}, should be a string specifying the image
5156 background color, or @code{nil} for the default color. This color is
5157 used for each pixel in the PBM that is 0. The default is the frame's
5162 The remaining image types that Emacs can support are:
5166 Image type @code{gif}.
5167 Supports the @code{:index} property. @xref{Multi-Frame Images}.
5170 Image type @code{jpeg}.
5173 Image type @code{png}.
5176 Image type @code{svg}.
5179 Image type @code{tiff}.
5180 Supports the @code{:index} property. @xref{Multi-Frame Images}.
5183 @node Defining Images
5184 @subsection Defining Images
5185 @cindex define image
5187 The functions @code{create-image}, @code{defimage} and
5188 @code{find-image} provide convenient ways to create image descriptors.
5190 @defun create-image file-or-data &optional type data-p &rest props
5191 This function creates and returns an image descriptor which uses the
5192 data in @var{file-or-data}. @var{file-or-data} can be a file name or
5193 a string containing the image data; @var{data-p} should be @code{nil}
5194 for the former case, non-@code{nil} for the latter case.
5196 The optional argument @var{type} is a symbol specifying the image type.
5197 If @var{type} is omitted or @code{nil}, @code{create-image} tries to
5198 determine the image type from the file's first few bytes, or else
5199 from the file's name.
5201 The remaining arguments, @var{props}, specify additional image
5202 properties---for example,
5204 @c ':heuristic-mask' is not documented?
5206 (create-image "foo.xpm" 'xpm nil :heuristic-mask t)
5209 The function returns @code{nil} if images of this type are not
5210 supported. Otherwise it returns an image descriptor.
5213 @defmac defimage symbol specs &optional doc
5214 This macro defines @var{symbol} as an image name. The arguments
5215 @var{specs} is a list which specifies how to display the image.
5216 The third argument, @var{doc}, is an optional documentation string.
5218 Each argument in @var{specs} has the form of a property list, and each
5219 one should specify at least the @code{:type} property and either the
5220 @code{:file} or the @code{:data} property. The value of @code{:type}
5221 should be a symbol specifying the image type, the value of
5222 @code{:file} is the file to load the image from, and the value of
5223 @code{:data} is a string containing the actual image data. Here is an
5227 (defimage test-image
5228 ((:type xpm :file "~/test1.xpm")
5229 (:type xbm :file "~/test1.xbm")))
5232 @code{defimage} tests each argument, one by one, to see if it is
5233 usable---that is, if the type is supported and the file exists. The
5234 first usable argument is used to make an image descriptor which is
5235 stored in @var{symbol}.
5237 If none of the alternatives will work, then @var{symbol} is defined
5241 @defun find-image specs
5242 This function provides a convenient way to find an image satisfying one
5243 of a list of image specifications @var{specs}.
5245 Each specification in @var{specs} is a property list with contents
5246 depending on image type. All specifications must at least contain the
5247 properties @code{:type @var{type}} and either @w{@code{:file @var{file}}}
5248 or @w{@code{:data @var{data}}}, where @var{type} is a symbol specifying
5249 the image type, e.g., @code{xbm}, @var{file} is the file to load the
5250 image from, and @var{data} is a string containing the actual image data.
5251 The first specification in the list whose @var{type} is supported, and
5252 @var{file} exists, is used to construct the image specification to be
5253 returned. If no specification is satisfied, @code{nil} is returned.
5255 The image is looked for in @code{image-load-path}.
5258 @defvar image-load-path
5259 This variable's value is a list of locations in which to search for
5260 image files. If an element is a string or a variable symbol whose
5261 value is a string, the string is taken to be the name of a directory
5262 to search. If an element is a variable symbol whose value is a list,
5263 that is taken to be a list of directory names to search.
5265 The default is to search in the @file{images} subdirectory of the
5266 directory specified by @code{data-directory}, then the directory
5267 specified by @code{data-directory}, and finally in the directories in
5268 @code{load-path}. Subdirectories are not automatically included in
5269 the search, so if you put an image file in a subdirectory, you have to
5270 supply the subdirectory name explicitly. For example, to find the
5271 image @file{images/foo/bar.xpm} within @code{data-directory}, you
5272 should specify the image as follows:
5275 (defimage foo-image '((:type xpm :file "foo/bar.xpm")))
5279 @defun image-load-path-for-library library image &optional path no-error
5280 This function returns a suitable search path for images used by the
5281 Lisp package @var{library}.
5283 The function searches for @var{image} first using @code{image-load-path},
5284 excluding @file{@code{data-directory}/images}, and then in
5285 @code{load-path}, followed by a path suitable for @var{library}, which
5286 includes @file{../../etc/images} and @file{../etc/images} relative to
5287 the library file itself, and finally in
5288 @file{@code{data-directory}/images}.
5290 Then this function returns a list of directories which contains first
5291 the directory in which @var{image} was found, followed by the value of
5292 @code{load-path}. If @var{path} is given, it is used instead of
5295 If @var{no-error} is non-@code{nil} and a suitable path can't be
5296 found, don't signal an error. Instead, return a list of directories as
5297 before, except that @code{nil} appears in place of the image directory.
5299 Here is an example of using @code{image-load-path-for-library}:
5302 (defvar image-load-path) ; shush compiler
5303 (let* ((load-path (image-load-path-for-library
5304 "mh-e" "mh-logo.xpm"))
5305 (image-load-path (cons (car load-path)
5307 (mh-tool-bar-folder-buttons-init))
5311 @node Showing Images
5312 @subsection Showing Images
5315 You can use an image descriptor by setting up the @code{display}
5316 property yourself, but it is easier to use the functions in this
5319 @defun insert-image image &optional string area slice
5320 This function inserts @var{image} in the current buffer at point. The
5321 value @var{image} should be an image descriptor; it could be a value
5322 returned by @code{create-image}, or the value of a symbol defined with
5323 @code{defimage}. The argument @var{string} specifies the text to put
5324 in the buffer to hold the image. If it is omitted or @code{nil},
5325 @code{insert-image} uses @code{" "} by default.
5327 The argument @var{area} specifies whether to put the image in a margin.
5328 If it is @code{left-margin}, the image appears in the left margin;
5329 @code{right-margin} specifies the right margin. If @var{area} is
5330 @code{nil} or omitted, the image is displayed at point within the
5333 The argument @var{slice} specifies a slice of the image to insert. If
5334 @var{slice} is @code{nil} or omitted the whole image is inserted.
5335 Otherwise, @var{slice} is a list @code{(@var{x} @var{y} @var{width}
5336 @var{height})} which specifies the @var{x} and @var{y} positions and
5337 @var{width} and @var{height} of the image area to insert. Integer
5338 values are in units of pixels. A floating-point number in the range
5339 0.0--1.0 stands for that fraction of the width or height of the entire
5342 Internally, this function inserts @var{string} in the buffer, and gives
5343 it a @code{display} property which specifies @var{image}. @xref{Display
5347 @cindex slice, image
5349 @defun insert-sliced-image image &optional string area rows cols
5350 This function inserts @var{image} in the current buffer at point, like
5351 @code{insert-image}, but splits the image into @var{rows}x@var{cols}
5352 equally sized slices.
5354 If an image is inserted ``sliced'', Emacs displays each slice as a
5355 separate image, and allow more intuitive scrolling up/down, instead of
5356 jumping up/down the entire image when paging through a buffer that
5357 displays (large) images.
5360 @defun put-image image pos &optional string area
5361 This function puts image @var{image} in front of @var{pos} in the
5362 current buffer. The argument @var{pos} should be an integer or a
5363 marker. It specifies the buffer position where the image should appear.
5364 The argument @var{string} specifies the text that should hold the image
5365 as an alternative to the default.
5367 The argument @var{image} must be an image descriptor, perhaps returned
5368 by @code{create-image} or stored by @code{defimage}.
5370 The argument @var{area} specifies whether to put the image in a margin.
5371 If it is @code{left-margin}, the image appears in the left margin;
5372 @code{right-margin} specifies the right margin. If @var{area} is
5373 @code{nil} or omitted, the image is displayed at point within the
5376 Internally, this function creates an overlay, and gives it a
5377 @code{before-string} property containing text that has a @code{display}
5378 property whose value is the image. (Whew!)
5381 @defun remove-images start end &optional buffer
5382 This function removes images in @var{buffer} between positions
5383 @var{start} and @var{end}. If @var{buffer} is omitted or @code{nil},
5384 images are removed from the current buffer.
5386 This removes only images that were put into @var{buffer} the way
5387 @code{put-image} does it, not images that were inserted with
5388 @code{insert-image} or in other ways.
5391 @defun image-size spec &optional pixels frame
5392 @cindex size of image
5393 This function returns the size of an image as a pair
5394 @w{@code{(@var{width} . @var{height})}}. @var{spec} is an image
5395 specification. @var{pixels} non-@code{nil} means return sizes
5396 measured in pixels, otherwise return sizes measured in canonical
5397 character units (fractions of the width/height of the frame's default
5398 font). @var{frame} is the frame on which the image will be displayed.
