2 @c This is part of the GNU Emacs Lisp Reference Manual.
3 @c Copyright (C) 1990-1995, 1998-2013 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 * Width:: How wide a character or string is on the screen.
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 vertical scroll bars.
27 * Display Property:: Enabling special display features.
28 * Images:: Displaying images in Emacs buffers.
29 * Buttons:: Adding clickable buttons to Emacs buffers.
30 * Abstract Display:: Emacs's Widget for Object Collections.
31 * Blinking:: How Emacs shows the matching open parenthesis.
32 * Character Display:: How Emacs displays individual characters.
33 * Beeping:: Audible signal to the user.
34 * Window Systems:: Which window system is being used.
35 * Bidirectional Display:: Display of bidirectional scripts, such as
40 @section Refreshing the Screen
42 The function @code{redraw-frame} clears and redisplays the entire
43 contents of a given frame (@pxref{Frames}). This is useful if the
46 @defun redraw-frame frame
47 This function clears and redisplays frame @var{frame}.
50 Even more powerful is @code{redraw-display}:
52 @deffn Command redraw-display
53 This function clears and redisplays all visible frames.
56 In Emacs, processing user input takes priority over redisplay. If
57 you call these functions when input is available, they don't redisplay
58 immediately, but the requested redisplay does happen
59 eventually---after all the input has been processed.
61 On text terminals, suspending and resuming Emacs normally also
62 refreshes the screen. Some terminal emulators record separate
63 contents for display-oriented programs such as Emacs and for ordinary
64 sequential display. If you are using such a terminal, you might want
65 to inhibit the redisplay on resumption.
67 @defopt no-redraw-on-reenter
68 @cindex suspend (cf. @code{no-redraw-on-reenter})
69 @cindex resume (cf. @code{no-redraw-on-reenter})
70 This variable controls whether Emacs redraws the entire screen after it
71 has been suspended and resumed. Non-@code{nil} means there is no need
72 to redraw, @code{nil} means redrawing is needed. The default is @code{nil}.
75 @node Forcing Redisplay
76 @section Forcing Redisplay
77 @cindex forcing redisplay
79 Emacs normally tries to redisplay the screen whenever it waits for
80 input. With the following function, you can request an immediate
81 attempt to redisplay, in the middle of Lisp code, without actually
84 @defun redisplay &optional force
85 This function tries immediately to redisplay. The optional argument
86 @var{force}, if non-@code{nil}, forces the redisplay to be performed,
87 instead of being preempted, even if input is pending and the variable
88 @code{redisplay-dont-pause} is @code{nil} (see below). If
89 @code{redisplay-dont-pause} is non-@code{nil} (the default), this
90 function redisplays in any case, i.e., @var{force} does nothing.
92 The function returns @code{t} if it actually tried to redisplay, and
93 @code{nil} otherwise. A value of @code{t} does not mean that
94 redisplay proceeded to completion; it could have been preempted by
98 @defvar redisplay-dont-pause
99 If this variable is @code{nil}, arriving input events preempt
100 redisplay; Emacs avoids starting a redisplay, and stops any redisplay
101 that is in progress, until the input has been processed. In
102 particular, @code{(redisplay)} returns @code{nil} without actually
103 redisplaying, if there is pending input.
105 The default value is @code{t}, which means that pending input does not
109 @defvar redisplay-preemption-period
110 If @code{redisplay-dont-pause} is @code{nil}, this variable specifies
111 how many seconds Emacs waits between checks for new input during
112 redisplay; if input arrives during this interval, redisplay stops and
113 the input is processed. The default value is 0.1; if the value is
114 @code{nil}, Emacs does not check for input during redisplay.
116 This variable has no effect when @code{redisplay-dont-pause} is
117 non-@code{nil} (the default).
120 Although @code{redisplay} tries immediately to redisplay, it does
121 not change how Emacs decides which parts of its frame(s) to redisplay.
122 By contrast, the following function adds certain windows to the
123 pending redisplay work (as if their contents had completely changed),
124 but does not immediately try to perform redisplay.
126 @defun force-window-update &optional object
127 This function forces some or all windows to be updated the next time
128 Emacs does a redisplay. If @var{object} is a window, that window is
129 to be updated. If @var{object} is a buffer or buffer name, all
130 windows displaying that buffer are to be updated. If @var{object} is
131 @code{nil} (or omitted), all windows are to be updated.
133 This function does not do a redisplay immediately; Emacs does that as
134 it waits for input, or when the function @code{redisplay} is called.
139 @cindex line wrapping
140 @cindex line truncation
141 @cindex continuation lines
142 @cindex @samp{$} in display
143 @cindex @samp{\} in display
145 When a line of text extends beyond the right edge of a window, Emacs
146 can @dfn{continue} the line (make it ``wrap'' to the next screen
147 line), or @dfn{truncate} the line (limit it to one screen line). The
148 additional screen lines used to display a long text line are called
149 @dfn{continuation} lines. Continuation is not the same as filling;
150 continuation happens on the screen only, not in the buffer contents,
151 and it breaks a line precisely at the right margin, not at a word
152 boundary. @xref{Filling}.
154 On a graphical display, tiny arrow images in the window fringes
155 indicate truncated and continued lines (@pxref{Fringes}). On a text
156 terminal, a @samp{$} in the rightmost column of the window indicates
157 truncation; a @samp{\} on the rightmost column indicates a line that
158 ``wraps''. (The display table can specify alternate characters to use
159 for this; @pxref{Display Tables}).
161 @defopt truncate-lines
162 If this buffer-local variable is non-@code{nil}, lines that extend
163 beyond the right edge of the window are truncated; otherwise, they are
164 continued. As a special exception, the variable
165 @code{truncate-partial-width-windows} takes precedence in
166 @dfn{partial-width} windows (i.e., windows that do not occupy the
170 @defopt truncate-partial-width-windows
171 @cindex partial-width windows
172 This variable controls line truncation in @dfn{partial-width} windows.
173 A partial-width window is one that does not occupy the entire frame
174 width (@pxref{Splitting Windows}). If the value is @code{nil}, line
175 truncation is determined by the variable @code{truncate-lines} (see
176 above). If the value is an integer @var{n}, lines are truncated if
177 the partial-width window has fewer than @var{n} columns, regardless of
178 the value of @code{truncate-lines}; if the partial-width window has
179 @var{n} or more columns, line truncation is determined by
180 @code{truncate-lines}. For any other non-@code{nil} value, lines are
181 truncated in every partial-width window, regardless of the value of
182 @code{truncate-lines}.
185 When horizontal scrolling (@pxref{Horizontal Scrolling}) is in use in
186 a window, that forces truncation.
189 If this buffer-local variable is non-@code{nil}, it defines a
190 @dfn{wrap prefix} which Emacs displays at the start of every
191 continuation line. (If lines are truncated, @code{wrap-prefix} is
192 never used.) Its value may be a string or an image (@pxref{Other
193 Display Specs}), or a stretch of whitespace such as specified by the
194 @code{:width} or @code{:align-to} display properties (@pxref{Specified
195 Space}). The value is interpreted in the same way as a @code{display}
196 text property. @xref{Display Property}.
198 A wrap prefix may also be specified for regions of text, using the
199 @code{wrap-prefix} text or overlay property. This takes precedence
200 over the @code{wrap-prefix} variable. @xref{Special Properties}.
204 If this buffer-local variable is non-@code{nil}, it defines a
205 @dfn{line prefix} which Emacs displays at the start of every
206 non-continuation line. Its value may be a string or an image
207 (@pxref{Other Display Specs}), or a stretch of whitespace such as
208 specified by the @code{:width} or @code{:align-to} display properties
209 (@pxref{Specified Space}). The value is interpreted in the same way
210 as a @code{display} text property. @xref{Display Property}.
212 A line prefix may also be specified for regions of text using the
213 @code{line-prefix} text or overlay property. This takes precedence
214 over the @code{line-prefix} variable. @xref{Special Properties}.
217 If your buffer contains @emph{very} long lines, and you use
218 continuation to display them, computing the continuation lines can
219 make redisplay slow. The column computation and indentation functions
220 also become slow. Then you might find it advisable to set
221 @code{cache-long-scans} to @code{t}.
223 @defvar cache-long-scans
224 If this variable is non-@code{nil}, various indentation and motion
225 functions, and Emacs redisplay, cache the results of scanning the
226 buffer, and consult the cache to avoid rescanning regions of the buffer
227 unless they are modified.
229 Turning on the cache slows down processing of short lines somewhat.
231 This variable is automatically buffer-local in every buffer.
235 @section The Echo Area
236 @cindex error display
239 @c FIXME: Why not use @xref{Minibuffers} directly? --xfq
240 The @dfn{echo area} is used for displaying error messages
241 (@pxref{Errors}), for messages made with the @code{message} primitive,
242 and for echoing keystrokes. It is not the same as the minibuffer,
243 despite the fact that the minibuffer appears (when active) in the same
244 place on the screen as the echo area. @xref{Minibuffer,, The
245 Minibuffer, emacs, The GNU Emacs Manual}.
247 Apart from the functions documented in this section, you can print
248 Lisp objects to the echo area by specifying @code{t} as the output
249 stream. @xref{Output Streams}.
252 * Displaying Messages:: Explicitly displaying text in the echo area.
253 * Progress:: Informing user about progress of a long operation.
254 * Logging Messages:: Echo area messages are logged for the user.
255 * Echo Area Customization:: Controlling the echo area.
258 @node Displaying Messages
259 @subsection Displaying Messages in the Echo Area
260 @cindex display message in echo area
262 This section describes the standard functions for displaying
263 messages in the echo area.
265 @defun message format-string &rest arguments
266 This function displays a message in the echo area.
267 @var{format-string} is a format string, and @var{arguments} are the
268 objects for its format specifications, like in the @code{format}
269 function (@pxref{Formatting Strings}). The resulting formatted string
270 is displayed in the echo area; if it contains @code{face} text
271 properties, it is displayed with the specified faces (@pxref{Faces}).
272 The string is also added to the @file{*Messages*} buffer, but without
273 text properties (@pxref{Logging Messages}).
275 In batch mode, the message is printed to the standard error stream,
276 followed by a newline.
278 If @var{format-string} is @code{nil} or the empty string,
279 @code{message} clears the echo area; if the echo area has been
280 expanded automatically, this brings it back to its normal size. If
281 the minibuffer is active, this brings the minibuffer contents back
282 onto the screen immediately.
286 (message "Minibuffer depth is %d."
288 @print{} Minibuffer depth is 0.
289 @result{} "Minibuffer depth is 0."
293 ---------- Echo Area ----------
294 Minibuffer depth is 0.
295 ---------- Echo Area ----------
299 To automatically display a message in the echo area or in a pop-buffer,
300 depending on its size, use @code{display-message-or-buffer} (see below).
303 @defmac with-temp-message message &rest body
304 This construct displays a message in the echo area temporarily, during
305 the execution of @var{body}. It displays @var{message}, executes
306 @var{body}, then returns the value of the last body form while restoring
307 the previous echo area contents.
310 @defun message-or-box format-string &rest arguments
311 This function displays a message like @code{message}, but may display it
312 in a dialog box instead of the echo area. If this function is called in
313 a command that was invoked using the mouse---more precisely, if
314 @code{last-nonmenu-event} (@pxref{Command Loop Info}) is either
315 @code{nil} or a list---then it uses a dialog box or pop-up menu to
316 display the message. Otherwise, it uses the echo area. (This is the
317 same criterion that @code{y-or-n-p} uses to make a similar decision; see
318 @ref{Yes-or-No Queries}.)
320 You can force use of the mouse or of the echo area by binding
321 @code{last-nonmenu-event} to a suitable value around the call.
324 @defun message-box format-string &rest arguments
326 This function displays a message like @code{message}, but uses a dialog
327 box (or a pop-up menu) whenever that is possible. If it is impossible
328 to use a dialog box or pop-up menu, because the terminal does not
329 support them, then @code{message-box} uses the echo area, like
333 @defun display-message-or-buffer message &optional buffer-name not-this-window frame
334 This function displays the message @var{message}, which may be either a
335 string or a buffer. If it is shorter than the maximum height of the
336 echo area, as defined by @code{max-mini-window-height}, it is displayed
337 in the echo area, using @code{message}. Otherwise,
338 @code{display-buffer} is used to show it in a pop-up buffer.
340 Returns either the string shown in the echo area, or when a pop-up
341 buffer is used, the window used to display it.
343 If @var{message} is a string, then the optional argument
344 @var{buffer-name} is the name of the buffer used to display it when a
345 pop-up buffer is used, defaulting to @file{*Message*}. In the case
346 where @var{message} is a string and displayed in the echo area, it is
347 not specified whether the contents are inserted into the buffer anyway.
349 The optional arguments @var{not-this-window} and @var{frame} are as for
350 @code{display-buffer}, and only used if a buffer is displayed.
353 @defun current-message
354 This function returns the message currently being displayed in the
355 echo area, or @code{nil} if there is none.
359 @subsection Reporting Operation Progress
360 @cindex progress reporting
362 When an operation can take a while to finish, you should inform the
363 user about the progress it makes. This way the user can estimate
364 remaining time and clearly see that Emacs is busy working, not hung.
365 A convenient way to do this is to use a @dfn{progress reporter}.
367 Here is a working example that does nothing useful:
370 (let ((progress-reporter
371 (make-progress-reporter "Collecting mana for Emacs..."
375 (progress-reporter-update progress-reporter k))
376 (progress-reporter-done progress-reporter))
379 @defun make-progress-reporter message &optional min-value max-value current-value min-change min-time
380 This function creates and returns a progress reporter object, which
381 you will use as an argument for the other functions listed below. The
382 idea is to precompute as much data as possible to make progress
385 When this progress reporter is subsequently used, it will display
386 @var{message} in the echo area, followed by progress percentage.
387 @var{message} is treated as a simple string. If you need it to depend
388 on a filename, for instance, use @code{format} before calling this
391 The arguments @var{min-value} and @var{max-value} should be numbers
392 standing for the starting and final states of the operation. For
393 instance, an operation that ``scans'' a buffer should set these to the
394 results of @code{point-min} and @code{point-max} correspondingly.
395 @var{max-value} should be greater than @var{min-value}.
397 Alternatively, you can set @var{min-value} and @var{max-value} to
398 @code{nil}. In that case, the progress reporter does not report
399 process percentages; it instead displays a ``spinner'' that rotates a
400 notch each time you update the progress reporter.
402 If @var{min-value} and @var{max-value} are numbers, you can give the
403 argument @var{current-value} a numerical value specifying the initial
404 progress; if omitted, this defaults to @var{min-value}.
406 The remaining arguments control the rate of echo area updates. The
407 progress reporter will wait for at least @var{min-change} more
408 percents of the operation to be completed before printing next
409 message; the default is one percent. @var{min-time} specifies the
410 minimum time in seconds to pass between successive prints; the default
411 is 0.2 seconds. (On some operating systems, the progress reporter may
412 handle fractions of seconds with varying precision).
414 This function calls @code{progress-reporter-update}, so the first
415 message is printed immediately.
418 @defun progress-reporter-update reporter &optional value
419 This function does the main work of reporting progress of your
420 operation. It displays the message of @var{reporter}, followed by
421 progress percentage determined by @var{value}. If percentage is zero,
422 or close enough according to the @var{min-change} and @var{min-time}
423 arguments, then it is omitted from the output.
425 @var{reporter} must be the result of a call to
426 @code{make-progress-reporter}. @var{value} specifies the current
427 state of your operation and must be between @var{min-value} and
428 @var{max-value} (inclusive) as passed to
429 @code{make-progress-reporter}. For instance, if you scan a buffer,
430 then @var{value} should be the result of a call to @code{point}.
432 This function respects @var{min-change} and @var{min-time} as passed
433 to @code{make-progress-reporter} and so does not output new messages
434 on every invocation. It is thus very fast and normally you should not
435 try to reduce the number of calls to it: resulting overhead will most
436 likely negate your effort.
439 @defun progress-reporter-force-update reporter &optional value new-message
440 This function is similar to @code{progress-reporter-update} except
441 that it prints a message in the echo area unconditionally.
443 The first two arguments have the same meaning as for
444 @code{progress-reporter-update}. Optional @var{new-message} allows
445 you to change the message of the @var{reporter}. Since this functions
446 always updates the echo area, such a change will be immediately
447 presented to the user.
450 @defun progress-reporter-done reporter
451 This function should be called when the operation is finished. It
452 prints the message of @var{reporter} followed by word ``done'' in the
455 You should always call this function and not hope for
456 @code{progress-reporter-update} to print ``100%''. Firstly, it may
457 never print it, there are many good reasons for this not to happen.
458 Secondly, ``done'' is more explicit.
461 @defmac dotimes-with-progress-reporter (var count [result]) message body@dots{}
462 This is a convenience macro that works the same way as @code{dotimes}
463 does, but also reports loop progress using the functions described
464 above. It allows you to save some typing.
466 You can rewrite the example in the beginning of this node using
470 (dotimes-with-progress-reporter
472 "Collecting some mana for Emacs..."
477 @node Logging Messages
478 @subsection Logging Messages in @file{*Messages*}
479 @cindex logging echo-area messages
481 Almost all the messages displayed in the echo area are also recorded
482 in the @file{*Messages*} buffer so that the user can refer back to
483 them. This includes all the messages that are output with
486 @defopt message-log-max
487 This variable specifies how many lines to keep in the @file{*Messages*}
488 buffer. The value @code{t} means there is no limit on how many lines to
489 keep. The value @code{nil} disables message logging entirely. Here's
490 how to display a message and prevent it from being logged:
493 (let (message-log-max)
498 To make @file{*Messages*} more convenient for the user, the logging
499 facility combines successive identical messages. It also combines
500 successive related messages for the sake of two cases: question
501 followed by answer, and a series of progress messages.
503 A ``question followed by an answer'' means two messages like the
504 ones produced by @code{y-or-n-p}: the first is @samp{@var{question}},
505 and the second is @samp{@var{question}...@var{answer}}. The first
506 message conveys no additional information beyond what's in the second,
507 so logging the second message discards the first from the log.
509 A ``series of progress messages'' means successive messages like
510 those produced by @code{make-progress-reporter}. They have the form
511 @samp{@var{base}...@var{how-far}}, where @var{base} is the same each
512 time, while @var{how-far} varies. Logging each message in the series
513 discards the previous one, provided they are consecutive.
515 The functions @code{make-progress-reporter} and @code{y-or-n-p}
516 don't have to do anything special to activate the message log
517 combination feature. It operates whenever two consecutive messages
518 are logged that share a common prefix ending in @samp{...}.
520 @node Echo Area Customization
521 @subsection Echo Area Customization
523 These variables control details of how the echo area works.
525 @defvar cursor-in-echo-area
526 This variable controls where the cursor appears when a message is
527 displayed in the echo area. If it is non-@code{nil}, then the cursor
528 appears at the end of the message. Otherwise, the cursor appears at
529 point---not in the echo area at all.
531 The value is normally @code{nil}; Lisp programs bind it to @code{t}
532 for brief periods of time.
535 @defvar echo-area-clear-hook
536 This normal hook is run whenever the echo area is cleared---either by
537 @code{(message nil)} or for any other reason.
540 @defopt echo-keystrokes
541 This variable determines how much time should elapse before command
542 characters echo. Its value must be an integer or floating point number,
544 number of seconds to wait before echoing. If the user types a prefix
545 key (such as @kbd{C-x}) and then delays this many seconds before
546 continuing, the prefix key is echoed in the echo area. (Once echoing
547 begins in a key sequence, all subsequent characters in the same key
548 sequence are echoed immediately.)
550 If the value is zero, then command input is not echoed.
553 @defvar message-truncate-lines
554 Normally, displaying a long message resizes the echo area to display
555 the entire message. But if the variable @code{message-truncate-lines}
556 is non-@code{nil}, the echo area does not resize, and the message is
560 The variable @code{max-mini-window-height}, which specifies the
561 maximum height for resizing minibuffer windows, also applies to the
562 echo area (which is really a special use of the minibuffer window;
563 @pxref{Minibuffer Misc}).
566 @section Reporting Warnings
569 @dfn{Warnings} are a facility for a program to inform the user of a
570 possible problem, but continue running.
573 * Warning Basics:: Warnings concepts and functions to report them.
574 * Warning Variables:: Variables programs bind to customize their warnings.
575 * Warning Options:: Variables users set to control display of warnings.
576 * Delayed Warnings:: Deferring a warning until the end of a command.
580 @subsection Warning Basics
581 @cindex severity level
583 Every warning has a textual message, which explains the problem for
584 the user, and a @dfn{severity level} which is a symbol. Here are the
585 possible severity levels, in order of decreasing severity, and their
590 A problem that will seriously impair Emacs operation soon
591 if you do not attend to it promptly.
593 A report of data or circumstances that are inherently wrong.
595 A report of data or circumstances that are not inherently wrong, but
596 raise suspicion of a possible problem.
598 A report of information that may be useful if you are debugging.
601 When your program encounters invalid input data, it can either
602 signal a Lisp error by calling @code{error} or @code{signal} or report
603 a warning with severity @code{:error}. Signaling a Lisp error is the
604 easiest thing to do, but it means the program cannot continue
605 processing. If you want to take the trouble to implement a way to
606 continue processing despite the bad data, then reporting a warning of
607 severity @code{:error} is the right way to inform the user of the
608 problem. For instance, the Emacs Lisp byte compiler can report an
609 error that way and continue compiling other functions. (If the
610 program signals a Lisp error and then handles it with
611 @code{condition-case}, the user won't see the error message; it could
612 show the message to the user by reporting it as a warning.)
614 @c FIXME: Why use ‘(bytecomp)’ instead of ‘'bytecomp’ or simply
615 @c ‘bytecomp’ here? The parens are part of ‘warning-type-format’ but
616 @c not part of the warning type. --xfq
618 Each warning has a @dfn{warning type} to classify it. The type is a
619 list of symbols. The first symbol should be the custom group that you
620 use for the program's user options. For example, byte compiler
621 warnings use the warning type @code{(bytecomp)}. You can also
622 subcategorize the warnings, if you wish, by using more symbols in the
625 @defun display-warning type message &optional level buffer-name
626 This function reports a warning, using @var{message} as the message
627 and @var{type} as the warning type. @var{level} should be the
628 severity level, with @code{:warning} being the default.
630 @var{buffer-name}, if non-@code{nil}, specifies the name of the buffer
631 for logging the warning. By default, it is @file{*Warnings*}.
634 @defun lwarn type level message &rest args
635 This function reports a warning using the value of @code{(format
636 @var{message} @var{args}...)} as the message in the @file{*Warnings*}
637 buffer. In other respects it is equivalent to @code{display-warning}.
640 @defun warn message &rest args
641 This function reports a warning using the value of @code{(format
642 @var{message} @var{args}...)} as the message, @code{(emacs)} as the
643 type, and @code{:warning} as the severity level. It exists for
644 compatibility only; we recommend not using it, because you should
645 specify a specific warning type.
648 @node Warning Variables
649 @subsection Warning Variables
651 Programs can customize how their warnings appear by binding
652 the variables described in this section.
654 @defvar warning-levels
655 This list defines the meaning and severity order of the warning
656 severity levels. Each element defines one severity level,
657 and they are arranged in order of decreasing severity.
659 Each element has the form @code{(@var{level} @var{string}
660 @var{function})}, where @var{level} is the severity level it defines.
661 @var{string} specifies the textual description of this level.
662 @var{string} should use @samp{%s} to specify where to put the warning
663 type information, or it can omit the @samp{%s} so as not to include
666 The optional @var{function}, if non-@code{nil}, is a function to call
667 with no arguments, to get the user's attention.
669 Normally you should not change the value of this variable.
672 @defvar warning-prefix-function
673 If non-@code{nil}, the value is a function to generate prefix text for
674 warnings. Programs can bind the variable to a suitable function.
675 @code{display-warning} calls this function with the warnings buffer
676 current, and the function can insert text in it. That text becomes
677 the beginning of the warning message.
679 The function is called with two arguments, the severity level and its
680 entry in @code{warning-levels}. It should return a list to use as the
681 entry (this value need not be an actual member of
682 @code{warning-levels}). By constructing this value, the function can
683 change the severity of the warning, or specify different handling for
684 a given severity level.
686 If the variable's value is @code{nil} then there is no function
690 @defvar warning-series
691 Programs can bind this variable to @code{t} to say that the next
692 warning should begin a series. When several warnings form a series,
693 that means to leave point on the first warning of the series, rather
694 than keep moving it for each warning so that it appears on the last one.
695 The series ends when the local binding is unbound and
696 @code{warning-series} becomes @code{nil} again.
698 The value can also be a symbol with a function definition. That is
699 equivalent to @code{t}, except that the next warning will also call
700 the function with no arguments with the warnings buffer current. The
701 function can insert text which will serve as a header for the series
704 Once a series has begun, the value is a marker which points to the
705 buffer position in the warnings buffer of the start of the series.
707 The variable's normal value is @code{nil}, which means to handle
708 each warning separately.
711 @defvar warning-fill-prefix
712 When this variable is non-@code{nil}, it specifies a fill prefix to
713 use for filling each warning's text.
716 @defvar warning-type-format
717 This variable specifies the format for displaying the warning type
718 in the warning message. The result of formatting the type this way
719 gets included in the message under the control of the string in the
720 entry in @code{warning-levels}. The default value is @code{" (%s)"}.
721 If you bind it to @code{""} then the warning type won't appear at
725 @node Warning Options
726 @subsection Warning Options
728 These variables are used by users to control what happens
729 when a Lisp program reports a warning.
731 @defopt warning-minimum-level
732 This user option specifies the minimum severity level that should be
733 shown immediately to the user. The default is @code{:warning}, which
734 means to immediately display all warnings except @code{:debug}
738 @defopt warning-minimum-log-level
739 This user option specifies the minimum severity level that should be
740 logged in the warnings buffer. The default is @code{:warning}, which
741 means to log all warnings except @code{:debug} warnings.
744 @defopt warning-suppress-types
745 This list specifies which warning types should not be displayed
746 immediately for the user. Each element of the list should be a list
747 of symbols. If its elements match the first elements in a warning
748 type, then that warning is not displayed immediately.
751 @defopt warning-suppress-log-types
752 This list specifies which warning types should not be logged in the
753 warnings buffer. Each element of the list should be a list of
754 symbols. If it matches the first few elements in a warning type, then
755 that warning is not logged.
758 @node Delayed Warnings
759 @subsection Delayed Warnings
761 Sometimes, you may wish to avoid showing a warning while a command is
762 running, and only show it only after the end of the command. You can
763 use the variable @code{delayed-warnings-list} for this.
765 @defvar delayed-warnings-list
766 The value of this variable is a list of warnings to be displayed after
767 the current command has finished. Each element must be a list
770 (@var{type} @var{message} [@var{level} [@var{buffer-name}]])
774 with the same form, and the same meanings, as the argument list of
775 @code{display-warning} (@pxref{Warning Basics}). Immediately after
776 running @code{post-command-hook} (@pxref{Command Overview}), the Emacs
777 command loop displays all the warnings specified by this variable,
778 then resets it to @code{nil}.
781 Programs which need to further customize the delayed warnings
782 mechanism can change the variable @code{delayed-warnings-hook}:
784 @defvar delayed-warnings-hook
785 This is a normal hook which is run by the Emacs command loop, after
786 @code{post-command-hook}, in order to to process and display delayed
789 Its default value is a list of two functions:
792 (collapse-delayed-warnings display-delayed-warnings)
795 @findex collapse-delayed-warnings
796 @findex display-delayed-warnings
798 The function @code{collapse-delayed-warnings} removes repeated entries
799 from @code{delayed-warnings-list}. The function
800 @code{display-delayed-warnings} calls @code{display-warning} on each
801 of the entries in @code{delayed-warnings-list}, in turn, and then sets
802 @code{delayed-warnings-list} to @code{nil}.
806 @section Invisible Text
808 @cindex invisible text
809 You can make characters @dfn{invisible}, so that they do not appear on
810 the screen, with the @code{invisible} property. This can be either a
811 text property (@pxref{Text Properties}) or an overlay property
812 (@pxref{Overlays}). Cursor motion also partly ignores these
813 characters; if the command loop finds that point is inside a range of
814 invisible text after a command, it relocates point to the other side
817 In the simplest case, any non-@code{nil} @code{invisible} property makes
818 a character invisible. This is the default case---if you don't alter
819 the default value of @code{buffer-invisibility-spec}, this is how the
820 @code{invisible} property works. You should normally use @code{t}
821 as the value of the @code{invisible} property if you don't plan
822 to set @code{buffer-invisibility-spec} yourself.
824 More generally, you can use the variable @code{buffer-invisibility-spec}
825 to control which values of the @code{invisible} property make text
826 invisible. This permits you to classify the text into different subsets
827 in advance, by giving them different @code{invisible} values, and
828 subsequently make various subsets visible or invisible by changing the
829 value of @code{buffer-invisibility-spec}.
831 Controlling visibility with @code{buffer-invisibility-spec} is
832 especially useful in a program to display the list of entries in a
833 database. It permits the implementation of convenient filtering
834 commands to view just a part of the entries in the database. Setting
835 this variable is very fast, much faster than scanning all the text in
836 the buffer looking for properties to change.
838 @defvar buffer-invisibility-spec
839 This variable specifies which kinds of @code{invisible} properties
840 actually make a character invisible. Setting this variable makes it
845 A character is invisible if its @code{invisible} property is
846 non-@code{nil}. This is the default.
849 Each element of the list specifies a criterion for invisibility; if a
850 character's @code{invisible} property fits any one of these criteria,
851 the character is invisible. The list can have two kinds of elements:
855 A character is invisible if its @code{invisible} property value is
856 @var{atom} or if it is a list with @var{atom} as a member; comparison
857 is done with @code{eq}.
