2 @c This is part of the GNU Emacs Lisp Reference Manual.
3 @c Copyright (C) 1990-1995, 1998-2012 Free Software Foundation, Inc.
4 @c See the file elisp.texi for copying conditions.
5 @setfilename ../../info/display
6 @node Display, System Interface, Processes, Top
9 This chapter describes a number of features related to the display
10 that Emacs presents to the user.
13 * Refresh Screen:: Clearing the screen and redrawing everything on it.
14 * Forcing Redisplay:: Forcing redisplay.
15 * Truncation:: Folding or wrapping long text lines.
16 * The Echo Area:: Displaying messages at the bottom of the screen.
17 * Warnings:: Displaying warning messages for the user.
18 * Invisible Text:: Hiding part of the buffer text.
19 * Selective Display:: Hiding part of the buffer text (the old way).
20 * Temporary Displays:: Displays that go away automatically.
21 * Overlays:: Use overlays to highlight parts of the buffer.
22 * Width:: How wide a character or string is on the screen.
23 * Line Height:: Controlling the height of lines.
24 * Faces:: A face defines a graphics style for text characters:
26 * Fringes:: Controlling window fringes.
27 * Scroll Bars:: Controlling vertical scroll bars.
28 * Display Property:: Enabling special display features.
29 * Images:: Displaying images in Emacs buffers.
30 * Buttons:: Adding clickable buttons to Emacs buffers.
31 * Abstract Display:: Emacs's Widget for Object Collections.
32 * Blinking:: How Emacs shows the matching open parenthesis.
33 * Character Display:: How Emacs displays individual characters.
34 * Beeping:: Audible signal to the user.
35 * Window Systems:: Which window system is being used.
36 * Bidirectional Display:: Display of bidirectional scripts, such as
41 @section Refreshing the Screen
43 The function @code{redraw-frame} clears and redisplays the entire
44 contents of a given frame (@pxref{Frames}). This is useful if the
47 @defun redraw-frame frame
48 This function clears and redisplays frame @var{frame}.
51 Even more powerful is @code{redraw-display}:
53 @deffn Command redraw-display
54 This function clears and redisplays all visible frames.
57 In Emacs, processing user input takes priority over redisplay. If
58 you call these functions when input is available, they don't redisplay
59 immediately, but the requested redisplay does happen
60 eventually---after all the input has been processed.
62 On text terminals, suspending and resuming Emacs normally also
63 refreshes the screen. Some terminal emulators record separate
64 contents for display-oriented programs such as Emacs and for ordinary
65 sequential display. If you are using such a terminal, you might want
66 to inhibit the redisplay on resumption.
68 @defopt no-redraw-on-reenter
69 @cindex suspend (cf. @code{no-redraw-on-reenter})
70 @cindex resume (cf. @code{no-redraw-on-reenter})
71 This variable controls whether Emacs redraws the entire screen after it
72 has been suspended and resumed. Non-@code{nil} means there is no need
73 to redraw, @code{nil} means redrawing is needed. The default is @code{nil}.
76 @node Forcing Redisplay
77 @section Forcing Redisplay
78 @cindex forcing redisplay
80 Emacs normally tries to redisplay the screen whenever it waits for
81 input. With the following function, you can request an immediate
82 attempt to redisplay, in the middle of Lisp code, without actually
85 @defun redisplay &optional force
86 This function tries immediately to redisplay. The optional argument
87 @var{force}, if non-@code{nil}, forces the redisplay to be performed,
88 instead of being preempted, even if input is pending and the variable
89 @code{redisplay-dont-pause} is @code{nil} (see below). If
90 @code{redisplay-dont-pause} is non-@code{nil} (the default), this
91 function redisplays in any case, i.e.@: @var{force} does nothing.
93 The function returns @code{t} if it actually tried to redisplay, and
94 @code{nil} otherwise. A value of @code{t} does not mean that
95 redisplay proceeded to completion; it could have been preempted by
99 @defvar redisplay-dont-pause
100 If this variable is @code{nil}, arriving input events preempt
101 redisplay; Emacs avoids starting a redisplay, and stops any redisplay
102 that is in progress, until the input has been processed. In
103 particular, @code{(redisplay)} returns @code{nil} without actually
104 redisplaying, if there is pending input.
106 The default value is @code{t}, which means that pending input does not
110 @defvar redisplay-preemption-period
111 If @code{redisplay-dont-pause} is @code{nil}, this variable specifies
112 how many seconds Emacs waits between checks for new input during
113 redisplay; if input arrives during this interval, redisplay stops and
114 the input is processed. The default value is 0.1; if the value is
115 @code{nil}, Emacs does not check for input during redisplay.
117 This variable has no effect when @code{redisplay-dont-pause} is
118 non-@code{nil} (the default).
121 Although @code{redisplay} tries immediately to redisplay, it does
122 not change how Emacs decides which parts of its frame(s) to redisplay.
123 By contrast, the following function adds certain windows to the
124 pending redisplay work (as if their contents had completely changed),
125 but does not immediately try to perform redisplay.
127 @defun force-window-update &optional object
128 This function forces some or all windows to be updated the next time
129 Emacs does a redisplay. If @var{object} is a window, that window is
130 to be updated. If @var{object} is a buffer or buffer name, all
131 windows displaying that buffer are to be updated. If @var{object} is
132 @code{nil} (or omitted), all windows are to be updated.
134 This function does not do a redisplay immediately; Emacs does that as
135 it waits for input, or when the function @code{redisplay} is called.
140 @cindex line wrapping
141 @cindex line truncation
142 @cindex continuation lines
143 @cindex @samp{$} in display
144 @cindex @samp{\} in display
146 When a line of text extends beyond the right edge of a window, Emacs
147 can @dfn{continue} the line (make it ``wrap'' to the next screen
148 line), or @dfn{truncate} the line (limit it to one screen line). The
149 additional screen lines used to display a long text line are called
150 @dfn{continuation} lines. Continuation is not the same as filling;
151 continuation happens on the screen only, not in the buffer contents,
152 and it breaks a line precisely at the right margin, not at a word
153 boundary. @xref{Filling}.
155 On a graphical display, tiny arrow images in the window fringes
156 indicate truncated and continued lines (@pxref{Fringes}). On a text
157 terminal, a @samp{$} in the rightmost column of the window indicates
158 truncation; a @samp{\} on the rightmost column indicates a line that
159 ``wraps''. (The display table can specify alternate characters to use
160 for this; @pxref{Display Tables}).
162 @defopt truncate-lines
163 If this buffer-local variable is non-@code{nil}, lines that extend
164 beyond the right edge of the window are truncated; otherwise, they are
165 continued. As a special exception, the variable
166 @code{truncate-partial-width-windows} takes precedence in
167 @dfn{partial-width} windows (i.e.@: windows that do not occupy the
171 @defopt truncate-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-line-scans} to @code{t}.
223 @defvar cache-long-line-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 The @dfn{echo area} is used for displaying error messages
240 (@pxref{Errors}), for messages made with the @code{message} primitive,
241 and for echoing keystrokes. It is not the same as the minibuffer,
242 despite the fact that the minibuffer appears (when active) in the same
243 place on the screen as the echo area. @xref{Minibuffer,, The
244 Minibuffer, emacs, The GNU Emacs Manual}.
246 Apart from the functions documented in this section, you can print
247 Lisp objects to the echo area by specifying @code{t} as the output
248 stream. @xref{Output Streams}.
251 * Displaying Messages:: Explicitly displaying text in the echo area.
252 * Progress:: Informing user about progress of a long operation.
253 * Logging Messages:: Echo area messages are logged for the user.
254 * Echo Area Customization:: Controlling the echo area.
257 @node Displaying Messages
258 @subsection Displaying Messages in the Echo Area
259 @cindex display message in echo area
261 This section describes the standard functions for displaying
262 messages in the echo area.
264 @defun message format-string &rest arguments
265 This function displays a message in the echo area.
266 @var{format-string} is a format string, and @var{arguments} are the
267 objects for its format specifications, like in the @code{format}
268 function (@pxref{Formatting Strings}). The resulting formatted string
269 is displayed in the echo area; if it contains @code{face} text
270 properties, it is displayed with the specified faces (@pxref{Faces}).
271 The string is also added to the @file{*Messages*} buffer, but without
272 text properties (@pxref{Logging Messages}).
274 In batch mode, the message is printed to the standard error stream,
275 followed by a newline.
277 If @var{format-string} is @code{nil} or the empty string,
278 @code{message} clears the echo area; if the echo area has been
279 expanded automatically, this brings it back to its normal size. If
280 the minibuffer is active, this brings the minibuffer contents back
281 onto the screen immediately.
285 (message "Minibuffer depth is %d."
287 @print{} Minibuffer depth is 0.
288 @result{} "Minibuffer depth is 0."
292 ---------- Echo Area ----------
293 Minibuffer depth is 0.
294 ---------- Echo Area ----------
298 To automatically display a message in the echo area or in a pop-buffer,
299 depending on its size, use @code{display-message-or-buffer} (see below).
302 @defmac with-temp-message message &rest body
303 This construct displays a message in the echo area temporarily, during
304 the execution of @var{body}. It displays @var{message}, executes
305 @var{body}, then returns the value of the last body form while restoring
306 the previous echo area contents.