5399 @var{frame} null or omitted means use the selected frame (@pxref{Input
5403 @defvar max-image-size
5404 This variable is used to define the maximum size of image that Emacs
5405 will load. Emacs will refuse to load (and display) any image that is
5406 larger than this limit.
5408 If the value is an integer, it directly specifies the maximum
5409 image height and width, measured in pixels. If it is floating
5410 point, it specifies the maximum image height and width
5411 as a ratio to the frame height and width. If the value is
5412 non-numeric, there is no explicit limit on the size of images.
5414 The purpose of this variable is to prevent unreasonably large images
5415 from accidentally being loaded into Emacs. It only takes effect the
5416 first time an image is loaded. Once an image is placed in the image
5417 cache, it can always be displayed, even if the value of
5418 @code{max-image-size} is subsequently changed (@pxref{Image Cache}).
5421 @node Multi-Frame Images
5422 @subsection Multi-Frame Images
5423 @cindex multi-frame images
5426 @cindex image animation
5427 @cindex image frames
5428 Some image files can contain more than one image. We say that there
5429 are multiple ``frames'' in the image. At present, Emacs supports
5430 multiple frames for GIF, TIFF, and certain ImageMagick formats such as
5433 The frames can be used either to represent multiple ``pages'' (this is
5434 usually the case with multi-frame TIFF files, for example), or to
5435 create animation (usually the case with multi-frame GIF files).
5437 A multi-frame image has a property @code{:index}, whose value is an
5438 integer (counting from 0) that specifies which frame is being displayed.
5440 @defun image-multi-frame-p image
5441 This function returns non-@code{nil} if @var{image} contains more than
5442 one frame. The actual return value is a cons @code{(@var{nimages}
5443 . @var{delay})}, where @var{nimages} is the number of frames and
5444 @var{delay} is the delay in seconds between them, or @code{nil}
5445 if the image does not specify a delay. Images that are intended to be
5446 animated usually specify a frame delay, whereas ones that are intended
5447 to be treated as multiple pages do not.
5450 @defun image-current-frame image
5451 This function returns the index of the current frame number for
5452 @var{image}, counting from 0.
5455 @defun image-show-frame image n &optional nocheck
5456 This function switches @var{image} to frame number @var{n}. It
5457 replaces a frame number outside the valid range with that of the end
5458 of the range, unless @var{nocheck} is non-@code{nil}. If @var{image}
5459 does not contain a frame with the specified number, the image displays
5463 @defun image-animate image &optional index limit
5464 This function animates @var{image}. The optional integer @var{index}
5465 specifies the frame from which to start (default 0). The optional
5466 argument @var{limit} controls the length of the animation. If omitted
5467 or @code{nil}, the image animates once only; if @code{t} it loops
5468 forever; if a number animation stops after that many seconds.
5471 @vindex image-minimum-frame-delay
5472 @vindex image-default-frame-delay
5473 @noindent Animation operates by means of a timer. Note that Emacs imposes a
5474 minimum frame delay of 0.01 (@code{image-minimum-frame-delay}) seconds.
5475 If the image itself does not specify a delay, Emacs uses
5476 @code{image-default-frame-delay}.
5478 @defun image-animate-timer image
5479 This function returns the timer responsible for animating @var{image},
5485 @subsection Image Cache
5488 Emacs caches images so that it can display them again more
5489 efficiently. When Emacs displays an image, it searches the image
5490 cache for an existing image specification @code{equal} to the desired
5491 specification. If a match is found, the image is displayed from the
5492 cache. Otherwise, Emacs loads the image normally.
5494 @defun image-flush spec &optional frame
5495 This function removes the image with specification @var{spec} from the
5496 image cache of frame @var{frame}. Image specifications are compared
5497 using @code{equal}. If @var{frame} is @code{nil}, it defaults to the
5498 selected frame. If @var{frame} is @code{t}, the image is flushed on
5499 all existing frames.
5501 In Emacs's current implementation, each graphical terminal possesses an
5502 image cache, which is shared by all the frames on that terminal
5503 (@pxref{Multiple Terminals}). Thus, refreshing an image in one frame
5504 also refreshes it in all other frames on the same terminal.
5507 One use for @code{image-flush} is to tell Emacs about a change in an
5508 image file. If an image specification contains a @code{:file}
5509 property, the image is cached based on the file's contents when the
5510 image is first displayed. Even if the file subsequently changes,
5511 Emacs continues displaying the old version of the image. Calling
5512 @code{image-flush} flushes the image from the cache, forcing Emacs to
5513 re-read the file the next time it needs to display that image.
5515 Another use for @code{image-flush} is for memory conservation. If
5516 your Lisp program creates a large number of temporary images over a
5517 period much shorter than @code{image-cache-eviction-delay} (see
5518 below), you can opt to flush unused images yourself, instead of
5519 waiting for Emacs to do it automatically.
5521 @defun clear-image-cache &optional filter
5522 This function clears an image cache, removing all the images stored in
5523 it. If @var{filter} is omitted or @code{nil}, it clears the cache for
5524 the selected frame. If @var{filter} is a frame, it clears the cache
5525 for that frame. If @var{filter} is @code{t}, all image caches are
5526 cleared. Otherwise, @var{filter} is taken to be a file name, and all
5527 images associated with that file name are removed from all image
5531 If an image in the image cache has not been displayed for a specified
5532 period of time, Emacs removes it from the cache and frees the
5535 @defvar image-cache-eviction-delay
5536 This variable specifies the number of seconds an image can remain in
5537 the cache without being displayed. When an image is not displayed for
5538 this length of time, Emacs removes it from the image cache.
5540 Under some circumstances, if the number of images in the cache grows
5541 too large, the actual eviction delay may be shorter than this.
5543 If the value is @code{nil}, Emacs does not remove images from the cache
5544 except when you explicitly clear it. This mode can be useful for
5550 @cindex buttons in buffers
5551 @cindex clickable buttons in buffers
5553 The Button package defines functions for inserting and manipulating
5554 @dfn{buttons} that can be activated with the mouse or via keyboard
5555 commands. These buttons are typically used for various kinds of
5558 A button is essentially a set of text or overlay properties,
5559 attached to a stretch of text in a buffer. These properties are
5560 called @dfn{button properties}. One of these properties, the
5561 @dfn{action property}, specifies a function which is called when the
5562 user invokes the button using the keyboard or the mouse. The action
5563 function may examine the button and use its other properties as
5566 In some ways, the Button package duplicates the functionality in the
5567 Widget package. @xref{Top, , Introduction, widget, The Emacs Widget
5568 Library}. The advantage of the Button package is that it is faster,
5569 smaller, and simpler to program. From the point of view of the user,
5570 the interfaces produced by the two packages are very similar.
5573 * Button Properties:: Button properties with special meanings.
5574 * Button Types:: Defining common properties for classes of buttons.
5575 * Making Buttons:: Adding buttons to Emacs buffers.
5576 * Manipulating Buttons:: Getting and setting properties of buttons.
5577 * Button Buffer Commands:: Buffer-wide commands and bindings for buttons.
5580 @node Button Properties
5581 @subsection Button Properties
5582 @cindex button properties
5584 Each button has an associated list of properties defining its
5585 appearance and behavior, and other arbitrary properties may be used
5586 for application specific purposes. The following properties have
5587 special meaning to the Button package:
5591 @kindex action @r{(button property)}
5592 The function to call when the user invokes the button, which is passed
5593 the single argument @var{button}. By default this is @code{ignore},
5597 @kindex mouse-action @r{(button property)}
5598 This is similar to @code{action}, and when present, will be used
5599 instead of @code{action} for button invocations resulting from
5600 mouse-clicks (instead of the user hitting @key{RET}). If not
5601 present, mouse-clicks use @code{action} instead.
5604 @kindex face @r{(button property)}
5605 This is an Emacs face controlling how buttons of this type are
5606 displayed; by default this is the @code{button} face.
5609 @kindex mouse-face @r{(button property)}
5610 This is an additional face which controls appearance during
5611 mouse-overs (merged with the usual button face); by default this is
5612 the usual Emacs @code{highlight} face.
5615 @kindex keymap @r{(button property)}
5616 The button's keymap, defining bindings active within the button
5617 region. By default this is the usual button region keymap, stored
5618 in the variable @code{button-map}, which defines @key{RET} and
5619 @key{mouse-2} to invoke the button.
5622 @kindex type @r{(button property)}
5623 The button type. @xref{Button Types}.
5626 @kindex help-index @r{(button property)}
5627 A string displayed by the Emacs tool-tip help system; by default,
5628 @code{"mouse-2, RET: Push this button"}.
5631 @kindex follow-link @r{(button property)}
5632 The follow-link property, defining how a @key{Mouse-1} click behaves
5633 on this button, @xref{Clickable Text}.
5636 @kindex button @r{(button property)}
5637 All buttons have a non-@code{nil} @code{button} property, which may be useful
5638 in finding regions of text that comprise buttons (which is what the
5639 standard button functions do).
5642 There are other properties defined for the regions of text in a
5643 button, but these are not generally interesting for typical uses.