859 @item (@var{atom} . t)
860 A character is invisible if its @code{invisible} property value is
861 @var{atom} or if it is a list with @var{atom} as a member; comparison
862 is done with @code{eq}. Moreover, a sequence of such characters
863 displays as an ellipsis.
868 Two functions are specifically provided for adding elements to
869 @code{buffer-invisibility-spec} and removing elements from it.
871 @defun add-to-invisibility-spec element
872 This function adds the element @var{element} to
873 @code{buffer-invisibility-spec}. If @code{buffer-invisibility-spec}
874 was @code{t}, it changes to a list, @code{(t)}, so that text whose
875 @code{invisible} property is @code{t} remains invisible.
878 @defun remove-from-invisibility-spec element
879 This removes the element @var{element} from
880 @code{buffer-invisibility-spec}. This does nothing if @var{element}
884 A convention for use of @code{buffer-invisibility-spec} is that a
885 major mode should use the mode's own name as an element of
886 @code{buffer-invisibility-spec} and as the value of the
887 @code{invisible} property:
890 ;; @r{If you want to display an ellipsis:}
891 (add-to-invisibility-spec '(my-symbol . t))
892 ;; @r{If you don't want ellipsis:}
893 (add-to-invisibility-spec 'my-symbol)
895 (overlay-put (make-overlay beginning end)
896 'invisible 'my-symbol)
898 ;; @r{When done with the invisibility:}
899 (remove-from-invisibility-spec '(my-symbol . t))
900 ;; @r{Or respectively:}
901 (remove-from-invisibility-spec 'my-symbol)
904 You can check for invisibility using the following function:
906 @defun invisible-p pos-or-prop
907 If @var{pos-or-prop} is a marker or number, this function returns a
908 non-@code{nil} value if the text at that position is invisible.
910 If @var{pos-or-prop} is any other kind of Lisp object, that is taken
911 to mean a possible value of the @code{invisible} text or overlay
912 property. In that case, this function returns a non-@code{nil} value
913 if that value would cause text to become invisible, based on the
914 current value of @code{buffer-invisibility-spec}.
917 @vindex line-move-ignore-invisible
918 Ordinarily, functions that operate on text or move point do not care
919 whether the text is invisible. The user-level line motion commands
920 ignore invisible newlines if @code{line-move-ignore-invisible} is
921 non-@code{nil} (the default), but only because they are explicitly
924 However, if a command ends with point inside or at the boundary of
925 invisible text, the main editing loop relocates point to one of the
926 two ends of the invisible text. Emacs chooses the direction of
927 relocation so that it is the same as the overall movement direction of
928 the command; if in doubt, it prefers a position where an inserted char
929 would not inherit the @code{invisible} property. Additionally, if the
930 text is not replaced by an ellipsis and the command only moved within
931 the invisible text, then point is moved one extra character so as to
932 try and reflect the command's movement by a visible movement of the
935 Thus, if the command moved point back to an invisible range (with the usual
936 stickiness), Emacs moves point back to the beginning of that range. If the
937 command moved point forward into an invisible range, Emacs moves point forward
938 to the first visible character that follows the invisible text and then forward
941 Incremental search can make invisible overlays visible temporarily
942 and/or permanently when a match includes invisible text. To enable
943 this, the overlay should have a non-@code{nil}
944 @code{isearch-open-invisible} property. The property value should be a
945 function to be called with the overlay as an argument. This function
946 should make the overlay visible permanently; it is used when the match
947 overlaps the overlay on exit from the search.
949 During the search, such overlays are made temporarily visible by
950 temporarily modifying their invisible and intangible properties. If you
951 want this to be done differently for a certain overlay, give it an
952 @code{isearch-open-invisible-temporary} property which is a function.
953 The function is called with two arguments: the first is the overlay, and
954 the second is @code{nil} to make the overlay visible, or @code{t} to
955 make it invisible again.
957 @node Selective Display
958 @section Selective Display
959 @c @cindex selective display Duplicates selective-display
961 @dfn{Selective display} refers to a pair of related features for
962 hiding certain lines on the screen.
964 @cindex explicit selective display
965 The first variant, explicit selective display, is designed for use
966 in a Lisp program: it controls which lines are hidden by altering the
967 text. This kind of hiding in some ways resembles the effect of the
968 @code{invisible} property (@pxref{Invisible Text}), but the two
969 features are different and do not work the same way.
971 In the second variant, the choice of lines to hide is made
972 automatically based on indentation. This variant is designed to be a
975 The way you control explicit selective display is by replacing a
976 newline (control-j) with a carriage return (control-m). The text that
977 was formerly a line following that newline is now hidden. Strictly
978 speaking, it is temporarily no longer a line at all, since only
979 newlines can separate lines; it is now part of the previous line.
981 Selective display does not directly affect editing commands. For
982 example, @kbd{C-f} (@code{forward-char}) moves point unhesitatingly
983 into hidden text. However, the replacement of newline characters with
984 carriage return characters affects some editing commands. For
985 example, @code{next-line} skips hidden lines, since it searches only
986 for newlines. Modes that use selective display can also define
987 commands that take account of the newlines, or that control which
988 parts of the text are hidden.
990 When you write a selectively displayed buffer into a file, all the
991 control-m's are output as newlines. This means that when you next read
992 in the file, it looks OK, with nothing hidden. The selective display
993 effect is seen only within Emacs.
995 @defvar selective-display
996 This buffer-local variable enables selective display. This means that
997 lines, or portions of lines, may be made hidden.
1001 If the value of @code{selective-display} is @code{t}, then the character
1002 control-m marks the start of hidden text; the control-m, and the rest
1003 of the line following it, are not displayed. This is explicit selective
1007 If the value of @code{selective-display} is a positive integer, then
1008 lines that start with more than that many columns of indentation are not
1012 When some portion of a buffer is hidden, the vertical movement
1013 commands operate as if that portion did not exist, allowing a single
1014 @code{next-line} command to skip any number of hidden lines.
1015 However, character movement commands (such as @code{forward-char}) do
1016 not skip the hidden portion, and it is possible (if tricky) to insert
1017 or delete text in an hidden portion.
1019 In the examples below, we show the @emph{display appearance} of the
1020 buffer @code{foo}, which changes with the value of
1021 @code{selective-display}. The @emph{contents} of the buffer do not
1026 (setq selective-display nil)
1029 ---------- Buffer: foo ----------
1036 ---------- Buffer: foo ----------
1040 (setq selective-display 2)
1043 ---------- Buffer: foo ----------
1048 ---------- Buffer: foo ----------
1053 @defopt selective-display-ellipses
1054 If this buffer-local variable is non-@code{nil}, then Emacs displays
1055 @samp{@dots{}} at the end of a line that is followed by hidden text.
1056 This example is a continuation of the previous one.
1060 (setq selective-display-ellipses t)
1063 ---------- Buffer: foo ----------
1068 ---------- Buffer: foo ----------
1072 You can use a display table to substitute other text for the ellipsis
1073 (@samp{@dots{}}). @xref{Display Tables}.
1076 @node Temporary Displays
1077 @section Temporary Displays
1079 Temporary displays are used by Lisp programs to put output into a
1080 buffer and then present it to the user for perusal rather than for
1081 editing. Many help commands use this feature.
1083 @defmac with-output-to-temp-buffer buffer-name forms@dots{}
1084 This function executes @var{forms} while arranging to insert any output
1085 they print into the buffer named @var{buffer-name}, which is first
1086 created if necessary, and put into Help mode. Finally, the buffer is
1087 displayed in some window, but not selected. (See the similar
1088 form @code{with-temp-buffer-window} below.)
1090 If the @var{forms} do not change the major mode in the output buffer,
1091 so that it is still Help mode at the end of their execution, then
1092 @code{with-output-to-temp-buffer} makes this buffer read-only at the
1093 end, and also scans it for function and variable names to make them
1094 into clickable cross-references. @xref{Docstring hyperlinks, , Tips
1095 for Documentation Strings}, in particular the item on hyperlinks in
1096 documentation strings, for more details.
1098 The string @var{buffer-name} specifies the temporary buffer, which
1099 need not already exist. The argument must be a string, not a buffer.
1100 The buffer is erased initially (with no questions asked), and it is
1101 marked as unmodified after @code{with-output-to-temp-buffer} exits.
1103 @code{with-output-to-temp-buffer} binds @code{standard-output} to the
1104 temporary buffer, then it evaluates the forms in @var{forms}. Output
1105 using the Lisp output functions within @var{forms} goes by default to
1106 that buffer (but screen display and messages in the echo area, although
1107 they are ``output'' in the general sense of the word, are not affected).
1108 @xref{Output Functions}.
1110 Several hooks are available for customizing the behavior
1111 of this construct; they are listed below.
1113 The value of the last form in @var{forms} is returned.
1117 ---------- Buffer: foo ----------
1118 This is the contents of foo.
1119 ---------- Buffer: foo ----------
1123 (with-output-to-temp-buffer "foo"
1125 (print standard-output))
1126 @result{} #<buffer foo>
1128 ---------- Buffer: foo ----------
1134 ---------- Buffer: foo ----------
1139 @defopt temp-buffer-show-function
1140 If this variable is non-@code{nil}, @code{with-output-to-temp-buffer}
1141 calls it as a function to do the job of displaying a help buffer. The
1142 function gets one argument, which is the buffer it should display.
1144 It is a good idea for this function to run @code{temp-buffer-show-hook}
1145 just as @code{with-output-to-temp-buffer} normally would, inside of
1146 @code{save-selected-window} and with the chosen window and buffer
1150 @defvar temp-buffer-setup-hook
1151 This normal hook is run by @code{with-output-to-temp-buffer} before
1152 evaluating @var{body}. When the hook runs, the temporary buffer is
1153 current. This hook is normally set up with a function to put the
1154 buffer in Help mode.
1157 @defvar temp-buffer-show-hook
1158 This normal hook is run by @code{with-output-to-temp-buffer} after
1159 displaying the temporary buffer. When the hook runs, the temporary buffer
1160 is current, and the window it was displayed in is selected.
1163 @defmac with-temp-buffer-window buffer-or-name action quit-function forms@dots{}
1164 This macro is similar to @code{with-output-to-temp-buffer}.
1165 Like that construct, it executes @var{forms} while arranging to insert
1166 any output they print into the buffer named @var{buffer-or-name}.
1167 Finally, the buffer is displayed in some window, but not selected.
1168 Unlike @code{with-output-to-temp-buffer}, this does not switch to Help
1171 The argument @var{buffer-or-name} specifies the temporary buffer.
1172 It can be either a buffer, which must already exist, or a string,
1173 in which case a buffer of that name is created if necessary.
1174 The buffer is marked as unmodified and read-only when
1175 @code{with-temp-buffer-window} exits.
1177 This macro does not call @code{temp-buffer-show-function}. Rather, it
1178 passes the @var{action} argument to @code{display-buffer} in order to
1181 The value of the last form in @var{forms} is returned, unless the
1182 argument @var{quit-function} is specified. In that case,
1183 it is called with two arguments: the window showing the buffer
1184 and the result of @var{forms}. The final return value is then
1185 whatever @var{quit-function} returns.
1187 @vindex temp-buffer-window-setup-hook
1188 @vindex temp-buffer-window-show-hook
1189 This macro uses the normal hooks @code{temp-buffer-window-setup-hook}
1190 and @code{temp-buffer-window-show-hook} in place of the analogous hooks
1191 run by @code{with-output-to-temp-buffer}.
1194 @defun momentary-string-display string position &optional char message
1195 This function momentarily displays @var{string} in the current buffer at
1196 @var{position}. It has no effect on the undo list or on the buffer's
1197 modification status.
1199 The momentary display remains until the next input event. If the next
1200 input event is @var{char}, @code{momentary-string-display} ignores it
1201 and returns. Otherwise, that event remains buffered for subsequent use
1202 as input. Thus, typing @var{char} will simply remove the string from
1203 the display, while typing (say) @kbd{C-f} will remove the string from
1204 the display and later (presumably) move point forward. The argument
1205 @var{char} is a space by default.
1207 The return value of @code{momentary-string-display} is not meaningful.
1209 If the string @var{string} does not contain control characters, you can
1210 do the same job in a more general way by creating (and then subsequently
1211 deleting) an overlay with a @code{before-string} property.
1212 @xref{Overlay Properties}.
1214 If @var{message} is non-@code{nil}, it is displayed in the echo area
1215 while @var{string} is displayed in the buffer. If it is @code{nil}, a
1216 default message says to type @var{char} to continue.
1218 In this example, point is initially located at the beginning of the
1223 ---------- Buffer: foo ----------
1224 This is the contents of foo.
1225 @point{}Second line.
1226 ---------- Buffer: foo ----------
1230 (momentary-string-display
1231 "**** Important Message! ****"
1233 "Type RET when done reading")
1238 ---------- Buffer: foo ----------
1239 This is the contents of foo.
1240 **** Important Message! ****Second line.
1241 ---------- Buffer: foo ----------
1243 ---------- Echo Area ----------
1244 Type RET when done reading
1245 ---------- Echo Area ----------
1253 @c FIXME: mention intervals in this section?
1255 You can use @dfn{overlays} to alter the appearance of a buffer's text on
1256 the screen, for the sake of presentation features. An overlay is an
1257 object that belongs to a particular buffer, and has a specified
1258 beginning and end. It also has properties that you can examine and set;
1259 these affect the display of the text within the overlay.
1261 @cindex scalability of overlays
1262 The visual effect of an overlay is the same as of the corresponding
1263 text property (@pxref{Text Properties}). However, due to a different
1264 implementation, overlays generally don't scale well (many operations
1265 take a time that is proportional to the number of overlays in the
1266 buffer). If you need to affect the visual appearance of many portions
1267 in the buffer, we recommend using text properties.
1269 An overlay uses markers to record its beginning and end; thus,
1270 editing the text of the buffer adjusts the beginning and end of each
1271 overlay so that it stays with the text. When you create the overlay,
1272 you can specify whether text inserted at the beginning should be
1273 inside the overlay or outside, and likewise for the end of the overlay.
1276 * Managing Overlays:: Creating and moving overlays.
1277 * Overlay Properties:: How to read and set properties.
1278 What properties do to the screen display.
1279 * Finding Overlays:: Searching for overlays.
1282 @node Managing Overlays
1283 @subsection Managing Overlays
1285 This section describes the functions to create, delete and move
1286 overlays, and to examine their contents. Overlay changes are not
1287 recorded in the buffer's undo list, since the overlays are not
1288 part of the buffer's contents.
1290 @defun overlayp object
1291 This function returns @code{t} if @var{object} is an overlay.
1294 @defun make-overlay start end &optional buffer front-advance rear-advance
1295 This function creates and returns an overlay that belongs to
1296 @var{buffer} and ranges from @var{start} to @var{end}. Both @var{start}
1297 and @var{end} must specify buffer positions; they may be integers or
1298 markers. If @var{buffer} is omitted, the overlay is created in the
1301 The arguments @var{front-advance} and @var{rear-advance} specify the
1302 marker insertion type for the start of the overlay and for the end of
1303 the overlay, respectively. @xref{Marker Insertion Types}. If they
1304 are both @code{nil}, the default, then the overlay extends to include
1305 any text inserted at the beginning, but not text inserted at the end.
1306 If @var{front-advance} is non-@code{nil}, text inserted at the
1307 beginning of the overlay is excluded from the overlay. If
1308 @var{rear-advance} is non-@code{nil}, text inserted at the end of the
1309 overlay is included in the overlay.
1312 @defun overlay-start overlay
1313 This function returns the position at which @var{overlay} starts,
1317 @defun overlay-end overlay
1318 This function returns the position at which @var{overlay} ends,
1322 @defun overlay-buffer overlay
1323 This function returns the buffer that @var{overlay} belongs to. It
1324 returns @code{nil} if @var{overlay} has been deleted.
1327 @defun delete-overlay overlay
1328 This function deletes @var{overlay}. The overlay continues to exist as
1329 a Lisp object, and its property list is unchanged, but it ceases to be
1330 attached to the buffer it belonged to, and ceases to have any effect on
1333 A deleted overlay is not permanently disconnected. You can give it a
1334 position in a buffer again by calling @code{move-overlay}.
1337 @defun move-overlay overlay start end &optional buffer
1338 This function moves @var{overlay} to @var{buffer}, and places its bounds
1339 at @var{start} and @var{end}. Both arguments @var{start} and @var{end}
1340 must specify buffer positions; they may be integers or markers.
1342 If @var{buffer} is omitted, @var{overlay} stays in the same buffer it
1343 was already associated with; if @var{overlay} was deleted, it goes into
1346 The return value is @var{overlay}.
1348 This is the only valid way to change the endpoints of an overlay. Do
1349 not try modifying the markers in the overlay by hand, as that fails to
1350 update other vital data structures and can cause some overlays to be
1354 @defun remove-overlays &optional start end name value
1355 This function removes all the overlays between @var{start} and
1356 @var{end} whose property @var{name} has the value @var{value}. It can
1357 move the endpoints of the overlays in the region, or split them.
1359 If @var{name} is omitted or @code{nil}, it means to delete all overlays in
1360 the specified region. If @var{start} and/or @var{end} are omitted or
1361 @code{nil}, that means the beginning and end of the buffer respectively.
1362 Therefore, @code{(remove-overlays)} removes all the overlays in the
1366 @defun copy-overlay overlay
1367 This function returns a copy of @var{overlay}. The copy has the same
1368 endpoints and properties as @var{overlay}. However, the marker
1369 insertion type for the start of the overlay and for the end of the
1370 overlay are set to their default values (@pxref{Marker Insertion
1374 Here are some examples:
1377 ;; @r{Create an overlay.}
1378 (setq foo (make-overlay 1 10))
1379 @result{} #<overlay from 1 to 10 in display.texi>
1384 (overlay-buffer foo)
1385 @result{} #<buffer display.texi>
1386 ;; @r{Give it a property we can check later.}
1387 (overlay-put foo 'happy t)
1389 ;; @r{Verify the property is present.}
1390 (overlay-get foo 'happy)
1392 ;; @r{Move the overlay.}
1393 (move-overlay foo 5 20)
1394 @result{} #<overlay from 5 to 20 in display.texi>
1399 ;; @r{Delete the overlay.}
1400 (delete-overlay foo)
1402 ;; @r{Verify it is deleted.}
1404 @result{} #<overlay in no buffer>
1405 ;; @r{A deleted overlay has no position.}
1410 (overlay-buffer foo)
1412 ;; @r{Undelete the overlay.}
1413 (move-overlay foo 1 20)
1414 @result{} #<overlay from 1 to 20 in display.texi>
1415 ;; @r{Verify the results.}
1420 (overlay-buffer foo)
1421 @result{} #<buffer display.texi>
1422 ;; @r{Moving and deleting the overlay does not change its properties.}
1423 (overlay-get foo 'happy)
1427 Emacs stores the overlays of each buffer in two lists, divided
1428 around an arbitrary ``center position''. One list extends backwards
1429 through the buffer from that center position, and the other extends
1430 forwards from that center position. The center position can be anywhere
1433 @defun overlay-recenter pos
1434 This function recenters the overlays of the current buffer around
1435 position @var{pos}. That makes overlay lookup faster for positions
1436 near @var{pos}, but slower for positions far away from @var{pos}.
1439 A loop that scans the buffer forwards, creating overlays, can run
1440 faster if you do @code{(overlay-recenter (point-max))} first.
1442 @node Overlay Properties
1443 @subsection Overlay Properties
1445 Overlay properties are like text properties in that the properties that
1446 alter how a character is displayed can come from either source. But in
1447 most respects they are different. @xref{Text Properties}, for comparison.
1449 Text properties are considered a part of the text; overlays and
1450 their properties are specifically considered not to be part of the
1451 text. Thus, copying text between various buffers and strings
1452 preserves text properties, but does not try to preserve overlays.
1453 Changing a buffer's text properties marks the buffer as modified,
1454 while moving an overlay or changing its properties does not. Unlike
1455 text property changes, overlay property changes are not recorded in
1456 the buffer's undo list.
1458 Since more than one overlay can specify a property value for the
1459 same character, Emacs lets you specify a priority value of each
1460 overlay. You should not make assumptions about which overlay will
1461 prevail when there is a conflict and they have the same priority.
1463 These functions read and set the properties of an overlay:
1465 @defun overlay-get overlay prop
1466 This function returns the value of property @var{prop} recorded in
1467 @var{overlay}, if any. If @var{overlay} does not record any value for
1468 that property, but it does have a @code{category} property which is a
1469 symbol, that symbol's @var{prop} property is used. Otherwise, the value
1473 @defun overlay-put overlay prop value
1474 This function sets the value of property @var{prop} recorded in
1475 @var{overlay} to @var{value}. It returns @var{value}.
1478 @defun overlay-properties overlay
1479 This returns a copy of the property list of @var{overlay}.
1482 See also the function @code{get-char-property} which checks both
1483 overlay properties and text properties for a given character.
1484 @xref{Examining Properties}.
1486 Many overlay properties have special meanings; here is a table
1491 @kindex priority @r{(overlay property)}
1492 This property's value (which should be a non-negative integer number)
1493 determines the priority of the overlay. No priority, or @code{nil},
1496 The priority matters when two or more overlays cover the same
1497 character and both specify the same property; the one whose
1498 @code{priority} value is larger overrides the other. For the
1499 @code{face} property, the higher priority overlay's value does not
1500 completely override the other value; instead, its face attributes
1501 override the face attributes of the lower priority @code{face}
1504 Currently, all overlays take priority over text properties. Please
1505 avoid using negative priority values, as we have not yet decided just
1506 what they should mean.
1509 @kindex window @r{(overlay property)}
1510 If the @code{window} property is non-@code{nil}, then the overlay
1511 applies only on that window.
1514 @kindex category @r{(overlay property)}
1515 If an overlay has a @code{category} property, we call it the
1516 @dfn{category} of the overlay. It should be a symbol. The properties
1517 of the symbol serve as defaults for the properties of the overlay.
1520 @kindex face @r{(overlay property)}
1521 This property controls the appearance of the text (@pxref{Faces}).
1522 The value of the property can be the following:
1526 A face name (a symbol or string).
1529 An anonymous face: a property list of the form @code{(@var{keyword}
1530 @var{value} @dots{})}, where each @var{keyword} is a face attribute
1531 name and @var{value} is a value for that attribute.
1534 A list of faces. Each list element should be either a face name or an
1535 anonymous face. This specifies a face which is an aggregate of the
1536 attributes of each of the listed faces. Faces occurring earlier in
1537 the list have higher priority.
1540 A cons cell of the form @code{(foreground-color . @var{color-name})}
1541 or @code{(background-color . @var{color-name})}. This specifies the
1542 foreground or background color, similar to @code{(:foreground
1543 @var{color-name})} or @code{(:background @var{color-name})}. This
1544 form is supported for backward compatibility only, and should be
1549 @kindex mouse-face @r{(overlay property)}
1550 This property is used instead of @code{face} when the mouse is within
1551 the range of the overlay. However, Emacs ignores all face attributes
1552 from this property that alter the text size (e.g., @code{:height},
1553 @code{:weight}, and @code{:slant}). Those attributes are always the
1554 same as in the unhighlighted text.
1557 @kindex display @r{(overlay property)}
1558 This property activates various features that change the
1559 way text is displayed. For example, it can make text appear taller
1560 or shorter, higher or lower, wider or narrower, or replaced with an image.
1561 @xref{Display Property}.
1564 @kindex help-echo @r{(overlay property)}
1565 If an overlay has a @code{help-echo} property, then when you move the
1566 mouse onto the text in the overlay, Emacs displays a help string in the
1567 echo area, or in the tooltip window. For details see @ref{Text
1571 @kindex field @r{(overlay property)}
1572 @c Copied from Special Properties.
1573 Consecutive characters with the same @code{field} property constitute a
1574 @emph{field}. Some motion functions including @code{forward-word} and
1575 @code{beginning-of-line} stop moving at a field boundary.
1578 @item modification-hooks
1579 @kindex modification-hooks @r{(overlay property)}
1580 This property's value is a list of functions to be called if any
1581 character within the overlay is changed or if text is inserted strictly
1584 The hook functions are called both before and after each change.
1585 If the functions save the information they receive, and compare notes
1586 between calls, they can determine exactly what change has been made
1589 When called before a change, each function receives four arguments: the
1590 overlay, @code{nil}, and the beginning and end of the text range to be
1593 When called after a change, each function receives five arguments: the
1594 overlay, @code{t}, the beginning and end of the text range just
1595 modified, and the length of the pre-change text replaced by that range.
1596 (For an insertion, the pre-change length is zero; for a deletion, that
1597 length is the number of characters deleted, and the post-change
1598 beginning and end are equal.)
1600 If these functions modify the buffer, they should bind
1601 @code{inhibit-modification-hooks} to @code{t} around doing so, to
1602 avoid confusing the internal mechanism that calls these hooks.
1604 Text properties also support the @code{modification-hooks} property,
1605 but the details are somewhat different (@pxref{Special Properties}).
1607 @item insert-in-front-hooks
1608 @kindex insert-in-front-hooks @r{(overlay property)}
1609 This property's value is a list of functions to be called before and
1610 after inserting text right at the beginning of the overlay. The calling
1611 conventions are the same as for the @code{modification-hooks} functions.
1613 @item insert-behind-hooks
1614 @kindex insert-behind-hooks @r{(overlay property)}
1615 This property's value is a list of functions to be called before and
1616 after inserting text right at the end of the overlay. The calling
1617 conventions are the same as for the @code{modification-hooks} functions.
1620 @kindex invisible @r{(overlay property)}
1621 The @code{invisible} property can make the text in the overlay
1622 invisible, which means that it does not appear on the screen.
1623 @xref{Invisible Text}, for details.
1626 @kindex intangible @r{(overlay property)}
1627 The @code{intangible} property on an overlay works just like the
1628 @code{intangible} text property. @xref{Special Properties}, for details.
1630 @item isearch-open-invisible
1631 This property tells incremental search how to make an invisible overlay
1632 visible, permanently, if the final match overlaps it. @xref{Invisible
1635 @item isearch-open-invisible-temporary
1636 This property tells incremental search how to make an invisible overlay
1637 visible, temporarily, during the search. @xref{Invisible Text}.
1640 @kindex before-string @r{(overlay property)}
1641 This property's value is a string to add to the display at the beginning
1642 of the overlay. The string does not appear in the buffer in any
1643 sense---only on the screen.
1646 @kindex after-string @r{(overlay property)}
1647 This property's value is a string to add to the display at the end of
1648 the overlay. The string does not appear in the buffer in any
1649 sense---only on the screen.
1652 This property specifies a display spec to prepend to each
1653 non-continuation line at display-time. @xref{Truncation}.
1656 This property specifies a display spec to prepend to each continuation
1657 line at display-time. @xref{Truncation}.
1660 @kindex evaporate @r{(overlay property)}
1661 If this property is non-@code{nil}, the overlay is deleted automatically
1662 if it becomes empty (i.e., if its length becomes zero). If you give
1663 an empty overlay a non-@code{nil} @code{evaporate} property, that deletes
1667 @cindex keymap of character (and overlays)
1668 @kindex keymap @r{(overlay property)}
1669 If this property is non-@code{nil}, it specifies a keymap for a portion of the
1670 text. This keymap is used when the character after point is within the
1671 overlay, and takes precedence over most other keymaps. @xref{Active Keymaps}.
1674 @kindex local-map @r{(overlay property)}
1675 The @code{local-map} property is similar to @code{keymap} but replaces the
1676 buffer's local map rather than augmenting existing keymaps. This also means it
1677 has lower precedence than minor mode keymaps.
1680 The @code{keymap} and @code{local-map} properties do not affect a
1681 string displayed by the @code{before-string}, @code{after-string}, or
1682 @code{display} properties. This is only relevant for mouse clicks and
1683 other mouse events that fall on the string, since point is never on
1684 the string. To bind special mouse events for the string, assign it a
1685 @code{keymap} or @code{local-map} text property. @xref{Special
1688 @node Finding Overlays
1689 @subsection Searching for Overlays
1691 @defun overlays-at pos
1692 This function returns a list of all the overlays that cover the
1693 character at position @var{pos} in the current buffer. The list is in
1694 no particular order. An overlay contains position @var{pos} if it
1695 begins at or before @var{pos}, and ends after @var{pos}.
1697 To illustrate usage, here is a Lisp function that returns a list of the
1698 overlays that specify property @var{prop} for the character at point:
1701 (defun find-overlays-specifying (prop)
1702 (let ((overlays (overlays-at (point)))
1705 (let ((overlay (car overlays)))
1706 (if (overlay-get overlay prop)
1707 (setq found (cons overlay found))))
1708 (setq overlays (cdr overlays)))
1713 @defun overlays-in beg end
1714 This function returns a list of the overlays that overlap the region
1715 @var{beg} through @var{end}. ``Overlap'' means that at least one
1716 character is contained within the overlay and also contained within the
1717 specified region; however, empty overlays are included in the result if
1718 they are located at @var{beg}, strictly between @var{beg} and @var{end},
1719 or at @var{end} when @var{end} denotes the position at the end of the
1723 @defun next-overlay-change pos
1724 This function returns the buffer position of the next beginning or end
1725 of an overlay, after @var{pos}. If there is none, it returns
1729 @defun previous-overlay-change pos
1730 This function returns the buffer position of the previous beginning or
1731 end of an overlay, before @var{pos}. If there is none, it returns
1735 As an example, here's a simplified (and inefficient) version of the
1736 primitive function @code{next-single-char-property-change}
1737 (@pxref{Property Search}). It searches forward from position
1738 @var{pos} for the next position where the value of a given property
1739 @code{prop}, as obtained from either overlays or text properties,
1743 (defun next-single-char-property-change (position prop)
1745 (goto-char position)
1746 (let ((propval (get-char-property (point) prop)))
1747 (while (and (not (eobp))
1748 (eq (get-char-property (point) prop) propval))
1749 (goto-char (min (next-overlay-change (point))
1750 (next-single-property-change (point) prop)))))
1757 Since not all characters have the same width, these functions let you
1758 check the width of a character. @xref{Primitive Indent}, and
1759 @ref{Screen Lines}, for related functions.