309 @defun message-or-box format-string &rest arguments
310 This function displays a message like @code{message}, but may display it
311 in a dialog box instead of the echo area. If this function is called in
312 a command that was invoked using the mouse---more precisely, if
313 @code{last-nonmenu-event} (@pxref{Command Loop Info}) is either
314 @code{nil} or a list---then it uses a dialog box or pop-up menu to
315 display the message. Otherwise, it uses the echo area. (This is the
316 same criterion that @code{y-or-n-p} uses to make a similar decision; see
317 @ref{Yes-or-No Queries}.)
319 You can force use of the mouse or of the echo area by binding
320 @code{last-nonmenu-event} to a suitable value around the call.
323 @defun message-box format-string &rest arguments
325 This function displays a message like @code{message}, but uses a dialog
326 box (or a pop-up menu) whenever that is possible. If it is impossible
327 to use a dialog box or pop-up menu, because the terminal does not
328 support them, then @code{message-box} uses the echo area, like
332 @defun display-message-or-buffer message &optional buffer-name not-this-window frame
333 This function displays the message @var{message}, which may be either a
334 string or a buffer. If it is shorter than the maximum height of the
335 echo area, as defined by @code{max-mini-window-height}, it is displayed
336 in the echo area, using @code{message}. Otherwise,
337 @code{display-buffer} is used to show it in a pop-up buffer.
339 Returns either the string shown in the echo area, or when a pop-up
340 buffer is used, the window used to display it.
342 If @var{message} is a string, then the optional argument
343 @var{buffer-name} is the name of the buffer used to display it when a
344 pop-up buffer is used, defaulting to @file{*Message*}. In the case
345 where @var{message} is a string and displayed in the echo area, it is
346 not specified whether the contents are inserted into the buffer anyway.
348 The optional arguments @var{not-this-window} and @var{frame} are as for
349 @code{display-buffer}, and only used if a buffer is displayed.
352 @defun current-message
353 This function returns the message currently being displayed in the
354 echo area, or @code{nil} if there is none.
358 @subsection Reporting Operation Progress
359 @cindex progress reporting
361 When an operation can take a while to finish, you should inform the
362 user about the progress it makes. This way the user can estimate
363 remaining time and clearly see that Emacs is busy working, not hung.
364 A convenient way to do this is to use a @dfn{progress reporter}.
366 Here is a working example that does nothing useful:
369 (let ((progress-reporter
370 (make-progress-reporter "Collecting mana for Emacs..."
374 (progress-reporter-update progress-reporter k))
375 (progress-reporter-done progress-reporter))
378 @defun make-progress-reporter message &optional min-value max-value current-value min-change min-time
379 This function creates and returns a progress reporter object, which
380 you will use as an argument for the other functions listed below. The
381 idea is to precompute as much data as possible to make progress
384 When this progress reporter is subsequently used, it will display
385 @var{message} in the echo area, followed by progress percentage.
386 @var{message} is treated as a simple string. If you need it to depend
387 on a filename, for instance, use @code{format} before calling this
390 The arguments @var{min-value} and @var{max-value} should be numbers
391 standing for the starting and final states of the operation. For
392 instance, an operation that ``scans'' a buffer should set these to the
393 results of @code{point-min} and @code{point-max} correspondingly.
394 @var{max-value} should be greater than @var{min-value}.
396 Alternatively, you can set @var{min-value} and @var{max-value} to
397 @code{nil}. In that case, the progress reporter does not report
398 process percentages; it instead displays a ``spinner'' that rotates a
399 notch each time you update the progress reporter.
401 If @var{min-value} and @var{max-value} are numbers, you can give the
402 argument @var{current-value} a numerical value specifying the initial
403 progress; if omitted, this defaults to @var{min-value}.
405 The remaining arguments control the rate of echo area updates. The
406 progress reporter will wait for at least @var{min-change} more
407 percents of the operation to be completed before printing next
408 message; the default is one percent. @var{min-time} specifies the
409 minimum time in seconds to pass between successive prints; the default
410 is 0.2 seconds. (On some operating systems, the progress reporter may
411 handle fractions of seconds with varying precision).
413 This function calls @code{progress-reporter-update}, so the first
414 message is printed immediately.
417 @defun progress-reporter-update reporter &optional value
418 This function does the main work of reporting progress of your
419 operation. It displays the message of @var{reporter}, followed by
420 progress percentage determined by @var{value}. If percentage is zero,
421 or close enough according to the @var{min-change} and @var{min-time}
422 arguments, then it is omitted from the output.
424 @var{reporter} must be the result of a call to
425 @code{make-progress-reporter}. @var{value} specifies the current
426 state of your operation and must be between @var{min-value} and
427 @var{max-value} (inclusive) as passed to
428 @code{make-progress-reporter}. For instance, if you scan a buffer,
429 then @var{value} should be the result of a call to @code{point}.
431 This function respects @var{min-change} and @var{min-time} as passed
432 to @code{make-progress-reporter} and so does not output new messages
433 on every invocation. It is thus very fast and normally you should not
434 try to reduce the number of calls to it: resulting overhead will most
435 likely negate your effort.
438 @defun progress-reporter-force-update reporter &optional value new-message
439 This function is similar to @code{progress-reporter-update} except
440 that it prints a message in the echo area unconditionally.
442 The first two arguments have the same meaning as for
443 @code{progress-reporter-update}. Optional @var{new-message} allows
444 you to change the message of the @var{reporter}. Since this functions
445 always updates the echo area, such a change will be immediately
446 presented to the user.
449 @defun progress-reporter-done reporter
450 This function should be called when the operation is finished. It
451 prints the message of @var{reporter} followed by word ``done'' in the
454 You should always call this function and not hope for
455 @code{progress-reporter-update} to print ``100%''. Firstly, it may
456 never print it, there are many good reasons for this not to happen.
457 Secondly, ``done'' is more explicit.
460 @defmac dotimes-with-progress-reporter (var count [result]) message body@dots{}
461 This is a convenience macro that works the same way as @code{dotimes}
462 does, but also reports loop progress using the functions described
463 above. It allows you to save some typing.
465 You can rewrite the example in the beginning of this node using
469 (dotimes-with-progress-reporter
471 "Collecting some mana for Emacs..."
476 @node Logging Messages
477 @subsection Logging Messages in @file{*Messages*}
478 @cindex logging echo-area messages
480 Almost all the messages displayed in the echo area are also recorded
481 in the @file{*Messages*} buffer so that the user can refer back to
482 them. This includes all the messages that are output with
485 @defopt message-log-max
486 This variable specifies how many lines to keep in the @file{*Messages*}
487 buffer. The value @code{t} means there is no limit on how many lines to
488 keep. The value @code{nil} disables message logging entirely. Here's
489 how to display a message and prevent it from being logged:
492 (let (message-log-max)
497 To make @file{*Messages*} more convenient for the user, the logging
498 facility combines successive identical messages. It also combines
499 successive related messages for the sake of two cases: question
500 followed by answer, and a series of progress messages.
502 A ``question followed by an answer'' means two messages like the
503 ones produced by @code{y-or-n-p}: the first is @samp{@var{question}},
504 and the second is @samp{@var{question}...@var{answer}}. The first
505 message conveys no additional information beyond what's in the second,
506 so logging the second message discards the first from the log.
508 A ``series of progress messages'' means successive messages like
509 those produced by @code{make-progress-reporter}. They have the form
510 @samp{@var{base}...@var{how-far}}, where @var{base} is the same each
511 time, while @var{how-far} varies. Logging each message in the series
512 discards the previous one, provided they are consecutive.
514 The functions @code{make-progress-reporter} and @code{y-or-n-p}
515 don't have to do anything special to activate the message log
516 combination feature. It operates whenever two consecutive messages
517 are logged that share a common prefix ending in @samp{...}.
519 @node Echo Area Customization
520 @subsection Echo Area Customization
522 These variables control details of how the echo area works.
524 @defvar cursor-in-echo-area
525 This variable controls where the cursor appears when a message is
526 displayed in the echo area. If it is non-@code{nil}, then the cursor
527 appears at the end of the message. Otherwise, the cursor appears at
528 point---not in the echo area at all.
530 The value is normally @code{nil}; Lisp programs bind it to @code{t}
531 for brief periods of time.
534 @defvar echo-area-clear-hook
535 This normal hook is run whenever the echo area is cleared---either by
536 @code{(message nil)} or for any other reason.
539 @defopt echo-keystrokes
540 This variable determines how much time should elapse before command
541 characters echo. Its value must be an integer or floating point number,
543 number of seconds to wait before echoing. If the user types a prefix
544 key (such as @kbd{C-x}) and then delays this many seconds before
545 continuing, the prefix key is echoed in the echo area. (Once echoing
546 begins in a key sequence, all subsequent characters in the same key
547 sequence are echoed immediately.)
549 If the value is zero, then command input is not echoed.
552 @defvar message-truncate-lines
553 Normally, displaying a long message resizes the echo area to display
554 the entire message. But if the variable @code{message-truncate-lines}
555 is non-@code{nil}, the echo area does not resize, and the message is
559 The variable @code{max-mini-window-height}, which specifies the
560 maximum height for resizing minibuffer windows, also applies to the
561 echo area (which is really a special use of the minibuffer window;
562 @pxref{Minibuffer Misc}).
565 @section Reporting Warnings
568 @dfn{Warnings} are a facility for a program to inform the user of a
569 possible problem, but continue running.
572 * Warning Basics:: Warnings concepts and functions to report them.
573 * Warning Variables:: Variables programs bind to customize their warnings.
574 * Warning Options:: Variables users set to control display of warnings.