5646 @subsection Button Types
5647 @cindex button types
5649 Every button has a @dfn{button type}, which defines default values
5650 for the button's properties. Button types are arranged in a
5651 hierarchy, with specialized types inheriting from more general types,
5652 so that it's easy to define special-purpose types of buttons for
5655 @defun define-button-type name &rest properties
5656 Define a `button type' called @var{name} (a symbol).
5657 The remaining arguments
5658 form a sequence of @var{property value} pairs, specifying default
5659 property values for buttons with this type (a button's type may be set
5660 by giving it a @code{type} property when creating the button, using
5661 the @code{:type} keyword argument).
5663 In addition, the keyword argument @code{:supertype} may be used to
5664 specify a button-type from which @var{name} inherits its default
5665 property values. Note that this inheritance happens only when
5666 @var{name} is defined; subsequent changes to a supertype are not
5667 reflected in its subtypes.
5670 Using @code{define-button-type} to define default properties for
5671 buttons is not necessary---buttons without any specified type use the
5672 built-in button-type @code{button}---but it is encouraged, since
5673 doing so usually makes the resulting code clearer and more efficient.
5675 @node Making Buttons
5676 @subsection Making Buttons
5677 @cindex making buttons
5679 Buttons are associated with a region of text, using an overlay or
5680 text properties to hold button-specific information, all of which are
5681 initialized from the button's type (which defaults to the built-in
5682 button type @code{button}). Like all Emacs text, the appearance of
5683 the button is governed by the @code{face} property; by default (via
5684 the @code{face} property inherited from the @code{button} button-type)
5685 this is a simple underline, like a typical web-page link.
5687 For convenience, there are two sorts of button-creation functions,
5688 those that add button properties to an existing region of a buffer,
5689 called @code{make-...button}, and those that also insert the button
5690 text, called @code{insert-...button}.
5692 The button-creation functions all take the @code{&rest} argument
5693 @var{properties}, which should be a sequence of @var{property value}
5694 pairs, specifying properties to add to the button; see @ref{Button
5695 Properties}. In addition, the keyword argument @code{:type} may be
5696 used to specify a button-type from which to inherit other properties;
5697 see @ref{Button Types}. Any properties not explicitly specified
5698 during creation will be inherited from the button's type (if the type
5699 defines such a property).
5701 The following functions add a button using an overlay
5702 (@pxref{Overlays}) to hold the button properties:
5704 @defun make-button beg end &rest properties
5705 This makes a button from @var{beg} to @var{end} in the
5706 current buffer, and returns it.
5709 @defun insert-button label &rest properties
5710 This insert a button with the label @var{label} at point,
5714 The following functions are similar, but using text properties
5715 (@pxref{Text Properties}) to hold the button properties. Such buttons
5716 do not add markers to the buffer, so editing in the buffer does not
5717 slow down if there is an extremely large numbers of buttons. However,
5718 if there is an existing face text property on the text (e.g., a face
5719 assigned by Font Lock mode), the button face may not be visible. Both
5720 of these functions return the starting position of the new button.
5722 @defun make-text-button beg end &rest properties
5723 This makes a button from @var{beg} to @var{end} in the current buffer,
5724 using text properties.
5727 @defun insert-text-button label &rest properties
5728 This inserts a button with the label @var{label} at point, using text
5732 @node Manipulating Buttons
5733 @subsection Manipulating Buttons
5734 @cindex manipulating buttons
5736 These are functions for getting and setting properties of buttons.
5737 Often these are used by a button's invocation function to determine
5740 Where a @var{button} parameter is specified, it means an object
5741 referring to a specific button, either an overlay (for overlay
5742 buttons), or a buffer-position or marker (for text property buttons).
5743 Such an object is passed as the first argument to a button's
5744 invocation function when it is invoked.
5746 @defun button-start button
5747 Return the position at which @var{button} starts.
5750 @defun button-end button
5751 Return the position at which @var{button} ends.
5754 @defun button-get button prop
5755 Get the property of button @var{button} named @var{prop}.
5758 @defun button-put button prop val
5759 Set @var{button}'s @var{prop} property to @var{val}.
5762 @defun button-activate button &optional use-mouse-action
5763 Call @var{button}'s @code{action} property (i.e., invoke it). If
5764 @var{use-mouse-action} is non-@code{nil}, try to invoke the button's
5765 @code{mouse-action} property instead of @code{action}; if the button
5766 has no @code{mouse-action} property, use @code{action} as normal.
5769 @defun button-label button
5770 Return @var{button}'s text label.
5773 @defun button-type button
5774 Return @var{button}'s button-type.
5777 @defun button-has-type-p button type
5778 Return @code{t} if @var{button} has button-type @var{type}, or one of
5779 @var{type}'s subtypes.
5782 @defun button-at pos
5783 Return the button at position @var{pos} in the current buffer, or
5784 @code{nil}. If the button at @var{pos} is a text property button, the
5785 return value is a marker pointing to @var{pos}.
5788 @defun button-type-put type prop val
5789 Set the button-type @var{type}'s @var{prop} property to @var{val}.
5792 @defun button-type-get type prop
5793 Get the property of button-type @var{type} named @var{prop}.
5796 @defun button-type-subtype-p type supertype
5797 Return @code{t} if button-type @var{type} is a subtype of @var{supertype}.
5800 @node Button Buffer Commands
5801 @subsection Button Buffer Commands
5802 @cindex button buffer commands
5804 These are commands and functions for locating and operating on
5805 buttons in an Emacs buffer.
5807 @code{push-button} is the command that a user uses to actually `push'
5808 a button, and is bound by default in the button itself to @key{RET}
5809 and to @key{mouse-2} using a local keymap in the button's overlay or
5810 text properties. Commands that are useful outside the buttons itself,
5811 such as @code{forward-button} and @code{backward-button} are
5812 additionally available in the keymap stored in
5813 @code{button-buffer-map}; a mode which uses buttons may want to use
5814 @code{button-buffer-map} as a parent keymap for its keymap.
5816 If the button has a non-@code{nil} @code{follow-link} property, and
5817 @code{mouse-1-click-follows-link} is set, a quick @key{Mouse-1} click
5818 will also activate the @code{push-button} command.
5819 @xref{Clickable Text}.
5821 @deffn Command push-button &optional pos use-mouse-action
5822 Perform the action specified by a button at location @var{pos}.
5823 @var{pos} may be either a buffer position or a mouse-event. If
5824 @var{use-mouse-action} is non-@code{nil}, or @var{pos} is a
5825 mouse-event (@pxref{Mouse Events}), try to invoke the button's
5826 @code{mouse-action} property instead of @code{action}; if the button
5827 has no @code{mouse-action} property, use @code{action} as normal.
5828 @var{pos} defaults to point, except when @code{push-button} is invoked
5829 interactively as the result of a mouse-event, in which case, the mouse
5830 event's position is used. If there's no button at @var{pos}, do
5831 nothing and return @code{nil}, otherwise return @code{t}.
5834 @deffn Command forward-button n &optional wrap display-message
5835 Move to the @var{n}th next button, or @var{n}th previous button if
5836 @var{n} is negative. If @var{n} is zero, move to the start of any
5837 button at point. If @var{wrap} is non-@code{nil}, moving past either
5838 end of the buffer continues from the other end. If
5839 @var{display-message} is non-@code{nil}, the button's help-echo string
5840 is displayed. Any button with a non-@code{nil} @code{skip} property
5841 is skipped over. Returns the button found.
5844 @deffn Command backward-button n &optional wrap display-message
5845 Move to the @var{n}th previous button, or @var{n}th next button if
5846 @var{n} is negative. If @var{n} is zero, move to the start of any
5847 button at point. If @var{wrap} is non-@code{nil}, moving past either
5848 end of the buffer continues from the other end. If
5849 @var{display-message} is non-@code{nil}, the button's help-echo string
5850 is displayed. Any button with a non-@code{nil} @code{skip} property
5851 is skipped over. Returns the button found.
5854 @defun next-button pos &optional count-current
5855 @defunx previous-button pos &optional count-current
5856 Return the next button after (for @code{next-button}) or before (for
5857 @code{previous-button}) position @var{pos} in the current buffer. If
5858 @var{count-current} is non-@code{nil}, count any button at @var{pos}
5859 in the search, instead of starting at the next button.
5862 @node Abstract Display
5863 @section Abstract Display
5865 @cindex display, abstract
5866 @cindex display, arbitrary objects
5867 @cindex model/view/controller
5868 @cindex view part, model/view/controller
5870 The Ewoc package constructs buffer text that represents a structure
5871 of Lisp objects, and updates the text to follow changes in that
5872 structure. This is like the ``view'' component in the
5873 ``model/view/controller'' design paradigm. Ewoc means ``Emacs's
5874 Widget for Object Collections''.
5876 An @dfn{ewoc} is a structure that organizes information required to
5877 construct buffer text that represents certain Lisp data. The buffer
5878 text of the ewoc has three parts, in order: first, fixed @dfn{header}
5879 text; next, textual descriptions of a series of data elements (Lisp
5880 objects that you specify); and last, fixed @dfn{footer} text.
5881 Specifically, an ewoc contains information on:
5885 The buffer which its text is generated in.
5888 The text's start position in the buffer.
5891 The header and footer strings.
5895 @c or "@cindex node, abstract display"?