1761 @defun char-width char
1762 This function returns the width in columns of the character
1763 @var{char}, if it were displayed in the current buffer (i.e., taking
1764 into account the buffer's display table, if any; @pxref{Display
1765 Tables}). The width of a tab character is usually @code{tab-width}
1766 (@pxref{Usual Display}).
1769 @defun string-width string
1770 This function returns the width in columns of the string @var{string},
1771 if it were displayed in the current buffer and the selected window.
1774 @defun truncate-string-to-width string width &optional start-column padding ellipsis
1775 This function returns the part of @var{string} that fits within
1776 @var{width} columns, as a new string.
1778 If @var{string} does not reach @var{width}, then the result ends where
1779 @var{string} ends. If one multi-column character in @var{string}
1780 extends across the column @var{width}, that character is not included in
1781 the result. Thus, the result can fall short of @var{width} but cannot
1784 The optional argument @var{start-column} specifies the starting column.
1785 If this is non-@code{nil}, then the first @var{start-column} columns of
1786 the string are omitted from the value. If one multi-column character in
1787 @var{string} extends across the column @var{start-column}, that
1788 character is not included.
1790 The optional argument @var{padding}, if non-@code{nil}, is a padding
1791 character added at the beginning and end of the result string, to extend
1792 it to exactly @var{width} columns. The padding character is used at the
1793 end of the result if it falls short of @var{width}. It is also used at
1794 the beginning of the result if one multi-column character in
1795 @var{string} extends across the column @var{start-column}.
1797 If @var{ellipsis} is non-@code{nil}, it should be a string which will
1798 replace the end of @var{string} (including any padding) if it extends
1799 beyond @var{width}, unless the display width of @var{string} is equal
1800 to or less than the display width of @var{ellipsis}. If
1801 @var{ellipsis} is non-@code{nil} and not a string, it stands for
1805 (truncate-string-to-width "\tab\t" 12 4)
1807 (truncate-string-to-width "\tab\t" 12 4 ?\s)
1813 @section Line Height
1815 @cindex height of a line
1817 The total height of each display line consists of the height of the
1818 contents of the line, plus optional additional vertical line spacing
1819 above or below the display line.
1821 The height of the line contents is the maximum height of any
1822 character or image on that display line, including the final newline
1823 if there is one. (A display line that is continued doesn't include a
1824 final newline.) That is the default line height, if you do nothing to
1825 specify a greater height. (In the most common case, this equals the
1826 height of the default frame font.)
1828 There are several ways to explicitly specify a larger line height,
1829 either by specifying an absolute height for the display line, or by
1830 specifying vertical space. However, no matter what you specify, the
1831 actual line height can never be less than the default.
1833 @kindex line-height @r{(text property)}
1834 A newline can have a @code{line-height} text or overlay property
1835 that controls the total height of the display line ending in that
1838 If the property value is @code{t}, the newline character has no
1839 effect on the displayed height of the line---the visible contents
1840 alone determine the height. This is useful for tiling small images
1841 (or image slices) without adding blank areas between the images.
1843 If the property value is a list of the form @code{(@var{height}
1844 @var{total})}, that adds extra space @emph{below} the display line.
1845 First Emacs uses @var{height} as a height spec to control extra space
1846 @emph{above} the line; then it adds enough space @emph{below} the line
1847 to bring the total line height up to @var{total}. In this case, the
1848 other ways to specify the line spacing are ignored.
1851 Any other kind of property value is a height spec, which translates
1852 into a number---the specified line height. There are several ways to
1853 write a height spec; here's how each of them translates into a number:
1857 If the height spec is a positive integer, the height value is that integer.
1859 If the height spec is a float, @var{float}, the numeric height value
1860 is @var{float} times the frame's default line height.
1861 @item (@var{face} . @var{ratio})
1862 If the height spec is a cons of the format shown, the numeric height
1863 is @var{ratio} times the height of face @var{face}. @var{ratio} can
1864 be any type of number, or @code{nil} which means a ratio of 1.
1865 If @var{face} is @code{t}, it refers to the current face.
1866 @item (nil . @var{ratio})
1867 If the height spec is a cons of the format shown, the numeric height
1868 is @var{ratio} times the height of the contents of the line.
1871 Thus, any valid height spec determines the height in pixels, one way
1872 or another. If the line contents' height is less than that, Emacs
1873 adds extra vertical space above the line to achieve the specified
1876 If you don't specify the @code{line-height} property, the line's
1877 height consists of the contents' height plus the line spacing.
1878 There are several ways to specify the line spacing for different
1879 parts of Emacs text.
1881 On graphical terminals, you can specify the line spacing for all
1882 lines in a frame, using the @code{line-spacing} frame parameter
1883 (@pxref{Layout Parameters}). However, if the default value of
1884 @code{line-spacing} is non-@code{nil}, it overrides the
1885 frame's @code{line-spacing} parameter. An integer value specifies the
1886 number of pixels put below lines. A floating point number specifies
1887 the spacing relative to the frame's default line height.
1889 @vindex line-spacing
1890 You can specify the line spacing for all lines in a buffer via the
1891 buffer-local @code{line-spacing} variable. An integer value specifies
1892 the number of pixels put below lines. A floating point number
1893 specifies the spacing relative to the default frame line height. This
1894 overrides line spacings specified for the frame.
1896 @kindex line-spacing @r{(text property)}
1897 Finally, a newline can have a @code{line-spacing} text or overlay
1898 property that overrides the default frame line spacing and the buffer
1899 local @code{line-spacing} variable, for the display line ending in
1902 One way or another, these mechanisms specify a Lisp value for the
1903 spacing of each line. The value is a height spec, and it translates
1904 into a Lisp value as described above. However, in this case the
1905 numeric height value specifies the line spacing, rather than the line
1908 On text terminals, the line spacing cannot be altered.
1914 A @dfn{face} is a collection of graphical attributes for displaying
1915 text: font, foreground color, background color, optional underlining,
1916 etc. Faces control how Emacs displays text in buffers, as well as
1917 other parts of the frame such as the mode line.
1919 @cindex anonymous face
1920 One way to represent a face is as a property list of attributes,
1921 like @code{(:foreground "red" :weight bold)}. Such a list is called
1922 an @dfn{anonymous face}. For example, you can assign an anonymous
1923 face as the value of the @code{face} text property, and Emacs will
1924 display the underlying text with the specified attributes.
1925 @xref{Special Properties}.
1928 More commonly, a face is referred to via a @dfn{face name}: a Lisp
1929 symbol associated with a set of face attributes@footnote{For backward
1930 compatibility, you can also use a string to specify a face name; that
1931 is equivalent to a Lisp symbol with the same name.}. Named faces are
1932 defined using the @code{defface} macro (@pxref{Defining Faces}).
1933 Emacs comes with several standard named faces (@pxref{Basic Faces}).
1935 Many parts of Emacs required named faces, and do not accept
1936 anonymous faces. These include the functions documented in
1937 @ref{Attribute Functions}, and the variable @code{font-lock-keywords}
1938 (@pxref{Search-based Fontification}). Unless otherwise stated, we
1939 will use the term @dfn{face} to refer only to named faces.
1942 This function returns a non-@code{nil} value if @var{object} is a
1943 named face: a Lisp symbol or string which serves as a face name.
1944 Otherwise, it returns @code{nil}.
1948 * Face Attributes:: What is in a face?
1949 * Defining Faces:: How to define a face.
1950 * Attribute Functions:: Functions to examine and set face attributes.
1951 * Displaying Faces:: How Emacs combines the faces specified for a character.
1952 * Face Remapping:: Remapping faces to alternative definitions.
1953 * Face Functions:: How to define and examine faces.
1954 * Auto Faces:: Hook for automatic face assignment.
1955 * Basic Faces:: Faces that are defined by default.
1956 * Font Selection:: Finding the best available font for a face.
1957 * Font Lookup:: Looking up the names of available fonts
1958 and information about them.
1959 * Fontsets:: A fontset is a collection of fonts
1960 that handle a range of character sets.
1961 * Low-Level Font:: Lisp representation for character display fonts.
1964 @node Face Attributes
1965 @subsection Face Attributes
1966 @cindex face attributes
1968 @dfn{Face attributes} determine the visual appearance of a face.
1969 The following table lists all the face attributes, their possible
1970 values, and their effects.
1972 Apart from the values given below, each face attribute can have the
1973 value @code{unspecified}. This special value means that the face
1974 doesn't specify that attribute directly. An @code{unspecified}
1975 attribute tells Emacs to refer instead to a parent face (see the
1976 description @code{:inherit} attribute below); or, failing that, to an
1977 underlying face (@pxref{Displaying Faces}). The @code{default} face
1978 must specify all attributes.
1980 Some of these attributes are meaningful only on certain kinds of
1981 displays. If your display cannot handle a certain attribute, the
1982 attribute is ignored.
1986 Font family or fontset (a string). @xref{Fonts,,, emacs, The GNU
1987 Emacs Manual}, for more information about font families. The function
1988 @code{font-family-list} (see below) returns a list of available family
1989 names. @xref{Fontsets}, for information about fontsets.
1992 The name of the @dfn{font foundry} for the font family specified by
1993 the @code{:family} attribute (a string). @xref{Fonts,,, emacs, The
1997 Relative character width. This should be one of the symbols
1998 @code{ultra-condensed}, @code{extra-condensed}, @code{condensed},
1999 @code{semi-condensed}, @code{normal}, @code{semi-expanded},
2000 @code{expanded}, @code{extra-expanded}, or @code{ultra-expanded}.
2003 The height of the font. In the simplest case, this is an integer in
2004 units of 1/10 point.
2006 The value can also be a floating point number or a function, which
2007 specifies the height relative to an @dfn{underlying face}
2008 (@pxref{Displaying Faces}). If the value is a floating point number,
2009 that specifies the amount by which to scale the height of the
2010 underlying face. If the value is a function, that function is called
2011 with one argument, the height of the underlying face, and returns the
2012 height of the new face. If the function is passed an integer
2013 argument, it must return an integer.
2015 The height of the default face must be specified using an integer;
2016 floating point and function values are not allowed.
2019 Font weight---one of the symbols (from densest to faintest)
2020 @code{ultra-bold}, @code{extra-bold}, @code{bold}, @code{semi-bold},
2021 @code{normal}, @code{semi-light}, @code{light}, @code{extra-light}, or
2022 @code{ultra-light}. On text terminals which support
2023 variable-brightness text, any weight greater than normal is displayed
2024 as extra bright, and any weight less than normal is displayed as
2029 Font slant---one of the symbols @code{italic}, @code{oblique},
2030 @code{normal}, @code{reverse-italic}, or @code{reverse-oblique}. On
2031 text terminals that support variable-brightness text, slanted text is
2032 displayed as half-bright.
2035 Foreground color, a string. The value can be a system-defined color
2036 name, or a hexadecimal color specification. @xref{Color Names}. On
2037 black-and-white displays, certain shades of gray are implemented by
2041 Background color, a string. The value can be a system-defined color
2042 name, or a hexadecimal color specification. @xref{Color Names}.
2044 @cindex underlined text
2046 Whether or not characters should be underlined, and in what
2047 way. The possible values of the @code{:underline} attribute are:
2054 Underline with the foreground color of the face.
2057 Underline in color @var{color}, a string specifying a color.
2059 @item @code{(:color @var{color} :style @var{style})}
2060 @var{color} is either a string, or the symbol @code{foreground-color},
2061 meaning the foreground color of the face. Omitting the attribute
2062 @code{:color} means to use the foreground color of the face.
2063 @var{style} should be a symbol @code{line} or @code{wave}, meaning to
2064 use a straight or wavy line. Omitting the attribute @code{:style}
2065 means to use a straight line.
2068 @cindex overlined text
2070 Whether or not characters should be overlined, and in what color.
2071 If the value is @code{t}, overlining uses the foreground color of the
2072 face. If the value is a string, overlining uses that color. The
2073 value @code{nil} means do not overline.
2075 @cindex strike-through text
2076 @item :strike-through
2077 Whether or not characters should be strike-through, and in what
2078 color. The value is used like that of @code{:overline}.
2083 Whether or not a box should be drawn around characters, its color, the
2084 width of the box lines, and 3D appearance. Here are the possible
2085 values of the @code{:box} attribute, and what they mean:
2092 Draw a box with lines of width 1, in the foreground color.
2095 Draw a box with lines of width 1, in color @var{color}.
2097 @item @code{(:line-width @var{width} :color @var{color} :style @var{style})}
2098 This way you can explicitly specify all aspects of the box. The value
2099 @var{width} specifies the width of the lines to draw; it defaults to
2100 1. A negative width @var{-n} means to draw a line of width @var{n}
2101 that occupies the space of the underlying text, thus avoiding any
2102 increase in the character height or width.
2104 The value @var{color} specifies the color to draw with. The default is
2105 the foreground color of the face for simple boxes, and the background
2106 color of the face for 3D boxes.
2108 The value @var{style} specifies whether to draw a 3D box. If it is
2109 @code{released-button}, the box looks like a 3D button that is not being
2110 pressed. If it is @code{pressed-button}, the box looks like a 3D button
2111 that is being pressed. If it is @code{nil} or omitted, a plain 2D box
2115 @item :inverse-video
2116 Whether or not characters should be displayed in inverse video. The
2117 value should be @code{t} (yes) or @code{nil} (no).
2120 The background stipple, a bitmap.
2122 The value can be a string; that should be the name of a file containing
2123 external-format X bitmap data. The file is found in the directories
2124 listed in the variable @code{x-bitmap-file-path}.
2126 Alternatively, the value can specify the bitmap directly, with a list
2127 of the form @code{(@var{width} @var{height} @var{data})}. Here,
2128 @var{width} and @var{height} specify the size in pixels, and
2129 @var{data} is a string containing the raw bits of the bitmap, row by
2130 row. Each row occupies @math{(@var{width} + 7) / 8} consecutive bytes
2131 in the string (which should be a unibyte string for best results).
2132 This means that each row always occupies at least one whole byte.
2134 If the value is @code{nil}, that means use no stipple pattern.
2136 Normally you do not need to set the stipple attribute, because it is
2137 used automatically to handle certain shades of gray.
2140 The font used to display the face. Its value should be a font object.
2141 @xref{Low-Level Font}, for information about font objects, font specs,
2144 When specifying this attribute using @code{set-face-attribute}
2145 (@pxref{Attribute Functions}), you may also supply a font spec, a font
2146 entity, or a string. Emacs converts such values to an appropriate
2147 font object, and stores that font object as the actual attribute
2148 value. If you specify a string, the contents of the string should be
2149 a font name (@pxref{Fonts,,, emacs, The GNU Emacs Manual}); if the
2150 font name is an XLFD containing wildcards, Emacs chooses the first
2151 font matching those wildcards. Specifying this attribute also changes
2152 the values of the @code{:family}, @code{:foundry}, @code{:width},
2153 @code{:height}, @code{:weight}, and @code{:slant} attributes.
2156 The name of a face from which to inherit attributes, or a list of face
2157 names. Attributes from inherited faces are merged into the face like
2158 an underlying face would be, with higher priority than underlying
2159 faces (@pxref{Displaying Faces}). If a list of faces is used,
2160 attributes from faces earlier in the list override those from later
2164 @defun font-family-list &optional frame
2165 This function returns a list of available font family names. The
2166 optional argument @var{frame} specifies the frame on which the text is
2167 to be displayed; if it is @code{nil}, the selected frame is used.
2170 @defopt underline-minimum-offset
2171 This variable specifies the minimum distance between the baseline and
2172 the underline, in pixels, when displaying underlined text.
2175 @defopt x-bitmap-file-path
2176 This variable specifies a list of directories for searching
2177 for bitmap files, for the @code{:stipple} attribute.
2180 @defun bitmap-spec-p object
2181 This returns @code{t} if @var{object} is a valid bitmap specification,
2182 suitable for use with @code{:stipple} (see above). It returns
2183 @code{nil} otherwise.
2186 @node Defining Faces
2187 @subsection Defining Faces
2190 The usual way to define a face is through the @code{defface} macro.
2191 This macro associates a face name (a symbol) with a default @dfn{face
2192 spec}. A face spec is a construct which specifies what attributes a
2193 face should have on any given terminal; for example, a face spec might
2194 specify one foreground color on high-color terminals, and a different
2195 foreground color on low-color terminals.
2197 People are sometimes tempted to create a variable whose value is a
2198 face name. In the vast majority of cases, this is not necessary; the
2199 usual procedure is to define a face with @code{defface}, and then use
2202 @defmac defface face spec doc [keyword value]@dots{}
2203 This macro declares @var{face} as a named face whose default face spec
2204 is given by @var{spec}. You should not quote the symbol @var{face},
2205 and it should not end in @samp{-face} (that would be redundant). The
2206 argument @var{doc} is a documentation string for the face. The
2207 additional @var{keyword} arguments have the same meanings as in
2208 @code{defgroup} and @code{defcustom} (@pxref{Common Keywords}).
2210 If @var{face} already has a default face spec, this macro does
2213 The default face spec determines @var{face}'s appearance when no
2214 customizations are in effect (@pxref{Customization}). If @var{face}
2215 has already been customized (via Custom themes or via customizations
2216 read from the init file), its appearance is determined by the custom
2217 face spec(s), which override the default face spec @var{spec}.
2218 However, if the customizations are subsequently removed, the
2219 appearance of @var{face} will again be determined by its default face
2222 As an exception, if you evaluate a @code{defface} form with
2223 @kbd{C-M-x} in Emacs Lisp mode (@code{eval-defun}), a special feature
2224 of @code{eval-defun} overrides any custom face specs on the face,
2225 causing the face to reflect exactly what the @code{defface} says.
2227 The @var{spec} argument is a @dfn{face spec}, which states how the
2228 face should appear on different kinds of terminals. It should be an
2229 alist whose elements each have the form
2232 (@var{display} . @var{plist})
2236 @var{display} specifies a class of terminals (see below). @var{plist}
2237 is a property list of face attributes and their values, specifying how
2238 the face appears on such terminals. For backward compatibility, you
2239 can also write an element as @code{(@var{display} @var{plist})}.
2241 The @var{display} part of an element of @var{spec} determines which
2242 terminals the element matches. If more than one element of @var{spec}
2243 matches a given terminal, the first element that matches is the one
2244 used for that terminal. There are three possibilities for
2248 @item @code{default}
2249 This element of @var{spec} doesn't match any terminal; instead, it
2250 specifies defaults that apply to all terminals. This element, if
2251 used, must be the first element of @var{spec}. Each of the following
2252 elements can override any or all of these defaults.
2255 This element of @var{spec} matches all terminals. Therefore, any
2256 subsequent elements of @var{spec} are never used. Normally @code{t}
2257 is used in the last (or only) element of @var{spec}.
2260 If @var{display} is a list, each element should have the form
2261 @code{(@var{characteristic} @var{value}@dots{})}. Here
2262 @var{characteristic} specifies a way of classifying terminals, and the
2263 @var{value}s are possible classifications which @var{display} should
2264 apply to. Here are the possible values of @var{characteristic}:
2268 The kind of window system the terminal uses---either @code{graphic}
2269 (any graphics-capable display), @code{x}, @code{pc} (for the MS-DOS
2270 console), @code{w32} (for MS Windows 9X/NT/2K/XP), or @code{tty} (a
2271 non-graphics-capable display). @xref{Window Systems, window-system}.
2274 What kinds of colors the terminal supports---either @code{color},
2275 @code{grayscale}, or @code{mono}.
2278 The kind of background---either @code{light} or @code{dark}.
2281 An integer that represents the minimum number of colors the terminal
2282 should support. This matches a terminal if its
2283 @code{display-color-cells} value is at least the specified integer.
2286 Whether or not the terminal can display the face attributes given in
2287 @var{value}@dots{} (@pxref{Face Attributes}). @xref{Display Face
2288 Attribute Testing}, for more information on exactly how this testing
2292 If an element of @var{display} specifies more than one @var{value} for
2293 a given @var{characteristic}, any of those values is acceptable. If
2294 @var{display} has more than one element, each element should specify a
2295 different @var{characteristic}; then @emph{each} characteristic of the
2296 terminal must match one of the @var{value}s specified for it in
2301 For example, here's the definition of the standard face
2306 '((((class color) (min-colors 88) (background light))
2307 :background "darkseagreen2")
2308 (((class color) (min-colors 88) (background dark))
2309 :background "darkolivegreen")
2310 (((class color) (min-colors 16) (background light))
2311 :background "darkseagreen2")
2312 (((class color) (min-colors 16) (background dark))
2313 :background "darkolivegreen")
2314 (((class color) (min-colors 8))
2315 :background "green" :foreground "black")
2316 (t :inverse-video t))
2317 "Basic face for highlighting."
2318 :group 'basic-faces)
2321 Internally, Emacs stores each face's default spec in its
2322 @code{face-defface-spec} symbol property (@pxref{Symbol Properties}).
2323 The @code{saved-face} property stores any face spec saved by the user
2324 using the customization buffer; the @code{customized-face} property
2325 stores the face spec customized for the current session, but not
2326 saved; and the @code{theme-face} property stores an alist associating
2327 the active customization settings and Custom themes with the face
2328 specs for that face. The face's documentation string is stored in the
2329 @code{face-documentation} property.
2331 Normally, a face is declared just once, using @code{defface}, and
2332 any further changes to its appearance are applied using the Customize
2333 framework (e.g., via the Customize user interface or via the
2334 @code{custom-set-faces} function; @pxref{Applying Customizations}), or
2335 by face remapping (@pxref{Face Remapping}). In the rare event that
2336 you need to change a face spec directly from Lisp, you can use the
2337 @code{face-spec-set} function.
2339 @defun face-spec-set face spec &optional spec-type
2340 This function applies @var{spec} as a face spec for @code{face}.
2341 @var{spec} should be a face spec, as described in the above
2342 documentation for @code{defface}.
2344 @cindex override spec @r{(for a face)}
2345 The argument @var{spec-type} determines which spec to set. If it is
2346 @code{nil} or @code{face-override-spec}, this function sets the
2347 @dfn{override spec}, which overrides over all other face specs on
2348 @var{face}. If it is @code{face-defface-spec}, this function sets the
2349 default face spec (the same one set by @code{defface}). If it is
2350 @code{reset}, this function clears out all customization specs and
2351 override specs from @var{face} (in this case, the value of @var{spec}
2352 is ignored). Any other value of @var{spec-type} is reserved for
2356 @node Attribute Functions
2357 @subsection Face Attribute Functions
2359 This section describes functions for directly accessing and
2360 modifying the attributes of a named face.
2362 @defun face-attribute face attribute &optional frame inherit
2363 This function returns the value of the @var{attribute} attribute for
2364 @var{face} on @var{frame}.
2366 If @var{frame} is @code{nil}, that means the selected frame
2367 (@pxref{Input Focus}). If @var{frame} is @code{t}, this function
2368 returns the value of the specified attribute for newly-created frames
2369 (this is normally @code{unspecified}, unless you have specified some
2370 value using @code{set-face-attribute}; see below).
2372 If @var{inherit} is @code{nil}, only attributes directly defined by
2373 @var{face} are considered, so the return value may be
2374 @code{unspecified}, or a relative value. If @var{inherit} is
2375 non-@code{nil}, @var{face}'s definition of @var{attribute} is merged
2376 with the faces specified by its @code{:inherit} attribute; however the
2377 return value may still be @code{unspecified} or relative. If
2378 @var{inherit} is a face or a list of faces, then the result is further
2379 merged with that face (or faces), until it becomes specified and
2382 To ensure that the return value is always specified and absolute, use
2383 a value of @code{default} for @var{inherit}; this will resolve any
2384 unspecified or relative values by merging with the @code{default} face
2385 (which is always completely specified).
2390 (face-attribute 'bold :weight)
2395 @c FIXME: Add an index for "relative face attribute", maybe here? --xfq
2396 @defun face-attribute-relative-p attribute value
2397 This function returns non-@code{nil} if @var{value}, when used as the
2398 value of the face attribute @var{attribute}, is relative. This means
2399 it would modify, rather than completely override, any value that comes
2400 from a subsequent face in the face list or that is inherited from
2403 @code{unspecified} is a relative value for all attributes. For
2404 @code{:height}, floating point and function values are also relative.
2409 (face-attribute-relative-p :height 2.0)
2414 @defun face-all-attributes face &optional frame
2415 This function returns an alist of attributes of @var{face}. The
2416 elements of the result are name-value pairs of the form
2417 @w{@code{(@var{attr-name} . @var{attr-value})}}. Optional argument
2418 @var{frame} specifies the frame whose definition of @var{face} to
2419 return; if omitted or @code{nil}, the returned value describes the
2420 default attributes of @var{face} for newly created frames.
2423 @defun merge-face-attribute attribute value1 value2
2424 If @var{value1} is a relative value for the face attribute
2425 @var{attribute}, returns it merged with the underlying value
2426 @var{value2}; otherwise, if @var{value1} is an absolute value for the
2427 face attribute @var{attribute}, returns @var{value1} unchanged.
2430 Normally, Emacs uses the face specs of each face to automatically
2431 calculate its attributes on each frame (@pxref{Defining Faces}). The
2432 function @code{set-face-attribute} can override this calculation by
2433 directly assigning attributes to a face, either on a specific frame or
2434 for all frames. This function is mostly intended for internal usage.
2436 @defun set-face-attribute face frame &rest arguments
2437 This function sets one or more attributes of @var{face} for
2438 @var{frame}. The attributes specifies in this way override the face
2439 spec(s) belonging to @var{face}.
2441 The extra arguments @var{arguments} specify the attributes to set, and
2442 the values for them. They should consist of alternating attribute
2443 names (such as @code{:family} or @code{:underline}) and values. Thus,
2446 (set-face-attribute 'foo nil :weight 'bold :slant 'italic)
2450 sets the attribute @code{:weight} to @code{bold} and the attribute
2451 @code{:slant} to @code{italic}.
2454 If @var{frame} is @code{t}, this function sets the default attributes
2455 for newly created frames. If @var{frame} is @code{nil}, this function
2456 sets the attributes for all existing frames, as well as for newly
2460 The following commands and functions mostly provide compatibility
2461 with old versions of Emacs. They work by calling
2462 @code{set-face-attribute}. Values of @code{t} and @code{nil} for
2463 their @var{frame} argument are handled just like
2464 @code{set-face-attribute} and @code{face-attribute}. The commands
2465 read their arguments using the minibuffer, if called interactively.
2467 @deffn Command set-face-foreground face color &optional frame
2468 @deffnx Command set-face-background face color &optional frame
2469 These set the @code{:foreground} attribute (or @code{:background}
2470 attribute, respectively) of @var{face} to @var{color}.
2473 @deffn Command set-face-stipple face pattern &optional frame
2474 This sets the @code{:stipple} attribute of @var{face} to
2478 @deffn Command set-face-font face font &optional frame
2479 This sets the @code{:font} attribute of @var{face} to @var{font}.
2482 @defun set-face-bold face bold-p &optional frame
2483 This sets the @code{:weight} attribute of @var{face} to @var{normal}
2484 if @var{bold-p} is @code{nil}, and to @var{bold} otherwise.
2487 @defun set-face-italic face italic-p &optional frame
2488 This sets the @code{:slant} attribute of @var{face} to @var{normal} if
2489 @var{italic-p} is @code{nil}, and to @var{italic} otherwise.
2492 @defun set-face-underline face underline &optional frame
2493 This sets the @code{:underline} attribute of @var{face} to
2497 @defun set-face-inverse-video face inverse-video-p &optional frame
2498 This sets the @code{:inverse-video} attribute of @var{face} to
2499 @var{inverse-video-p}.
2502 @deffn Command invert-face face &optional frame
2503 This swaps the foreground and background colors of face @var{face}.
2506 The following functions examine the attributes of a face. They
2507 mostly provide compatibility with old versions of Emacs. If you don't
2508 specify @var{frame}, they refer to the selected frame; @code{t} refers
2509 to the default data for new frames. They return @code{unspecified} if
2510 the face doesn't define any value for that attribute. If
2511 @var{inherit} is @code{nil}, only an attribute directly defined by the
2512 face is returned. If @var{inherit} is non-@code{nil}, any faces
2513 specified by its @code{:inherit} attribute are considered as well, and
2514 if @var{inherit} is a face or a list of faces, then they are also
2515 considered, until a specified attribute is found. To ensure that the
2516 return value is always specified, use a value of @code{default} for
2519 @defun face-font face &optional frame
2520 This function returns the name of the font of face @var{face}.
2523 @defun face-foreground face &optional frame inherit
2524 @defunx face-background face &optional frame inherit
2525 These functions return the foreground color (or background color,
2526 respectively) of face @var{face}, as a string.
2529 @defun face-stipple face &optional frame inherit
2530 This function returns the name of the background stipple pattern of face
2531 @var{face}, or @code{nil} if it doesn't have one.
2534 @defun face-bold-p face &optional frame inherit
2535 This function returns a non-@code{nil} value if the @code{:weight}
2536 attribute of @var{face} is bolder than normal (i.e., one of
2537 @code{semi-bold}, @code{bold}, @code{extra-bold}, or
2538 @code{ultra-bold}). Otherwise, it returns @code{nil}.
2541 @defun face-italic-p face &optional frame inherit
2542 This function returns a non-@code{nil} value if the @code{:slant}
2543 attribute of @var{face} is @code{italic} or @code{oblique}, and
2544 @code{nil} otherwise.
2547 @defun face-underline-p face &optional frame inherit
2548 This function returns non-@code{nil} if face @var{face} specifies
2549 a non-@code{nil} @code{:underline} attribute.
2552 @defun face-inverse-video-p face &optional frame inherit
2553 This function returns non-@code{nil} if face @var{face} specifies
2554 a non-@code{nil} @code{:inverse-video} attribute.