575 * Delayed Warnings:: Deferring a warning until the end of a command.
579 @subsection Warning Basics
580 @cindex severity level
582 Every warning has a textual message, which explains the problem for
583 the user, and a @dfn{severity level} which is a symbol. Here are the
584 possible severity levels, in order of decreasing severity, and their
589 A problem that will seriously impair Emacs operation soon
590 if you do not attend to it promptly.
592 A report of data or circumstances that are inherently wrong.
594 A report of data or circumstances that are not inherently wrong, but
595 raise suspicion of a possible problem.
597 A report of information that may be useful if you are debugging.
600 When your program encounters invalid input data, it can either
601 signal a Lisp error by calling @code{error} or @code{signal} or report
602 a warning with severity @code{:error}. Signaling a Lisp error is the
603 easiest thing to do, but it means the program cannot continue
604 processing. If you want to take the trouble to implement a way to
605 continue processing despite the bad data, then reporting a warning of
606 severity @code{:error} is the right way to inform the user of the
607 problem. For instance, the Emacs Lisp byte compiler can report an
608 error that way and continue compiling other functions. (If the
609 program signals a Lisp error and then handles it with
610 @code{condition-case}, the user won't see the error message; it could
611 show the message to the user by reporting it as a warning.)
614 Each warning has a @dfn{warning type} to classify it. The type is a
615 list of symbols. The first symbol should be the custom group that you
616 use for the program's user options. For example, byte compiler
617 warnings use the warning type @code{(bytecomp)}. You can also
618 subcategorize the warnings, if you wish, by using more symbols in the
621 @defun display-warning type message &optional level buffer-name
622 This function reports a warning, using @var{message} as the message
623 and @var{type} as the warning type. @var{level} should be the
624 severity level, with @code{:warning} being the default.
626 @var{buffer-name}, if non-@code{nil}, specifies the name of the buffer
627 for logging the warning. By default, it is @file{*Warnings*}.
630 @defun lwarn type level message &rest args
631 This function reports a warning using the value of @code{(format
632 @var{message} @var{args}...)} as the message. In other respects it is
633 equivalent to @code{display-warning}.
636 @defun warn message &rest args
637 This function reports a warning using the value of @code{(format
638 @var{message} @var{args}...)} as the message, @code{(emacs)} as the
639 type, and @code{:warning} as the severity level. It exists for
640 compatibility only; we recommend not using it, because you should
641 specify a specific warning type.
644 @node Warning Variables
645 @subsection Warning Variables
647 Programs can customize how their warnings appear by binding
648 the variables described in this section.
650 @defvar warning-levels
651 This list defines the meaning and severity order of the warning
652 severity levels. Each element defines one severity level,
653 and they are arranged in order of decreasing severity.
655 Each element has the form @code{(@var{level} @var{string}
656 @var{function})}, where @var{level} is the severity level it defines.
657 @var{string} specifies the textual description of this level.
658 @var{string} should use @samp{%s} to specify where to put the warning
659 type information, or it can omit the @samp{%s} so as not to include
662 The optional @var{function}, if non-@code{nil}, is a function to call
663 with no arguments, to get the user's attention.
665 Normally you should not change the value of this variable.
668 @defvar warning-prefix-function
669 If non-@code{nil}, the value is a function to generate prefix text for
670 warnings. Programs can bind the variable to a suitable function.
671 @code{display-warning} calls this function with the warnings buffer
672 current, and the function can insert text in it. That text becomes
673 the beginning of the warning message.
675 The function is called with two arguments, the severity level and its
676 entry in @code{warning-levels}. It should return a list to use as the
677 entry (this value need not be an actual member of
678 @code{warning-levels}). By constructing this value, the function can
679 change the severity of the warning, or specify different handling for
680 a given severity level.
682 If the variable's value is @code{nil} then there is no function
686 @defvar warning-series
687 Programs can bind this variable to @code{t} to say that the next
688 warning should begin a series. When several warnings form a series,
689 that means to leave point on the first warning of the series, rather
690 than keep moving it for each warning so that it appears on the last one.
691 The series ends when the local binding is unbound and
692 @code{warning-series} becomes @code{nil} again.
694 The value can also be a symbol with a function definition. That is
695 equivalent to @code{t}, except that the next warning will also call
696 the function with no arguments with the warnings buffer current. The
697 function can insert text which will serve as a header for the series
700 Once a series has begun, the value is a marker which points to the
701 buffer position in the warnings buffer of the start of the series.
703 The variable's normal value is @code{nil}, which means to handle
704 each warning separately.
707 @defvar warning-fill-prefix
708 When this variable is non-@code{nil}, it specifies a fill prefix to
709 use for filling each warning's text.
712 @defvar warning-type-format
713 This variable specifies the format for displaying the warning type
714 in the warning message. The result of formatting the type this way
715 gets included in the message under the control of the string in the
716 entry in @code{warning-levels}. The default value is @code{" (%s)"}.
717 If you bind it to @code{""} then the warning type won't appear at
721 @node Warning Options
722 @subsection Warning Options
724 These variables are used by users to control what happens
725 when a Lisp program reports a warning.
727 @defopt warning-minimum-level
728 This user option specifies the minimum severity level that should be
729 shown immediately to the user. The default is @code{:warning}, which
730 means to immediately display all warnings except @code{:debug}
734 @defopt warning-minimum-log-level
735 This user option specifies the minimum severity level that should be
736 logged in the warnings buffer. The default is @code{:warning}, which
737 means to log all warnings except @code{:debug} warnings.
740 @defopt warning-suppress-types
741 This list specifies which warning types should not be displayed
742 immediately for the user. Each element of the list should be a list
743 of symbols. If its elements match the first elements in a warning
744 type, then that warning is not displayed immediately.
747 @defopt warning-suppress-log-types
748 This list specifies which warning types should not be logged in the
749 warnings buffer. Each element of the list should be a list of
750 symbols. If it matches the first few elements in a warning type, then
751 that warning is not logged.
754 @node Delayed Warnings
755 @subsection Delayed Warnings
757 Sometimes, you may wish to avoid showing a warning while a command is
758 running, and only show it only after the end of the command. You can
759 use the variable @code{delayed-warnings-list} for this.
761 @defvar delayed-warnings-list
762 The value of this variable is a list of warnings to be displayed after
763 the current command has finished. Each element must be a list
766 (@var{type} @var{message} [@var{level} [@var{buffer-name}]])
770 with the same form, and the same meanings, as the argument list of
771 @code{display-warning} (@pxref{Warning Basics}). Immediately after
772 running @code{post-command-hook} (@pxref{Command Overview}), the Emacs
773 command loop displays all the warnings specified by this variable,
774 then resets it to @code{nil}.
777 Programs which need to further customize the delayed warnings
778 mechanism can change the variable @code{delayed-warnings-hook}:
780 @defvar delayed-warnings-hook
781 This is a normal hook which is run by the Emacs command loop, after
782 @code{post-command-hook}, in order to to process and display delayed
785 Its default value is a list of two functions:
788 (collapse-delayed-warnings display-delayed-warnings)
791 @findex collapse-delayed-warnings
792 @findex display-delayed-warnings
794 The function @code{collapse-delayed-warnings} iterates through
795 @code{delayed-warnings-list}, removing repeated entries. The function
796 @code{display-delayed-warnings} calls @code{display-warning} on each
797 of the entries in @code{delayed-warnings-list}, in turn, and then sets
798 @code{delayed-warnings-list} to @code{nil}.
802 @section Invisible Text
804 @cindex invisible text
805 You can make characters @dfn{invisible}, so that they do not appear on
806 the screen, with the @code{invisible} property. This can be either a
807 text property (@pxref{Text Properties}) or an overlay property
808 (@pxref{Overlays}). Cursor motion also partly ignores these
809 characters; if the command loop finds that point is inside a range of
810 invisible text after a command, it relocates point to the other side
813 In the simplest case, any non-@code{nil} @code{invisible} property makes
814 a character invisible. This is the default case---if you don't alter
815 the default value of @code{buffer-invisibility-spec}, this is how the
816 @code{invisible} property works. You should normally use @code{t}
817 as the value of the @code{invisible} property if you don't plan
818 to set @code{buffer-invisibility-spec} yourself.
820 More generally, you can use the variable @code{buffer-invisibility-spec}
821 to control which values of the @code{invisible} property make text
822 invisible. This permits you to classify the text into different subsets
823 in advance, by giving them different @code{invisible} values, and
824 subsequently make various subsets visible or invisible by changing the
825 value of @code{buffer-invisibility-spec}.
827 Controlling visibility with @code{buffer-invisibility-spec} is
828 especially useful in a program to display the list of entries in a
829 database. It permits the implementation of convenient filtering
830 commands to view just a part of the entries in the database. Setting
831 this variable is very fast, much faster than scanning all the text in
832 the buffer looking for properties to change.
834 @defvar buffer-invisibility-spec
835 This variable specifies which kinds of @code{invisible} properties
836 actually make a character invisible. Setting this variable makes it
841 A character is invisible if its @code{invisible} property is
842 non-@code{nil}. This is the default.
845 Each element of the list specifies a criterion for invisibility; if a
846 character's @code{invisible} property fits any one of these criteria,
847 the character is invisible. The list can have two kinds of elements:
851 A character is invisible if its @code{invisible} property value is
852 @var{atom} or if it is a list with @var{atom} as a member; comparison
853 is done with @code{eq}.