5896 A doubly-linked chain of @dfn{nodes}, each of which contains:
5900 A @dfn{data element}, a single Lisp object.
5903 Links to the preceding and following nodes in the chain.
5907 A @dfn{pretty-printer} function which is responsible for
5908 inserting the textual representation of a data
5909 element value into the current buffer.
5912 Typically, you define an ewoc with @code{ewoc-create}, and then pass
5913 the resulting ewoc structure to other functions in the Ewoc package to
5914 build nodes within it, and display it in the buffer. Once it is
5915 displayed in the buffer, other functions determine the correspondence
5916 between buffer positions and nodes, move point from one node's textual
5917 representation to another, and so forth. @xref{Abstract Display
5920 @cindex encapsulation, ewoc
5921 @c or "@cindex encapsulation, abstract display"?
5922 A node @dfn{encapsulates} a data element much the way a variable
5923 holds a value. Normally, encapsulation occurs as a part of adding a
5924 node to the ewoc. You can retrieve the data element value and place a
5925 new value in its place, like so:
5928 (ewoc-data @var{node})
5931 (ewoc-set-data @var{node} @var{new-value})
5932 @result{} @var{new-value}
5936 You can also use, as the data element value, a Lisp object (list or
5937 vector) that is a container for the ``real'' value, or an index into
5938 some other structure. The example (@pxref{Abstract Display Example})
5939 uses the latter approach.
5941 When the data changes, you will want to update the text in the
5942 buffer. You can update all nodes by calling @code{ewoc-refresh}, or
5943 just specific nodes using @code{ewoc-invalidate}, or all nodes
5944 satisfying a predicate using @code{ewoc-map}. Alternatively, you can
5945 delete invalid nodes using @code{ewoc-delete} or @code{ewoc-filter},
5946 and add new nodes in their place. Deleting a node from an ewoc deletes
5947 its associated textual description from buffer, as well.
5950 * Abstract Display Functions:: Functions in the Ewoc package.
5951 * Abstract Display Example:: Example of using Ewoc.
5954 @node Abstract Display Functions
5955 @subsection Abstract Display Functions
5957 In this subsection, @var{ewoc} and @var{node} stand for the
5958 structures described above (@pxref{Abstract Display}), while
5959 @var{data} stands for an arbitrary Lisp object used as a data element.
5961 @defun ewoc-create pretty-printer &optional header footer nosep
5962 This constructs and returns a new ewoc, with no nodes (and thus no data
5963 elements). @var{pretty-printer} should be a function that takes one
5964 argument, a data element of the sort you plan to use in this ewoc, and
5965 inserts its textual description at point using @code{insert} (and never
5966 @code{insert-before-markers}, because that would interfere with the
5967 Ewoc package's internal mechanisms).
5969 Normally, a newline is automatically inserted after the header,
5970 the footer and every node's textual description. If @var{nosep}
5971 is non-@code{nil}, no newline is inserted. This may be useful for
5972 displaying an entire ewoc on a single line, for example, or for
5973 making nodes ``invisible'' by arranging for @var{pretty-printer}
5974 to do nothing for those nodes.
5976 An ewoc maintains its text in the buffer that is current when
5977 you create it, so switch to the intended buffer before calling
5981 @defun ewoc-buffer ewoc
5982 This returns the buffer where @var{ewoc} maintains its text.
5985 @defun ewoc-get-hf ewoc
5986 This returns a cons cell @code{(@var{header} . @var{footer})}
5987 made from @var{ewoc}'s header and footer.
5990 @defun ewoc-set-hf ewoc header footer
5991 This sets the header and footer of @var{ewoc} to the strings
5992 @var{header} and @var{footer}, respectively.
5995 @defun ewoc-enter-first ewoc data
5996 @defunx ewoc-enter-last ewoc data
5997 These add a new node encapsulating @var{data}, putting it, respectively,
5998 at the beginning or end of @var{ewoc}'s chain of nodes.
6001 @defun ewoc-enter-before ewoc node data
6002 @defunx ewoc-enter-after ewoc node data
6003 These add a new node encapsulating @var{data}, adding it to
6004 @var{ewoc} before or after @var{node}, respectively.
6007 @defun ewoc-prev ewoc node
6008 @defunx ewoc-next ewoc node
6009 These return, respectively, the previous node and the next node of @var{node}
6013 @defun ewoc-nth ewoc n
6014 This returns the node in @var{ewoc} found at zero-based index @var{n}.
6015 A negative @var{n} means count from the end. @code{ewoc-nth} returns
6016 @code{nil} if @var{n} is out of range.
6019 @defun ewoc-data node
6020 This extracts the data encapsulated by @var{node} and returns it.
6023 @defun ewoc-set-data node data
6024 This sets the data encapsulated by @var{node} to @var{data}.
6027 @defun ewoc-locate ewoc &optional pos guess
6028 This determines the node in @var{ewoc} which contains point (or
6029 @var{pos} if specified), and returns that node. If @var{ewoc} has no
6030 nodes, it returns @code{nil}. If @var{pos} is before the first node,
6031 it returns the first node; if @var{pos} is after the last node, it returns
6032 the last node. The optional third arg @var{guess}
6033 should be a node that is likely to be near @var{pos}; this doesn't
6034 alter the result, but makes the function run faster.
6037 @defun ewoc-location node
6038 This returns the start position of @var{node}.
6041 @defun ewoc-goto-prev ewoc arg
6042 @defunx ewoc-goto-next ewoc arg
6043 These move point to the previous or next, respectively, @var{arg}th node
6044 in @var{ewoc}. @code{ewoc-goto-prev} does not move if it is already at
6045 the first node or if @var{ewoc} is empty, whereas @code{ewoc-goto-next}
6046 moves past the last node, returning @code{nil}. Excepting this special
6047 case, these functions return the node moved to.
6050 @defun ewoc-goto-node ewoc node
6051 This moves point to the start of @var{node} in @var{ewoc}.
6054 @defun ewoc-refresh ewoc
6055 This function regenerates the text of @var{ewoc}. It works by
6056 deleting the text between the header and the footer, i.e., all the
6057 data elements' representations, and then calling the pretty-printer
6058 function for each node, one by one, in order.
6061 @defun ewoc-invalidate ewoc &rest nodes
6062 This is similar to @code{ewoc-refresh}, except that only @var{nodes} in
6063 @var{ewoc} are updated instead of the entire set.
6066 @defun ewoc-delete ewoc &rest nodes
6067 This deletes each node in @var{nodes} from @var{ewoc}.
6070 @defun ewoc-filter ewoc predicate &rest args
6071 This calls @var{predicate} for each data element in @var{ewoc} and
6072 deletes those nodes for which @var{predicate} returns @code{nil}.
6073 Any @var{args} are passed to @var{predicate}.
6076 @defun ewoc-collect ewoc predicate &rest args
6077 This calls @var{predicate} for each data element in @var{ewoc}
6078 and returns a list of those elements for which @var{predicate}
6079 returns non-@code{nil}. The elements in the list are ordered
6080 as in the buffer. Any @var{args} are passed to @var{predicate}.
6083 @defun ewoc-map map-function ewoc &rest args
6084 This calls @var{map-function} for each data element in @var{ewoc} and
6085 updates those nodes for which @var{map-function} returns non-@code{nil}.
6086 Any @var{args} are passed to @var{map-function}.
6089 @node Abstract Display Example
6090 @subsection Abstract Display Example
6092 Here is a simple example using functions of the ewoc package to
6093 implement a ``color components display'', an area in a buffer that
6094 represents a vector of three integers (itself representing a 24-bit RGB
6095 value) in various ways.
6098 (setq colorcomp-ewoc nil
6100 colorcomp-mode-map nil
6101 colorcomp-labels ["Red" "Green" "Blue"])
6103 (defun colorcomp-pp (data)
6105 (let ((comp (aref colorcomp-data data)))
6106 (insert (aref colorcomp-labels data) "\t: #x"
6107 (format "%02X" comp) " "
6108 (make-string (ash comp -2) ?#) "\n"))
6109 (let ((cstr (format "#%02X%02X%02X"
6110 (aref colorcomp-data 0)
6111 (aref colorcomp-data 1)
6112 (aref colorcomp-data 2)))
6113 (samp " (sample text) "))
6115 (propertize samp 'face
6116 `(foreground-color . ,cstr))
6117 (propertize samp 'face
6118 `(background-color . ,cstr))
6121 (defun colorcomp (color)
6122 "Allow fiddling with COLOR in a new buffer.