2557 @node Displaying Faces
2558 @subsection Displaying Faces
2560 When Emacs displays a given piece of text, the visual appearance of
2561 the text may be determined by faces drawn from different sources. If
2562 these various sources together specify more than one face for a
2563 particular character, Emacs merges the attributes of the various
2564 faces. Here is the order in which Emacs merges the faces, from
2565 highest to lowest priority:
2569 If the text consists of a special glyph, the glyph can specify a
2570 particular face. @xref{Glyphs}.
2573 If the text lies within an active region, Emacs highlights it using
2574 the @code{region} face. @xref{Standard Faces,,, emacs, The GNU Emacs
2578 If the text lies within an overlay with a non-@code{nil} @code{face}
2579 property, Emacs applies the face(s) specified by that property. If
2580 the overlay has a @code{mouse-face} property and the mouse is ``near
2581 enough'' to the overlay, Emacs applies the face or face attributes
2582 specified by the @code{mouse-face} property instead. @xref{Overlay
2585 When multiple overlays cover one character, an overlay with higher
2586 priority overrides those with lower priority. @xref{Overlays}.
2589 If the text contains a @code{face} or @code{mouse-face} property,
2590 Emacs applies the specified faces and face attributes. @xref{Special
2591 Properties}. (This is how Font Lock mode faces are applied.
2592 @xref{Font Lock Mode}.)
2595 If the text lies within the mode line of the selected window, Emacs
2596 applies the @code{mode-line} face. For the mode line of a
2597 non-selected window, Emacs applies the @code{mode-line-inactive} face.
2598 For a header line, Emacs applies the @code{header-line} face.
2601 If any given attribute has not been specified during the preceding
2602 steps, Emacs applies the attribute of the @code{default} face.
2605 At each stage, if a face has a valid @code{:inherit} attribute,
2606 Emacs treats any attribute with an @code{unspecified} value as having
2607 the corresponding value drawn from the parent face(s). @pxref{Face
2608 Attributes}. Note that the parent face(s) may also leave the
2609 attribute unspecified; in that case, the attribute remains unspecified
2610 at the next level of face merging.
2612 @node Face Remapping
2613 @subsection Face Remapping
2615 The variable @code{face-remapping-alist} is used for buffer-local or
2616 global changes in the appearance of a face. For instance, it is used
2617 to implement the @code{text-scale-adjust} command (@pxref{Text
2618 Scale,,, emacs, The GNU Emacs Manual}).
2620 @defvar face-remapping-alist
2621 The value of this variable is an alist whose elements have the form
2622 @code{(@var{face} . @var{remapping})}. This causes Emacs to display
2623 any text having the face @var{face} with @var{remapping}, rather than
2624 the ordinary definition of @var{face}.
2626 @var{remapping} may be any face spec suitable for a @code{face} text
2627 property: either a face (i.e., a face name or a property list of
2628 attribute/value pairs), or a list of faces. For details, see the
2629 description of the @code{face} text property in @ref{Special
2630 Properties}. @var{remapping} serves as the complete specification for
2631 the remapped face---it replaces the normal definition of @var{face},
2632 instead of modifying it.
2634 If @code{face-remapping-alist} is buffer-local, its local value takes
2635 effect only within that buffer.
2637 Note: face remapping is non-recursive. If @var{remapping} references
2638 the same face name @var{face}, either directly or via the
2639 @code{:inherit} attribute of some other face in @var{remapping}, that
2640 reference uses the normal definition of @var{face}. For instance, if
2641 the @code{mode-line} face is remapped using this entry in
2642 @code{face-remapping-alist}:
2645 (mode-line italic mode-line)
2649 then the new definition of the @code{mode-line} face inherits from the
2650 @code{italic} face, and the @emph{normal} (non-remapped) definition of
2651 @code{mode-line} face.
2654 @cindex relative remapping, faces
2655 @cindex base remapping, faces
2656 The following functions implement a higher-level interface to
2657 @code{face-remapping-alist}. Most Lisp code should use these
2658 functions instead of setting @code{face-remapping-alist} directly, to
2659 avoid trampling on remappings applied elsewhere. These functions are
2660 intended for buffer-local remappings, so they all make
2661 @code{face-remapping-alist} buffer-local as a side-effect. They manage
2662 @code{face-remapping-alist} entries of the form
2665 (@var{face} @var{relative-spec-1} @var{relative-spec-2} @var{...} @var{base-spec})
2669 where, as explained above, each of the @var{relative-spec-N} and
2670 @var{base-spec} is either a face name, or a property list of
2671 attribute/value pairs. Each of the @dfn{relative remapping} entries,
2672 @var{relative-spec-N}, is managed by the
2673 @code{face-remap-add-relative} and @code{face-remap-remove-relative}
2674 functions; these are intended for simple modifications like changing
2675 the text size. The @dfn{base remapping} entry, @var{base-spec}, has
2676 the lowest priority and is managed by the @code{face-remap-set-base}
2677 and @code{face-remap-reset-base} functions; it is intended for major
2678 modes to remap faces in the buffers they control.
2680 @defun face-remap-add-relative face &rest specs
2681 This functions adds the face spec in @var{specs} as relative
2682 remappings for face @var{face} in the current buffer. The remaining
2683 arguments, @var{specs}, should form either a list of face names, or a
2684 property list of attribute/value pairs.
2686 The return value is a Lisp object that serves as a ``cookie''; you can
2687 pass this object as an argument to @code{face-remap-remove-relative}
2688 if you need to remove the remapping later.
2691 ;; Remap the `escape-glyph' face into a combination
2692 ;; of the `highlight' and `italic' faces:
2693 (face-remap-add-relative 'escape-glyph 'highlight 'italic)
2695 ;; Increase the size of the `default' face by 50%:
2696 (face-remap-add-relative 'default :height 1.5)
2700 @defun face-remap-remove-relative cookie
2701 This function removes a relative remapping previously added by
2702 @code{face-remap-add-relative}. @var{cookie} should be the Lisp
2703 object returned by @code{face-remap-add-relative} when the remapping
2707 @defun face-remap-set-base face &rest specs
2708 This function sets the base remapping of @var{face} in the current
2709 buffer to @var{specs}. If @var{specs} is empty, the default base
2710 remapping is restored, similar to calling @code{face-remap-reset-base}
2711 (see below); note that this is different from @var{specs} containing a
2712 single value @code{nil}, which has the opposite result (the global
2713 definition of @var{face} is ignored).
2715 This overwrites the default @var{base-spec}, which inherits the global
2716 face definition, so it is up to the caller to add such inheritance if
2720 @defun face-remap-reset-base face
2721 This function sets the base remapping of @var{face} to its default
2722 value, which inherits from @var{face}'s global definition.
2725 @node Face Functions
2726 @subsection Functions for Working with Faces
2728 Here are additional functions for creating and working with faces.
2731 This function returns a list of all defined face names.
2735 This function returns the @dfn{face number} of face @var{face}. This
2736 is a number that uniquely identifies a face at low levels within
2737 Emacs. It is seldom necessary to refer to a face by its face number.
2740 @defun face-documentation face
2741 This function returns the documentation string of face @var{face}, or
2742 @code{nil} if none was specified for it.
2745 @defun face-equal face1 face2 &optional frame
2746 This returns @code{t} if the faces @var{face1} and @var{face2} have the
2747 same attributes for display.
2750 @defun face-differs-from-default-p face &optional frame
2751 This returns non-@code{nil} if the face @var{face} displays
2752 differently from the default face.
2756 @cindex alias, for faces
2757 A @dfn{face alias} provides an equivalent name for a face. You can
2758 define a face alias by giving the alias symbol the @code{face-alias}
2759 property, with a value of the target face name. The following example
2760 makes @code{modeline} an alias for the @code{mode-line} face.
2763 (put 'modeline 'face-alias 'mode-line)
2766 @defmac define-obsolete-face-alias obsolete-face current-face when
2767 This macro defines @code{obsolete-face} as an alias for
2768 @var{current-face}, and also marks it as obsolete, indicating that it
2769 may be removed in future. @var{when} should be a string indicating
2770 when @code{obsolete-face} was made obsolete (usually a version number
2775 @subsection Automatic Face Assignment
2776 @cindex automatic face assignment
2777 @cindex faces, automatic choice
2779 This hook is used for automatically assigning faces to text in the
2780 buffer. It is part of the implementation of Jit-Lock mode, used by
2783 @defvar fontification-functions
2784 This variable holds a list of functions that are called by Emacs
2785 redisplay as needed, just before doing redisplay. They are called even
2786 when Font Lock Mode isn't enabled. When Font Lock Mode is enabled, this
2787 variable usually holds just one function, @code{jit-lock-function}.
2789 The functions are called in the order listed, with one argument, a
2790 buffer position @var{pos}. Collectively they should attempt to assign
2791 faces to the text in the current buffer starting at @var{pos}.
2793 The functions should record the faces they assign by setting the
2794 @code{face} property. They should also add a non-@code{nil}
2795 @code{fontified} property to all the text they have assigned faces to.
2796 That property tells redisplay that faces have been assigned to that text
2799 It is probably a good idea for the functions to do nothing if the
2800 character after @var{pos} already has a non-@code{nil} @code{fontified}
2801 property, but this is not required. If one function overrides the
2802 assignments made by a previous one, the properties after the last
2803 function finishes are the ones that really matter.
2805 For efficiency, we recommend writing these functions so that they
2806 usually assign faces to around 400 to 600 characters at each call.
2810 @subsection Basic Faces
2812 If your Emacs Lisp program needs to assign some faces to text, it is
2813 often a good idea to use certain existing faces or inherit from them,
2814 rather than defining entirely new faces. This way, if other users
2815 have customized the basic faces to give Emacs a certain look, your
2816 program will ``fit in'' without additional customization.
2818 Some of the basic faces defined in Emacs are listed below. In
2819 addition to these, you might want to make use of the Font Lock faces
2820 for syntactic highlighting, if highlighting is not already handled by
2821 Font Lock mode, or if some Font Lock faces are not in use.
2822 @xref{Faces for Font Lock}.
2826 The default face, whose attributes are all specified. All other faces
2827 implicitly inherit from it: any unspecified attribute defaults to the
2828 attribute on this face (@pxref{Face Attributes}).
2835 @itemx variable-pitch
2836 These have the attributes indicated by their names (e.g., @code{bold}
2837 has a bold @code{:weight} attribute), with all other attributes
2838 unspecified (and so given by @code{default}).
2841 For ``dimmed out'' text. For example, it is used for the ignored
2842 part of a filename in the minibuffer (@pxref{Minibuffer File,,
2843 Minibuffers for File Names, emacs, The GNU Emacs Manual}).
2847 For clickable text buttons that send the user to a different
2848 buffer or ``location''.
2851 For stretches of text that should temporarily stand out. For example,
2852 it is commonly assigned to the @code{mouse-face} property for cursor
2853 highlighting (@pxref{Special Properties}).
2856 For text matching a search command.
2861 For text concerning errors, warnings, or successes. For example,
2862 these are used for messages in @file{*Compilation*} buffers.
2865 @node Font Selection
2866 @subsection Font Selection
2867 @cindex font selection
2868 @cindex selecting a font
2870 Before Emacs can draw a character on a graphical display, it must
2871 select a @dfn{font} for that character@footnote{In this context, the
2872 term @dfn{font} has nothing to do with Font Lock (@pxref{Font Lock
2873 Mode}).}. @xref{Fonts,,, emacs, The GNU Emacs Manual}. Normally,
2874 Emacs automatically chooses a font based on the faces assigned to that
2875 character---specifically, the face attributes @code{:family},
2876 @code{:weight}, @code{:slant}, and @code{:width} (@pxref{Face
2877 Attributes}). The choice of font also depends on the character to be
2878 displayed; some fonts can only display a limited set of characters.
2879 If no available font exactly fits the requirements, Emacs looks for
2880 the @dfn{closest matching font}. The variables in this section
2881 control how Emacs makes this selection.
2883 @defopt face-font-family-alternatives
2884 If a given family is specified but does not exist, this variable
2885 specifies alternative font families to try. Each element should have
2889 (@var{family} @var{alternate-families}@dots{})
2892 If @var{family} is specified but not available, Emacs will try the other
2893 families given in @var{alternate-families}, one by one, until it finds a
2894 family that does exist.
2897 @defopt face-font-selection-order
2898 If there is no font that exactly matches all desired face attributes
2899 (@code{:width}, @code{:height}, @code{:weight}, and @code{:slant}),
2900 this variable specifies the order in which these attributes should be
2901 considered when selecting the closest matching font. The value should
2902 be a list containing those four attribute symbols, in order of
2903 decreasing importance. The default is @code{(:width :height :weight
2906 Font selection first finds the best available matches for the first
2907 attribute in the list; then, among the fonts which are best in that
2908 way, it searches for the best matches in the second attribute, and so
2911 The attributes @code{:weight} and @code{:width} have symbolic values in
2912 a range centered around @code{normal}. Matches that are more extreme
2913 (farther from @code{normal}) are somewhat preferred to matches that are
2914 less extreme (closer to @code{normal}); this is designed to ensure that
2915 non-normal faces contrast with normal ones, whenever possible.
2917 One example of a case where this variable makes a difference is when the
2918 default font has no italic equivalent. With the default ordering, the
2919 @code{italic} face will use a non-italic font that is similar to the
2920 default one. But if you put @code{:slant} before @code{:height}, the
2921 @code{italic} face will use an italic font, even if its height is not
2925 @defopt face-font-registry-alternatives
2926 This variable lets you specify alternative font registries to try, if a
2927 given registry is specified and doesn't exist. Each element should have
2931 (@var{registry} @var{alternate-registries}@dots{})
2934 If @var{registry} is specified but not available, Emacs will try the
2935 other registries given in @var{alternate-registries}, one by one,
2936 until it finds a registry that does exist.
2939 @cindex scalable fonts
2940 Emacs can make use of scalable fonts, but by default it does not use
2943 @defopt scalable-fonts-allowed
2944 This variable controls which scalable fonts to use. A value of
2945 @code{nil}, the default, means do not use scalable fonts. @code{t}
2946 means to use any scalable font that seems appropriate for the text.
2948 Otherwise, the value must be a list of regular expressions. Then a
2949 scalable font is enabled for use if its name matches any regular
2950 expression in the list. For example,
2953 (setq scalable-fonts-allowed '("muleindian-2$"))
2957 allows the use of scalable fonts with registry @code{muleindian-2}.
2960 @defvar face-font-rescale-alist
2961 This variable specifies scaling for certain faces. Its value should
2962 be a list of elements of the form
2965 (@var{fontname-regexp} . @var{scale-factor})
2968 If @var{fontname-regexp} matches the font name that is about to be
2969 used, this says to choose a larger similar font according to the
2970 factor @var{scale-factor}. You would use this feature to normalize
2971 the font size if certain fonts are bigger or smaller than their
2972 nominal heights and widths would suggest.
2976 @subsection Looking Up Fonts
2978 @defun x-list-fonts name &optional reference-face frame maximum width
2979 This function returns a list of available font names that match
2980 @var{name}. @var{name} should be a string containing a font name in
2981 either the Fontconfig, GTK, or XLFD format (@pxref{Fonts,,, emacs, The
2982 GNU Emacs Manual}). Within an XLFD string, wildcard characters may be
2983 used: the @samp{*} character matches any substring, and the @samp{?}
2984 character matches any single character. Case is ignored when matching
2987 If the optional arguments @var{reference-face} and @var{frame} are
2988 specified, the returned list includes only fonts that are the same
2989 size as @var{reference-face} (a face name) currently is on the frame
2992 The optional argument @var{maximum} sets a limit on how many fonts to
2993 return. If it is non-@code{nil}, then the return value is truncated
2994 after the first @var{maximum} matching fonts. Specifying a small
2995 value for @var{maximum} can make this function much faster, in cases
2996 where many fonts match the pattern.
2998 The optional argument @var{width} specifies a desired font width. If
2999 it is non-@code{nil}, the function only returns those fonts whose
3000 characters are (on average) @var{width} times as wide as
3001 @var{reference-face}.
3004 @defun x-family-fonts &optional family frame
3005 This function returns a list describing the available fonts for family
3006 @var{family} on @var{frame}. If @var{family} is omitted or @code{nil},
3007 this list applies to all families, and therefore, it contains all
3008 available fonts. Otherwise, @var{family} must be a string; it may
3009 contain the wildcards @samp{?} and @samp{*}.
3011 The list describes the display that @var{frame} is on; if @var{frame} is
3012 omitted or @code{nil}, it applies to the selected frame's display
3013 (@pxref{Input Focus}).
3015 Each element in the list is a vector of the following form:
3018 [@var{family} @var{width} @var{point-size} @var{weight} @var{slant}
3019 @var{fixed-p} @var{full} @var{registry-and-encoding}]
3022 The first five elements correspond to face attributes; if you
3023 specify these attributes for a face, it will use this font.
3025 The last three elements give additional information about the font.
3026 @var{fixed-p} is non-@code{nil} if the font is fixed-pitch.
3027 @var{full} is the full name of the font, and
3028 @var{registry-and-encoding} is a string giving the registry and
3029 encoding of the font.
3033 @subsection Fontsets
3035 A @dfn{fontset} is a list of fonts, each assigned to a range of
3036 character codes. An individual font cannot display the whole range of
3037 characters that Emacs supports, but a fontset can. Fontsets have names,
3038 just as fonts do, and you can use a fontset name in place of a font name
3039 when you specify the ``font'' for a frame or a face. Here is
3040 information about defining a fontset under Lisp program control.
3042 @defun create-fontset-from-fontset-spec fontset-spec &optional style-variant-p noerror
3043 This function defines a new fontset according to the specification
3044 string @var{fontset-spec}. The string should have this format:
3047 @var{fontpattern}, @r{[}@var{charset}:@var{font}@r{]@dots{}}
3051 Whitespace characters before and after the commas are ignored.
3053 The first part of the string, @var{fontpattern}, should have the form of
3054 a standard X font name, except that the last two fields should be
3055 @samp{fontset-@var{alias}}.
3057 The new fontset has two names, one long and one short. The long name is
3058 @var{fontpattern} in its entirety. The short name is
3059 @samp{fontset-@var{alias}}. You can refer to the fontset by either
3060 name. If a fontset with the same name already exists, an error is
3061 signaled, unless @var{noerror} is non-@code{nil}, in which case this
3062 function does nothing.
3064 If optional argument @var{style-variant-p} is non-@code{nil}, that says
3065 to create bold, italic and bold-italic variants of the fontset as well.
3066 These variant fontsets do not have a short name, only a long one, which
3067 is made by altering @var{fontpattern} to indicate the bold and/or italic
3070 The specification string also says which fonts to use in the fontset.
3071 See below for the details.
3074 The construct @samp{@var{charset}:@var{font}} specifies which font to
3075 use (in this fontset) for one particular character set. Here,
3076 @var{charset} is the name of a character set, and @var{font} is the font
3077 to use for that character set. You can use this construct any number of
3078 times in the specification string.
3080 For the remaining character sets, those that you don't specify
3081 explicitly, Emacs chooses a font based on @var{fontpattern}: it replaces
3082 @samp{fontset-@var{alias}} with a value that names one character set.
3083 For the @acronym{ASCII} character set, @samp{fontset-@var{alias}} is replaced
3084 with @samp{ISO8859-1}.
3086 In addition, when several consecutive fields are wildcards, Emacs
3087 collapses them into a single wildcard. This is to prevent use of
3088 auto-scaled fonts. Fonts made by scaling larger fonts are not usable
3089 for editing, and scaling a smaller font is not useful because it is
3090 better to use the smaller font in its own size, which Emacs does.
3092 Thus if @var{fontpattern} is this,
3095 -*-fixed-medium-r-normal-*-24-*-*-*-*-*-fontset-24
3099 the font specification for @acronym{ASCII} characters would be this:
3102 -*-fixed-medium-r-normal-*-24-*-ISO8859-1
3106 and the font specification for Chinese GB2312 characters would be this:
3109 -*-fixed-medium-r-normal-*-24-*-gb2312*-*
3112 You may not have any Chinese font matching the above font
3113 specification. Most X distributions include only Chinese fonts that
3114 have @samp{song ti} or @samp{fangsong ti} in the @var{family} field. In
3115 such a case, @samp{Fontset-@var{n}} can be specified as below:
3118 Emacs.Fontset-0: -*-fixed-medium-r-normal-*-24-*-*-*-*-*-fontset-24,\
3119 chinese-gb2312:-*-*-medium-r-normal-*-24-*-gb2312*-*
3123 Then, the font specifications for all but Chinese GB2312 characters have
3124 @samp{fixed} in the @var{family} field, and the font specification for
3125 Chinese GB2312 characters has a wild card @samp{*} in the @var{family}
3128 @defun set-fontset-font name character font-spec &optional frame add
3129 This function modifies the existing fontset @var{name} to use the font
3130 matching with @var{font-spec} for the character @var{character}.
3132 If @var{name} is @code{nil}, this function modifies the fontset of the
3133 selected frame or that of @var{frame} if @var{frame} is not
3136 If @var{name} is @code{t}, this function modifies the default
3137 fontset, whose short name is @samp{fontset-default}.
3139 @var{character} may be a cons; @code{(@var{from} . @var{to})}, where
3140 @var{from} and @var{to} are character codepoints. In that case, use
3141 @var{font-spec} for all characters in the range @var{from} and @var{to}
3144 @var{character} may be a charset. In that case, use
3145 @var{font-spec} for all character in the charsets.
3147 @var{character} may be a script name. In that case, use
3148 @var{font-spec} for all character in the charsets.
3150 @var{font-spec} may be a cons; @code{(@var{family} . @var{registry})},
3151 where @var{family} is a family name of a font (possibly including a
3152 foundry name at the head), @var{registry} is a registry name of a font
3153 (possibly including an encoding name at the tail).
3155 @var{font-spec} may be a font name string.
3157 The optional argument @var{add}, if non-@code{nil}, specifies how to
3158 add @var{font-spec} to the font specifications previously set. If it
3159 is @code{prepend}, @var{font-spec} is prepended. If it is
3160 @code{append}, @var{font-spec} is appended. By default,
3161 @var{font-spec} overrides the previous settings.
3163 For instance, this changes the default fontset to use a font of which
3164 family name is @samp{Kochi Gothic} for all characters belonging to
3165 the charset @code{japanese-jisx0208}.
3168 (set-fontset-font t 'japanese-jisx0208
3169 (font-spec :family "Kochi Gothic"))
3173 @defun char-displayable-p char
3174 This function returns @code{t} if Emacs ought to be able to display
3175 @var{char}. More precisely, if the selected frame's fontset has a
3176 font to display the character set that @var{char} belongs to.
3178 Fontsets can specify a font on a per-character basis; when the fontset
3179 does that, this function's value may not be accurate.
3182 @node Low-Level Font
3183 @subsection Low-Level Font Representation
3184 @cindex font property
3186 Normally, it is not necessary to manipulate fonts directly. In case
3187 you need to do so, this section explains how.
3189 In Emacs Lisp, fonts are represented using three different Lisp
3190 object types: @dfn{font objects}, @dfn{font specs}, and @dfn{font
3193 @defun fontp object &optional type
3194 Return @code{t} if @var{object} is a font object, font spec, or font
3195 entity. Otherwise, return @code{nil}.
3197 The optional argument @var{type}, if non-@code{nil}, determines the
3198 exact type of Lisp object to check for. In that case, @var{type}
3199 should be one of @code{font-object}, @code{font-spec}, or
3204 A font object is a Lisp object that represents a font that Emacs has
3205 @dfn{opened}. Font objects cannot be modified in Lisp, but they can
3208 @defun font-at position &optional window string
3209 Return the font object that is being used to display the character at
3210 position @var{position} in the window @var{window}. If @var{window}
3211 is @code{nil}, it defaults to the selected window. If @var{string} is
3212 @code{nil}, @var{position} specifies a position in the current buffer;
3213 otherwise, @var{string} should be a string, and @var{position}
3214 specifies a position in that string.
3218 A font spec is a Lisp object that contains a set of specifications
3219 that can be used to find a font. More than one font may match the
3220 specifications in a font spec.
3222 @defun font-spec &rest arguments
3223 Return a new font spec using the specifications in @var{arguments},
3224 which should come in @code{property}-@code{value} pairs. The possible
3225 specifications are as follows:
3229 The font name (a string), in either XLFD, Fontconfig, or GTK format.
3230 @xref{Fonts,,, emacs, The GNU Emacs Manual}.
3237 These have the same meanings as the face attributes of the same name.
3238 @xref{Face Attributes}.
3241 The font size---either a non-negative integer that specifies the pixel
3242 size, or a floating point number that specifies the point size.
3245 Additional typographic style information for the font, such as
3246 @samp{sans}. The value should be a string or a symbol.
3248 @cindex font registry
3250 The charset registry and encoding of the font, such as
3251 @samp{iso8859-1}. The value should be a string or a symbol.
3254 The script that the font must support (a symbol).
3257 @cindex OpenType font
3258 The font must be an OpenType font that supports these OpenType
3259 features, provided Emacs is compiled with support for @samp{libotf} (a
3260 library for performing complex text layout in certain scripts). The
3261 value must be a list of the form
3264 @code{(@var{script-tag} @var{langsys-tag} @var{gsub} @var{gpos})}
3267 where @var{script-tag} is the OpenType script tag symbol;
3268 @var{langsys-tag} is the OpenType language system tag symbol, or
3269 @code{nil} to use the default language system; @code{gsub} is a list
3270 of OpenType GSUB feature tag symbols, or @code{nil} if none is
3271 required; and @code{gpos} is a list of OpenType GPOS feature tag
3272 symbols, or @code{nil} if none is required. If @code{gsub} or
3273 @code{gpos} is a list, a @code{nil} element in that list means that
3274 the font must not match any of the remaining tag symbols. The
3275 @code{gpos} element may be omitted.
3279 @defun font-put font-spec property value
3280 Set the font property @var{property} in the font-spec @var{font-spec}
3285 A font entity is a reference to a font that need not be open. Its
3286 properties are intermediate between a font object and a font spec:
3287 like a font object, and unlike a font spec, it refers to a single,
3288 specific font. Unlike a font object, creating a font entity does not
3289 load the contents of that font into computer memory. Emacs may open
3290 multiple font objects of different sizes from a single font entity
3291 referring to a scalable font.
3293 @defun find-font font-spec &optional frame
3294 This function returns a font entity that best matches the font spec
3295 @var{font-spec} on frame @var{frame}. If @var{frame} is @code{nil},
3296 it defaults to the selected frame.
3299 @defun list-fonts font-spec &optional frame num prefer
3300 This function returns a list of all font entities that match the font
3301 spec @var{font-spec}.
3303 The optional argument @var{frame}, if non-@code{nil}, specifies the
3304 frame on which the fonts are to be displayed. The optional argument
3305 @var{num}, if non-@code{nil}, should be an integer that specifies the
3306 maximum length of the returned list. The optional argument
3307 @var{prefer}, if non-@code{nil}, should be another font spec, which is
3308 used to control the order of the returned list; the returned font
3309 entities are sorted in order of decreasing ``closeness'' to that font
3313 If you call @code{set-face-attribute} and pass a font spec, font
3314 entity, or font name string as the value of the @code{:font}
3315 attribute, Emacs opens the best ``matching'' font that is available
3316 for display. It then stores the corresponding font object as the
3317 actual value of the @code{:font} attribute for that face.
3319 The following functions can be used to obtain information about a
3320 font. For these functions, the @var{font} argument can be a font
3321 object, a font entity, or a font spec.
3323 @defun font-get font property
3324 This function returns the value of the font property @var{property}
3327 If @var{font} is a font spec and the font spec does not specify
3328 @var{property}, the return value is @code{nil}. If @var{font} is a
3329 font object or font entity, the value for the @var{:script} property
3330 may be a list of scripts supported by the font.
3333 @defun font-face-attributes font &optional frame
3334 This function returns a list of face attributes corresponding to
3335 @var{font}. The optional argument @var{frame} specifies the frame on
3336 which the font is to be displayed. If it is @code{nil}, the selected
3337 frame is used. The return value has the form
3340 (:family @var{family} :height @var{height} :weight @var{weight}
3341 :slant @var{slant} :width @var{width})
3344 where the values of @var{family}, @var{height}, @var{weight},
3345 @var{slant}, and @var{width} are face attribute values. Some of these
3346 key-attribute pairs may be omitted from the list if they are not
3347 specified by @var{font}.
3350 @defun font-xlfd-name font &optional fold-wildcards
3351 This function returns the XLFD (X Logical Font Descriptor), a string,
3352 matching @var{font}. @xref{Fonts,,, emacs, The GNU Emacs Manual}, for
3353 information about XLFDs. If the name is too long for an XLFD (which
3354 can contain at most 255 characters), the function returns @code{nil}.
3356 If the optional argument @var{fold-wildcards} is non-@code{nil},
3357 consecutive wildcards in the XLFD are folded into one.
3364 On graphical displays, Emacs draws @dfn{fringes} next to each
3365 window: thin vertical strips down the sides which can display bitmaps
3366 indicating truncation, continuation, horizontal scrolling, and so on.
3369 * Fringe Size/Pos:: Specifying where to put the window fringes.
3370 * Fringe Indicators:: Displaying indicator icons in the window fringes.
3371 * Fringe Cursors:: Displaying cursors in the right fringe.
3372 * Fringe Bitmaps:: Specifying bitmaps for fringe indicators.
3373 * Customizing Bitmaps:: Specifying your own bitmaps to use in the fringes.
3374 * Overlay Arrow:: Display of an arrow to indicate position.
3377 @node Fringe Size/Pos
3378 @subsection Fringe Size and Position
3380 The following buffer-local variables control the position and width
3381 of fringes in windows showing that buffer.