855 @item (@var{atom} . t)
856 A character is invisible if its @code{invisible} property value is
857 @var{atom} or if it is a list with @var{atom} as a member; comparison
858 is done with @code{eq}. Moreover, a sequence of such characters
859 displays as an ellipsis.
864 Two functions are specifically provided for adding elements to
865 @code{buffer-invisibility-spec} and removing elements from it.
867 @defun add-to-invisibility-spec element
868 This function adds the element @var{element} to
869 @code{buffer-invisibility-spec}. If @code{buffer-invisibility-spec}
870 was @code{t}, it changes to a list, @code{(t)}, so that text whose
871 @code{invisible} property is @code{t} remains invisible.
874 @defun remove-from-invisibility-spec element
875 This removes the element @var{element} from
876 @code{buffer-invisibility-spec}. This does nothing if @var{element}
880 A convention for use of @code{buffer-invisibility-spec} is that a
881 major mode should use the mode's own name as an element of
882 @code{buffer-invisibility-spec} and as the value of the
883 @code{invisible} property:
886 ;; @r{If you want to display an ellipsis:}
887 (add-to-invisibility-spec '(my-symbol . t))
888 ;; @r{If you don't want ellipsis:}
889 (add-to-invisibility-spec 'my-symbol)
891 (overlay-put (make-overlay beginning end)
892 'invisible 'my-symbol)
894 ;; @r{When done with the invisibility:}
895 (remove-from-invisibility-spec '(my-symbol . t))
896 ;; @r{Or respectively:}
897 (remove-from-invisibility-spec 'my-symbol)
900 You can check for invisibility using the following function:
902 @defun invisible-p pos-or-prop
903 If @var{pos-or-prop} is a marker or number, this function returns a
904 non-@code{nil} value if the text at that position is invisible.
906 If @var{pos-or-prop} is any other kind of Lisp object, that is taken
907 to mean a possible value of the @code{invisible} text or overlay
908 property. In that case, this function returns a non-@code{nil} value
909 if that value would cause text to become invisible, based on the
910 current value of @code{buffer-invisibility-spec}.
913 @vindex line-move-ignore-invisible
914 Ordinarily, functions that operate on text or move point do not care
915 whether the text is invisible. The user-level line motion commands
916 ignore invisible newlines if @code{line-move-ignore-invisible} is
917 non-@code{nil} (the default), but only because they are explicitly
920 However, if a command ends with point inside or at the boundary of
921 invisible text, the main editing loop relocates point to one of the
922 two ends of the invisible text. Emacs chooses the direction of
923 relocation so that it is the same as the overall movement direction of
924 the command; if in doubt, it prefers a position where an inserted char
925 would not inherit the @code{invisible} property. Additionally, if the
926 text is not replaced by an ellipsis and the command only moved within
927 the invisible text, then point is moved one extra character so as to
928 try and reflect the command's movement by a visible movement of the
931 Thus, if the command moved point back to an invisible range (with the usual
932 stickiness), Emacs moves point back to the beginning of that range. If the
933 command moved point forward into an invisible range, Emacs moves point forward
934 to the first visible character that follows the invisible text and then forward
937 Incremental search can make invisible overlays visible temporarily
938 and/or permanently when a match includes invisible text. To enable
939 this, the overlay should have a non-@code{nil}
940 @code{isearch-open-invisible} property. The property value should be a
941 function to be called with the overlay as an argument. This function
942 should make the overlay visible permanently; it is used when the match
943 overlaps the overlay on exit from the search.
945 During the search, such overlays are made temporarily visible by
946 temporarily modifying their invisible and intangible properties. If you
947 want this to be done differently for a certain overlay, give it an
948 @code{isearch-open-invisible-temporary} property which is a function.
949 The function is called with two arguments: the first is the overlay, and
950 the second is @code{nil} to make the overlay visible, or @code{t} to
951 make it invisible again.
953 @node Selective Display
954 @section Selective Display
955 @c @cindex selective display Duplicates selective-display
957 @dfn{Selective display} refers to a pair of related features for
958 hiding certain lines on the screen.
960 The first variant, explicit selective display, is designed for use
961 in a Lisp program: it controls which lines are hidden by altering the
962 text. This kind of hiding in some ways resembles the effect of the
963 @code{invisible} property (@pxref{Invisible Text}), but the two
964 features are different and do not work the same way.
966 In the second variant, the choice of lines to hide is made
967 automatically based on indentation. This variant is designed to be a
970 The way you control explicit selective display is by replacing a
971 newline (control-j) with a carriage return (control-m). The text that
972 was formerly a line following that newline is now hidden. Strictly
973 speaking, it is temporarily no longer a line at all, since only
974 newlines can separate lines; it is now part of the previous line.
976 Selective display does not directly affect editing commands. For
977 example, @kbd{C-f} (@code{forward-char}) moves point unhesitatingly
978 into hidden text. However, the replacement of newline characters with
979 carriage return characters affects some editing commands. For
980 example, @code{next-line} skips hidden lines, since it searches only
981 for newlines. Modes that use selective display can also define
982 commands that take account of the newlines, or that control which
983 parts of the text are hidden.
985 When you write a selectively displayed buffer into a file, all the
986 control-m's are output as newlines. This means that when you next read
987 in the file, it looks OK, with nothing hidden. The selective display
988 effect is seen only within Emacs.
990 @defvar selective-display
991 This buffer-local variable enables selective display. This means that
992 lines, or portions of lines, may be made hidden.
996 If the value of @code{selective-display} is @code{t}, then the character
997 control-m marks the start of hidden text; the control-m, and the rest
998 of the line following it, are not displayed. This is explicit selective
1002 If the value of @code{selective-display} is a positive integer, then
1003 lines that start with more than that many columns of indentation are not
1007 When some portion of a buffer is hidden, the vertical movement
1008 commands operate as if that portion did not exist, allowing a single
1009 @code{next-line} command to skip any number of hidden lines.
1010 However, character movement commands (such as @code{forward-char}) do
1011 not skip the hidden portion, and it is possible (if tricky) to insert
1012 or delete text in an hidden portion.
1014 In the examples below, we show the @emph{display appearance} of the
1015 buffer @code{foo}, which changes with the value of
1016 @code{selective-display}. The @emph{contents} of the buffer do not
1021 (setq selective-display nil)
1024 ---------- Buffer: foo ----------
1031 ---------- Buffer: foo ----------
1035 (setq selective-display 2)
1038 ---------- Buffer: foo ----------
1043 ---------- Buffer: foo ----------
1048 @defopt selective-display-ellipses
1049 If this buffer-local variable is non-@code{nil}, then Emacs displays
1050 @samp{@dots{}} at the end of a line that is followed by hidden text.
1051 This example is a continuation of the previous one.
1055 (setq selective-display-ellipses t)
1058 ---------- Buffer: foo ----------
1063 ---------- Buffer: foo ----------
1067 You can use a display table to substitute other text for the ellipsis
1068 (@samp{@dots{}}). @xref{Display Tables}.
1071 @node Temporary Displays
1072 @section Temporary Displays
1074 Temporary displays are used by Lisp programs to put output into a
1075 buffer and then present it to the user for perusal rather than for
1076 editing. Many help commands use this feature.
1078 @defmac with-output-to-temp-buffer buffer-name forms@dots{}
1079 This function executes @var{forms} while arranging to insert any output
1080 they print into the buffer named @var{buffer-name}, which is first
1081 created if necessary, and put into Help mode. Finally, the buffer is
1082 displayed in some window, but not selected.
1084 If the @var{forms} do not change the major mode in the output buffer,
1085 so that it is still Help mode at the end of their execution, then
1086 @code{with-output-to-temp-buffer} makes this buffer read-only at the
1087 end, and also scans it for function and variable names to make them
1088 into clickable cross-references. @xref{Docstring hyperlinks, , Tips
1089 for Documentation Strings}, in particular the item on hyperlinks in
1090 documentation strings, for more details.
1092 The string @var{buffer-name} specifies the temporary buffer, which
1093 need not already exist. The argument must be a string, not a buffer.
1094 The buffer is erased initially (with no questions asked), and it is
1095 marked as unmodified after @code{with-output-to-temp-buffer} exits.
1097 @code{with-output-to-temp-buffer} binds @code{standard-output} to the
1098 temporary buffer, then it evaluates the forms in @var{forms}. Output
1099 using the Lisp output functions within @var{forms} goes by default to
1100 that buffer (but screen display and messages in the echo area, although
1101 they are ``output'' in the general sense of the word, are not affected).
1102 @xref{Output Functions}.
1104 Several hooks are available for customizing the behavior
1105 of this construct; they are listed below.
1107 The value of the last form in @var{forms} is returned.
1111 ---------- Buffer: foo ----------
1112 This is the contents of foo.
1113 ---------- Buffer: foo ----------
1117 (with-output-to-temp-buffer "foo"
1119 (print standard-output))
1120 @result{} #<buffer foo>
1122 ---------- Buffer: foo ----------
1127 ---------- Buffer: foo ----------
1132 @defopt temp-buffer-show-function
1133 If this variable is non-@code{nil}, @code{with-output-to-temp-buffer}
1134 calls it as a function to do the job of displaying a help buffer. The
1135 function gets one argument, which is the buffer it should display.