6123 The buffer is in Color Components mode."
6124 (interactive "sColor (name or #RGB or #RRGGBB): ")
6125 (when (string= "" color)
6126 (setq color "green"))
6127 (unless (color-values color)
6128 (error "No such color: %S" color))
6130 (generate-new-buffer (format "originally: %s" color)))
6131 (kill-all-local-variables)
6132 (setq major-mode 'colorcomp-mode
6133 mode-name "Color Components")
6134 (use-local-map colorcomp-mode-map)
6136 (buffer-disable-undo)
6137 (let ((data (apply 'vector (mapcar (lambda (n) (ash n -8))
6138 (color-values color))))
6139 (ewoc (ewoc-create 'colorcomp-pp
6140 "\nColor Components\n\n"
6141 (substitute-command-keys
6142 "\n\\@{colorcomp-mode-map@}"))))
6143 (set (make-local-variable 'colorcomp-data) data)
6144 (set (make-local-variable 'colorcomp-ewoc) ewoc)
6145 (ewoc-enter-last ewoc 0)
6146 (ewoc-enter-last ewoc 1)
6147 (ewoc-enter-last ewoc 2)
6148 (ewoc-enter-last ewoc nil)))
6151 @cindex controller part, model/view/controller
6152 This example can be extended to be a ``color selection widget'' (in
6153 other words, the controller part of the ``model/view/controller''
6154 design paradigm) by defining commands to modify @code{colorcomp-data}
6155 and to ``finish'' the selection process, and a keymap to tie it all
6156 together conveniently.
6159 (defun colorcomp-mod (index limit delta)
6160 (let ((cur (aref colorcomp-data index)))
6161 (unless (= limit cur)
6162 (aset colorcomp-data index (+ cur delta)))
6165 (ewoc-nth colorcomp-ewoc index)
6166 (ewoc-nth colorcomp-ewoc -1))))
6168 (defun colorcomp-R-more () (interactive) (colorcomp-mod 0 255 1))
6169 (defun colorcomp-G-more () (interactive) (colorcomp-mod 1 255 1))
6170 (defun colorcomp-B-more () (interactive) (colorcomp-mod 2 255 1))
6171 (defun colorcomp-R-less () (interactive) (colorcomp-mod 0 0 -1))
6172 (defun colorcomp-G-less () (interactive) (colorcomp-mod 1 0 -1))
6173 (defun colorcomp-B-less () (interactive) (colorcomp-mod 2 0 -1))
6175 (defun colorcomp-copy-as-kill-and-exit ()
6176 "Copy the color components into the kill ring and kill the buffer.
6177 The string is formatted #RRGGBB (hash followed by six hex digits)."
6179 (kill-new (format "#%02X%02X%02X"
6180 (aref colorcomp-data 0)
6181 (aref colorcomp-data 1)
6182 (aref colorcomp-data 2)))
6185 (setq colorcomp-mode-map
6186 (let ((m (make-sparse-keymap)))
6188 (define-key m "i" 'colorcomp-R-less)
6189 (define-key m "o" 'colorcomp-R-more)
6190 (define-key m "k" 'colorcomp-G-less)
6191 (define-key m "l" 'colorcomp-G-more)
6192 (define-key m "," 'colorcomp-B-less)
6193 (define-key m "." 'colorcomp-B-more)
6194 (define-key m " " 'colorcomp-copy-as-kill-and-exit)
6198 Note that we never modify the data in each node, which is fixed when the
6199 ewoc is created to be either @code{nil} or an index into the vector
6200 @code{colorcomp-data}, the actual color components.
6203 @section Blinking Parentheses
6204 @cindex parenthesis matching
6205 @cindex blinking parentheses
6206 @cindex balancing parentheses
6208 This section describes the mechanism by which Emacs shows a matching
6209 open parenthesis when the user inserts a close parenthesis.
6211 @defvar blink-paren-function
6212 The value of this variable should be a function (of no arguments) to
6213 be called whenever a character with close parenthesis syntax is inserted.
6214 The value of @code{blink-paren-function} may be @code{nil}, in which
6215 case nothing is done.
6218 @defopt blink-matching-paren
6219 If this variable is @code{nil}, then @code{blink-matching-open} does
6223 @defopt blink-matching-paren-distance
6224 This variable specifies the maximum distance to scan for a matching
6225 parenthesis before giving up.
6228 @defopt blink-matching-delay
6229 This variable specifies the number of seconds to keep indicating the
6230 matching parenthesis. A fraction of a second often gives good
6231 results, but the default is 1, which works on all systems.
6234 @deffn Command blink-matching-open
6235 This function is the default value of @code{blink-paren-function}. It
6236 assumes that point follows a character with close parenthesis syntax
6237 and applies the appropriate effect momentarily to the matching opening
6238 character. If that character is not already on the screen, it
6239 displays the character's context in the echo area. To avoid long
6240 delays, this function does not search farther than
6241 @code{blink-matching-paren-distance} characters.
6243 Here is an example of calling this function explicitly.
6247 (defun interactive-blink-matching-open ()
6248 "Indicate momentarily the start of parenthesized sexp before point."
6252 (let ((blink-matching-paren-distance
6254 (blink-matching-paren t))
6255 (blink-matching-open)))
6260 @node Character Display
6261 @section Character Display
6263 This section describes how characters are actually displayed by
6264 Emacs. Typically, a character is displayed as a @dfn{glyph} (a
6265 graphical symbol which occupies one character position on the screen),
6266 whose appearance corresponds to the character itself. For example,
6267 the character @samp{a} (character code 97) is displayed as @samp{a}.
6268 Some characters, however, are displayed specially. For example, the
6269 formfeed character (character code 12) is usually displayed as a
6270 sequence of two glyphs, @samp{^L}, while the newline character
6271 (character code 10) starts a new screen line.
6273 You can modify how each character is displayed by defining a
6274 @dfn{display table}, which maps each character code into a sequence of
6275 glyphs. @xref{Display Tables}.
6278 * Usual Display:: The usual conventions for displaying characters.
6279 * Display Tables:: What a display table consists of.
6280 * Active Display Table:: How Emacs selects a display table to use.
6281 * Glyphs:: How to define a glyph, and what glyphs mean.
6282 * Glyphless Chars:: How glyphless characters are drawn.
6286 @subsection Usual Display Conventions
6288 Here are the conventions for displaying each character code (in the
6289 absence of a display table, which can override these
6294 conventions; @pxref{Display Tables}).
6297 @cindex printable ASCII characters
6300 The @dfn{printable @acronym{ASCII} characters}, character codes 32
6301 through 126 (consisting of numerals, English letters, and symbols like
6302 @samp{#}) are displayed literally.
6305 The tab character (character code 9) displays as whitespace stretching
6306 up to the next tab stop column. @xref{Text Display,,, emacs, The GNU
6307 Emacs Manual}. The variable @code{tab-width} controls the number of
6308 spaces per tab stop (see below).
6311 The newline character (character code 10) has a special effect: it
6312 ends the preceding line and starts a new line.
6314 @cindex ASCII control characters
6316 The non-printable @dfn{@acronym{ASCII} control characters}---character
6317 codes 0 through 31, as well as the @key{DEL} character (character code
6318 127)---display in one of two ways according to the variable
6319 @code{ctl-arrow}. If this variable is non-@code{nil} (the default),
6320 these characters are displayed as sequences of two glyphs, where the
6321 first glyph is @samp{^} (a display table can specify a glyph to use
6322 instead of @samp{^}); e.g., the @key{DEL} character is displayed as
6325 If @code{ctl-arrow} is @code{nil}, these characters are displayed as
6326 octal escapes (see below).
6328 This rule also applies to carriage return (character code 13), if that
6329 character appears in the buffer. But carriage returns usually do not
6330 appear in buffer text; they are eliminated as part of end-of-line
6331 conversion (@pxref{Coding System Basics}).
6333 @cindex octal escapes
6335 @dfn{Raw bytes} are non-@acronym{ASCII} characters with codes 128
6336 through 255 (@pxref{Text Representations}). These characters display
6337 as @dfn{octal escapes}: sequences of four glyphs, where the first
6338 glyph is the @acronym{ASCII} code for @samp{\}, and the others are
6339 digit characters representing the character code in octal. (A display
6340 table can specify a glyph to use instead of @samp{\}.)
6343 Each non-@acronym{ASCII} character with code above 255 is displayed
6344 literally, if the terminal supports it. If the terminal does not
6345 support it, the character is said to be @dfn{glyphless}, and it is
6346 usually displayed using a placeholder glyph. For example, if a
6347 graphical terminal has no font for a character, Emacs usually displays
6348 a box containing the character code in hexadecimal. @xref{Glyphless
6352 The above display conventions apply even when there is a display
6353 table, for any character whose entry in the active display table is
6354 @code{nil}. Thus, when you set up a display table, you need only
6355 specify the characters for which you want special behavior.
6357 The following variables affect how certain characters are displayed
6358 on the screen. Since they change the number of columns the characters
6359 occupy, they also affect the indentation functions. They also affect
6360 how the mode line is displayed; if you want to force redisplay of the
6361 mode line using the new values, call the function
6362 @code{force-mode-line-update} (@pxref{Mode Line Format}).
6365 @cindex control characters in display
6366 This buffer-local variable controls how control characters are
6367 displayed. If it is non-@code{nil}, they are displayed as a caret
6368 followed by the character: @samp{^A}. If it is @code{nil}, they are
6369 displayed as octal escapes: a backslash followed by three octal
6370 digits, as in @samp{\001}.
6374 The value of this buffer-local variable is the spacing between tab
6375 stops used for displaying tab characters in Emacs buffers. The value
6376 is in units of columns, and the default is 8. Note that this feature
6377 is completely independent of the user-settable tab stops used by the
6378 command @code{tab-to-tab-stop}. @xref{Indent Tabs}.