3383 @defvar fringes-outside-margins
3384 The fringes normally appear between the display margins and the window
3385 text. If the value is non-@code{nil}, they appear outside the display
3386 margins. @xref{Display Margins}.
3389 @defvar left-fringe-width
3390 This variable, if non-@code{nil}, specifies the width of the left
3391 fringe in pixels. A value of @code{nil} means to use the left fringe
3392 width from the window's frame.
3395 @defvar right-fringe-width
3396 This variable, if non-@code{nil}, specifies the width of the right
3397 fringe in pixels. A value of @code{nil} means to use the right fringe
3398 width from the window's frame.
3401 Any buffer which does not specify values for these variables uses
3402 the values specified by the @code{left-fringe} and @code{right-fringe}
3403 frame parameters (@pxref{Layout Parameters}).
3405 The above variables actually take effect via the function
3406 @code{set-window-buffer} (@pxref{Buffers and Windows}), which calls
3407 @code{set-window-fringes} as a subroutine. If you change one of these
3408 variables, the fringe display is not updated in existing windows
3409 showing the buffer, unless you call @code{set-window-buffer} again in
3410 each affected window. You can also use @code{set-window-fringes} to
3411 control the fringe display in individual windows.
3413 @defun set-window-fringes window left &optional right outside-margins
3414 This function sets the fringe widths of window @var{window}.
3415 If @var{window} is @code{nil}, the selected window is used.
3417 The argument @var{left} specifies the width in pixels of the left
3418 fringe, and likewise @var{right} for the right fringe. A value of
3419 @code{nil} for either one stands for the default width. If
3420 @var{outside-margins} is non-@code{nil}, that specifies that fringes
3421 should appear outside of the display margins.
3424 @defun window-fringes &optional window
3425 This function returns information about the fringes of a window
3426 @var{window}. If @var{window} is omitted or @code{nil}, the selected
3427 window is used. The value has the form @code{(@var{left-width}
3428 @var{right-width} @var{outside-margins})}.
3432 @node Fringe Indicators
3433 @subsection Fringe Indicators
3434 @cindex fringe indicators
3435 @cindex indicators, fringe
3437 @dfn{Fringe indicators} are tiny icons displayed in the window
3438 fringe to indicate truncated or continued lines, buffer boundaries,
3441 @defopt indicate-empty-lines
3442 @cindex fringes, and empty line indication
3443 @cindex empty lines, indicating
3444 When this is non-@code{nil}, Emacs displays a special glyph in the
3445 fringe of each empty line at the end of the buffer, on graphical
3446 displays. @xref{Fringes}. This variable is automatically
3447 buffer-local in every buffer.
3450 @defopt indicate-buffer-boundaries
3451 @cindex buffer boundaries, indicating
3452 This buffer-local variable controls how the buffer boundaries and
3453 window scrolling are indicated in the window fringes.
3455 Emacs can indicate the buffer boundaries---that is, the first and last
3456 line in the buffer---with angle icons when they appear on the screen.
3457 In addition, Emacs can display an up-arrow in the fringe to show
3458 that there is text above the screen, and a down-arrow to show
3459 there is text below the screen.
3461 There are three kinds of basic values:
3465 Don't display any of these fringe icons.
3467 Display the angle icons and arrows in the left fringe.
3469 Display the angle icons and arrows in the right fringe.
3471 Display the angle icons in the left fringe
3472 and don't display the arrows.
3475 Otherwise the value should be an alist that specifies which fringe
3476 indicators to display and where. Each element of the alist should
3477 have the form @code{(@var{indicator} . @var{position})}. Here,
3478 @var{indicator} is one of @code{top}, @code{bottom}, @code{up},
3479 @code{down}, and @code{t} (which covers all the icons not yet
3480 specified), while @var{position} is one of @code{left}, @code{right}
3483 For example, @code{((top . left) (t . right))} places the top angle
3484 bitmap in left fringe, and the bottom angle bitmap as well as both
3485 arrow bitmaps in right fringe. To show the angle bitmaps in the left
3486 fringe, and no arrow bitmaps, use @code{((top . left) (bottom . left))}.
3489 @defvar fringe-indicator-alist
3490 This buffer-local variable specifies the mapping from logical fringe
3491 indicators to the actual bitmaps displayed in the window fringes. The
3492 value is an alist of elements @code{(@var{indicator}
3493 . @var{bitmaps})}, where @var{indicator} specifies a logical indicator
3494 type and @var{bitmaps} specifies the fringe bitmaps to use for that
3497 Each @var{indicator} should be one of the following symbols:
3500 @item @code{truncation}, @code{continuation}.
3501 Used for truncation and continuation lines.
3503 @item @code{up}, @code{down}, @code{top}, @code{bottom}, @code{top-bottom}
3504 Used when @code{indicate-buffer-boundaries} is non-@code{nil}:
3505 @code{up} and @code{down} indicate a buffer boundary lying above or
3506 below the window edge; @code{top} and @code{bottom} indicate the
3507 topmost and bottommost buffer text line; and @code{top-bottom}
3508 indicates where there is just one line of text in the buffer.
3510 @item @code{empty-line}
3511 Used to indicate empty lines when @code{indicate-empty-lines} is
3514 @item @code{overlay-arrow}
3515 Used for overlay arrows (@pxref{Overlay Arrow}).
3516 @c Is this used anywhere?
3517 @c @item Unknown bitmap indicator:
3521 Each @var{bitmaps} value may be a list of symbols @code{(@var{left}
3522 @var{right} [@var{left1} @var{right1}])}. The @var{left} and
3523 @var{right} symbols specify the bitmaps shown in the left and/or right
3524 fringe, for the specific indicator. @var{left1} and @var{right1} are
3525 specific to the @code{bottom} and @code{top-bottom} indicators, and
3526 are used to indicate that the last text line has no final newline.
3527 Alternatively, @var{bitmaps} may be a single symbol which is used in
3528 both left and right fringes.
3530 @xref{Fringe Bitmaps}, for a list of standard bitmap symbols and how
3531 to define your own. In addition, @code{nil} represents the empty
3532 bitmap (i.e., an indicator that is not shown).
3534 When @code{fringe-indicator-alist} has a buffer-local value, and
3535 there is no bitmap defined for a logical indicator, or the bitmap is
3536 @code{t}, the corresponding value from the default value of
3537 @code{fringe-indicator-alist} is used.
3540 @node Fringe Cursors
3541 @subsection Fringe Cursors
3542 @cindex fringe cursors
3543 @cindex cursor, fringe
3545 When a line is exactly as wide as the window, Emacs displays the
3546 cursor in the right fringe instead of using two lines. Different
3547 bitmaps are used to represent the cursor in the fringe depending on
3548 the current buffer's cursor type.
3550 @defopt overflow-newline-into-fringe
3551 If this is non-@code{nil}, lines exactly as wide as the window (not
3552 counting the final newline character) are not continued. Instead,
3553 when point is at the end of the line, the cursor appears in the right
3557 @defvar fringe-cursor-alist
3558 This variable specifies the mapping from logical cursor type to the
3559 actual fringe bitmaps displayed in the right fringe. The value is an
3560 alist where each element has the form @code{(@var{cursor-type}
3561 . @var{bitmap})}, which means to use the fringe bitmap @var{bitmap} to
3562 display cursors of type @var{cursor-type}.
3564 Each @var{cursor-type} should be one of @code{box}, @code{hollow},
3565 @code{bar}, @code{hbar}, or @code{hollow-small}. The first four have
3566 the same meanings as in the @code{cursor-type} frame parameter
3567 (@pxref{Cursor Parameters}). The @code{hollow-small} type is used
3568 instead of @code{hollow} when the normal @code{hollow-rectangle}
3569 bitmap is too tall to fit on a specific display line.
3571 Each @var{bitmap} should be a symbol specifying the fringe bitmap to
3572 be displayed for that logical cursor type.
3574 See the next subsection for details.
3577 @xref{Fringe Bitmaps}.
3580 @c FIXME: I can't find the ‘fringes-indicator-alist’ variable. Maybe
3581 @c it should be ‘fringe-indicator-alist’ or ‘fringe-cursor-alist’? --xfq
3582 When @code{fringe-cursor-alist} has a buffer-local value, and there is
3583 no bitmap defined for a cursor type, the corresponding value from the
3584 default value of @code{fringes-indicator-alist} is used.
3587 @node Fringe Bitmaps
3588 @subsection Fringe Bitmaps
3589 @cindex fringe bitmaps
3590 @cindex bitmaps, fringe
3592 The @dfn{fringe bitmaps} are the actual bitmaps which represent the
3593 logical fringe indicators for truncated or continued lines, buffer
3594 boundaries, overlay arrows, etc. Each bitmap is represented by a
3597 These symbols are referred to by the variables
3598 @code{fringe-indicator-alist} and @code{fringe-cursor-alist},
3599 described in the previous subsections.
3602 These symbols are referred to by the variable
3603 @code{fringe-indicator-alist}, which maps fringe indicators to bitmaps
3604 (@pxref{Fringe Indicators}), and the variable
3605 @code{fringe-cursor-alist}, which maps fringe cursors to bitmaps
3606 (@pxref{Fringe Cursors}).
3609 Lisp programs can also directly display a bitmap in the left or
3610 right fringe, by using a @code{display} property for one of the
3611 characters appearing in the line (@pxref{Other Display Specs}). Such
3612 a display specification has the form
3615 (@var{fringe} @var{bitmap} [@var{face}])
3619 @var{fringe} is either the symbol @code{left-fringe} or
3620 @code{right-fringe}. @var{bitmap} is a symbol identifying the bitmap
3621 to display. The optional @var{face} names a face whose foreground
3622 color is used to display the bitmap; this face is automatically merged
3623 with the @code{fringe} face.
3625 Here is a list of the standard fringe bitmaps defined in Emacs, and
3626 how they are currently used in Emacs (via
3627 @code{fringe-indicator-alist} and @code{fringe-cursor-alist}):
3630 @item @code{left-arrow}, @code{right-arrow}
3631 Used to indicate truncated lines.
3633 @item @code{left-curly-arrow}, @code{right-curly-arrow}
3634 Used to indicate continued lines.
3636 @item @code{right-triangle}, @code{left-triangle}
3637 The former is used by overlay arrows. The latter is unused.
3639 @item @code{up-arrow}, @code{down-arrow}, @code{top-left-angle} @code{top-right-angle}
3640 @itemx @code{bottom-left-angle}, @code{bottom-right-angle}
3641 @itemx @code{top-right-angle}, @code{top-left-angle}
3642 @itemx @code{left-bracket}, @code{right-bracket}, @code{top-right-angle}, @code{top-left-angle}
3643 Used to indicate buffer boundaries.
3645 @item @code{filled-rectangle}, @code{hollow-rectangle}
3646 @itemx @code{filled-square}, @code{hollow-square}
3647 @itemx @code{vertical-bar}, @code{horizontal-bar}
3648 Used for different types of fringe cursors.
3650 @item @code{empty-line}, @code{exclamation-mark}, @code{question-mark}, @code{exclamation-mark}
3651 Not used by core Emacs features.
3655 The next subsection describes how to define your own fringe bitmaps.
3657 @defun fringe-bitmaps-at-pos &optional pos window
3658 This function returns the fringe bitmaps of the display line
3659 containing position @var{pos} in window @var{window}. The return
3660 value has the form @code{(@var{left} @var{right} @var{ov})}, where @var{left}
3661 is the symbol for the fringe bitmap in the left fringe (or @code{nil}
3662 if no bitmap), @var{right} is similar for the right fringe, and @var{ov}
3663 is non-@code{nil} if there is an overlay arrow in the left fringe.
3665 The value is @code{nil} if @var{pos} is not visible in @var{window}.
3666 If @var{window} is @code{nil}, that stands for the selected window.
3667 If @var{pos} is @code{nil}, that stands for the value of point in
3671 @node Customizing Bitmaps
3672 @subsection Customizing Fringe Bitmaps
3673 @cindex fringe bitmaps, customizing
3675 @defun define-fringe-bitmap bitmap bits &optional height width align
3676 This function defines the symbol @var{bitmap} as a new fringe bitmap,
3677 or replaces an existing bitmap with that name.
3679 The argument @var{bits} specifies the image to use. It should be
3680 either a string or a vector of integers, where each element (an
3681 integer) corresponds to one row of the bitmap. Each bit of an integer
3682 corresponds to one pixel of the bitmap, where the low bit corresponds
3683 to the rightmost pixel of the bitmap.
3685 The height is normally the length of @var{bits}. However, you
3686 can specify a different height with non-@code{nil} @var{height}. The width
3687 is normally 8, but you can specify a different width with non-@code{nil}
3688 @var{width}. The width must be an integer between 1 and 16.
3690 The argument @var{align} specifies the positioning of the bitmap
3691 relative to the range of rows where it is used; the default is to
3692 center the bitmap. The allowed values are @code{top}, @code{center},
3695 The @var{align} argument may also be a list @code{(@var{align}
3696 @var{periodic})} where @var{align} is interpreted as described above.
3697 If @var{periodic} is non-@code{nil}, it specifies that the rows in
3698 @code{bits} should be repeated enough times to reach the specified
3702 @defun destroy-fringe-bitmap bitmap
3703 This function destroy the fringe bitmap identified by @var{bitmap}.
3704 If @var{bitmap} identifies a standard fringe bitmap, it actually
3705 restores the standard definition of that bitmap, instead of
3706 eliminating it entirely.
3709 @defun set-fringe-bitmap-face bitmap &optional face
3710 This sets the face for the fringe bitmap @var{bitmap} to @var{face}.
3711 If @var{face} is @code{nil}, it selects the @code{fringe} face. The
3712 bitmap's face controls the color to draw it in.
3714 @var{face} is merged with the @code{fringe} face, so normally
3715 @var{face} should specify only the foreground color.
3719 @subsection The Overlay Arrow
3720 @c @cindex overlay arrow Duplicates variable names
3722 The @dfn{overlay arrow} is useful for directing the user's attention
3723 to a particular line in a buffer. For example, in the modes used for
3724 interface to debuggers, the overlay arrow indicates the line of code
3725 about to be executed. This feature has nothing to do with
3726 @dfn{overlays} (@pxref{Overlays}).
3728 @defvar overlay-arrow-string
3729 This variable holds the string to display to call attention to a
3730 particular line, or @code{nil} if the arrow feature is not in use.
3731 On a graphical display the contents of the string are ignored; instead a
3732 glyph is displayed in the fringe area to the left of the display area.
3735 @defvar overlay-arrow-position
3736 This variable holds a marker that indicates where to display the overlay
3737 arrow. It should point at the beginning of a line. On a non-graphical
3738 display the arrow text
3739 appears at the beginning of that line, overlaying any text that would
3740 otherwise appear. Since the arrow is usually short, and the line
3741 usually begins with indentation, normally nothing significant is
3744 The overlay-arrow string is displayed in any given buffer if the value
3745 of @code{overlay-arrow-position} in that buffer points into that
3746 buffer. Thus, it is possible to display multiple overlay arrow strings
3747 by creating buffer-local bindings of @code{overlay-arrow-position}.
3748 However, it is usually cleaner to use
3749 @code{overlay-arrow-variable-list} to achieve this result.
3750 @c !!! overlay-arrow-position: but the overlay string may remain in the display
3751 @c of some other buffer until an update is required. This should be fixed
3755 You can do a similar job by creating an overlay with a
3756 @code{before-string} property. @xref{Overlay Properties}.
3758 You can define multiple overlay arrows via the variable
3759 @code{overlay-arrow-variable-list}.
3761 @defvar overlay-arrow-variable-list
3762 This variable's value is a list of variables, each of which specifies
3763 the position of an overlay arrow. The variable
3764 @code{overlay-arrow-position} has its normal meaning because it is on
3768 Each variable on this list can have properties
3769 @code{overlay-arrow-string} and @code{overlay-arrow-bitmap} that
3770 specify an overlay arrow string (for text terminals) or fringe bitmap
3771 (for graphical terminals) to display at the corresponding overlay
3772 arrow position. If either property is not set, the default
3773 @code{overlay-arrow-string} or @code{overlay-arrow} fringe indicator
3777 @section Scroll Bars
3780 Normally the frame parameter @code{vertical-scroll-bars} controls
3781 whether the windows in the frame have vertical scroll bars, and
3782 whether they are on the left or right. The frame parameter
3783 @code{scroll-bar-width} specifies how wide they are (@code{nil}
3784 meaning the default). @xref{Layout Parameters}.
3786 @defun frame-current-scroll-bars &optional frame
3787 This function reports the scroll bar type settings for frame
3788 @var{frame}. The value is a cons cell
3789 @code{(@var{vertical-type} .@: @var{horizontal-type})}, where
3790 @var{vertical-type} is either @code{left}, @code{right}, or @code{nil}
3791 (which means no scroll bar.) @var{horizontal-type} is meant to
3792 specify the horizontal scroll bar type, but since they are not
3793 implemented, it is always @code{nil}.
3796 @vindex vertical-scroll-bar
3797 You can enable or disable scroll bars for a particular buffer,
3798 by setting the variable @code{vertical-scroll-bar}. This variable
3799 automatically becomes buffer-local when set. The possible values are
3800 @code{left}, @code{right}, @code{t}, which means to use the
3801 frame's default, and @code{nil} for no scroll bar.
3803 You can also control this for individual windows. Call the function
3804 @code{set-window-scroll-bars} to specify what to do for a specific window:
3806 @defun set-window-scroll-bars window width &optional vertical-type horizontal-type
3807 This function sets the width and type of scroll bars for window
3810 @var{width} specifies the scroll bar width in pixels (@code{nil} means
3811 use the width specified for the frame). @var{vertical-type} specifies
3812 whether to have a vertical scroll bar and, if so, where. The possible
3813 values are @code{left}, @code{right} and @code{nil}, just like the
3814 values of the @code{vertical-scroll-bars} frame parameter.
3816 The argument @var{horizontal-type} is meant to specify whether and
3817 where to have horizontal scroll bars, but since they are not
3818 implemented, it has no effect. If @var{window} is @code{nil}, the
3819 selected window is used.
3822 @defun window-scroll-bars &optional window
3823 Report the width and type of scroll bars specified for @var{window}.
3824 If @var{window} is omitted or @code{nil}, the selected window is used.
3825 The value is a list of the form @code{(@var{width}
3826 @var{cols} @var{vertical-type} @var{horizontal-type})}. The value
3827 @var{width} is the value that was specified for the width (which may
3828 be @code{nil}); @var{cols} is the number of columns that the scroll
3829 bar actually occupies.
3831 @var{horizontal-type} is not actually meaningful.
3834 If you don't specify these values for a window with
3835 @code{set-window-scroll-bars}, the buffer-local variables
3836 @code{scroll-bar-mode} and @code{scroll-bar-width} in the buffer being
3837 displayed control the window's vertical scroll bars. The function
3838 @code{set-window-buffer} examines these variables. If you change them
3839 in a buffer that is already visible in a window, you can make the
3840 window take note of the new values by calling @code{set-window-buffer}
3841 specifying the same buffer that is already displayed.
3843 @defopt scroll-bar-mode
3844 This variable, always local in all buffers, controls whether and where
3845 to put scroll bars in windows displaying the buffer. The possible values
3846 are @code{nil} for no scroll bar, @code{left} to put a scroll bar on
3847 the left, and @code{right} to put a scroll bar on the right.
3850 @defun window-current-scroll-bars &optional window
3851 This function reports the scroll bar type for window @var{window}.
3852 If @var{window} is omitted or @code{nil}, the selected window is used.
3853 The value is a cons cell
3854 @code{(@var{vertical-type} .@: @var{horizontal-type})}. Unlike
3855 @code{window-scroll-bars}, this reports the scroll bar type actually
3856 used, once frame defaults and @code{scroll-bar-mode} are taken into
3860 @defvar scroll-bar-width
3861 This variable, always local in all buffers, specifies the width of the
3862 buffer's scroll bars, measured in pixels. A value of @code{nil} means
3863 to use the value specified by the frame.
3866 @node Display Property
3867 @section The @code{display} Property
3868 @cindex display specification
3869 @kindex display @r{(text property)}
3871 The @code{display} text property (or overlay property) is used to
3872 insert images into text, and to control other aspects of how text
3873 displays. The value of the @code{display} property should be a
3874 display specification, or a list or vector containing several display
3875 specifications. Display specifications in the same @code{display}
3876 property value generally apply in parallel to the text they cover.
3878 If several sources (overlays and/or a text property) specify values
3879 for the @code{display} property, only one of the values takes effect,
3880 following the rules of @code{get-char-property}. @xref{Examining
3883 The rest of this section describes several kinds of
3884 display specifications and what they mean.
3887 * Replacing Specs:: Display specs that replace the text.
3888 * Specified Space:: Displaying one space with a specified width.
3889 * Pixel Specification:: Specifying space width or height in pixels.
3890 * Other Display Specs:: Displaying an image; adjusting the height,
3891 spacing, and other properties of text.
3892 * Display Margins:: Displaying text or images to the side of the main text.
3895 @node Replacing Specs
3896 @subsection Display Specs That Replace The Text
3898 Some kinds of display specifications specify something to display
3899 instead of the text that has the property. These are called
3900 @dfn{replacing} display specifications. Emacs does not allow the user
3901 to interactively move point into the middle of buffer text that is
3902 replaced in this way.
3904 If a list of display specifications includes more than one replacing
3905 display specification, the first overrides the rest. Replacing
3906 display specifications make most other display specifications
3907 irrelevant, since those don't apply to the replacement.
3909 For replacing display specifications, ``the text that has the
3910 property'' means all the consecutive characters that have the same
3911 Lisp object as their @code{display} property; these characters are
3912 replaced as a single unit. If two characters have different Lisp
3913 objects as their @code{display} properties (i.e., objects which are
3914 not @code{eq}), they are handled separately.
3916 Here is an example which illustrates this point. A string serves as
3917 a replacing display specification, which replaces the text that has
3918 the property with the specified string (@pxref{Other Display Specs}).
3919 Consider the following function:
3924 (let ((string (concat "A"))
3925 (start (+ i i (point-min))))
3926 (put-text-property start (1+ start) 'display string)
3927 (put-text-property start (+ 2 start) 'display string))))
3931 This function gives each of the first ten characters in the buffer a
3932 @code{display} property which is a string @code{"A"}, but they don't
3933 all get the same string object. The first two characters get the same
3934 string object, so they are replaced with one @samp{A}; the fact that
3935 the display property was assigned in two separate calls to
3936 @code{put-text-property} is irrelevant. Similarly, the next two
3937 characters get a second string (@code{concat} creates a new string
3938 object), so they are replaced with one @samp{A}; and so on. Thus, the
3939 ten characters appear as five A's.
3941 @node Specified Space
3942 @subsection Specified Spaces
3943 @cindex spaces, specified height or width
3944 @cindex variable-width spaces
3946 To display a space of specified width and/or height, use a display
3947 specification of the form @code{(space . @var{props})}, where
3948 @var{props} is a property list (a list of alternating properties and
3949 values). You can put this property on one or more consecutive
3950 characters; a space of the specified height and width is displayed in
3951 place of @emph{all} of those characters. These are the properties you
3952 can use in @var{props} to specify the weight of the space:
3955 @item :width @var{width}
3956 If @var{width} is an integer or floating point number, it specifies
3957 that the space width should be @var{width} times the normal character
3958 width. @var{width} can also be a @dfn{pixel width} specification
3959 (@pxref{Pixel Specification}).
3961 @item :relative-width @var{factor}
3962 Specifies that the width of the stretch should be computed from the
3963 first character in the group of consecutive characters that have the
3964 same @code{display} property. The space width is the width of that
3965 character, multiplied by @var{factor}.
3967 @item :align-to @var{hpos}
3968 Specifies that the space should be wide enough to reach @var{hpos}.
3969 If @var{hpos} is a number, it is measured in units of the normal
3970 character width. @var{hpos} can also be a @dfn{pixel width}
3971 specification (@pxref{Pixel Specification}).
3974 You should use one and only one of the above properties. You can
3975 also specify the height of the space, with these properties:
3978 @item :height @var{height}
3979 Specifies the height of the space.
3980 If @var{height} is an integer or floating point number, it specifies
3981 that the space height should be @var{height} times the normal character
3982 height. The @var{height} may also be a @dfn{pixel height} specification
3983 (@pxref{Pixel Specification}).
3985 @item :relative-height @var{factor}
3986 Specifies the height of the space, multiplying the ordinary height
3987 of the text having this display specification by @var{factor}.
3989 @item :ascent @var{ascent}
3990 If the value of @var{ascent} is a non-negative number no greater than
3991 100, it specifies that @var{ascent} percent of the height of the space
3992 should be considered as the ascent of the space---that is, the part
3993 above the baseline. The ascent may also be specified in pixel units
3994 with a @dfn{pixel ascent} specification (@pxref{Pixel Specification}).
3998 Don't use both @code{:height} and @code{:relative-height} together.
4000 The @code{:width} and @code{:align-to} properties are supported on
4001 non-graphic terminals, but the other space properties in this section
4004 Note that space properties are treated as paragraph separators for
4005 the purposes of reordering bidirectional text for display.
4006 @xref{Bidirectional Display}, for the details.
4008 @node Pixel Specification
4009 @subsection Pixel Specification for Spaces
4010 @cindex spaces, pixel specification
4012 The value of the @code{:width}, @code{:align-to}, @code{:height},
4013 and @code{:ascent} properties can be a special kind of expression that
4014 is evaluated during redisplay. The result of the evaluation is used
4015 as an absolute number of pixels.
4017 The following expressions are supported:
4021 @var{expr} ::= @var{num} | (@var{num}) | @var{unit} | @var{elem} | @var{pos} | @var{image} | @var{form}
4022 @var{num} ::= @var{integer} | @var{float} | @var{symbol}
4023 @var{unit} ::= in | mm | cm | width | height
4026 @var{elem} ::= left-fringe | right-fringe | left-margin | right-margin
4028 @var{pos} ::= left | center | right
4029 @var{form} ::= (@var{num} . @var{expr}) | (@var{op} @var{expr} ...)
4034 The form @var{num} specifies a fraction of the default frame font
4035 height or width. The form @code{(@var{num})} specifies an absolute
4036 number of pixels. If @var{num} is a symbol, @var{symbol}, its
4037 buffer-local variable binding is used.
4039 The @code{in}, @code{mm}, and @code{cm} units specify the number of
4040 pixels per inch, millimeter, and centimeter, respectively. The
4041 @code{width} and @code{height} units correspond to the default width
4042 and height of the current face. An image specification @code{image}
4043 corresponds to the width or height of the image.
4045 The elements @code{left-fringe}, @code{right-fringe},
4046 @code{left-margin}, @code{right-margin}, @code{scroll-bar}, and
4047 @code{text} specify to the width of the corresponding area of the
4050 The @code{left}, @code{center}, and @code{right} positions can be
4051 used with @code{:align-to} to specify a position relative to the left
4052 edge, center, or right edge of the text area.
4054 Any of the above window elements (except @code{text}) can also be
4055 used with @code{:align-to} to specify that the position is relative to
4056 the left edge of the given area. Once the base offset for a relative
4057 position has been set (by the first occurrence of one of these
4058 symbols), further occurrences of these symbols are interpreted as the
4059 width of the specified area. For example, to align to the center of
4060 the left-margin, use
4063 :align-to (+ left-margin (0.5 . left-margin))
4066 If no specific base offset is set for alignment, it is always relative
4067 to the left edge of the text area. For example, @samp{:align-to 0} in a
4068 header-line aligns with the first text column in the text area.
4070 A value of the form @code{(@var{num} . @var{expr})} stands for the
4071 product of the values of @var{num} and @var{expr}. For example,
4072 @code{(2 . in)} specifies a width of 2 inches, while @code{(0.5 .
4073 @var{image})} specifies half the width (or height) of the specified
4076 The form @code{(+ @var{expr} ...)} adds up the value of the
4077 expressions. The form @code{(- @var{expr} ...)} negates or subtracts
4078 the value of the expressions.
4080 @node Other Display Specs
4081 @subsection Other Display Specifications
4083 Here are the other sorts of display specifications that you can use
4084 in the @code{display} text property.
4088 Display @var{string} instead of the text that has this property.
4090 Recursive display specifications are not supported---@var{string}'s
4091 @code{display} properties, if any, are not used.
4093 @item (image . @var{image-props})
4094 This kind of display specification is an image descriptor (@pxref{Images}).
4095 When used as a display specification, it means to display the image
4096 instead of the text that has the display specification.
4098 @item (slice @var{x} @var{y} @var{width} @var{height})
4099 This specification together with @code{image} specifies a @dfn{slice}
4100 (a partial area) of the image to display. The elements @var{y} and
4101 @var{x} specify the top left corner of the slice, within the image;
4102 @var{width} and @var{height} specify the width and height of the
4103 slice. Integer values are numbers of pixels. A floating point number
4104 in the range 0.0--1.0 stands for that fraction of the width or height
4105 of the entire image.
4107 @item ((margin nil) @var{string})
4108 A display specification of this form means to display @var{string}
4109 instead of the text that has the display specification, at the same
4110 position as that text. It is equivalent to using just @var{string},
4111 but it is done as a special case of marginal display (@pxref{Display
4114 @item (left-fringe @var{bitmap} @r{[}@var{face}@r{]})
4115 @itemx (right-fringe @var{bitmap} @r{[}@var{face}@r{]})
4116 This display specification on any character of a line of text causes
4117 the specified @var{bitmap} be displayed in the left or right fringes
4118 for that line, instead of the characters that have the display
4119 specification. The optional @var{face} specifies the colors to be
4120 used for the bitmap. @xref{Fringe Bitmaps}, for the details.
4122 @item (space-width @var{factor})
4123 This display specification affects all the space characters within the
4124 text that has the specification. It displays all of these spaces
4125 @var{factor} times as wide as normal. The element @var{factor} should
4126 be an integer or float. Characters other than spaces are not affected
4127 at all; in particular, this has no effect on tab characters.