1137 It is a good idea for this function to run @code{temp-buffer-show-hook}
1138 just as @code{with-output-to-temp-buffer} normally would, inside of
1139 @code{save-selected-window} and with the chosen window and buffer
1143 @defvar temp-buffer-setup-hook
1144 This normal hook is run by @code{with-output-to-temp-buffer} before
1145 evaluating @var{body}. When the hook runs, the temporary buffer is
1146 current. This hook is normally set up with a function to put the
1147 buffer in Help mode.
1150 @defvar temp-buffer-show-hook
1151 This normal hook is run by @code{with-output-to-temp-buffer} after
1152 displaying the temporary buffer. When the hook runs, the temporary buffer
1153 is current, and the window it was displayed in is selected.
1156 @defun momentary-string-display string position &optional char message
1157 This function momentarily displays @var{string} in the current buffer at
1158 @var{position}. It has no effect on the undo list or on the buffer's
1159 modification status.
1161 The momentary display remains until the next input event. If the next
1162 input event is @var{char}, @code{momentary-string-display} ignores it
1163 and returns. Otherwise, that event remains buffered for subsequent use
1164 as input. Thus, typing @var{char} will simply remove the string from
1165 the display, while typing (say) @kbd{C-f} will remove the string from
1166 the display and later (presumably) move point forward. The argument
1167 @var{char} is a space by default.
1169 The return value of @code{momentary-string-display} is not meaningful.
1171 If the string @var{string} does not contain control characters, you can
1172 do the same job in a more general way by creating (and then subsequently
1173 deleting) an overlay with a @code{before-string} property.
1174 @xref{Overlay Properties}.
1176 If @var{message} is non-@code{nil}, it is displayed in the echo area
1177 while @var{string} is displayed in the buffer. If it is @code{nil}, a
1178 default message says to type @var{char} to continue.
1180 In this example, point is initially located at the beginning of the
1185 ---------- Buffer: foo ----------
1186 This is the contents of foo.
1187 @point{}Second line.
1188 ---------- Buffer: foo ----------
1192 (momentary-string-display
1193 "**** Important Message! ****"
1195 "Type RET when done reading")
1200 ---------- Buffer: foo ----------
1201 This is the contents of foo.
1202 **** Important Message! ****Second line.
1203 ---------- Buffer: foo ----------
1205 ---------- Echo Area ----------
1206 Type RET when done reading
1207 ---------- Echo Area ----------
1216 You can use @dfn{overlays} to alter the appearance of a buffer's text on
1217 the screen, for the sake of presentation features. An overlay is an
1218 object that belongs to a particular buffer, and has a specified
1219 beginning and end. It also has properties that you can examine and set;
1220 these affect the display of the text within the overlay.
1222 @cindex scalability of overlays
1223 The visual effect of an overlay is the same as of the corresponding
1224 text property (@pxref{Text Properties}). However, due to a different
1225 implementation, overlays generally don't scale well (many operations
1226 take a time that is proportional to the number of overlays in the
1227 buffer). If you need to affect the visual appearance of many portions
1228 in the buffer, we recommend using text properties.
1230 An overlay uses markers to record its beginning and end; thus,
1231 editing the text of the buffer adjusts the beginning and end of each
1232 overlay so that it stays with the text. When you create the overlay,
1233 you can specify whether text inserted at the beginning should be
1234 inside the overlay or outside, and likewise for the end of the overlay.
1237 * Managing Overlays:: Creating and moving overlays.
1238 * Overlay Properties:: How to read and set properties.
1239 What properties do to the screen display.
1240 * Finding Overlays:: Searching for overlays.
1243 @node Managing Overlays
1244 @subsection Managing Overlays
1246 This section describes the functions to create, delete and move
1247 overlays, and to examine their contents. Overlay changes are not
1248 recorded in the buffer's undo list, since the overlays are not
1249 part of the buffer's contents.
1251 @defun overlayp object
1252 This function returns @code{t} if @var{object} is an overlay.
1255 @defun make-overlay start end &optional buffer front-advance rear-advance
1256 This function creates and returns an overlay that belongs to
1257 @var{buffer} and ranges from @var{start} to @var{end}. Both @var{start}
1258 and @var{end} must specify buffer positions; they may be integers or
1259 markers. If @var{buffer} is omitted, the overlay is created in the
1262 The arguments @var{front-advance} and @var{rear-advance} specify the
1263 marker insertion type for the start of the overlay and for the end of
1264 the overlay, respectively. @xref{Marker Insertion Types}. If they
1265 are both @code{nil}, the default, then the overlay extends to include
1266 any text inserted at the beginning, but not text inserted at the end.
1267 If @var{front-advance} is non-@code{nil}, text inserted at the
1268 beginning of the overlay is excluded from the overlay. If
1269 @var{rear-advance} is non-@code{nil}, text inserted at the end of the
1270 overlay is included in the overlay.
1273 @defun overlay-start overlay
1274 This function returns the position at which @var{overlay} starts,
1278 @defun overlay-end overlay
1279 This function returns the position at which @var{overlay} ends,
1283 @defun overlay-buffer overlay
1284 This function returns the buffer that @var{overlay} belongs to. It
1285 returns @code{nil} if @var{overlay} has been deleted.
1288 @defun delete-overlay overlay
1289 This function deletes @var{overlay}. The overlay continues to exist as
1290 a Lisp object, and its property list is unchanged, but it ceases to be
1291 attached to the buffer it belonged to, and ceases to have any effect on
1294 A deleted overlay is not permanently disconnected. You can give it a
1295 position in a buffer again by calling @code{move-overlay}.
1298 @defun move-overlay overlay start end &optional buffer
1299 This function moves @var{overlay} to @var{buffer}, and places its bounds
1300 at @var{start} and @var{end}. Both arguments @var{start} and @var{end}
1301 must specify buffer positions; they may be integers or markers.
1303 If @var{buffer} is omitted, @var{overlay} stays in the same buffer it
1304 was already associated with; if @var{overlay} was deleted, it goes into
1307 The return value is @var{overlay}.
1309 This is the only valid way to change the endpoints of an overlay. Do
1310 not try modifying the markers in the overlay by hand, as that fails to
1311 update other vital data structures and can cause some overlays to be
1315 @defun remove-overlays &optional start end name value
1316 This function removes all the overlays between @var{start} and
1317 @var{end} whose property @var{name} has the value @var{value}. It can
1318 move the endpoints of the overlays in the region, or split them.
1320 If @var{name} is omitted or @code{nil}, it means to delete all overlays in
1321 the specified region. If @var{start} and/or @var{end} are omitted or
1322 @code{nil}, that means the beginning and end of the buffer respectively.
1323 Therefore, @code{(remove-overlays)} removes all the overlays in the
1327 @defun copy-overlay overlay
1328 This function returns a copy of @var{overlay}. The copy has the same
1329 endpoints and properties as @var{overlay}. However, the marker
1330 insertion type for the start of the overlay and for the end of the
1331 overlay are set to their default values (@pxref{Marker Insertion
1335 Here are some examples:
1338 ;; @r{Create an overlay.}
1339 (setq foo (make-overlay 1 10))
1340 @result{} #<overlay from 1 to 10 in display.texi>
1345 (overlay-buffer foo)
1346 @result{} #<buffer display.texi>
1347 ;; @r{Give it a property we can check later.}
1348 (overlay-put foo 'happy t)
1350 ;; @r{Verify the property is present.}
1351 (overlay-get foo 'happy)
1353 ;; @r{Move the overlay.}
1354 (move-overlay foo 5 20)
1355 @result{} #<overlay from 5 to 20 in display.texi>
1360 ;; @r{Delete the overlay.}
1361 (delete-overlay foo)
1363 ;; @r{Verify it is deleted.}
1365 @result{} #<overlay in no buffer>
1366 ;; @r{A deleted overlay has no position.}
1371 (overlay-buffer foo)
1373 ;; @r{Undelete the overlay.}
1374 (move-overlay foo 1 20)
1375 @result{} #<overlay from 1 to 20 in display.texi>
1376 ;; @r{Verify the results.}
1381 (overlay-buffer foo)
1382 @result{} #<buffer display.texi>
1383 ;; @r{Moving and deleting the overlay does not change its properties.}
1384 (overlay-get foo 'happy)
1388 Emacs stores the overlays of each buffer in two lists, divided
1389 around an arbitrary ``center position''. One list extends backwards
1390 through the buffer from that center position, and the other extends
1391 forwards from that center position. The center position can be anywhere
1394 @defun overlay-recenter pos
1395 This function recenters the overlays of the current buffer around
1396 position @var{pos}. That makes overlay lookup faster for positions
1397 near @var{pos}, but slower for positions far away from @var{pos}.
1400 A loop that scans the buffer forwards, creating overlays, can run
1401 faster if you do @code{(overlay-recenter (point-max))} first.
1403 @node Overlay Properties
1404 @subsection Overlay Properties
1406 Overlay properties are like text properties in that the properties that
1407 alter how a character is displayed can come from either source. But in
1408 most respects they are different. @xref{Text Properties}, for comparison.
1410 Text properties are considered a part of the text; overlays and
1411 their properties are specifically considered not to be part of the
1412 text. Thus, copying text between various buffers and strings
1413 preserves text properties, but does not try to preserve overlays.
1414 Changing a buffer's text properties marks the buffer as modified,
1415 while moving an overlay or changing its properties does not. Unlike
1416 text property changes, overlay property changes are not recorded in
1417 the buffer's undo list.
1419 Since more than one overlay can specify a property value for the
1420 same character, Emacs lets you specify a priority value of each
1421 overlay. You should not make assumptions about which overlay will
1422 prevail when there is a conflict and they have the same priority.