6381 @node Display Tables
6382 @subsection Display Tables
6384 @cindex display table
6385 A display table is a special-purpose char-table
6386 (@pxref{Char-Tables}), with @code{display-table} as its subtype, which
6387 is used to override the usual character display conventions. This
6388 section describes how to make, inspect, and assign elements to a
6389 display table object.
6391 @defun make-display-table
6392 This creates and returns a display table. The table initially has
6393 @code{nil} in all elements.
6396 The ordinary elements of the display table are indexed by character
6397 codes; the element at index @var{c} says how to display the character
6398 code @var{c}. The value should be @code{nil} (which means to display
6399 the character @var{c} according to the usual display conventions;
6400 @pxref{Usual Display}), or a vector of glyph codes (which means to
6401 display the character @var{c} as those glyphs; @pxref{Glyphs}).
6403 @strong{Warning:} if you use the display table to change the display
6404 of newline characters, the whole buffer will be displayed as one long
6407 The display table also has six ``extra slots'' which serve special
6408 purposes. Here is a table of their meanings; @code{nil} in any slot
6409 means to use the default for that slot, as stated below.
6413 The glyph for the end of a truncated screen line (the default for this
6414 is @samp{$}). @xref{Glyphs}. On graphical terminals, Emacs uses
6415 arrows in the fringes to indicate truncation, so the display table has
6419 The glyph for the end of a continued line (the default is @samp{\}).
6420 On graphical terminals, Emacs uses curved arrows in the fringes to
6421 indicate continuation, so the display table has no effect.
6424 The glyph for indicating a character displayed as an octal character
6425 code (the default is @samp{\}).
6428 The glyph for indicating a control character (the default is @samp{^}).
6431 A vector of glyphs for indicating the presence of invisible lines (the
6432 default is @samp{...}). @xref{Selective Display}.
6435 The glyph used to draw the border between side-by-side windows (the
6436 default is @samp{|}). @xref{Splitting Windows}. This takes effect only
6437 when there are no scroll bars; if scroll bars are supported and in use,
6438 a scroll bar separates the two windows.
6441 For example, here is how to construct a display table that mimics
6442 the effect of setting @code{ctl-arrow} to a non-@code{nil} value
6443 (@pxref{Glyphs}, for the function @code{make-glyph-code}):
6446 (setq disptab (make-display-table))
6451 (vector (make-glyph-code ?^ 'escape-glyph)
6452 (make-glyph-code (+ i 64) 'escape-glyph)))))
6454 (vector (make-glyph-code ?^ 'escape-glyph)
6455 (make-glyph-code ?? 'escape-glyph)))))
6458 @defun display-table-slot display-table slot
6459 This function returns the value of the extra slot @var{slot} of
6460 @var{display-table}. The argument @var{slot} may be a number from 0 to
6461 5 inclusive, or a slot name (symbol). Valid symbols are
6462 @code{truncation}, @code{wrap}, @code{escape}, @code{control},
6463 @code{selective-display}, and @code{vertical-border}.
6466 @defun set-display-table-slot display-table slot value
6467 This function stores @var{value} in the extra slot @var{slot} of
6468 @var{display-table}. The argument @var{slot} may be a number from 0 to
6469 5 inclusive, or a slot name (symbol). Valid symbols are
6470 @code{truncation}, @code{wrap}, @code{escape}, @code{control},
6471 @code{selective-display}, and @code{vertical-border}.
6474 @defun describe-display-table display-table
6475 This function displays a description of the display table
6476 @var{display-table} in a help buffer.
6479 @deffn Command describe-current-display-table
6480 This command displays a description of the current display table in a
6484 @node Active Display Table
6485 @subsection Active Display Table
6486 @cindex active display table
6488 Each window can specify a display table, and so can each buffer.
6489 The window's display table, if there is one, takes precedence over the
6490 buffer's display table. If neither exists, Emacs tries to use the
6491 standard display table; if that is @code{nil}, Emacs uses the usual
6492 character display conventions (@pxref{Usual Display}).
6494 Note that display tables affect how the mode line is displayed, so
6495 if you want to force redisplay of the mode line using a new display
6496 table, call @code{force-mode-line-update} (@pxref{Mode Line Format}).
6498 @defun window-display-table &optional window
6499 This function returns @var{window}'s display table, or @code{nil} if
6500 there is none. The default for @var{window} is the selected window.
6503 @defun set-window-display-table window table
6504 This function sets the display table of @var{window} to @var{table}.
6505 The argument @var{table} should be either a display table or
6509 @defvar buffer-display-table
6510 This variable is automatically buffer-local in all buffers; its value
6511 specifies the buffer's display table. If it is @code{nil}, there is
6512 no buffer display table.
6515 @defvar standard-display-table
6516 The value of this variable is the standard display table, which is
6517 used when Emacs is displaying a buffer in a window with neither a
6518 window display table nor a buffer display table defined. Its default
6522 The @file{disp-table} library defines several functions for changing
6523 the standard display table.
6530 A @dfn{glyph} is a graphical symbol which occupies a single
6531 character position on the screen. Each glyph is represented in Lisp
6532 as a @dfn{glyph code}, which specifies a character and optionally a
6533 face to display it in (@pxref{Faces}). The main use of glyph codes is
6534 as the entries of display tables (@pxref{Display Tables}). The
6535 following functions are used to manipulate glyph codes:
6537 @defun make-glyph-code char &optional face
6538 This function returns a glyph code representing char @var{char} with
6539 face @var{face}. If @var{face} is omitted or @code{nil}, the glyph
6540 uses the default face; in that case, the glyph code is an integer. If
6541 @var{face} is non-@code{nil}, the glyph code is not necessarily an
6545 @defun glyph-char glyph
6546 This function returns the character of glyph code @var{glyph}.
6549 @defun glyph-face glyph
6550 This function returns face of glyph code @var{glyph}, or @code{nil} if
6551 @var{glyph} uses the default face.
6555 You can set up a @dfn{glyph table} to change how glyph codes are
6556 actually displayed on text terminals. This feature is semi-obsolete;
6557 use @code{glyphless-char-display} instead (@pxref{Glyphless Chars}).
6560 The value of this variable, if non-@code{nil}, is the current glyph
6561 table. It takes effect only on character terminals; on graphical
6562 displays, all glyphs are displayed literally. The glyph table should
6563 be a vector whose @var{g}th element specifies how to display glyph
6564 code @var{g}, where @var{g} is the glyph code for a glyph whose face
6565 is unspecified. Each element should be one of the following:
6569 Display this glyph literally.
6572 Display this glyph by sending the specified string to the terminal.
6575 Display the specified glyph code instead.
6578 Any integer glyph code greater than or equal to the length of the
6579 glyph table is displayed literally.
6583 @node Glyphless Chars
6584 @subsection Glyphless Character Display
6585 @cindex glyphless characters
6587 @dfn{Glyphless characters} are characters which are displayed in a
6588 special way, e.g., as a box containing a hexadecimal code, instead of
6589 being displayed literally. These include characters which are
6590 explicitly defined to be glyphless, as well as characters for which
6591 there is no available font (on a graphical display), and characters
6592 which cannot be encoded by the terminal's coding system (on a text
6595 @defvar glyphless-char-display
6596 The value of this variable is a char-table which defines glyphless
6597 characters and how they are displayed. Each entry must be one of the
6598 following display methods:
6602 Display the character in the usual way.
6604 @item @code{zero-width}
6605 Don't display the character.
6607 @item @code{thin-space}
6608 Display a thin space, 1-pixel wide on graphical displays, or
6609 1-character wide on text terminals.
6611 @item @code{empty-box}
6612 Display an empty box.
6614 @item @code{hex-code}
6615 Display a box containing the Unicode codepoint of the character, in
6616 hexadecimal notation.
6618 @item an @acronym{ASCII} string
6619 Display a box containing that string.
6621 @item a cons cell @code{(@var{graphical} . @var{text})}
6622 Display with @var{graphical} on graphical displays, and with
6623 @var{text} on text terminals. Both @var{graphical} and @var{text}
6624 must be one of the display methods described above.
6628 The @code{thin-space}, @code{empty-box}, @code{hex-code}, and
6629 @acronym{ASCII} string display methods are drawn with the
6630 @code{glyphless-char} face.
6632 The char-table has one extra slot, which determines how to display any
6633 character that cannot be displayed with any available font, or cannot
6634 be encoded by the terminal's coding system. Its value should be one
6635 of the above display methods, except @code{zero-width} or a cons cell.
6637 If a character has a non-@code{nil} entry in an active display table,
6638 the display table takes effect; in this case, Emacs does not consult
6639 @code{glyphless-char-display} at all.
6642 @defopt glyphless-char-display-control
6643 This user option provides a convenient way to set
6644 @code{glyphless-char-display} for groups of similar characters. Do
6645 not set its value directly from Lisp code; the value takes effect only
6646 via a custom @code{:set} function (@pxref{Variable Definitions}),
6647 which updates @code{glyphless-char-display}.