4129 @item (height @var{height})
4130 This display specification makes the text taller or shorter.
4131 Here are the possibilities for @var{height}:
4134 @item @code{(+ @var{n})}
4135 @c FIXME: Add an index for "step"? --xfq
4136 This means to use a font that is @var{n} steps larger. A ``step'' is
4137 defined by the set of available fonts---specifically, those that match
4138 what was otherwise specified for this text, in all attributes except
4139 height. Each size for which a suitable font is available counts as
4140 another step. @var{n} should be an integer.
4142 @item @code{(- @var{n})}
4143 This means to use a font that is @var{n} steps smaller.
4145 @item a number, @var{factor}
4146 A number, @var{factor}, means to use a font that is @var{factor} times
4147 as tall as the default font.
4149 @item a symbol, @var{function}
4150 A symbol is a function to compute the height. It is called with the
4151 current height as argument, and should return the new height to use.
4153 @item anything else, @var{form}
4154 If the @var{height} value doesn't fit the previous possibilities, it is
4155 a form. Emacs evaluates it to get the new height, with the symbol
4156 @code{height} bound to the current specified font height.
4159 @item (raise @var{factor})
4160 This kind of display specification raises or lowers the text
4161 it applies to, relative to the baseline of the line.
4163 @var{factor} must be a number, which is interpreted as a multiple of the
4164 height of the affected text. If it is positive, that means to display
4165 the characters raised. If it is negative, that means to display them
4168 If the text also has a @code{height} display specification, that does
4169 not affect the amount of raising or lowering, which is based on the
4170 faces used for the text.
4173 @c We put all the `@code{(when ...)}' on one line to encourage
4174 @c makeinfo's end-of-sentence heuristics to DTRT. Previously, the dot
4175 @c was at eol; the info file ended up w/ two spaces rendered after it.
4176 You can make any display specification conditional. To do that,
4177 package it in another list of the form
4178 @code{(when @var{condition} . @var{spec})}.
4179 Then the specification @var{spec} applies only when
4180 @var{condition} evaluates to a non-@code{nil} value. During the
4181 evaluation, @code{object} is bound to the string or buffer having the
4182 conditional @code{display} property. @code{position} and
4183 @code{buffer-position} are bound to the position within @code{object}
4184 and the buffer position where the @code{display} property was found,
4185 respectively. Both positions can be different when @code{object} is a
4188 @node Display Margins
4189 @subsection Displaying in the Margins
4190 @cindex display margins
4191 @cindex margins, display
4193 A buffer can have blank areas called @dfn{display margins} on the
4194 left and on the right. Ordinary text never appears in these areas,
4195 but you can put things into the display margins using the
4196 @code{display} property. There is currently no way to make text or
4197 images in the margin mouse-sensitive.
4199 The way to display something in the margins is to specify it in a
4200 margin display specification in the @code{display} property of some
4201 text. This is a replacing display specification, meaning that the
4202 text you put it on does not get displayed; the margin display appears,
4203 but that text does not.
4205 A margin display specification looks like @code{((margin
4206 right-margin) @var{spec})} or @code{((margin left-margin) @var{spec})}.
4207 Here, @var{spec} is another display specification that says what to
4208 display in the margin. Typically it is a string of text to display,
4209 or an image descriptor.
4211 To display something in the margin @emph{in association with}
4212 certain buffer text, without altering or preventing the display of
4213 that text, put a @code{before-string} property on the text and put the
4214 margin display specification on the contents of the before-string.
4216 Before the display margins can display anything, you must give
4217 them a nonzero width. The usual way to do that is to set these
4220 @defvar left-margin-width
4221 This variable specifies the width of the left margin, in character
4222 cell (a.k.a.@: ``column'') units. It is buffer-local in all buffers.
4223 A value of @code{nil} means no left marginal area.
4226 @defvar right-margin-width
4227 This variable specifies the width of the right margin, in character
4228 cell units. It is buffer-local in all buffers. A value of @code{nil}
4229 means no right marginal area.
4232 Setting these variables does not immediately affect the window. These
4233 variables are checked when a new buffer is displayed in the window.
4234 Thus, you can make changes take effect by calling
4235 @code{set-window-buffer}.
4237 You can also set the margin widths immediately.
4239 @defun set-window-margins window left &optional right
4240 This function specifies the margin widths for window @var{window}, in
4241 character cell units. The argument @var{left} controls the left
4242 margin, and @var{right} controls the right margin (default @code{0}).
4245 @defun window-margins &optional window
4246 This function returns the width of the left and right margins of
4247 @var{window} as a cons cell of the form @w{@code{(@var{left}
4248 . @var{right})}}. If one of the two marginal areas does not exist,
4249 its width is returned as @code{nil}; if neither of the two margins exist,
4250 the function returns @code{(nil)}. If @var{window} is @code{nil}, the
4251 selected window is used.
4256 @cindex images in buffers
4258 To display an image in an Emacs buffer, you must first create an image
4259 descriptor, then use it as a display specifier in the @code{display}
4260 property of text that is displayed (@pxref{Display Property}).
4262 Emacs is usually able to display images when it is run on a
4263 graphical terminal. Images cannot be displayed in a text terminal, on
4264 certain graphical terminals that lack the support for this, or if
4265 Emacs is compiled without image support. You can use the function
4266 @code{display-images-p} to determine if images can in principle be
4267 displayed (@pxref{Display Feature Testing}).
4270 * Image Formats:: Supported image formats.
4271 * Image Descriptors:: How to specify an image for use in @code{:display}.
4272 * XBM Images:: Special features for XBM format.
4273 * XPM Images:: Special features for XPM format.
4274 * PostScript Images:: Special features for PostScript format.
4275 * ImageMagick Images:: Special features available through ImageMagick.
4276 * Other Image Types:: Various other formats are supported.
4277 * Defining Images:: Convenient ways to define an image for later use.
4278 * Showing Images:: Convenient ways to display an image once it is defined.
4279 * Multi-Frame Images:: Some images contain more than one frame.
4280 * Image Cache:: Internal mechanisms of image display.
4284 @subsection Image Formats
4285 @cindex image formats
4288 Emacs can display a number of different image formats. Some of
4289 these image formats are supported only if particular support libraries
4290 are installed. On some platforms, Emacs can load support libraries on
4291 demand; if so, the variable @code{dynamic-library-alist} can be used
4292 to modify the set of known names for these dynamic libraries.
4293 @xref{Dynamic Libraries}.
4295 Supported image formats (and the required support libraries) include
4296 PBM and XBM (which do not depend on support libraries and are always
4297 available), XPM (@code{libXpm}), GIF (@code{libgif} or
4298 @code{libungif}), PostScript (@code{gs}), JPEG (@code{libjpeg}), TIFF
4299 (@code{libtiff}), PNG (@code{libpng}), and SVG (@code{librsvg}).
4301 Each of these image formats is associated with an @dfn{image type
4302 symbol}. The symbols for the above formats are, respectively,
4303 @code{pbm}, @code{xbm}, @code{xpm}, @code{gif}, @code{postscript},
4304 @code{jpeg}, @code{tiff}, @code{png}, and @code{svg}.
4306 Furthermore, if you build Emacs with ImageMagick
4307 (@code{libMagickWand}) support, Emacs can display any image format
4308 that ImageMagick can. @xref{ImageMagick Images}. All images
4309 displayed via ImageMagick have type symbol @code{imagemagick}.
4312 This variable contains a list of type symbols for image formats which
4313 are potentially supported in the current configuration.
4315 ``Potentially'' means that Emacs knows about the image types, not
4316 necessarily that they can be used (for example, they could depend on
4317 unavailable dynamic libraries). To know which image types are really
4318 available, use @code{image-type-available-p}.
4321 @defun image-type-available-p type
4322 This function returns non-@code{nil} if images of type @var{type} can
4323 be loaded and displayed. @var{type} must be an image type symbol.
4325 For image types whose support libraries are statically linked, this
4326 function always returns @code{t}. For image types whose support
4327 libraries are dynamically loaded, it returns @code{t} if the library
4328 could be loaded and @code{nil} otherwise.
4331 @node Image Descriptors
4332 @subsection Image Descriptors
4333 @cindex image descriptor
4335 An @dfn{image descriptor} is a list which specifies the underlying
4336 data for an image, and how to display it. It is typically used as the
4337 value of a @code{display} overlay or text property (@pxref{Other
4338 Display Specs}); but @xref{Showing Images}, for convenient helper
4339 functions to insert images into buffers.
4341 Each image descriptor has the form @code{(image . @var{props})},
4342 where @var{props} is a property list of alternating keyword symbols
4343 and values, including at least the pair @code{:type @var{TYPE}} which
4344 specifies the image type.
4346 The following is a list of properties that are meaningful for all
4347 image types (there are also properties which are meaningful only for
4348 certain image types, as documented in the following subsections):
4351 @item :type @var{type}
4354 @xref{Image Formats}.
4356 Every image descriptor must include this property.
4358 @item :file @var{file}
4359 This says to load the image from file @var{file}. If @var{file} is
4360 not an absolute file name, it is expanded in @code{data-directory}.
4362 @item :data @var{data}
4363 This specifies the raw image data. Each image descriptor must have
4364 either @code{:data} or @code{:file}, but not both.
4366 For most image types, the value of a @code{:data} property should be a
4367 string containing the image data. Some image types do not support
4368 @code{:data}; for some others, @code{:data} alone is not enough, so
4369 you need to use other image properties along with @code{:data}. See
4370 the following subsections for details.
4372 @item :margin @var{margin}
4373 This specifies how many pixels to add as an extra margin around the
4374 image. The value, @var{margin}, must be a non-negative number, or a
4375 pair @code{(@var{x} . @var{y})} of such numbers. If it is a pair,
4376 @var{x} specifies how many pixels to add horizontally, and @var{y}
4377 specifies how many pixels to add vertically. If @code{:margin} is not
4378 specified, the default is zero.
4380 @item :ascent @var{ascent}
4381 This specifies the amount of the image's height to use for its
4382 ascent---that is, the part above the baseline. The value,
4383 @var{ascent}, must be a number in the range 0 to 100, or the symbol
4386 If @var{ascent} is a number, that percentage of the image's height is
4387 used for its ascent.
4389 If @var{ascent} is @code{center}, the image is vertically centered
4390 around a centerline which would be the vertical centerline of text drawn
4391 at the position of the image, in the manner specified by the text
4392 properties and overlays that apply to the image.
4394 If this property is omitted, it defaults to 50.
4396 @item :relief @var{relief}
4397 This adds a shadow rectangle around the image. The value,
4398 @var{relief}, specifies the width of the shadow lines, in pixels. If
4399 @var{relief} is negative, shadows are drawn so that the image appears
4400 as a pressed button; otherwise, it appears as an unpressed button.
4402 @item :conversion @var{algorithm}
4403 This specifies a conversion algorithm that should be applied to the
4404 image before it is displayed; the value, @var{algorithm}, specifies
4410 Specifies the Laplace edge detection algorithm, which blurs out small
4411 differences in color while highlighting larger differences. People
4412 sometimes consider this useful for displaying the image for a
4413 ``disabled'' button.
4415 @item (edge-detection :matrix @var{matrix} :color-adjust @var{adjust})
4416 @cindex edge detection, images
4417 Specifies a general edge-detection algorithm. @var{matrix} must be
4418 either a nine-element list or a nine-element vector of numbers. A pixel
4419 at position @math{x/y} in the transformed image is computed from
4420 original pixels around that position. @var{matrix} specifies, for each
4421 pixel in the neighborhood of @math{x/y}, a factor with which that pixel
4422 will influence the transformed pixel; element @math{0} specifies the
4423 factor for the pixel at @math{x-1/y-1}, element @math{1} the factor for
4424 the pixel at @math{x/y-1} etc., as shown below:
4427 $$\pmatrix{x-1/y-1 & x/y-1 & x+1/y-1 \cr
4428 x-1/y & x/y & x+1/y \cr
4429 x-1/y+1& x/y+1 & x+1/y+1 \cr}$$
4434 (x-1/y-1 x/y-1 x+1/y-1
4436 x-1/y+1 x/y+1 x+1/y+1)
4440 The resulting pixel is computed from the color intensity of the color
4441 resulting from summing up the RGB values of surrounding pixels,
4442 multiplied by the specified factors, and dividing that sum by the sum
4443 of the factors' absolute values.
4445 Laplace edge-detection currently uses a matrix of
4448 $$\pmatrix{1 & 0 & 0 \cr
4461 Emboss edge-detection uses a matrix of
4464 $$\pmatrix{ 2 & -1 & 0 \cr
4478 Specifies transforming the image so that it looks ``disabled''.
4481 @item :mask @var{mask}
4482 If @var{mask} is @code{heuristic} or @code{(heuristic @var{bg})}, build
4483 a clipping mask for the image, so that the background of a frame is
4484 visible behind the image. If @var{bg} is not specified, or if @var{bg}
4485 is @code{t}, determine the background color of the image by looking at
4486 the four corners of the image, assuming the most frequently occurring
4487 color from the corners is the background color of the image. Otherwise,
4488 @var{bg} must be a list @code{(@var{red} @var{green} @var{blue})}
4489 specifying the color to assume for the background of the image.
4491 If @var{mask} is @code{nil}, remove a mask from the image, if it has
4492 one. Images in some formats include a mask which can be removed by
4493 specifying @code{:mask nil}.
4495 @item :pointer @var{shape}
4496 This specifies the pointer shape when the mouse pointer is over this
4497 image. @xref{Pointer Shape}, for available pointer shapes.
4499 @item :map @var{map}
4501 This associates an image map of @dfn{hot spots} with this image.
4503 An image map is an alist where each element has the format
4504 @code{(@var{area} @var{id} @var{plist})}. An @var{area} is specified
4505 as either a rectangle, a circle, or a polygon.
4507 A rectangle is a cons
4508 @code{(rect . ((@var{x0} . @var{y0}) . (@var{x1} . @var{y1})))}
4509 which specifies the pixel coordinates of the upper left and bottom right
4510 corners of the rectangle area.
4513 @code{(circle . ((@var{x0} . @var{y0}) . @var{r}))}
4514 which specifies the center and the radius of the circle; @var{r} may
4515 be a float or integer.
4518 @code{(poly . [@var{x0} @var{y0} @var{x1} @var{y1} ...])}
4519 where each pair in the vector describes one corner in the polygon.
4521 When the mouse pointer lies on a hot-spot area of an image, the
4522 @var{plist} of that hot-spot is consulted; if it contains a @code{help-echo}
4523 property, that defines a tool-tip for the hot-spot, and if it contains
4524 a @code{pointer} property, that defines the shape of the mouse cursor when
4525 it is on the hot-spot.
4526 @xref{Pointer Shape}, for available pointer shapes.
4528 When you click the mouse when the mouse pointer is over a hot-spot, an
4529 event is composed by combining the @var{id} of the hot-spot with the
4530 mouse event; for instance, @code{[area4 mouse-1]} if the hot-spot's
4531 @var{id} is @code{area4}.
4534 @defun image-mask-p spec &optional frame
4535 This function returns @code{t} if image @var{spec} has a mask bitmap.
4536 @var{frame} is the frame on which the image will be displayed.
4537 @var{frame} @code{nil} or omitted means to use the selected frame
4538 (@pxref{Input Focus}).
4542 @subsection XBM Images
4545 To use XBM format, specify @code{xbm} as the image type. This image
4546 format doesn't require an external library, so images of this type are
4549 Additional image properties supported for the @code{xbm} image type are:
4552 @item :foreground @var{foreground}
4553 The value, @var{foreground}, should be a string specifying the image
4554 foreground color, or @code{nil} for the default color. This color is
4555 used for each pixel in the XBM that is 1. The default is the frame's
4558 @item :background @var{background}
4559 The value, @var{background}, should be a string specifying the image
4560 background color, or @code{nil} for the default color. This color is
4561 used for each pixel in the XBM that is 0. The default is the frame's
4565 If you specify an XBM image using data within Emacs instead of an
4566 external file, use the following three properties:
4569 @item :data @var{data}
4570 The value, @var{data}, specifies the contents of the image.
4571 There are three formats you can use for @var{data}:
4575 A vector of strings or bool-vectors, each specifying one line of the
4576 image. Do specify @code{:height} and @code{:width}.
4579 A string containing the same byte sequence as an XBM file would contain.
4580 You must not specify @code{:height} and @code{:width} in this case,
4581 because omitting them is what indicates the data has the format of an
4582 XBM file. The file contents specify the height and width of the image.
4585 A string or a bool-vector containing the bits of the image (plus perhaps
4586 some extra bits at the end that will not be used). It should contain at
4587 least @var{width} * @code{height} bits. In this case, you must specify
4588 @code{:height} and @code{:width}, both to indicate that the string
4589 contains just the bits rather than a whole XBM file, and to specify the
4593 @item :width @var{width}
4594 The value, @var{width}, specifies the width of the image, in pixels.
4596 @item :height @var{height}
4597 The value, @var{height}, specifies the height of the image, in pixels.
4601 @subsection XPM Images
4604 To use XPM format, specify @code{xpm} as the image type. The
4605 additional image property @code{:color-symbols} is also meaningful with
4606 the @code{xpm} image type:
4609 @item :color-symbols @var{symbols}
4610 The value, @var{symbols}, should be an alist whose elements have the
4611 form @code{(@var{name} . @var{color})}. In each element, @var{name} is
4612 the name of a color as it appears in the image file, and @var{color}
4613 specifies the actual color to use for displaying that name.
4616 @node PostScript Images
4617 @subsection PostScript Images
4618 @cindex postscript images
4620 To use PostScript for an image, specify image type @code{postscript}.
4621 This works only if you have Ghostscript installed. You must always use
4622 these three properties:
4625 @item :pt-width @var{width}
4626 The value, @var{width}, specifies the width of the image measured in
4627 points (1/72 inch). @var{width} must be an integer.
4629 @item :pt-height @var{height}
4630 The value, @var{height}, specifies the height of the image in points
4631 (1/72 inch). @var{height} must be an integer.
4633 @item :bounding-box @var{box}
4634 The value, @var{box}, must be a list or vector of four integers, which
4635 specifying the bounding box of the PostScript image, analogous to the
4636 @samp{BoundingBox} comment found in PostScript files.
4639 %%BoundingBox: 22 171 567 738
4643 @node ImageMagick Images
4644 @subsection ImageMagick Images
4645 @cindex ImageMagick images
4646 @cindex images, support for more formats
4648 If you build Emacs with ImageMagick support, you can use the
4649 ImageMagick library to load many image formats (@pxref{File
4650 Conveniences,,, emacs, The GNU Emacs Manual}). The image type symbol
4651 for images loaded via ImageMagick is @code{imagemagick}, regardless of
4652 the actual underlying image format.
4654 @defun imagemagick-types
4655 This function returns a list of image file extensions supported by the
4656 current ImageMagick installation. Each list element is a symbol
4657 representing an internal ImageMagick name for an image type, such as
4658 @code{BMP} for @file{.bmp} images.
4661 @defopt imagemagick-enabled-types
4662 The value of this variable is a list of ImageMagick image types which
4663 Emacs may attempt to render using ImageMagick. Each list element
4664 should be one of the symbols in the list returned by
4665 @code{imagemagick-types}, or an equivalent string. Alternatively, a
4666 value of @code{t} enables ImageMagick for all possible image types.
4667 Regardless of the value of this variable,
4668 @code{imagemagick-types-inhibit} (see below) takes precedence.
4671 @defopt imagemagick-types-inhibit
4672 The value of this variable lists the ImageMagick image types which
4673 should never be rendered using ImageMagick, regardless of the value of
4674 @code{imagemagick-enabled-types}. A value of @code{t} disables
4675 ImageMagick entirely.
4678 Images loaded with ImageMagick support the following additional
4679 image descriptor properties:
4682 @item :background @var{background}
4683 @var{background}, if non-@code{nil}, should be a string specifying a
4684 color, which is used as the image's background color if the image
4685 supports transparency. If the value is @code{nil}, it defaults to the
4686 frame's background color.
4688 @item :width, :height
4689 The @code{:width} and @code{:height} keywords are used for scaling the
4690 image. If only one of them is specified, the other one will be
4691 calculated so as to preserve the aspect ratio. If both are specified,
4692 aspect ratio may not be preserved.
4694 @item :max-width, :max-height
4695 The @code{:max-width} and @code{:max-height} keywords are used for
4696 scaling if the size of the image of the image exceeds these values.
4697 If @code{:width} is set it will have precedence over @code{max-width},
4698 and if @code{:height} is set it will have precedence over
4699 @code{max-height}, but you can otherwise mix these keywords as you
4700 wish. @code{:max-width} and @code{:max-height} will always preserve
4704 ImageMagick tries to auto-detect the image type, but it isn't always
4705 able to. By using @code{:format-type}, we can give ImageMagick a hint
4706 to try to help it. It's used in conjunction with the
4707 @code{image-format-suffixes} variable, which provides a mapping from
4708 content types to file name suffixes. This is then given to
4709 ImageMagick as a file name hint.
4712 Specifies a rotation angle in degrees.
4715 @c Doesn't work: http://debbugs.gnu.org/7978
4716 @xref{Multi-Frame Images}.
4719 @node Other Image Types
4720 @subsection Other Image Types
4723 For PBM images, specify image type @code{pbm}. Color, gray-scale and
4724 monochromatic images are supported. For mono PBM images, two additional
4725 image properties are supported.
4728 @item :foreground @var{foreground}
4729 The value, @var{foreground}, should be a string specifying the image
4730 foreground color, or @code{nil} for the default color. This color is
4731 used for each pixel in the PBM that is 1. The default is the frame's
4734 @item :background @var{background}
4735 The value, @var{background}, should be a string specifying the image
4736 background color, or @code{nil} for the default color. This color is
4737 used for each pixel in the PBM that is 0. The default is the frame's
4742 The remaining image types that Emacs can support are:
4746 Image type @code{gif}.
4747 Supports the @code{:index} property. @xref{Multi-Frame Images}.
4750 Image type @code{jpeg}.
4753 Image type @code{png}.
4756 Image type @code{svg}.
4759 Image type @code{tiff}.
4760 Supports the @code{:index} property. @xref{Multi-Frame Images}.
4763 @node Defining Images
4764 @subsection Defining Images
4766 The functions @code{create-image}, @code{defimage} and
4767 @code{find-image} provide convenient ways to create image descriptors.
4769 @defun create-image file-or-data &optional type data-p &rest props
4770 This function creates and returns an image descriptor which uses the
4771 data in @var{file-or-data}. @var{file-or-data} can be a file name or
4772 a string containing the image data; @var{data-p} should be @code{nil}
4773 for the former case, non-@code{nil} for the latter case.
4775 The optional argument @var{type} is a symbol specifying the image type.
4776 If @var{type} is omitted or @code{nil}, @code{create-image} tries to
4777 determine the image type from the file's first few bytes, or else
4778 from the file's name.
4780 The remaining arguments, @var{props}, specify additional image
4781 properties---for example,
4784 (create-image "foo.xpm" 'xpm nil :heuristic-mask t)
4787 The function returns @code{nil} if images of this type are not
4788 supported. Otherwise it returns an image descriptor.
4791 @defmac defimage symbol specs &optional doc
4792 This macro defines @var{symbol} as an image name. The arguments
4793 @var{specs} is a list which specifies how to display the image.
4794 The third argument, @var{doc}, is an optional documentation string.
4796 Each argument in @var{specs} has the form of a property list, and each
4797 one should specify at least the @code{:type} property and either the
4798 @code{:file} or the @code{:data} property. The value of @code{:type}
4799 should be a symbol specifying the image type, the value of
4800 @code{:file} is the file to load the image from, and the value of
4801 @code{:data} is a string containing the actual image data. Here is an
4805 (defimage test-image
4806 ((:type xpm :file "~/test1.xpm")
4807 (:type xbm :file "~/test1.xbm")))
4810 @code{defimage} tests each argument, one by one, to see if it is
4811 usable---that is, if the type is supported and the file exists. The
4812 first usable argument is used to make an image descriptor which is
4813 stored in @var{symbol}.
4815 If none of the alternatives will work, then @var{symbol} is defined
4819 @defun find-image specs
4820 This function provides a convenient way to find an image satisfying one
4821 of a list of image specifications @var{specs}.
4823 Each specification in @var{specs} is a property list with contents
4824 depending on image type. All specifications must at least contain the
4825 properties @code{:type @var{type}} and either @w{@code{:file @var{file}}}
4826 or @w{@code{:data @var{DATA}}}, where @var{type} is a symbol specifying
4827 the image type, e.g., @code{xbm}, @var{file} is the file to load the
4828 image from, and @var{data} is a string containing the actual image data.
4829 The first specification in the list whose @var{type} is supported, and
4830 @var{file} exists, is used to construct the image specification to be
4831 returned. If no specification is satisfied, @code{nil} is returned.
4833 The image is looked for in @code{image-load-path}.
4836 @defvar image-load-path
4837 This variable's value is a list of locations in which to search for
4838 image files. If an element is a string or a variable symbol whose
4839 value is a string, the string is taken to be the name of a directory
4840 to search. If an element is a variable symbol whose value is a list,
4841 that is taken to be a list of directory names to search.
4843 The default is to search in the @file{images} subdirectory of the
4844 directory specified by @code{data-directory}, then the directory
4845 specified by @code{data-directory}, and finally in the directories in
4846 @code{load-path}. Subdirectories are not automatically included in
4847 the search, so if you put an image file in a subdirectory, you have to
4848 supply the subdirectory name explicitly. For example, to find the
4849 image @file{images/foo/bar.xpm} within @code{data-directory}, you
4850 should specify the image as follows:
4853 (defimage foo-image '((:type xpm :file "foo/bar.xpm")))
4857 @defun image-load-path-for-library library image &optional path no-error
4858 This function returns a suitable search path for images used by the
4859 Lisp package @var{library}.
4861 The function searches for @var{image} first using @code{image-load-path},
4862 excluding @file{@code{data-directory}/images}, and then in
4863 @code{load-path}, followed by a path suitable for @var{library}, which
4864 includes @file{../../etc/images} and @file{../etc/images} relative to
4865 the library file itself, and finally in
4866 @file{@code{data-directory}/images}.
4868 Then this function returns a list of directories which contains first
4869 the directory in which @var{image} was found, followed by the value of
4870 @code{load-path}. If @var{path} is given, it is used instead of
4873 If @var{no-error} is non-@code{nil} and a suitable path can't be
4874 found, don't signal an error. Instead, return a list of directories as
4875 before, except that @code{nil} appears in place of the image directory.
4877 Here is an example of using @code{image-load-path-for-library}:
4880 (defvar image-load-path) ; shush compiler
4881 (let* ((load-path (image-load-path-for-library
4882 "mh-e" "mh-logo.xpm"))
4883 (image-load-path (cons (car load-path)
4885 (mh-tool-bar-folder-buttons-init))
4889 @node Showing Images
4890 @subsection Showing Images
4892 You can use an image descriptor by setting up the @code{display}
4893 property yourself, but it is easier to use the functions in this
4896 @defun insert-image image &optional string area slice
4897 This function inserts @var{image} in the current buffer at point. The
4898 value @var{image} should be an image descriptor; it could be a value
4899 returned by @code{create-image}, or the value of a symbol defined with
4900 @code{defimage}. The argument @var{string} specifies the text to put
4901 in the buffer to hold the image. If it is omitted or @code{nil},
4902 @code{insert-image} uses @code{" "} by default.
4904 The argument @var{area} specifies whether to put the image in a margin.
4905 If it is @code{left-margin}, the image appears in the left margin;
4906 @code{right-margin} specifies the right margin. If @var{area} is
4907 @code{nil} or omitted, the image is displayed at point within the
4910 The argument @var{slice} specifies a slice of the image to insert. If
4911 @var{slice} is @code{nil} or omitted the whole image is inserted.
4912 Otherwise, @var{slice} is a list @code{(@var{x} @var{y} @var{width}
4913 @var{height})} which specifies the @var{x} and @var{y} positions and
4914 @var{width} and @var{height} of the image area to insert. Integer
4915 values are in units of pixels. A floating point number in the range
4916 0.0--1.0 stands for that fraction of the width or height of the entire
4919 Internally, this function inserts @var{string} in the buffer, and gives
4920 it a @code{display} property which specifies @var{image}. @xref{Display
4924 @cindex slice, image
4926 @defun insert-sliced-image image &optional string area rows cols
4927 This function inserts @var{image} in the current buffer at point, like
4928 @code{insert-image}, but splits the image into @var{rows}x@var{cols}
4929 equally sized slices.
4931 If an image is inserted ``sliced'', Emacs displays each slice as a
4932 separate image, and allow more intuitive scrolling up/down, instead of
4933 jumping up/down the entire image when paging through a buffer that
4934 displays (large) images.
4937 @defun put-image image pos &optional string area
4938 This function puts image @var{image} in front of @var{pos} in the
4939 current buffer. The argument @var{pos} should be an integer or a
4940 marker. It specifies the buffer position where the image should appear.
4941 The argument @var{string} specifies the text that should hold the image
4942 as an alternative to the default.
4944 The argument @var{image} must be an image descriptor, perhaps returned
4945 by @code{create-image} or stored by @code{defimage}.
4947 The argument @var{area} specifies whether to put the image in a margin.
4948 If it is @code{left-margin}, the image appears in the left margin;
4949 @code{right-margin} specifies the right margin. If @var{area} is
4950 @code{nil} or omitted, the image is displayed at point within the
4953 Internally, this function creates an overlay, and gives it a
4954 @code{before-string} property containing text that has a @code{display}
4955 property whose value is the image. (Whew!)
4958 @defun remove-images start end &optional buffer
4959 This function removes images in @var{buffer} between positions
4960 @var{start} and @var{end}. If @var{buffer} is omitted or @code{nil},
4961 images are removed from the current buffer.