1424 These functions read and set the properties of an overlay:
1426 @defun overlay-get overlay prop
1427 This function returns the value of property @var{prop} recorded in
1428 @var{overlay}, if any. If @var{overlay} does not record any value for
1429 that property, but it does have a @code{category} property which is a
1430 symbol, that symbol's @var{prop} property is used. Otherwise, the value
1434 @defun overlay-put overlay prop value
1435 This function sets the value of property @var{prop} recorded in
1436 @var{overlay} to @var{value}. It returns @var{value}.
1439 @defun overlay-properties overlay
1440 This returns a copy of the property list of @var{overlay}.
1443 See also the function @code{get-char-property} which checks both
1444 overlay properties and text properties for a given character.
1445 @xref{Examining Properties}.
1447 Many overlay properties have special meanings; here is a table
1452 @kindex priority @r{(overlay property)}
1453 This property's value (which should be a non-negative integer number)
1454 determines the priority of the overlay. No priority, or @code{nil},
1457 The priority matters when two or more overlays cover the same
1458 character and both specify the same property; the one whose
1459 @code{priority} value is larger overrides the other. For the
1460 @code{face} property, the higher priority overlay's value does not
1461 completely override the other value; instead, its face attributes
1462 override the face attributes of the lower priority @code{face}
1465 Currently, all overlays take priority over text properties. Please
1466 avoid using negative priority values, as we have not yet decided just
1467 what they should mean.
1470 @kindex window @r{(overlay property)}
1471 If the @code{window} property is non-@code{nil}, then the overlay
1472 applies only on that window.
1475 @kindex category @r{(overlay property)}
1476 If an overlay has a @code{category} property, we call it the
1477 @dfn{category} of the overlay. It should be a symbol. The properties
1478 of the symbol serve as defaults for the properties of the overlay.
1481 @kindex face @r{(overlay property)}
1482 This property controls the way text is displayed---for example, which
1483 font and which colors. @xref{Faces}, for more information.
1485 In the simplest case, the value is a face name. It can also be a list;
1486 then each element can be any of these possibilities:
1490 A face name (a symbol or string).
1493 A property list of face attributes. This has the form (@var{keyword}
1494 @var{value} @dots{}), where each @var{keyword} is a face attribute
1495 name and @var{value} is a meaningful value for that attribute. With
1496 this feature, you do not need to create a face each time you want to
1497 specify a particular attribute for certain text. @xref{Face
1501 A cons cell, of the form @code{(foreground-color . @var{color-name})}
1502 or @code{(background-color . @var{color-name})}. These elements
1503 specify just the foreground color or just the background color.
1505 @code{(foreground-color . @var{color-name})} has the same effect as
1506 @code{(:foreground @var{color-name})}; likewise for the background.
1510 @kindex mouse-face @r{(overlay property)}
1511 This property is used instead of @code{face} when the mouse is within
1512 the range of the overlay. However, Emacs ignores all face attributes
1513 from this property that alter the text size (e.g. @code{:height},
1514 @code{:weight}, and @code{:slant}). Those attributes are always the
1515 same as in the unhighlighted text.
1518 @kindex display @r{(overlay property)}
1519 This property activates various features that change the
1520 way text is displayed. For example, it can make text appear taller
1521 or shorter, higher or lower, wider or narrower, or replaced with an image.
1522 @xref{Display Property}.
1525 @kindex help-echo @r{(overlay property)}
1526 If an overlay has a @code{help-echo} property, then when you move the
1527 mouse onto the text in the overlay, Emacs displays a help string in the
1528 echo area, or in the tooltip window. For details see @ref{Text
1531 @item modification-hooks
1532 @kindex modification-hooks @r{(overlay property)}
1533 This property's value is a list of functions to be called if any
1534 character within the overlay is changed or if text is inserted strictly
1537 The hook functions are called both before and after each change.
1538 If the functions save the information they receive, and compare notes
1539 between calls, they can determine exactly what change has been made
1542 When called before a change, each function receives four arguments: the
1543 overlay, @code{nil}, and the beginning and end of the text range to be
1546 When called after a change, each function receives five arguments: the
1547 overlay, @code{t}, the beginning and end of the text range just
1548 modified, and the length of the pre-change text replaced by that range.
1549 (For an insertion, the pre-change length is zero; for a deletion, that
1550 length is the number of characters deleted, and the post-change
1551 beginning and end are equal.)
1553 If these functions modify the buffer, they should bind
1554 @code{inhibit-modification-hooks} to @code{t} around doing so, to
1555 avoid confusing the internal mechanism that calls these hooks.
1557 Text properties also support the @code{modification-hooks} property,
1558 but the details are somewhat different (@pxref{Special Properties}).
1560 @item insert-in-front-hooks
1561 @kindex insert-in-front-hooks @r{(overlay property)}
1562 This property's value is a list of functions to be called before and
1563 after inserting text right at the beginning of the overlay. The calling
1564 conventions are the same as for the @code{modification-hooks} functions.
1566 @item insert-behind-hooks
1567 @kindex insert-behind-hooks @r{(overlay property)}
1568 This property's value is a list of functions to be called before and
1569 after inserting text right at the end of the overlay. The calling
1570 conventions are the same as for the @code{modification-hooks} functions.
1573 @kindex invisible @r{(overlay property)}
1574 The @code{invisible} property can make the text in the overlay
1575 invisible, which means that it does not appear on the screen.
1576 @xref{Invisible Text}, for details.
1579 @kindex intangible @r{(overlay property)}
1580 The @code{intangible} property on an overlay works just like the
1581 @code{intangible} text property. @xref{Special Properties}, for details.
1583 @item isearch-open-invisible
1584 This property tells incremental search how to make an invisible overlay
1585 visible, permanently, if the final match overlaps it. @xref{Invisible
1588 @item isearch-open-invisible-temporary
1589 This property tells incremental search how to make an invisible overlay
1590 visible, temporarily, during the search. @xref{Invisible Text}.
1593 @kindex before-string @r{(overlay property)}
1594 This property's value is a string to add to the display at the beginning
1595 of the overlay. The string does not appear in the buffer in any
1596 sense---only on the screen.
1599 @kindex after-string @r{(overlay property)}
1600 This property's value is a string to add to the display at the end of
1601 the overlay. The string does not appear in the buffer in any
1602 sense---only on the screen.
1605 This property specifies a display spec to prepend to each
1606 non-continuation line at display-time. @xref{Truncation}.
1609 This property specifies a display spec to prepend to each continuation
1610 line at display-time. @xref{Truncation}.
1613 @kindex evaporate @r{(overlay property)}
1614 If this property is non-@code{nil}, the overlay is deleted automatically
1615 if it becomes empty (i.e., if its length becomes zero). If you give
1616 an empty overlay a non-@code{nil} @code{evaporate} property, that deletes
1620 @cindex keymap of character (and overlays)
1621 @kindex local-map @r{(overlay property)}
1622 If this property is non-@code{nil}, it specifies a keymap for a portion
1623 of the text. The property's value replaces the buffer's local map, when
1624 the character after point is within the overlay. @xref{Active Keymaps}.
1627 @kindex keymap @r{(overlay property)}
1628 The @code{keymap} property is similar to @code{local-map} but overrides the
1629 buffer's local map (and the map specified by the @code{local-map}
1630 property) rather than replacing it.
1633 The @code{local-map} and @code{keymap} properties do not affect a
1634 string displayed by the @code{before-string}, @code{after-string}, or
1635 @code{display} properties. This is only relevant for mouse clicks and
1636 other mouse events that fall on the string, since point is never on
1637 the string. To bind special mouse events for the string, assign it a
1638 @code{local-map} or @code{keymap} text property. @xref{Special
1641 @node Finding Overlays
1642 @subsection Searching for Overlays
1644 @defun overlays-at pos
1645 This function returns a list of all the overlays that cover the
1646 character at position @var{pos} in the current buffer. The list is in
1647 no particular order. An overlay contains position @var{pos} if it
1648 begins at or before @var{pos}, and ends after @var{pos}.
1650 To illustrate usage, here is a Lisp function that returns a list of the
1651 overlays that specify property @var{prop} for the character at point:
1654 (defun find-overlays-specifying (prop)
1655 (let ((overlays (overlays-at (point)))
1658 (let ((overlay (car overlays)))
1659 (if (overlay-get overlay prop)
1660 (setq found (cons overlay found))))
1661 (setq overlays (cdr overlays)))
1666 @defun overlays-in beg end
1667 This function returns a list of the overlays that overlap the region
1668 @var{beg} through @var{end}. ``Overlap'' means that at least one
1669 character is contained within the overlay and also contained within the
1670 specified region; however, empty overlays are included in the result if
1671 they are located at @var{beg}, strictly between @var{beg} and @var{end},
1672 or at @var{end} when @var{end} denotes the position at the end of the
1676 @defun next-overlay-change pos
1677 This function returns the buffer position of the next beginning or end
1678 of an overlay, after @var{pos}. If there is none, it returns
1682 @defun previous-overlay-change pos
1683 This function returns the buffer position of the previous beginning or
1684 end of an overlay, before @var{pos}. If there is none, it returns
1688 As an example, here's a simplified (and inefficient) version of the
1689 primitive function @code{next-single-char-property-change}
1690 (@pxref{Property Search}). It searches forward from position
1691 @var{pos} for the next position where the value of a given property
1692 @code{prop}, as obtained from either overlays or text properties,
1696 (defun next-single-char-property-change (position prop)
1698 (goto-char position)
1699 (let ((propval (get-char-property (point) prop)))
1700 (while (and (not (eobp))
1701 (eq (get-char-property (point) prop) propval))
1702 (goto-char (min (next-overlay-change (point))
1703 (next-single-property-change (point) prop)))))
1710 Since not all characters have the same width, these functions let you
1711 check the width of a character. @xref{Primitive Indent}, and
1712 @ref{Screen Lines}, for related functions.