6649 Its value should be an alist of elements @code{(@var{group}
6650 . @var{method})}, where @var{group} is a symbol specifying a group of
6651 characters, and @var{method} is a symbol specifying how to display
6654 @var{group} should be one of the following:
6658 @acronym{ASCII} control characters @code{U+0000} to @code{U+001F},
6659 excluding the newline and tab characters (normally displayed as escape
6660 sequences like @samp{^A}; @pxref{Text Display,, How Text Is Displayed,
6661 emacs, The GNU Emacs Manual}).
6664 Non-@acronym{ASCII}, non-printing characters @code{U+0080} to
6665 @code{U+009F} (normally displayed as octal escape sequences like
6668 @item format-control
6669 Characters of Unicode General Category `Cf', such as @samp{U+200E}
6670 (Left-to-Right Mark), but excluding characters that have graphic
6671 images, such as @samp{U+00AD} (Soft Hyphen).
6674 Characters for there is no suitable font, or which cannot be encoded
6675 by the terminal's coding system.
6678 @c FIXME: this can also be `acronym', but that's not currently
6679 @c completely implemented; it applies only to the format-control
6680 @c group, and only works if the acronym is in `char-acronym-table'.
6681 The @var{method} symbol should be one of @code{zero-width},
6682 @code{thin-space}, @code{empty-box}, or @code{hex-code}. These have
6683 the same meanings as in @code{glyphless-char-display}, above.
6690 This section describes how to make Emacs ring the bell (or blink the
6691 screen) to attract the user's attention. Be conservative about how
6692 often you do this; frequent bells can become irritating. Also be
6693 careful not to use just beeping when signaling an error is more
6694 appropriate (@pxref{Errors}).
6696 @defun ding &optional do-not-terminate
6697 @cindex keyboard macro termination
6698 This function beeps, or flashes the screen (see @code{visible-bell} below).
6699 It also terminates any keyboard macro currently executing unless
6700 @var{do-not-terminate} is non-@code{nil}.
6703 @defun beep &optional do-not-terminate
6704 This is a synonym for @code{ding}.
6707 @defopt visible-bell
6708 This variable determines whether Emacs should flash the screen to
6709 represent a bell. Non-@code{nil} means yes, @code{nil} means no.
6710 This is effective on graphical displays, and on text terminals
6711 provided the terminal's Termcap entry defines the visible bell
6712 capability (@samp{vb}).
6715 @defvar ring-bell-function
6716 If this is non-@code{nil}, it specifies how Emacs should ``ring the
6717 bell''. Its value should be a function of no arguments. If this is
6718 non-@code{nil}, it takes precedence over the @code{visible-bell}
6722 @node Window Systems
6723 @section Window Systems
6725 Emacs works with several window systems, most notably the X Window
6726 System. Both Emacs and X use the term ``window'', but use it
6727 differently. An Emacs frame is a single window as far as X is
6728 concerned; the individual Emacs windows are not known to X at all.
6730 @defvar window-system
6731 This terminal-local variable tells Lisp programs what window system
6732 Emacs is using for displaying the frame. The possible values are
6736 @cindex X Window System
6737 Emacs is displaying the frame using X.
6739 Emacs is displaying the frame using native MS-Windows GUI.
6741 Emacs is displaying the frame using the Nextstep interface (used on
6742 GNUstep and Mac OS X).
6744 Emacs is displaying the frame using MS-DOS direct screen writes.
6746 Emacs is displaying the frame on a character-based terminal.
6750 @defvar initial-window-system
6751 This variable holds the value of @code{window-system} used for the
6752 first frame created by Emacs during startup. (When Emacs is invoked
6753 with the @option{--daemon} option, it does not create any initial
6754 frames, so @code{initial-window-system} is @code{nil}. @xref{Initial
6755 Options, daemon,, emacs, The GNU Emacs Manual}.)
6758 @defun window-system &optional frame
6759 This function returns a symbol whose name tells what window system is
6760 used for displaying @var{frame} (which defaults to the currently
6761 selected frame). The list of possible symbols it returns is the same
6762 one documented for the variable @code{window-system} above.
6765 Do @emph{not} use @code{window-system} and
6766 @code{initial-window-system} as predicates or boolean flag variables,
6767 if you want to write code that works differently on text terminals and
6768 graphic displays. That is because @code{window-system} is not a good
6769 indicator of Emacs capabilities on a given display type. Instead, use
6770 @code{display-graphic-p} or any of the other @code{display-*-p}
6771 predicates described in @ref{Display Feature Testing}.
6773 @node Bidirectional Display
6774 @section Bidirectional Display
6775 @cindex bidirectional display
6776 @cindex right-to-left text
6778 Emacs can display text written in scripts, such as Arabic, Farsi,
6779 and Hebrew, whose natural ordering for horizontal text display runs
6780 from right to left. Furthermore, segments of Latin script and digits
6781 embedded in right-to-left text are displayed left-to-right, while
6782 segments of right-to-left script embedded in left-to-right text
6783 (e.g., Arabic or Hebrew text in comments or strings in a program
6784 source file) are appropriately displayed right-to-left. We call such
6785 mixtures of left-to-right and right-to-left text @dfn{bidirectional
6786 text}. This section describes the facilities and options for editing
6787 and displaying bidirectional text.
6789 @cindex logical order
6790 @cindex reading order
6791 @cindex visual order
6792 @cindex unicode bidirectional algorithm
6794 @cindex bidirectional reordering
6795 @cindex reordering, of bidirectional text
6796 Text is stored in Emacs buffers and strings in @dfn{logical} (or
6797 @dfn{reading}) order, i.e., the order in which a human would read
6798 each character. In right-to-left and bidirectional text, the order in
6799 which characters are displayed on the screen (called @dfn{visual
6800 order}) is not the same as logical order; the characters' screen
6801 positions do not increase monotonically with string or buffer
6802 position. In performing this @dfn{bidirectional reordering}, Emacs
6803 follows the Unicode Bidirectional Algorithm (a.k.a.@: @acronym{UBA}),
6804 which is described in Annex #9 of the Unicode standard
6805 (@url{http://www.unicode.org/reports/tr9/}). Emacs provides a ``Full
6806 Bidirectionality'' class implementation of the @acronym{UBA},
6807 consistent with the requirements of the Unicode Standard v7.0.
6809 @defvar bidi-display-reordering
6810 If the value of this buffer-local variable is non-@code{nil} (the
6811 default), Emacs performs bidirectional reordering for display. The
6812 reordering affects buffer text, as well as display strings and overlay
6813 strings from text and overlay properties in the buffer (@pxref{Overlay
6814 Properties}, and @pxref{Display Property}). If the value is
6815 @code{nil}, Emacs does not perform bidirectional reordering in the
6818 The default value of @code{bidi-display-reordering} controls the
6819 reordering of strings which are not directly supplied by a buffer,
6820 including the text displayed in mode lines (@pxref{Mode Line Format})
6821 and header lines (@pxref{Header Lines}).
6824 @cindex unibyte buffers, and bidi reordering
6825 Emacs never reorders the text of a unibyte buffer, even if
6826 @code{bidi-display-reordering} is non-@code{nil} in the buffer. This
6827 is because unibyte buffers contain raw bytes, not characters, and thus
6828 lack the directionality properties required for reordering.
6829 Therefore, to test whether text in a buffer will be reordered for
6830 display, it is not enough to test the value of
6831 @code{bidi-display-reordering} alone. The correct test is this:
6834 (if (and enable-multibyte-characters
6835 bidi-display-reordering)
6836 ;; Buffer is being reordered for display
6840 However, unibyte display and overlay strings @emph{are} reordered if
6841 their parent buffer is reordered. This is because plain-@sc{ascii}
6842 strings are stored by Emacs as unibyte strings. If a unibyte display
6843 or overlay string includes non-@sc{ascii} characters, these characters
6844 are assumed to have left-to-right direction.
6846 @cindex display properties, and bidi reordering of text
6847 Text covered by @code{display} text properties, by overlays with
6848 @code{display} properties whose value is a string, and by any other
6849 properties that replace buffer text, is treated as a single unit when
6850 it is reordered for display. That is, the entire chunk of text
6851 covered by these properties is reordered together. Moreover, the
6852 bidirectional properties of the characters in such a chunk of text are
6853 ignored, and Emacs reorders them as if they were replaced with a
6854 single character @code{U+FFFC}, known as the @dfn{Object Replacement
6855 Character}. This means that placing a display property over a portion
6856 of text may change the way that the surrounding text is reordered for
6857 display. To prevent this unexpected effect, always place such
6858 properties on text whose directionality is identical with text that
6861 @cindex base direction of a paragraph
6862 Each paragraph of bidirectional text has a @dfn{base direction},
6863 either right-to-left or left-to-right. Left-to-right paragraphs are
6864 displayed beginning at the left margin of the window, and are
6865 truncated or continued when the text reaches the right margin.
6866 Right-to-left paragraphs are displayed beginning at the right margin,
6867 and are continued or truncated at the left margin.
6869 By default, Emacs determines the base direction of each paragraph by
6870 looking at the text at its beginning. The precise method of
6871 determining the base direction is specified by the @acronym{UBA}; in a
6872 nutshell, the first character in a paragraph that has an explicit
6873 directionality determines the base direction of the paragraph.