4963 This removes only images that were put into @var{buffer} the way
4964 @code{put-image} does it, not images that were inserted with
4965 @code{insert-image} or in other ways.
4968 @defun image-size spec &optional pixels frame
4969 This function returns the size of an image as a pair
4970 @w{@code{(@var{width} . @var{height})}}. @var{spec} is an image
4971 specification. @var{pixels} non-@code{nil} means return sizes
4972 measured in pixels, otherwise return sizes measured in canonical
4973 character units (fractions of the width/height of the frame's default
4974 font). @var{frame} is the frame on which the image will be displayed.
4975 @var{frame} null or omitted means use the selected frame (@pxref{Input
4979 @defvar max-image-size
4980 This variable is used to define the maximum size of image that Emacs
4981 will load. Emacs will refuse to load (and display) any image that is
4982 larger than this limit.
4984 If the value is an integer, it directly specifies the maximum
4985 image height and width, measured in pixels. If it is a floating
4986 point number, it specifies the maximum image height and width
4987 as a ratio to the frame height and width. If the value is
4988 non-numeric, there is no explicit limit on the size of images.
4990 The purpose of this variable is to prevent unreasonably large images
4991 from accidentally being loaded into Emacs. It only takes effect the
4992 first time an image is loaded. Once an image is placed in the image
4993 cache, it can always be displayed, even if the value of
4994 @var{max-image-size} is subsequently changed (@pxref{Image Cache}).
4997 @node Multi-Frame Images
4998 @subsection Multi-Frame Images
5001 @cindex image animation
5002 @cindex image frames
5003 Some image files can contain more than one image. We say that there
5004 are multiple ``frames'' in the image. At present, Emacs supports
5005 multiple frames for GIF, TIFF, and certain ImageMagick formats such as
5008 The frames can be used either to represent multiple ``pages'' (this is
5009 usually the case with multi-frame TIFF files, for example), or to
5010 create animation (usually the case with multi-frame GIF files).
5012 A multi-frame image has a property @code{:index}, whose value is an
5013 integer (counting from 0) that specifies which frame is being displayed.
5015 @defun image-multi-frame-p image
5016 This function returns non-@code{nil} if @var{image} contains more than
5017 one frame. The actual return value is a cons @code{(@var{nimages}
5018 . @var{delay})}, where @var{nimages} is the number of frames and
5019 @var{delay} is the delay in seconds between them, or @code{nil}
5020 if the image does not specify a delay. Images that are intended to be
5021 animated usually specify a frame delay, whereas ones that are intended
5022 to be treated as multiple pages do not.
5025 @defun image-current-frame image
5026 This function returns the index of the current frame number for
5027 @var{image}, counting from 0.
5030 @defun image-show-frame image n &optional nocheck
5031 This function switches @var{image} to frame number @var{n}. It
5032 replaces a frame number outside the valid range with that of the end
5033 of the range, unless @var{nocheck} is non-@code{nil}. If @var{image}
5034 does not contain a frame with the specified number, the image displays
5038 @defun image-animate image &optional index limit
5039 This function animates @var{image}. The optional integer @var{index}
5040 specifies the frame from which to start (default 0). The optional
5041 argument @var{limit} controls the length of the animation. If omitted
5042 or @code{nil}, the image animates once only; if @code{t} it loops
5043 forever; if a number animation stops after that many seconds.
5046 @noindent Animation operates by means of a timer. Note that Emacs imposes a
5047 minimum frame delay of 0.01 (@code{image-minimum-frame-delay}) seconds.
5048 If the image itself does not specify a delay, Emacs uses
5049 @code{image-default-frame-delay}.
5051 @defun image-animate-timer image
5052 This function returns the timer responsible for animating @var{image},
5058 @subsection Image Cache
5061 Emacs caches images so that it can display them again more
5062 efficiently. When Emacs displays an image, it searches the image
5063 cache for an existing image specification @code{equal} to the desired
5064 specification. If a match is found, the image is displayed from the
5065 cache. Otherwise, Emacs loads the image normally.
5067 @defun image-flush spec &optional frame
5068 This function removes the image with specification @var{spec} from the
5069 image cache of frame @var{frame}. Image specifications are compared
5070 using @code{equal}. If @var{frame} is @code{nil}, it defaults to the
5071 selected frame. If @var{frame} is @code{t}, the image is flushed on
5072 all existing frames.
5074 In Emacs's current implementation, each graphical terminal possesses an
5075 image cache, which is shared by all the frames on that terminal
5076 (@pxref{Multiple Terminals}). Thus, refreshing an image in one frame
5077 also refreshes it in all other frames on the same terminal.
5080 One use for @code{image-flush} is to tell Emacs about a change in an
5081 image file. If an image specification contains a @code{:file}
5082 property, the image is cached based on the file's contents when the
5083 image is first displayed. Even if the file subsequently changes,
5084 Emacs continues displaying the old version of the image. Calling
5085 @code{image-flush} flushes the image from the cache, forcing Emacs to
5086 re-read the file the next time it needs to display that image.
5088 Another use for @code{image-flush} is for memory conservation. If
5089 your Lisp program creates a large number of temporary images over a
5090 period much shorter than @code{image-cache-eviction-delay} (see
5091 below), you can opt to flush unused images yourself, instead of
5092 waiting for Emacs to do it automatically.
5094 @defun clear-image-cache &optional filter
5095 This function clears an image cache, removing all the images stored in
5096 it. If @var{filter} is omitted or @code{nil}, it clears the cache for
5097 the selected frame. If @var{filter} is a frame, it clears the cache
5098 for that frame. If @var{filter} is @code{t}, all image caches are
5099 cleared. Otherwise, @var{filter} is taken to be a file name, and all
5100 images associated with that file name are removed from all image
5104 If an image in the image cache has not been displayed for a specified
5105 period of time, Emacs removes it from the cache and frees the
5108 @defvar image-cache-eviction-delay
5109 This variable specifies the number of seconds an image can remain in
5110 the cache without being displayed. When an image is not displayed for
5111 this length of time, Emacs removes it from the image cache.
5113 Under some circumstances, if the number of images in the cache grows
5114 too large, the actual eviction delay may be shorter than this.
5116 If the value is @code{nil}, Emacs does not remove images from the cache
5117 except when you explicitly clear it. This mode can be useful for
5123 @cindex buttons in buffers
5124 @cindex clickable buttons in buffers
5126 The Button package defines functions for inserting and manipulating
5127 @dfn{buttons} that can be activated with the mouse or via keyboard
5128 commands. These buttons are typically used for various kinds of
5131 A button is essentially a set of text or overlay properties,
5132 attached to a stretch of text in a buffer. These properties are
5133 called @dfn{button properties}. One of these properties, the
5134 @dfn{action property}, specifies a function which is called when the
5135 user invokes the button using the keyboard or the mouse. The action
5136 function may examine the button and use its other properties as
5139 In some ways, the Button package duplicates the functionality in the
5140 Widget package. @xref{Top, , Introduction, widget, The Emacs Widget
5141 Library}. The advantage of the Button package is that it is faster,
5142 smaller, and simpler to program. From the point of view of the user,
5143 the interfaces produced by the two packages are very similar.
5146 * Button Properties:: Button properties with special meanings.
5147 * Button Types:: Defining common properties for classes of buttons.
5148 * Making Buttons:: Adding buttons to Emacs buffers.
5149 * Manipulating Buttons:: Getting and setting properties of buttons.
5150 * Button Buffer Commands:: Buffer-wide commands and bindings for buttons.
5153 @node Button Properties
5154 @subsection Button Properties
5155 @cindex button properties
5157 Each button has an associated list of properties defining its
5158 appearance and behavior, and other arbitrary properties may be used
5159 for application specific purposes. The following properties have
5160 special meaning to the Button package:
5164 @kindex action @r{(button property)}
5165 The function to call when the user invokes the button, which is passed
5166 the single argument @var{button}. By default this is @code{ignore},
5170 @kindex mouse-action @r{(button property)}
5171 This is similar to @code{action}, and when present, will be used
5172 instead of @code{action} for button invocations resulting from
5173 mouse-clicks (instead of the user hitting @key{RET}). If not
5174 present, mouse-clicks use @code{action} instead.
5177 @kindex face @r{(button property)}
5178 This is an Emacs face controlling how buttons of this type are
5179 displayed; by default this is the @code{button} face.
5182 @kindex mouse-face @r{(button property)}
5183 This is an additional face which controls appearance during
5184 mouse-overs (merged with the usual button face); by default this is
5185 the usual Emacs @code{highlight} face.
5188 @kindex keymap @r{(button property)}
5189 The button's keymap, defining bindings active within the button
5190 region. By default this is the usual button region keymap, stored
5191 in the variable @code{button-map}, which defines @key{RET} and
5192 @key{mouse-2} to invoke the button.
5195 @kindex type @r{(button property)}
5196 The button type. @xref{Button Types}.
5199 @kindex help-index @r{(button property)}
5200 A string displayed by the Emacs tool-tip help system; by default,
5201 @code{"mouse-2, RET: Push this button"}.
5204 @kindex follow-link @r{(button property)}
5205 The follow-link property, defining how a @key{Mouse-1} click behaves
5206 on this button, @xref{Clickable Text}.
5209 @kindex button @r{(button property)}
5210 All buttons have a non-@code{nil} @code{button} property, which may be useful
5211 in finding regions of text that comprise buttons (which is what the
5212 standard button functions do).
5215 There are other properties defined for the regions of text in a
5216 button, but these are not generally interesting for typical uses.
5219 @subsection Button Types
5220 @cindex button types
5222 Every button has a @dfn{button type}, which defines default values
5223 for the button's properties. Button types are arranged in a
5224 hierarchy, with specialized types inheriting from more general types,
5225 so that it's easy to define special-purpose types of buttons for
5228 @defun define-button-type name &rest properties
5229 Define a `button type' called @var{name} (a symbol).
5230 The remaining arguments
5231 form a sequence of @var{property value} pairs, specifying default
5232 property values for buttons with this type (a button's type may be set
5233 by giving it a @code{type} property when creating the button, using
5234 the @code{:type} keyword argument).
5236 In addition, the keyword argument @code{:supertype} may be used to
5237 specify a button-type from which @var{name} inherits its default
5238 property values. Note that this inheritance happens only when
5239 @var{name} is defined; subsequent changes to a supertype are not
5240 reflected in its subtypes.
5243 Using @code{define-button-type} to define default properties for
5244 buttons is not necessary---buttons without any specified type use the
5245 built-in button-type @code{button}---but it is encouraged, since
5246 doing so usually makes the resulting code clearer and more efficient.
5248 @node Making Buttons
5249 @subsection Making Buttons
5250 @cindex making buttons
5252 Buttons are associated with a region of text, using an overlay or
5253 text properties to hold button-specific information, all of which are
5254 initialized from the button's type (which defaults to the built-in
5255 button type @code{button}). Like all Emacs text, the appearance of
5256 the button is governed by the @code{face} property; by default (via
5257 the @code{face} property inherited from the @code{button} button-type)
5258 this is a simple underline, like a typical web-page link.
5260 For convenience, there are two sorts of button-creation functions,
5261 those that add button properties to an existing region of a buffer,
5262 called @code{make-...button}, and those that also insert the button
5263 text, called @code{insert-...button}.
5265 The button-creation functions all take the @code{&rest} argument
5266 @var{properties}, which should be a sequence of @var{property value}
5267 pairs, specifying properties to add to the button; see @ref{Button
5268 Properties}. In addition, the keyword argument @code{:type} may be
5269 used to specify a button-type from which to inherit other properties;
5270 see @ref{Button Types}. Any properties not explicitly specified
5271 during creation will be inherited from the button's type (if the type
5272 defines such a property).
5274 The following functions add a button using an overlay
5275 (@pxref{Overlays}) to hold the button properties:
5277 @defun make-button beg end &rest properties
5278 This makes a button from @var{beg} to @var{end} in the
5279 current buffer, and returns it.
5282 @defun insert-button label &rest properties
5283 This insert a button with the label @var{label} at point,
5287 The following functions are similar, but using text properties
5288 (@pxref{Text Properties}) to hold the button properties. Such buttons
5289 do not add markers to the buffer, so editing in the buffer does not
5290 slow down if there is an extremely large numbers of buttons. However,
5291 if there is an existing face text property on the text (e.g., a face
5292 assigned by Font Lock mode), the button face may not be visible. Both
5293 of these functions return the starting position of the new button.
5295 @defun make-text-button beg end &rest properties
5296 This makes a button from @var{beg} to @var{end} in the current buffer,
5297 using text properties.
5300 @defun insert-text-button label &rest properties
5301 This inserts a button with the label @var{label} at point, using text
5305 @node Manipulating Buttons
5306 @subsection Manipulating Buttons
5307 @cindex manipulating buttons
5309 These are functions for getting and setting properties of buttons.
5310 Often these are used by a button's invocation function to determine
5313 Where a @var{button} parameter is specified, it means an object
5314 referring to a specific button, either an overlay (for overlay
5315 buttons), or a buffer-position or marker (for text property buttons).
5316 Such an object is passed as the first argument to a button's
5317 invocation function when it is invoked.
5319 @defun button-start button
5320 Return the position at which @var{button} starts.
5323 @defun button-end button
5324 Return the position at which @var{button} ends.
5327 @defun button-get button prop
5328 Get the property of button @var{button} named @var{prop}.
5331 @defun button-put button prop val
5332 Set @var{button}'s @var{prop} property to @var{val}.
5335 @defun button-activate button &optional use-mouse-action
5336 Call @var{button}'s @code{action} property (i.e., invoke it). If
5337 @var{use-mouse-action} is non-@code{nil}, try to invoke the button's
5338 @code{mouse-action} property instead of @code{action}; if the button
5339 has no @code{mouse-action} property, use @code{action} as normal.
5342 @defun button-label button
5343 Return @var{button}'s text label.
5346 @defun button-type button
5347 Return @var{button}'s button-type.
5350 @defun button-has-type-p button type
5351 Return @code{t} if @var{button} has button-type @var{type}, or one of
5352 @var{type}'s subtypes.
5355 @defun button-at pos
5356 Return the button at position @var{pos} in the current buffer, or
5357 @code{nil}. If the button at @var{pos} is a text property button, the
5358 return value is a marker pointing to @var{pos}.
5361 @defun button-type-put type prop val
5362 Set the button-type @var{type}'s @var{prop} property to @var{val}.
5365 @defun button-type-get type prop
5366 Get the property of button-type @var{type} named @var{prop}.
5369 @defun button-type-subtype-p type supertype
5370 Return @code{t} if button-type @var{type} is a subtype of @var{supertype}.
5373 @node Button Buffer Commands
5374 @subsection Button Buffer Commands
5375 @cindex button buffer commands
5377 These are commands and functions for locating and operating on
5378 buttons in an Emacs buffer.
5380 @code{push-button} is the command that a user uses to actually `push'
5381 a button, and is bound by default in the button itself to @key{RET}
5382 and to @key{mouse-2} using a local keymap in the button's overlay or
5383 text properties. Commands that are useful outside the buttons itself,
5384 such as @code{forward-button} and @code{backward-button} are
5385 additionally available in the keymap stored in
5386 @code{button-buffer-map}; a mode which uses buttons may want to use
5387 @code{button-buffer-map} as a parent keymap for its keymap.
5389 If the button has a non-@code{nil} @code{follow-link} property, and
5390 @var{mouse-1-click-follows-link} is set, a quick @key{Mouse-1} click
5391 will also activate the @code{push-button} command.
5392 @xref{Clickable Text}.
5394 @deffn Command push-button &optional pos use-mouse-action
5395 Perform the action specified by a button at location @var{pos}.
5396 @var{pos} may be either a buffer position or a mouse-event. If
5397 @var{use-mouse-action} is non-@code{nil}, or @var{pos} is a
5398 mouse-event (@pxref{Mouse Events}), try to invoke the button's
5399 @code{mouse-action} property instead of @code{action}; if the button
5400 has no @code{mouse-action} property, use @code{action} as normal.
5401 @var{pos} defaults to point, except when @code{push-button} is invoked
5402 interactively as the result of a mouse-event, in which case, the mouse
5403 event's position is used. If there's no button at @var{pos}, do
5404 nothing and return @code{nil}, otherwise return @code{t}.
5407 @deffn Command forward-button n &optional wrap display-message
5408 Move to the @var{n}th next button, or @var{n}th previous button if
5409 @var{n} is negative. If @var{n} is zero, move to the start of any
5410 button at point. If @var{wrap} is non-@code{nil}, moving past either
5411 end of the buffer continues from the other end. If
5412 @var{display-message} is non-@code{nil}, the button's help-echo string
5413 is displayed. Any button with a non-@code{nil} @code{skip} property
5414 is skipped over. Returns the button found.
5417 @deffn Command backward-button n &optional wrap display-message
5418 Move to the @var{n}th previous button, or @var{n}th next button if
5419 @var{n} is negative. If @var{n} is zero, move to the start of any
5420 button at point. If @var{wrap} is non-@code{nil}, moving past either
5421 end of the buffer continues from the other end. If
5422 @var{display-message} is non-@code{nil}, the button's help-echo string
5423 is displayed. Any button with a non-@code{nil} @code{skip} property
5424 is skipped over. Returns the button found.
5427 @defun next-button pos &optional count-current
5428 @defunx previous-button pos &optional count-current
5429 Return the next button after (for @code{next-button} or before (for
5430 @code{previous-button}) position @var{pos} in the current buffer. If
5431 @var{count-current} is non-@code{nil}, count any button at @var{pos}
5432 in the search, instead of starting at the next button.
5435 @node Abstract Display
5436 @section Abstract Display
5438 @cindex display, abstract
5439 @cindex display, arbitrary objects
5440 @cindex model/view/controller
5441 @cindex view part, model/view/controller
5443 The Ewoc package constructs buffer text that represents a structure
5444 of Lisp objects, and updates the text to follow changes in that
5445 structure. This is like the ``view'' component in the
5446 ``model/view/controller'' design paradigm.
5448 An @dfn{ewoc} is a structure that organizes information required to
5449 construct buffer text that represents certain Lisp data. The buffer
5450 text of the ewoc has three parts, in order: first, fixed @dfn{header}
5451 text; next, textual descriptions of a series of data elements (Lisp
5452 objects that you specify); and last, fixed @dfn{footer} text.
5453 Specifically, an ewoc contains information on:
5457 The buffer which its text is generated in.
5460 The text's start position in the buffer.
5463 The header and footer strings.
5466 A doubly-linked chain of @dfn{nodes}, each of which contains:
5470 A @dfn{data element}, a single Lisp object.
5473 Links to the preceding and following nodes in the chain.
5477 A @dfn{pretty-printer} function which is responsible for
5478 inserting the textual representation of a data
5479 element value into the current buffer.
5482 Typically, you define an ewoc with @code{ewoc-create}, and then pass
5483 the resulting ewoc structure to other functions in the Ewoc package to
5484 build nodes within it, and display it in the buffer. Once it is
5485 displayed in the buffer, other functions determine the correspondence
5486 between buffer positions and nodes, move point from one node's textual
5487 representation to another, and so forth. @xref{Abstract Display
5490 A node @dfn{encapsulates} a data element much the way a variable
5491 holds a value. Normally, encapsulation occurs as a part of adding a
5492 node to the ewoc. You can retrieve the data element value and place a
5493 new value in its place, like so:
5496 (ewoc-data @var{node})
5499 (ewoc-set-data @var{node} @var{new-value})
5500 @result{} @var{new-value}
5504 You can also use, as the data element value, a Lisp object (list or
5505 vector) that is a container for the ``real'' value, or an index into
5506 some other structure. The example (@pxref{Abstract Display Example})
5507 uses the latter approach.
5509 When the data changes, you will want to update the text in the
5510 buffer. You can update all nodes by calling @code{ewoc-refresh}, or
5511 just specific nodes using @code{ewoc-invalidate}, or all nodes
5512 satisfying a predicate using @code{ewoc-map}. Alternatively, you can
5513 delete invalid nodes using @code{ewoc-delete} or @code{ewoc-filter},
5514 and add new nodes in their place. Deleting a node from an ewoc deletes
5515 its associated textual description from buffer, as well.
5518 * Abstract Display Functions:: Functions in the Ewoc package.
5519 * Abstract Display Example:: Example of using Ewoc.
5522 @node Abstract Display Functions
5523 @subsection Abstract Display Functions
5525 In this subsection, @var{ewoc} and @var{node} stand for the
5526 structures described above (@pxref{Abstract Display}), while
5527 @var{data} stands for an arbitrary Lisp object used as a data element.
5529 @defun ewoc-create pretty-printer &optional header footer nosep
5530 This constructs and returns a new ewoc, with no nodes (and thus no data
5531 elements). @var{pretty-printer} should be a function that takes one
5532 argument, a data element of the sort you plan to use in this ewoc, and
5533 inserts its textual description at point using @code{insert} (and never
5534 @code{insert-before-markers}, because that would interfere with the
5535 Ewoc package's internal mechanisms).
5537 Normally, a newline is automatically inserted after the header,
5538 the footer and every node's textual description. If @var{nosep}
5539 is non-@code{nil}, no newline is inserted. This may be useful for
5540 displaying an entire ewoc on a single line, for example, or for
5541 making nodes ``invisible'' by arranging for @var{pretty-printer}
5542 to do nothing for those nodes.
5544 An ewoc maintains its text in the buffer that is current when
5545 you create it, so switch to the intended buffer before calling
5549 @defun ewoc-buffer ewoc
5550 This returns the buffer where @var{ewoc} maintains its text.
5553 @defun ewoc-get-hf ewoc
5554 This returns a cons cell @code{(@var{header} . @var{footer})}
5555 made from @var{ewoc}'s header and footer.
5558 @defun ewoc-set-hf ewoc header footer
5559 This sets the header and footer of @var{ewoc} to the strings
5560 @var{header} and @var{footer}, respectively.
5563 @defun ewoc-enter-first ewoc data
5564 @defunx ewoc-enter-last ewoc data
5565 These add a new node encapsulating @var{data}, putting it, respectively,
5566 at the beginning or end of @var{ewoc}'s chain of nodes.
5569 @defun ewoc-enter-before ewoc node data
5570 @defunx ewoc-enter-after ewoc node data
5571 These add a new node encapsulating @var{data}, adding it to
5572 @var{ewoc} before or after @var{node}, respectively.
5575 @defun ewoc-prev ewoc node
5576 @defunx ewoc-next ewoc node
5577 These return, respectively, the previous node and the next node of @var{node}
5581 @defun ewoc-nth ewoc n
5582 This returns the node in @var{ewoc} found at zero-based index @var{n}.
5583 A negative @var{n} means count from the end. @code{ewoc-nth} returns
5584 @code{nil} if @var{n} is out of range.
5587 @defun ewoc-data node
5588 This extracts the data encapsulated by @var{node} and returns it.
5591 @defun ewoc-set-data node data
5592 This sets the data encapsulated by @var{node} to @var{data}.
5595 @defun ewoc-locate ewoc &optional pos guess
5596 This determines the node in @var{ewoc} which contains point (or
5597 @var{pos} if specified), and returns that node. If @var{ewoc} has no
5598 nodes, it returns @code{nil}. If @var{pos} is before the first node,
5599 it returns the first node; if @var{pos} is after the last node, it returns
5600 the last node. The optional third arg @var{guess}
5601 should be a node that is likely to be near @var{pos}; this doesn't
5602 alter the result, but makes the function run faster.
5605 @defun ewoc-location node
5606 This returns the start position of @var{node}.
5609 @defun ewoc-goto-prev ewoc arg
5610 @defunx ewoc-goto-next ewoc arg
5611 These move point to the previous or next, respectively, @var{arg}th node
5612 in @var{ewoc}. @code{ewoc-goto-prev} does not move if it is already at
5613 the first node or if @var{ewoc} is empty, whereas @code{ewoc-goto-next}
5614 moves past the last node, returning @code{nil}. Excepting this special
5615 case, these functions return the node moved to.
5618 @defun ewoc-goto-node ewoc node
5619 This moves point to the start of @var{node} in @var{ewoc}.
5622 @defun ewoc-refresh ewoc
5623 This function regenerates the text of @var{ewoc}. It works by
5624 deleting the text between the header and the footer, i.e., all the
5625 data elements' representations, and then calling the pretty-printer
5626 function for each node, one by one, in order.
5629 @defun ewoc-invalidate ewoc &rest nodes
5630 This is similar to @code{ewoc-refresh}, except that only @var{nodes} in
5631 @var{ewoc} are updated instead of the entire set.
5634 @defun ewoc-delete ewoc &rest nodes
5635 This deletes each node in @var{nodes} from @var{ewoc}.
5638 @defun ewoc-filter ewoc predicate &rest args
5639 This calls @var{predicate} for each data element in @var{ewoc} and
5640 deletes those nodes for which @var{predicate} returns @code{nil}.
5641 Any @var{args} are passed to @var{predicate}.
5644 @defun ewoc-collect ewoc predicate &rest args
5645 This calls @var{predicate} for each data element in @var{ewoc}
5646 and returns a list of those elements for which @var{predicate}
5647 returns non-@code{nil}. The elements in the list are ordered
5648 as in the buffer. Any @var{args} are passed to @var{predicate}.
5651 @defun ewoc-map map-function ewoc &rest args
5652 This calls @var{map-function} for each data element in @var{ewoc} and
5653 updates those nodes for which @var{map-function} returns non-@code{nil}.
5654 Any @var{args} are passed to @var{map-function}.
5657 @node Abstract Display Example
5658 @subsection Abstract Display Example
5660 Here is a simple example using functions of the ewoc package to
5661 implement a ``color components display'', an area in a buffer that
5662 represents a vector of three integers (itself representing a 24-bit RGB
5663 value) in various ways.
5666 (setq colorcomp-ewoc nil
5668 colorcomp-mode-map nil
5669 colorcomp-labels ["Red" "Green" "Blue"])
5671 (defun colorcomp-pp (data)
5673 (let ((comp (aref colorcomp-data data)))
5674 (insert (aref colorcomp-labels data) "\t: #x"
5675 (format "%02X" comp) " "
5676 (make-string (ash comp -2) ?#) "\n"))
5677 (let ((cstr (format "#%02X%02X%02X"
5678 (aref colorcomp-data 0)
5679 (aref colorcomp-data 1)
5680 (aref colorcomp-data 2)))
5681 (samp " (sample text) "))
5683 (propertize samp 'face
5684 `(foreground-color . ,cstr))
5685 (propertize samp 'face
5686 `(background-color . ,cstr))
5689 (defun colorcomp (color)
5690 "Allow fiddling with COLOR in a new buffer.
5691 The buffer is in Color Components mode."
5692 (interactive "sColor (name or #RGB or #RRGGBB): ")
5693 (when (string= "" color)
5694 (setq color "green"))
5695 (unless (color-values color)
5696 (error "No such color: %S" color))
5698 (generate-new-buffer (format "originally: %s" color)))
5699 (kill-all-local-variables)
5700 (setq major-mode 'colorcomp-mode
5701 mode-name "Color Components")
5702 (use-local-map colorcomp-mode-map)
5704 (buffer-disable-undo)
5705 (let ((data (apply 'vector (mapcar (lambda (n) (ash n -8))
5706 (color-values color))))
5707 (ewoc (ewoc-create 'colorcomp-pp
5708 "\nColor Components\n\n"
5709 (substitute-command-keys
5710 "\n\\@{colorcomp-mode-map@}"))))
5711 (set (make-local-variable 'colorcomp-data) data)
5712 (set (make-local-variable 'colorcomp-ewoc) ewoc)
5713 (ewoc-enter-last ewoc 0)
5714 (ewoc-enter-last ewoc 1)
5715 (ewoc-enter-last ewoc 2)
5716 (ewoc-enter-last ewoc nil)))
5719 @cindex controller part, model/view/controller
5720 This example can be extended to be a ``color selection widget'' (in
5721 other words, the controller part of the ``model/view/controller''
5722 design paradigm) by defining commands to modify @code{colorcomp-data}
5723 and to ``finish'' the selection process, and a keymap to tie it all
5724 together conveniently.
5727 (defun colorcomp-mod (index limit delta)
5728 (let ((cur (aref colorcomp-data index)))
5729 (unless (= limit cur)
5730 (aset colorcomp-data index (+ cur delta)))
5733 (ewoc-nth colorcomp-ewoc index)
5734 (ewoc-nth colorcomp-ewoc -1))))
5736 (defun colorcomp-R-more () (interactive) (colorcomp-mod 0 255 1))
5737 (defun colorcomp-G-more () (interactive) (colorcomp-mod 1 255 1))
5738 (defun colorcomp-B-more () (interactive) (colorcomp-mod 2 255 1))
5739 (defun colorcomp-R-less () (interactive) (colorcomp-mod 0 0 -1))
5740 (defun colorcomp-G-less () (interactive) (colorcomp-mod 1 0 -1))
5741 (defun colorcomp-B-less () (interactive) (colorcomp-mod 2 0 -1))
5743 (defun colorcomp-copy-as-kill-and-exit ()
5744 "Copy the color components into the kill ring and kill the buffer.
5745 The string is formatted #RRGGBB (hash followed by six hex digits)."
5747 (kill-new (format "#%02X%02X%02X"
5748 (aref colorcomp-data 0)
5749 (aref colorcomp-data 1)
5750 (aref colorcomp-data 2)))
5753 (setq colorcomp-mode-map
5754 (let ((m (make-sparse-keymap)))
5756 (define-key m "i" 'colorcomp-R-less)
5757 (define-key m "o" 'colorcomp-R-more)
5758 (define-key m "k" 'colorcomp-G-less)
5759 (define-key m "l" 'colorcomp-G-more)
5760 (define-key m "," 'colorcomp-B-less)
5761 (define-key m "." 'colorcomp-B-more)
5762 (define-key m " " 'colorcomp-copy-as-kill-and-exit)
5766 Note that we never modify the data in each node, which is fixed when the
5767 ewoc is created to be either @code{nil} or an index into the vector
5768 @code{colorcomp-data}, the actual color components.