1714 @defun char-width char
1715 This function returns the width in columns of the character
1716 @var{char}, if it were displayed in the current buffer (i.e.@: taking
1717 into account the buffer's display table, if any; @pxref{Display
1718 Tables}). The width of a tab character is usually @code{tab-width}
1719 (@pxref{Usual Display}).
1722 @defun string-width string
1723 This function returns the width in columns of the string @var{string},
1724 if it were displayed in the current buffer and the selected window.
1727 @defun truncate-string-to-width string width &optional start-column padding ellipsis
1728 This function returns the part of @var{string} that fits within
1729 @var{width} columns, as a new string.
1731 If @var{string} does not reach @var{width}, then the result ends where
1732 @var{string} ends. If one multi-column character in @var{string}
1733 extends across the column @var{width}, that character is not included in
1734 the result. Thus, the result can fall short of @var{width} but cannot
1737 The optional argument @var{start-column} specifies the starting column.
1738 If this is non-@code{nil}, then the first @var{start-column} columns of
1739 the string are omitted from the value. If one multi-column character in
1740 @var{string} extends across the column @var{start-column}, that
1741 character is not included.
1743 The optional argument @var{padding}, if non-@code{nil}, is a padding
1744 character added at the beginning and end of the result string, to extend
1745 it to exactly @var{width} columns. The padding character is used at the
1746 end of the result if it falls short of @var{width}. It is also used at
1747 the beginning of the result if one multi-column character in
1748 @var{string} extends across the column @var{start-column}.
1750 If @var{ellipsis} is non-@code{nil}, it should be a string which will
1751 replace the end of @var{str} (including any padding) if it extends
1752 beyond @var{end-column}, unless the display width of @var{str} is
1753 equal to or less than the display width of @var{ellipsis}. If
1754 @var{ellipsis} is non-@code{nil} and not a string, it stands for
1758 (truncate-string-to-width "\tab\t" 12 4)
1760 (truncate-string-to-width "\tab\t" 12 4 ?\s)
1766 @section Line Height
1769 The total height of each display line consists of the height of the
1770 contents of the line, plus optional additional vertical line spacing
1771 above or below the display line.
1773 The height of the line contents is the maximum height of any
1774 character or image on that display line, including the final newline
1775 if there is one. (A display line that is continued doesn't include a
1776 final newline.) That is the default line height, if you do nothing to
1777 specify a greater height. (In the most common case, this equals the
1778 height of the default frame font.)
1780 There are several ways to explicitly specify a larger line height,
1781 either by specifying an absolute height for the display line, or by
1782 specifying vertical space. However, no matter what you specify, the
1783 actual line height can never be less than the default.
1785 @kindex line-height @r{(text property)}
1786 A newline can have a @code{line-height} text or overlay property
1787 that controls the total height of the display line ending in that
1790 If the property value is @code{t}, the newline character has no
1791 effect on the displayed height of the line---the visible contents
1792 alone determine the height. This is useful for tiling small images
1793 (or image slices) without adding blank areas between the images.
1795 If the property value is a list of the form @code{(@var{height}
1796 @var{total})}, that adds extra space @emph{below} the display line.
1797 First Emacs uses @var{height} as a height spec to control extra space
1798 @emph{above} the line; then it adds enough space @emph{below} the line
1799 to bring the total line height up to @var{total}. In this case, the
1800 other ways to specify the line spacing are ignored.
1802 Any other kind of property value is a height spec, which translates
1803 into a number---the specified line height. There are several ways to
1804 write a height spec; here's how each of them translates into a number:
1808 If the height spec is a positive integer, the height value is that integer.
1810 If the height spec is a float, @var{float}, the numeric height value
1811 is @var{float} times the frame's default line height.
1812 @item (@var{face} . @var{ratio})
1813 If the height spec is a cons of the format shown, the numeric height
1814 is @var{ratio} times the height of face @var{face}. @var{ratio} can
1815 be any type of number, or @code{nil} which means a ratio of 1.
1816 If @var{face} is @code{t}, it refers to the current face.
1817 @item (nil . @var{ratio})
1818 If the height spec is a cons of the format shown, the numeric height
1819 is @var{ratio} times the height of the contents of the line.
1822 Thus, any valid height spec determines the height in pixels, one way
1823 or another. If the line contents' height is less than that, Emacs
1824 adds extra vertical space above the line to achieve the specified
1827 If you don't specify the @code{line-height} property, the line's
1828 height consists of the contents' height plus the line spacing.
1829 There are several ways to specify the line spacing for different
1830 parts of Emacs text.
1832 On graphical terminals, you can specify the line spacing for all
1833 lines in a frame, using the @code{line-spacing} frame parameter
1834 (@pxref{Layout Parameters}). However, if the default value of
1835 @code{line-spacing} is non-@code{nil}, it overrides the
1836 frame's @code{line-spacing} parameter. An integer value specifies the
1837 number of pixels put below lines. A floating point number specifies
1838 the spacing relative to the frame's default line height.
1840 @vindex line-spacing
1841 You can specify the line spacing for all lines in a buffer via the
1842 buffer-local @code{line-spacing} variable. An integer value specifies
1843 the number of pixels put below lines. A floating point number
1844 specifies the spacing relative to the default frame line height. This
1845 overrides line spacings specified for the frame.
1847 @kindex line-spacing @r{(text property)}
1848 Finally, a newline can have a @code{line-spacing} text or overlay
1849 property that overrides the default frame line spacing and the buffer
1850 local @code{line-spacing} variable, for the display line ending in
1853 One way or another, these mechanisms specify a Lisp value for the
1854 spacing of each line. The value is a height spec, and it translates
1855 into a Lisp value as described above. However, in this case the
1856 numeric height value specifies the line spacing, rather than the line
1859 On text terminals, the line spacing cannot be altered.
1865 A @dfn{face} is a collection of graphical @dfn{attributes} for
1866 displaying text: font, foreground color, background color, optional
1867 underlining, and so on. Faces control how Emacs displays text in
1868 buffers, as well as other parts of the frame such as the mode line.
1869 @xref{Standard Faces,,, emacs, The GNU Emacs Manual}, for the list of
1870 faces Emacs normally comes with.
1873 For most purposes, you refer to a face in Lisp programs using its
1874 @dfn{face name}, which is usually a Lisp symbol. For backward
1875 compatibility, a face name can also be a string, which is equivalent
1876 to a Lisp symbol of the same name.
1879 This function returns a non-@code{nil} value if @var{object} is a Lisp
1880 symbol or string that names a face. Otherwise, it returns @code{nil}.
1883 By default, each face name corresponds to the same set of attributes
1884 in all frames. But you can also assign a face name a special set of
1885 attributes in one frame (@pxref{Attribute Functions}).
1888 * Defining Faces:: How to define a face.
1889 * Face Attributes:: What is in a face?
1890 * Attribute Functions:: Functions to examine and set face attributes.
1891 * Displaying Faces:: How Emacs combines the faces specified for a character.
1892 * Face Remapping:: Remapping faces to alternative definitions.
1893 * Face Functions:: How to define and examine faces.
1894 * Auto Faces:: Hook for automatic face assignment.
1895 * Basic Faces:: Faces that are defined by default.
1896 * Font Selection:: Finding the best available font for a face.
1897 * Font Lookup:: Looking up the names of available fonts
1898 and information about them.
1899 * Fontsets:: A fontset is a collection of fonts
1900 that handle a range of character sets.
1901 * Low-Level Font:: Lisp representation for character display fonts.
1904 @node Defining Faces
1905 @subsection Defining Faces
1907 The @code{defface} macro defines a face and specifies its default
1908 appearance. The user can subsequently customize the face using the
1909 Customize interface (@pxref{Customization}).
1911 @defmac defface face spec doc [keyword value]@dots{}
1912 This macro declares @var{face} as a customizable face whose default
1913 attributes are given by @var{spec}. You should not quote the symbol
1914 @var{face}, and it should not end in @samp{-face} (that would be
1915 redundant). The argument @var{doc} is a documentation string for the
1916 face. The additional @var{keyword} arguments have the same meanings
1917 as in @code{defgroup} and @code{defcustom} (@pxref{Common Keywords}).
1919 When @code{defface} executes, it defines the face according to
1920 @var{spec}, then uses any customizations that were read from the
1921 init file (@pxref{Init File}) to override that specification.
1923 When you evaluate a @code{defface} form with @kbd{C-M-x} in Emacs
1924 Lisp mode (@code{eval-defun}), a special feature of @code{eval-defun}
1925 overrides any customizations of the face. This way, the face reflects
1926 exactly what the @code{defface} says.
1928 @cindex face specification
1929 The @var{spec} argument is a @dfn{face specification}, which states
1930 how the face should appear on different kinds of terminals. It should
1931 be an alist whose elements each have the form @code{(@var{display}
1932 @var{atts})}. @var{display} specifies a class of terminals (see
1933 below), while @var{atts} is a property list of face attributes and
1934 their values, specifying the appearance of the face on matching
1937 (see the next section for details about face attributes).