6874 However, sometimes a buffer may need to force a certain base direction
6875 for its paragraphs. For example, buffers containing program source
6876 code should force all paragraphs to be displayed left-to-right. You
6877 can use following variable to do this:
6879 @defvar bidi-paragraph-direction
6880 If the value of this buffer-local variable is the symbol
6881 @code{right-to-left} or @code{left-to-right}, all paragraphs in the
6882 buffer are assumed to have that specified direction. Any other value
6883 is equivalent to @code{nil} (the default), which means to determine
6884 the base direction of each paragraph from its contents.
6886 @cindex @code{prog-mode}, and @code{bidi-paragraph-direction}
6887 Modes for program source code should set this to @code{left-to-right}.
6888 Prog mode does this by default, so modes derived from Prog mode do not
6889 need to set this explicitly (@pxref{Basic Major Modes}).
6892 @defun current-bidi-paragraph-direction &optional buffer
6893 This function returns the paragraph direction at point in the named
6894 @var{buffer}. The returned value is a symbol, either
6895 @code{left-to-right} or @code{right-to-left}. If @var{buffer} is
6896 omitted or @code{nil}, it defaults to the current buffer. If the
6897 buffer-local value of the variable @code{bidi-paragraph-direction} is
6898 non-@code{nil}, the returned value will be identical to that value;
6899 otherwise, the returned value reflects the paragraph direction
6900 determined dynamically by Emacs. For buffers whose value of
6901 @code{bidi-display-reordering} is @code{nil} as well as unibyte
6902 buffers, this function always returns @code{left-to-right}.
6905 @cindex visual-order cursor motion
6906 Sometimes there's a need to move point in strict visual order,
6907 either to the left or to the right of its current screen position.
6908 Emacs provides a primitive to do that.
6910 @defun move-point-visually direction
6911 This function moves point of the currently selected window to the
6912 buffer position that appears immediately to the right or to the left
6913 of point on the screen. If @var{direction} is positive, point will
6914 move one screen position to the right, otherwise it will move one
6915 screen position to the left. Note that, depending on the surrounding
6916 bidirectional context, this could potentially move point many buffer
6917 positions away. If invoked at the end of a screen line, the function
6918 moves point to the rightmost or leftmost screen position of the next
6919 or previous screen line, as appropriate for the value of
6922 The function returns the new buffer position as its value.
6925 @cindex layout on display, and bidirectional text
6926 @cindex jumbled display of bidirectional text
6927 @cindex concatenating bidirectional strings
6928 Bidirectional reordering can have surprising and unpleasant effects
6929 when two strings with bidirectional content are juxtaposed in a
6930 buffer, or otherwise programmatically concatenated into a string of
6931 text. A typical problematic case is when a buffer consists of
6932 sequences of text ``fields'' separated by whitespace or punctuation
6933 characters, like Buffer Menu mode or Rmail Summary Mode. Because the
6934 punctuation characters used as separators have @dfn{weak
6935 directionality}, they take on the directionality of surrounding text.
6936 As result, a numeric field that follows a field with bidirectional
6937 content can be displayed @emph{to the left} of the preceding field,
6938 messing up the expected layout. There are several ways to avoid this
6943 Append the special character @code{U+200E}, LEFT-TO-RIGHT MARK, or
6944 @acronym{LRM}, to the end of each field that may have bidirectional
6945 content, or prepend it to the beginning of the following field. The
6946 function @code{bidi-string-mark-left-to-right}, described below, comes
6947 in handy for this purpose. (In a right-to-left paragraph, use
6948 @code{U+200F}, RIGHT-TO-LEFT MARK, or @acronym{RLM}, instead.) This
6949 is one of the solutions recommended by the UBA.
6952 Include the tab character in the field separator. The tab character
6953 plays the role of @dfn{segment separator} in bidirectional reordering,
6954 causing the text on either side to be reordered separately.
6956 @cindex @code{space} display spec, and bidirectional text
6958 Separate fields with a @code{display} property or overlay with a
6959 property value of the form @code{(space . PROPS)} (@pxref{Specified
6960 Space}). Emacs treats this display specification as a @dfn{paragraph
6961 separator}, and reorders the text on either side separately.
6964 @defun bidi-string-mark-left-to-right string
6965 This function returns its argument @var{string}, possibly modified,
6966 such that the result can be safely concatenated with another string,
6967 or juxtaposed with another string in a buffer, without disrupting the
6968 relative layout of this string and the next one on display. If the
6969 string returned by this function is displayed as part of a
6970 left-to-right paragraph, it will always appear on display to the left
6971 of the text that follows it. The function works by examining the
6972 characters of its argument, and if any of those characters could cause
6973 reordering on display, the function appends the @acronym{LRM}
6974 character to the string. The appended @acronym{LRM} character is made
6975 invisible by giving it an @code{invisible} text property of @code{t}
6976 (@pxref{Invisible Text}).
6979 The reordering algorithm uses the bidirectional properties of the
6980 characters stored as their @code{bidi-class} property
6981 (@pxref{Character Properties}). Lisp programs can change these
6982 properties by calling the @code{put-char-code-property} function.
6983 However, doing this requires a thorough understanding of the
6984 @acronym{UBA}, and is therefore not recommended. Any changes to the
6985 bidirectional properties of a character have global effect: they
6986 affect all Emacs frames and windows.
6988 Similarly, the @code{mirroring} property is used to display the
6989 appropriate mirrored character in the reordered text. Lisp programs
6990 can affect the mirrored display by changing this property. Again, any
6991 such changes affect all of Emacs display.
6993 @cindex overriding bidirectional properties
6994 @cindex directional overrides
6997 The bidirectional properties of characters can be overridden by
6998 inserting into the text special directional control characters,
6999 LEFT-TO-RIGHT OVERRIDE (@acronym{LRO}) and RIGHT-TO-LEFT OVERRIDE
7000 (@acronym{RLO}). Any characters between a @acronym{RLO} and the
7001 following newline or POP DIRECTIONAL FORMATTING (@acronym{PDF})
7002 control character, whichever comes first, will be displayed as if they
7003 were strong right-to-left characters, i.e.@: they will be reversed on
7004 display. Similarly, any characters between @acronym{LRO} and
7005 @acronym{PDF} or newline will display as if they were strong
7006 left-to-right, and will @emph{not} be reversed even if they are strong
7007 right-to-left characters.
7009 @cindex phishing using directional overrides
7010 @cindex malicious use of directional overrides
7011 These overrides are useful when you want to make some text
7012 unaffected by the reordering algorithm, and instead directly control
7013 the display order. But they can also be used for malicious purposes,
7014 known as @dfn{phishing}. Specifically, a URL on a Web page or a link
7015 in an email message can be manipulated to make its visual appearance
7016 unrecognizable, or similar to some popular benign location, while the
7017 real location, interpreted by a browser in the logical order, is very
7020 Emacs provides a primitive that applications can use to detect
7021 instances of text whose bidirectional properties were overridden so as
7022 to make a left-to-right character display as if it were a
7023 right-to-left character, or vise versa.
7025 @defun bidi-find-overridden-directionality from to &optional object
7026 This function looks at the text of the specified @var{object} between
7027 positions @var{from} (inclusive) and @var{to} (exclusive), and returns
7028 the first position where it finds a strong left-to-right character
7029 whose directional properties were forced to display the character as
7030 right-to-left, or for a strong right-to-left character that was forced
7031 to display as left-to-right. If it finds no such characters in the
7032 specified region of text, it returns @code{nil}.
7034 The optional argument @var{object} specifies which text to search, and
7035 defaults to the current buffer. If @var{object} is non-@code{nil}, it
7036 can be some other buffer, or it can be a string or a window. If it is
7037 a string, the function searches that string. If it is a window, the
7038 function searches the buffer displayed in that window. If a buffer
7039 whose text you want to examine is displayed in some window, we
7040 recommend to specify it by that window, rather than pass the buffer to
7041 the function. This is because telling the function about the window
7042 allows it to correctly account for window-specific overlays, which
7043 might change the result of the function if some text in the buffer is
7044 covered by overlays.
7047 @cindex copying bidirectional text, preserve visual order
7048 @cindex visual order, preserve when copying bidirectional text
7049 When text that includes mixed right-to-left and left-to-right
7050 characters and bidirectional controls is copied into a different
7051 location, it can change its visual appearance, and also can affect the
7052 visual appearance of the surrounding text at destination. This is
7053 because reordering of bidirectional text specified by the
7054 @acronym{UBA} has non-trivial context-dependent effects both on the
7055 copied text and on the text at copy destination that will surround it.
7057 Sometimes, a Lisp program may need to preserve the exact visual
7058 appearance of the copied text at destination, and of the text that
7059 surrounds the copy. Lisp programs can use the following function to
7060 achieve that effect.
7062 @defun buffer-substring-with-bidi-context start end &optional no-properties
7063 This function works similar to @code{buffer-substring} (@pxref{Buffer
7064 Contents}), but it prepends and appends to the copied text bidi
7065 directional control characters necessary to preserve the visual
7066 appearance of the text when it is inserted at another place. Optional
7067 argument @var{no-properties}, if non-@code{nil}, means remove the text
7068 properties from the copy of the text.