5771 @section Blinking Parentheses
5772 @cindex parenthesis matching
5773 @cindex blinking parentheses
5774 @cindex balancing parentheses
5776 This section describes the mechanism by which Emacs shows a matching
5777 open parenthesis when the user inserts a close parenthesis.
5779 @defvar blink-paren-function
5780 The value of this variable should be a function (of no arguments) to
5781 be called whenever a character with close parenthesis syntax is inserted.
5782 The value of @code{blink-paren-function} may be @code{nil}, in which
5783 case nothing is done.
5786 @defopt blink-matching-paren
5787 If this variable is @code{nil}, then @code{blink-matching-open} does
5791 @defopt blink-matching-paren-distance
5792 This variable specifies the maximum distance to scan for a matching
5793 parenthesis before giving up.
5796 @defopt blink-matching-delay
5797 This variable specifies the number of seconds for the cursor to remain
5798 at the matching parenthesis. A fraction of a second often gives
5799 good results, but the default is 1, which works on all systems.
5802 @deffn Command blink-matching-open
5803 This function is the default value of @code{blink-paren-function}. It
5804 assumes that point follows a character with close parenthesis syntax and
5805 moves the cursor momentarily to the matching opening character. If that
5806 character is not already on the screen, it displays the character's
5807 context in the echo area. To avoid long delays, this function does not
5808 search farther than @code{blink-matching-paren-distance} characters.
5810 Here is an example of calling this function explicitly.
5814 (defun interactive-blink-matching-open ()
5815 "Indicate momentarily the start of sexp before point."
5819 (let ((blink-matching-paren-distance
5821 (blink-matching-paren t))
5822 (blink-matching-open)))
5827 @node Character Display
5828 @section Character Display
5830 This section describes how characters are actually displayed by
5831 Emacs. Typically, a character is displayed as a @dfn{glyph} (a
5832 graphical symbol which occupies one character position on the screen),
5833 whose appearance corresponds to the character itself. For example,
5834 the character @samp{a} (character code 97) is displayed as @samp{a}.
5835 Some characters, however, are displayed specially. For example, the
5836 formfeed character (character code 12) is usually displayed as a
5837 sequence of two glyphs, @samp{^L}, while the newline character
5838 (character code 10) starts a new screen line.
5840 You can modify how each character is displayed by defining a
5841 @dfn{display table}, which maps each character code into a sequence of
5842 glyphs. @xref{Display Tables}.
5845 * Usual Display:: The usual conventions for displaying characters.
5846 * Display Tables:: What a display table consists of.
5847 * Active Display Table:: How Emacs selects a display table to use.
5848 * Glyphs:: How to define a glyph, and what glyphs mean.
5849 * Glyphless Chars:: How glyphless characters are drawn.
5853 @subsection Usual Display Conventions
5855 Here are the conventions for displaying each character code (in the
5856 absence of a display table, which can override these
5861 conventions; @pxref{Display Tables}).
5864 @cindex printable ASCII characters
5867 The @dfn{printable @acronym{ASCII} characters}, character codes 32
5868 through 126 (consisting of numerals, English letters, and symbols like
5869 @samp{#}) are displayed literally.
5872 The tab character (character code 9) displays as whitespace stretching
5873 up to the next tab stop column. @xref{Text Display,,, emacs, The GNU
5874 Emacs Manual}. The variable @code{tab-width} controls the number of
5875 spaces per tab stop (see below).
5878 The newline character (character code 10) has a special effect: it
5879 ends the preceding line and starts a new line.
5881 @cindex ASCII control characters
5883 The non-printable @dfn{@acronym{ASCII} control characters}---character
5884 codes 0 through 31, as well as the @key{DEL} character (character code
5885 127)---display in one of two ways according to the variable
5886 @code{ctl-arrow}. If this variable is non-@code{nil} (the default),
5887 these characters are displayed as sequences of two glyphs, where the
5888 first glyph is @samp{^} (a display table can specify a glyph to use
5889 instead of @samp{^}); e.g., the @key{DEL} character is displayed as
5892 If @code{ctl-arrow} is @code{nil}, these characters are displayed as
5893 octal escapes (see below).
5895 This rule also applies to carriage return (character code 13), if that
5896 character appears in the buffer. But carriage returns usually do not
5897 appear in buffer text; they are eliminated as part of end-of-line
5898 conversion (@pxref{Coding System Basics}).
5900 @cindex octal escapes
5902 @dfn{Raw bytes} are non-@acronym{ASCII} characters with codes 128
5903 through 255 (@pxref{Text Representations}). These characters display
5904 as @dfn{octal escapes}: sequences of four glyphs, where the first
5905 glyph is the @acronym{ASCII} code for @samp{\}, and the others are
5906 digit characters representing the character code in octal. (A display
5907 table can specify a glyph to use instead of @samp{\}.)
5910 Each non-@acronym{ASCII} character with code above 255 is displayed
5911 literally, if the terminal supports it. If the terminal does not
5912 support it, the character is said to be @dfn{glyphless}, and it is
5913 usually displayed using a placeholder glyph. For example, if a
5914 graphical terminal has no font for a character, Emacs usually displays
5915 a box containing the character code in hexadecimal. @xref{Glyphless
5919 The above display conventions apply even when there is a display
5920 table, for any character whose entry in the active display table is
5921 @code{nil}. Thus, when you set up a display table, you need only
5922 specify the characters for which you want special behavior.
5924 The following variables affect how certain characters are displayed
5925 on the screen. Since they change the number of columns the characters
5926 occupy, they also affect the indentation functions. They also affect
5927 how the mode line is displayed; if you want to force redisplay of the
5928 mode line using the new values, call the function
5929 @code{force-mode-line-update} (@pxref{Mode Line Format}).
5932 @cindex control characters in display
5933 This buffer-local variable controls how control characters are
5934 displayed. If it is non-@code{nil}, they are displayed as a caret
5935 followed by the character: @samp{^A}. If it is @code{nil}, they are
5936 displayed as octal escapes: a backslash followed by three octal
5937 digits, as in @samp{\001}.
5941 The value of this buffer-local variable is the spacing between tab
5942 stops used for displaying tab characters in Emacs buffers. The value
5943 is in units of columns, and the default is 8. Note that this feature
5944 is completely independent of the user-settable tab stops used by the
5945 command @code{tab-to-tab-stop}. @xref{Indent Tabs}.
5948 @node Display Tables
5949 @subsection Display Tables
5951 @cindex display table
5952 A display table is a special-purpose char-table
5953 (@pxref{Char-Tables}), with @code{display-table} as its subtype, which
5954 is used to override the usual character display conventions. This
5955 section describes how to make, inspect, and assign elements to a
5956 display table object.
5958 @defun make-display-table
5959 This creates and returns a display table. The table initially has
5960 @code{nil} in all elements.
5963 The ordinary elements of the display table are indexed by character
5964 codes; the element at index @var{c} says how to display the character
5965 code @var{c}. The value should be @code{nil} (which means to display
5966 the character @var{c} according to the usual display conventions;
5967 @pxref{Usual Display}), or a vector of glyph codes (which means to
5968 display the character @var{c} as those glyphs; @pxref{Glyphs}).
5970 @strong{Warning:} if you use the display table to change the display
5971 of newline characters, the whole buffer will be displayed as one long
5974 The display table also has six ``extra slots'' which serve special
5975 purposes. Here is a table of their meanings; @code{nil} in any slot
5976 means to use the default for that slot, as stated below.
5980 The glyph for the end of a truncated screen line (the default for this
5981 is @samp{$}). @xref{Glyphs}. On graphical terminals, Emacs uses
5982 arrows in the fringes to indicate truncation, so the display table has
5986 The glyph for the end of a continued line (the default is @samp{\}).
5987 On graphical terminals, Emacs uses curved arrows in the fringes to
5988 indicate continuation, so the display table has no effect.
5991 The glyph for indicating a character displayed as an octal character
5992 code (the default is @samp{\}).
5995 The glyph for indicating a control character (the default is @samp{^}).
5998 A vector of glyphs for indicating the presence of invisible lines (the
5999 default is @samp{...}). @xref{Selective Display}.
6002 The glyph used to draw the border between side-by-side windows (the
6003 default is @samp{|}). @xref{Splitting Windows}. This takes effect only
6004 when there are no scroll bars; if scroll bars are supported and in use,
6005 a scroll bar separates the two windows.
6008 For example, here is how to construct a display table that mimics
6009 the effect of setting @code{ctl-arrow} to a non-@code{nil} value
6010 (@pxref{Glyphs}, for the function @code{make-glyph-code}):
6013 (setq disptab (make-display-table))
6018 (vector (make-glyph-code ?^ 'escape-glyph)
6019 (make-glyph-code (+ i 64) 'escape-glyph)))))
6021 (vector (make-glyph-code ?^ 'escape-glyph)
6022 (make-glyph-code ?? 'escape-glyph)))))
6025 @defun display-table-slot display-table slot
6026 This function returns the value of the extra slot @var{slot} of
6027 @var{display-table}. The argument @var{slot} may be a number from 0 to
6028 5 inclusive, or a slot name (symbol). Valid symbols are
6029 @code{truncation}, @code{wrap}, @code{escape}, @code{control},
6030 @code{selective-display}, and @code{vertical-border}.
6033 @defun set-display-table-slot display-table slot value
6034 This function stores @var{value} in the extra slot @var{slot} of
6035 @var{display-table}. The argument @var{slot} may be a number from 0 to
6036 5 inclusive, or a slot name (symbol). Valid symbols are
6037 @code{truncation}, @code{wrap}, @code{escape}, @code{control},
6038 @code{selective-display}, and @code{vertical-border}.
6041 @defun describe-display-table display-table
6042 This function displays a description of the display table
6043 @var{display-table} in a help buffer.
6046 @deffn Command describe-current-display-table
6047 This command displays a description of the current display table in a
6051 @node Active Display Table
6052 @subsection Active Display Table
6053 @cindex active display table
6055 Each window can specify a display table, and so can each buffer.
6056 The window's display table, if there is one, takes precedence over the
6057 buffer's display table. If neither exists, Emacs tries to use the
6058 standard display table; if that is @code{nil}, Emacs uses the usual
6059 character display conventions (@pxref{Usual Display}).
6061 Note that display tables affect how the mode line is displayed, so
6062 if you want to force redisplay of the mode line using a new display
6063 table, call @code{force-mode-line-update} (@pxref{Mode Line Format}).
6065 @defun window-display-table &optional window
6066 This function returns @var{window}'s display table, or @code{nil} if
6067 there is none. The default for @var{window} is the selected window.
6070 @defun set-window-display-table window table
6071 This function sets the display table of @var{window} to @var{table}.
6072 The argument @var{table} should be either a display table or
6076 @defvar buffer-display-table
6077 This variable is automatically buffer-local in all buffers; its value
6078 specifies the buffer's display table. If it is @code{nil}, there is
6079 no buffer display table.
6082 @defvar standard-display-table
6083 The value of this variable is the standard display table, which is
6084 used when Emacs is displaying a buffer in a window with neither a
6085 window display table nor a buffer display table defined. Its default
6089 The @file{disp-table} library defines several functions for changing
6090 the standard display table.
6096 A @dfn{glyph} is a graphical symbol which occupies a single
6097 character position on the screen. Each glyph is represented in Lisp
6098 as a @dfn{glyph code}, which specifies a character and optionally a
6099 face to display it in (@pxref{Faces}). The main use of glyph codes is
6100 as the entries of display tables (@pxref{Display Tables}). The
6101 following functions are used to manipulate glyph codes:
6103 @defun make-glyph-code char &optional face
6104 This function returns a glyph code representing char @var{char} with
6105 face @var{face}. If @var{face} is omitted or @code{nil}, the glyph
6106 uses the default face; in that case, the glyph code is an integer. If
6107 @var{face} is non-@code{nil}, the glyph code is not necessarily an
6111 @defun glyph-char glyph
6112 This function returns the character of glyph code @var{glyph}.
6115 @defun glyph-face glyph
6116 This function returns face of glyph code @var{glyph}, or @code{nil} if
6117 @var{glyph} uses the default face.
6121 You can set up a @dfn{glyph table} to change how glyph codes are
6122 actually displayed on text terminals. This feature is semi-obsolete;
6123 use @code{glyphless-char-display} instead (@pxref{Glyphless Chars}).
6126 The value of this variable, if non-@code{nil}, is the current glyph
6127 table. It takes effect only on character terminals; on graphical
6128 displays, all glyphs are displayed literally. The glyph table should
6129 be a vector whose @var{g}th element specifies how to display glyph
6130 code @var{g}, where @var{g} is the glyph code for a glyph whose face
6131 is unspecified. Each element should be one of the following:
6135 Display this glyph literally.
6138 Display this glyph by sending the specified string to the terminal.
6141 Display the specified glyph code instead.
6144 Any integer glyph code greater than or equal to the length of the
6145 glyph table is displayed literally.
6149 @node Glyphless Chars
6150 @subsection Glyphless Character Display
6151 @cindex glyphless characters
6153 @dfn{Glyphless characters} are characters which are displayed in a
6154 special way, e.g., as a box containing a hexadecimal code, instead of
6155 being displayed literally. These include characters which are
6156 explicitly defined to be glyphless, as well as characters for which
6157 there is no available font (on a graphical display), and characters
6158 which cannot be encoded by the terminal's coding system (on a text
6161 @defvar glyphless-char-display
6162 The value of this variable is a char-table which defines glyphless
6163 characters and how they are displayed. Each entry must be one of the
6164 following display methods:
6168 Display the character in the usual way.
6170 @item @code{zero-width}
6171 Don't display the character.
6173 @item @code{thin-space}
6174 Display a thin space, 1-pixel wide on graphical displays, or
6175 1-character wide on text terminals.
6177 @item @code{empty-box}
6178 Display an empty box.
6180 @item @code{hex-code}
6181 Display a box containing the Unicode codepoint of the character, in
6182 hexadecimal notation.
6184 @item an @acronym{ASCII} string
6185 Display a box containing that string.
6187 @item a cons cell @code{(@var{graphical} . @var{text})}
6188 Display with @var{graphical} on graphical displays, and with
6189 @var{text} on text terminals. Both @var{graphical} and @var{text}
6190 must be one of the display methods described above.
6194 The @code{thin-space}, @code{empty-box}, @code{hex-code}, and
6195 @acronym{ASCII} string display methods are drawn with the
6196 @code{glyphless-char} face.
6198 The char-table has one extra slot, which determines how to display any
6199 character that cannot be displayed with any available font, or cannot
6200 be encoded by the terminal's coding system. Its value should be one
6201 of the above display methods, except @code{zero-width} or a cons cell.
6203 If a character has a non-@code{nil} entry in an active display table,
6204 the display table takes effect; in this case, Emacs does not consult
6205 @code{glyphless-char-display} at all.
6208 @defopt glyphless-char-display-control
6209 This user option provides a convenient way to set
6210 @code{glyphless-char-display} for groups of similar characters. Do
6211 not set its value directly from Lisp code; the value takes effect only
6212 via a custom @code{:set} function (@pxref{Variable Definitions}),
6213 which updates @code{glyphless-char-display}.
6215 Its value should be an alist of elements @code{(@var{group}
6216 . @var{method})}, where @var{group} is a symbol specifying a group of
6217 characters, and @var{method} is a symbol specifying how to display
6220 @var{group} should be one of the following:
6224 @acronym{ASCII} control characters @code{U+0000} to @code{U+001F},
6225 excluding the newline and tab characters (normally displayed as escape
6226 sequences like @samp{^A}; @pxref{Text Display,, How Text Is Displayed,
6227 emacs, The GNU Emacs Manual}).
6230 Non-@acronym{ASCII}, non-printing characters @code{U+0080} to
6231 @code{U+009F} (normally displayed as octal escape sequences like
6234 @item format-control
6235 Characters of Unicode General Category `Cf', such as @samp{U+200E}
6236 (Left-to-Right Mark), but excluding characters that have graphic
6237 images, such as @samp{U+00AD} (Soft Hyphen).
6240 Characters for there is no suitable font, or which cannot be encoded
6241 by the terminal's coding system.
6244 @c FIXME: this can also be `acronym', but that's not currently
6245 @c completely implemented; it applies only to the format-control
6246 @c group, and only works if the acronym is in `char-acronym-table'.
6247 The @var{method} symbol should be one of @code{zero-width},
6248 @code{thin-space}, @code{empty-box}, or @code{hex-code}. These have
6249 the same meanings as in @code{glyphless-char-display}, above.
6256 This section describes how to make Emacs ring the bell (or blink the
6257 screen) to attract the user's attention. Be conservative about how
6258 often you do this; frequent bells can become irritating. Also be
6259 careful not to use just beeping when signaling an error is more
6260 appropriate (@pxref{Errors}).
6262 @defun ding &optional do-not-terminate
6263 @cindex keyboard macro termination
6264 This function beeps, or flashes the screen (see @code{visible-bell} below).
6265 It also terminates any keyboard macro currently executing unless
6266 @var{do-not-terminate} is non-@code{nil}.
6269 @defun beep &optional do-not-terminate
6270 This is a synonym for @code{ding}.
6273 @defopt visible-bell
6274 This variable determines whether Emacs should flash the screen to
6275 represent a bell. Non-@code{nil} means yes, @code{nil} means no.
6276 This is effective on graphical displays, and on text terminals
6277 provided the terminal's Termcap entry defines the visible bell
6278 capability (@samp{vb}).
6281 @defvar ring-bell-function
6282 If this is non-@code{nil}, it specifies how Emacs should ``ring the
6283 bell''. Its value should be a function of no arguments. If this is
6284 non-@code{nil}, it takes precedence over the @code{visible-bell}
6288 @node Window Systems
6289 @section Window Systems
6291 Emacs works with several window systems, most notably the X Window
6292 System. Both Emacs and X use the term ``window'', but use it
6293 differently. An Emacs frame is a single window as far as X is
6294 concerned; the individual Emacs windows are not known to X at all.
6296 @defvar window-system
6297 This terminal-local variable tells Lisp programs what window system
6298 Emacs is using for displaying the frame. The possible values are
6302 @cindex X Window System
6303 Emacs is displaying the frame using X.
6305 Emacs is displaying the frame using native MS-Windows GUI.
6307 Emacs is displaying the frame using the Nextstep interface (used on
6308 GNUstep and Mac OS X).
6310 Emacs is displaying the frame using MS-DOS direct screen writes.
6312 Emacs is displaying the frame on a character-based terminal.
6316 @defvar initial-window-system
6317 This variable holds the value of @code{window-system} used for the
6318 first frame created by Emacs during startup. (When Emacs is invoked
6319 with the @option{--daemon} option, it does not create any initial
6320 frames, so @code{initial-window-system} is @code{nil}. @xref{Initial
6321 Options, daemon,, emacs, The GNU Emacs Manual}.)
6324 @defun window-system &optional frame
6325 This function returns a symbol whose name tells what window system is
6326 used for displaying @var{frame} (which defaults to the currently
6327 selected frame). The list of possible symbols it returns is the same
6328 one documented for the variable @code{window-system} above.
6331 Do @emph{not} use @code{window-system} and
6332 @code{initial-window-system} as predicates or boolean flag variables,
6333 if you want to write code that works differently on text terminals and
6334 graphic displays. That is because @code{window-system} is not a good
6335 indicator of Emacs capabilities on a given display type. Instead, use
6336 @code{display-graphic-p} or any of the other @code{display-*-p}
6337 predicates described in @ref{Display Feature Testing}.
6339 @defvar window-setup-hook
6340 This variable is a normal hook which Emacs runs after handling the
6341 initialization files. Emacs runs this hook after it has completed
6342 loading your init file, the default initialization file (if
6343 any), and the terminal-specific Lisp code, and running the hook
6344 @code{term-setup-hook}.
6346 This hook is used for internal purposes: setting up communication with
6347 the window system, and creating the initial window. Users should not
6351 @node Bidirectional Display
6352 @section Bidirectional Display
6353 @cindex bidirectional display
6354 @cindex right-to-left text
6356 Emacs can display text written in scripts, such as Arabic, Farsi,
6357 and Hebrew, whose natural ordering for horizontal text display runs
6358 from right to left. Furthermore, segments of Latin script and digits
6359 embedded in right-to-left text are displayed left-to-right, while
6360 segments of right-to-left script embedded in left-to-right text
6361 (e.g., Arabic or Hebrew text in comments or strings in a program
6362 source file) are appropriately displayed right-to-left. We call such
6363 mixtures of left-to-right and right-to-left text @dfn{bidirectional
6364 text}. This section describes the facilities and options for editing
6365 and displaying bidirectional text.
6367 @cindex logical order
6368 @cindex reading order
6369 @cindex visual order
6370 @cindex unicode bidirectional algorithm
6371 @cindex bidirectional reordering
6372 Text is stored in Emacs buffers and strings in @dfn{logical} (or
6373 @dfn{reading}) order, i.e., the order in which a human would read
6374 each character. In right-to-left and bidirectional text, the order in
6375 which characters are displayed on the screen (called @dfn{visual
6376 order}) is not the same as logical order; the characters' screen
6377 positions do not increase monotonically with string or buffer
6378 position. In performing this @dfn{bidirectional reordering}, Emacs
6379 follows the Unicode Bidirectional Algorithm (a.k.a.@: @acronym{UBA}),
6380 which is described in Annex #9 of the Unicode standard
6381 (@url{http://www.unicode.org/reports/tr9/}). Emacs provides a ``Full
6382 Bidirectionality'' class implementation of the @acronym{UBA}.
6384 @defvar bidi-display-reordering
6385 If the value of this buffer-local variable is non-@code{nil} (the
6386 default), Emacs performs bidirectional reordering for display. The
6387 reordering affects buffer text, as well as display strings and overlay
6388 strings from text and overlay properties in the buffer (@pxref{Overlay
6389 Properties}, and @pxref{Display Property}). If the value is
6390 @code{nil}, Emacs does not perform bidirectional reordering in the
6393 The default value of @code{bidi-display-reordering} controls the
6394 reordering of strings which are not directly supplied by a buffer,
6395 including the text displayed in mode lines (@pxref{Mode Line Format})
6396 and header lines (@pxref{Header Lines}).
6399 @cindex unibyte buffers, and bidi reordering
6400 Emacs never reorders the text of a unibyte buffer, even if
6401 @code{bidi-display-reordering} is non-@code{nil} in the buffer. This
6402 is because unibyte buffers contain raw bytes, not characters, and thus
6403 lack the directionality properties required for reordering.
6404 Therefore, to test whether text in a buffer will be reordered for
6405 display, it is not enough to test the value of
6406 @code{bidi-display-reordering} alone. The correct test is this:
6409 (if (and enable-multibyte-characters
6410 bidi-display-reordering)
6411 ;; Buffer is being reordered for display
6415 However, unibyte display and overlay strings @emph{are} reordered if
6416 their parent buffer is reordered. This is because plain-@sc{ascii}
6417 strings are stored by Emacs as unibyte strings. If a unibyte display
6418 or overlay string includes non-@sc{ascii} characters, these characters
6419 are assumed to have left-to-right direction.
6421 @cindex display properties, and bidi reordering of text
6422 Text covered by @code{display} text properties, by overlays with
6423 @code{display} properties whose value is a string, and by any other
6424 properties that replace buffer text, is treated as a single unit when
6425 it is reordered for display. That is, the entire chunk of text
6426 covered by these properties is reordered together. Moreover, the
6427 bidirectional properties of the characters in such a chunk of text are
6428 ignored, and Emacs reorders them as if they were replaced with a
6429 single character @code{U+FFFC}, known as the @dfn{Object Replacement
6430 Character}. This means that placing a display property over a portion
6431 of text may change the way that the surrounding text is reordered for
6432 display. To prevent this unexpected effect, always place such
6433 properties on text whose directionality is identical with text that
6436 @cindex base direction of a paragraph
6437 Each paragraph of bidirectional text has a @dfn{base direction},
6438 either right-to-left or left-to-right. Left-to-right paragraphs are
6439 displayed beginning at the left margin of the window, and are
6440 truncated or continued when the text reaches the right margin.
6441 Right-to-left paragraphs are displayed beginning at the right margin,
6442 and are continued or truncated at the left margin.
6444 By default, Emacs determines the base direction of each paragraph by
6445 looking at the text at its beginning. The precise method of
6446 determining the base direction is specified by the @acronym{UBA}; in a
6447 nutshell, the first character in a paragraph that has an explicit
6448 directionality determines the base direction of the paragraph.
6449 However, sometimes a buffer may need to force a certain base direction
6450 for its paragraphs. For example, buffers containing program source
6451 code should force all paragraphs to be displayed left-to-right. You
6452 can use following variable to do this:
6454 @defvar bidi-paragraph-direction
6455 If the value of this buffer-local variable is the symbol
6456 @code{right-to-left} or @code{left-to-right}, all paragraphs in the
6457 buffer are assumed to have that specified direction. Any other value
6458 is equivalent to @code{nil} (the default), which means to determine
6459 the base direction of each paragraph from its contents.
6461 @cindex @code{prog-mode}, and @code{bidi-paragraph-direction}
6462 Modes for program source code should set this to @code{left-to-right}.
6463 Prog mode does this by default, so modes derived from Prog mode do not
6464 need to set this explicitly (@pxref{Basic Major Modes}).
6467 @defun current-bidi-paragraph-direction &optional buffer
6468 This function returns the paragraph direction at point in the named
6469 @var{buffer}. The returned value is a symbol, either
6470 @code{left-to-right} or @code{right-to-left}. If @var{buffer} is
6471 omitted or @code{nil}, it defaults to the current buffer. If the
6472 buffer-local value of the variable @code{bidi-paragraph-direction} is
6473 non-@code{nil}, the returned value will be identical to that value;
6474 otherwise, the returned value reflects the paragraph direction
6475 determined dynamically by Emacs. For buffers whose value of
6476 @code{bidi-display-reordering} is @code{nil} as well as unibyte
6477 buffers, this function always returns @code{left-to-right}.
6480 @cindex visual-order cursor motion
6481 Sometimes there's a need to move point in strict visual order,
6482 either to the left or to the right of its current screen position.
6483 Emacs provides a primitive to do that.
6485 @defun move-point-visually direction
6486 This function moves point of the currently selected window to the
6487 buffer position that appears immediately to the right or to the left
6488 of point on the screen. If @var{direction} is positive, point will
6489 move one screen position to the right, otherwise it will move one
6490 screen position to the left. Note that, depending on the surrounding
6491 bidirectional context, this could potentially move point many buffer
6492 positions away. If invoked at the end of a screen line, the function
6493 moves point to the rightmost or leftmost screen position of the next
6494 or previous screen line, as appropriate for the value of
6497 The function returns the new buffer position as its value.
6500 @cindex layout on display, and bidirectional text
6501 @cindex jumbled display of bidirectional text
6502 @cindex concatenating bidirectional strings
6503 Bidirectional reordering can have surprising and unpleasant effects
6504 when two strings with bidirectional content are juxtaposed in a
6505 buffer, or otherwise programmatically concatenated into a string of
6506 text. A typical problematic case is when a buffer consists of
6507 sequences of text ``fields'' separated by whitespace or punctuation
6508 characters, like Buffer Menu mode or Rmail Summary Mode. Because the
6509 punctuation characters used as separators have @dfn{weak
6510 directionality}, they take on the directionality of surrounding text.
6511 As result, a numeric field that follows a field with bidirectional
6512 content can be displayed @emph{to the left} of the preceding field,
6513 messing up the expected layout. There are several ways to avoid this
6518 Append the special character @code{U+200E}, LEFT-TO-RIGHT MARK, or
6519 @acronym{LRM}, to the end of each field that may have bidirectional
6520 content, or prepend it to the beginning of the following field. The
6521 function @code{bidi-string-mark-left-to-right}, described below, comes
6522 in handy for this purpose. (In a right-to-left paragraph, use
6523 @code{U+200F}, RIGHT-TO-LEFT MARK, or @acronym{RLM}, instead.) This
6524 is one of the solutions recommended by the UBA.
6527 Include the tab character in the field separator. The tab character
6528 plays the role of @dfn{segment separator} in bidirectional reordering,
6529 causing the text on either side to be reordered separately.
6531 @cindex @code{space} display spec, and bidirectional text
6533 Separate fields with a @code{display} property or overlay with a
6534 property value of the form @code{(space . PROPS)} (@pxref{Specified
6535 Space}). Emacs treats this display specification as a @dfn{paragraph
6536 separator}, and reorders the text on either side separately.
6539 @defun bidi-string-mark-left-to-right string
6540 This function returns its argument @var{string}, possibly modified,
6541 such that the result can be safely concatenated with another string,
6542 or juxtaposed with another string in a buffer, without disrupting the
6543 relative layout of this string and the next one on display. If the
6544 string returned by this function is displayed as part of a
6545 left-to-right paragraph, it will always appear on display to the left
6546 of the text that follows it. The function works by examining the
6547 characters of its argument, and if any of those characters could cause
6548 reordering on display, the function appends the @acronym{LRM}
6549 character to the string. The appended @acronym{LRM} character is made
6550 invisible by giving it an @code{invisible} text property of @code{t}
6551 (@pxref{Invisible Text}).
6554 The reordering algorithm uses the bidirectional properties of the
6555 characters stored as their @code{bidi-class} property
6556 (@pxref{Character Properties}). Lisp programs can change these
6557 properties by calling the @code{put-char-code-property} function.
6558 However, doing this requires a thorough understanding of the
6559 @acronym{UBA}, and is therefore not recommended. Any changes to the
6560 bidirectional properties of a character have global effect: they
6561 affect all Emacs frames and windows.
6563 Similarly, the @code{mirroring} property is used to display the
6564 appropriate mirrored character in the reordered text. Lisp programs
6565 can affect the mirrored display by changing this property. Again, any
6566 such changes affect all of Emacs display.