1940 (@pxref{Face Attributes}, for details about face attributes).
1943 The @var{display} part of an element of @var{spec} determines which
1944 frames the element matches. If more than one element of @var{spec}
1945 matches a given frame, the first element that matches is the one used
1946 for that frame. There are three possibilities for @var{display}:
1949 @item @code{default}
1950 This element of @var{spec} doesn't match any frames; instead, it
1951 specifies defaults that apply to all frames. This kind of element, if
1952 used, must be the first element of @var{spec}. Each of the following
1953 elements can override any or all of these defaults.
1956 This element of @var{spec} matches all frames. Therefore, any
1957 subsequent elements of @var{spec} are never used. Normally
1958 @code{t} is used in the last (or only) element of @var{spec}.
1961 If @var{display} is a list, each element should have the form
1962 @code{(@var{characteristic} @var{value}@dots{})}. Here
1963 @var{characteristic} specifies a way of classifying frames, and the
1964 @var{value}s are possible classifications which @var{display} should
1965 apply to. Here are the possible values of @var{characteristic}:
1969 The kind of window system the frame uses---either @code{graphic} (any
1970 graphics-capable display), @code{x}, @code{pc} (for the MS-DOS console),
1971 @code{w32} (for MS Windows 9X/NT/2K/XP), or @code{tty}
1972 (a non-graphics-capable display).
1973 @xref{Window Systems, window-system}.
1976 What kinds of colors the frame supports---either @code{color},
1977 @code{grayscale}, or @code{mono}.
1980 The kind of background---either @code{light} or @code{dark}.
1983 An integer that represents the minimum number of colors the frame
1984 should support. This matches a frame if its
1985 @code{display-color-cells} value is at least the specified integer.
1988 Whether or not the frame can display the face attributes given in
1989 @var{value}@dots{} (@pxref{Face Attributes}). @xref{Display Face
1990 Attribute Testing}, for more information on exactly how this testing
1994 If an element of @var{display} specifies more than one @var{value} for a
1995 given @var{characteristic}, any of those values is acceptable. If
1996 @var{display} has more than one element, each element should specify a
1997 different @var{characteristic}; then @emph{each} characteristic of the
1998 frame must match one of the @var{value}s specified for it in
2003 Here's how the standard face @code{highlight} is defined:
2007 '((((class color) (min-colors 88) (background light))
2008 :background "darkseagreen2")
2009 (((class color) (min-colors 88) (background dark))
2010 :background "darkolivegreen")
2011 (((class color) (min-colors 16) (background light))
2012 :background "darkseagreen2")
2013 (((class color) (min-colors 16) (background dark))
2014 :background "darkolivegreen")
2015 (((class color) (min-colors 8))
2016 :background "green" :foreground "black")
2017 (t :inverse-video t))
2018 "Basic face for highlighting."
2019 :group 'basic-faces)
2022 Internally, Emacs stores the face's default specification in its
2023 @code{face-defface-spec} symbol property (@pxref{Property Lists}).
2024 The @code{saved-face} property stores the face specification saved by
2025 the user, using the customization buffer; the @code{customized-face}
2026 property stores the face specification customized for the current
2027 session, but not saved; and the @code{theme-face} property stores an
2028 alist associating the active customization settings and Custom themes
2029 with their specifications for that face. The face's documentation
2030 string is stored in the @code{face-documentation} property. But
2031 normally you should not try to set any of these properties directly.
2032 @xref{Applying Customizations}, for the @code{custom-set-faces}
2033 function, which is used to apply customized face settings.
2035 People are sometimes tempted to create variables whose values
2036 specify a face to use. In the vast majority of cases, this is not
2037 necessary; it is preferable to simply use faces directly.
2039 @defopt frame-background-mode
2040 This option, if non-@code{nil}, specifies the background type to use for
2041 interpreting face definitions. If it is @code{dark}, then Emacs treats
2042 all frames as if they had a dark background, regardless of their actual
2043 background colors. If it is @code{light}, then Emacs treats all frames
2044 as if they had a light background.
2047 @node Face Attributes
2048 @subsection Face Attributes
2049 @cindex face attributes
2051 The effect of using a face is determined by a fixed set of @dfn{face
2052 attributes}. This table lists all the face attributes, their possible
2053 values, and their effects. You can specify more than one face for a
2054 given piece of text; Emacs merges the attributes of all the faces to
2055 determine how to display the text. @xref{Displaying Faces}.
2057 In addition to the values given below, each face attribute can also
2058 have the value @code{unspecified}. This special value means the face
2059 doesn't specify that attribute. In face merging, when the first face
2060 fails to specify a particular attribute, the next face gets a chance.
2061 However, the @code{default} face must specify all attributes.
2063 Some of these attributes are meaningful only on certain kinds of
2064 displays. If your display cannot handle a certain attribute, the
2065 attribute is ignored.
2069 Font family or fontset (a string). @xref{Fonts,,, emacs, The GNU
2070 Emacs Manual}. If you specify a font family name, the wild-card
2071 characters @samp{*} and @samp{?} are allowed. The function
2072 @code{font-family-list}, described below, returns a list of available
2073 family names. @xref{Fontsets}, for information about fontsets.
2076 The name of the @dfn{font foundry} for the font family specified by
2077 the @code{:family} attribute (a string). The wild-card characters
2078 @samp{*} and @samp{?} are allowed. @xref{Fonts,,, emacs, The GNU
2082 Relative proportionate character width, also known as the character
2083 set width. This should be one of the symbols @code{ultra-condensed},
2084 @code{extra-condensed}, @code{condensed}, @code{semi-condensed},
2085 @code{normal}, @code{semi-expanded}, @code{expanded},
2086 @code{extra-expanded}, or @code{ultra-expanded}.
2089 The height of the font. In the simplest case, this is an integer in
2090 units of 1/10 point.
2092 The value can also be a floating point number or a function, which
2093 specifies the height relative to an @dfn{underlying face} (i.e., a
2094 face that has a lower priority in the list described in
2095 @ref{Displaying Faces}). If the value is a floating point number,
2096 that specifies the amount by which to scale the height of the
2097 underlying face. If the value is a function, that function is called
2098 with one argument, the height of the underlying face, and returns the
2099 height of the new face. If the function is passed an integer
2100 argument, it must return an integer.
2102 The height of the default face must be specified using an integer;
2103 floating point and function values are not allowed.
2106 Font weight---one of the symbols (from densest to faintest)
2107 @code{ultra-bold}, @code{extra-bold}, @code{bold}, @code{semi-bold},
2108 @code{normal}, @code{semi-light}, @code{light}, @code{extra-light}, or
2109 @code{ultra-light}. On text terminals which support
2110 variable-brightness text, any weight greater than normal is displayed
2111 as extra bright, and any weight less than normal is displayed as
2115 Font slant---one of the symbols @code{italic}, @code{oblique},
2116 @code{normal}, @code{reverse-italic}, or @code{reverse-oblique}. On
2117 text terminals that support variable-brightness text, slanted text is
2118 displayed as half-bright.
2121 Foreground color, a string. The value can be a system-defined color
2122 name, or a hexadecimal color specification. @xref{Color Names}. On
2123 black-and-white displays, certain shades of gray are implemented by
2127 Background color, a string. The value can be a system-defined color
2128 name, or a hexadecimal color specification. @xref{Color Names}.
2131 Whether or not characters should be underlined, and in what color. If
2132 the value is @code{t}, underlining uses the foreground color of the
2133 face. If the value is a string, underlining uses that color. The
2134 value @code{nil} means do not underline.
2137 Whether or not characters should be overlined, and in what color.
2138 The value is used like that of @code{:underline}.
2140 @item :strike-through
2141 Whether or not characters should be strike-through, and in what
2142 color. The value is used like that of @code{:underline}.
2145 Whether or not a box should be drawn around characters, its color, the
2146 width of the box lines, and 3D appearance. Here are the possible
2147 values of the @code{:box} attribute, and what they mean:
2154 Draw a box with lines of width 1, in the foreground color.
2157 Draw a box with lines of width 1, in color @var{color}.
2159 @item @code{(:line-width @var{width} :color @var{color} :style @var{style})}
2160 This way you can explicitly specify all aspects of the box. The value
2161 @var{width} specifies the width of the lines to draw; it defaults to
2162 1. A negative width @var{-n} means to draw a line of width @var{n}
2163 that occupies the space of the underlying text, thus avoiding any
2164 increase in the character height or width.
2166 The value @var{color} specifies the color to draw with. The default is
2167 the foreground color of the face for simple boxes, and the background
2168 color of the face for 3D boxes.
2170 The value @var{style} specifies whether to draw a 3D box. If it is
2171 @code{released-button}, the box looks like a 3D button that is not being
2172 pressed. If it is @code{pressed-button}, the box looks like a 3D button
2173 that is being pressed. If it is @code{nil} or omitted, a plain 2D box
2177 @item :inverse-video
2178 Whether or not characters should be displayed in inverse video. The
2179 value should be @code{t} (yes) or @code{nil} (no).
2182 The background stipple, a bitmap.
2184 The value can be a string; that should be the name of a file containing
2185 external-format X bitmap data. The file is found in the directories
2186 listed in the variable @code{x-bitmap-file-path}.
2188 Alternatively, the value can specify the bitmap directly, with a list
2189 of the form @code{(@var{width} @var{height} @var{data})}. Here,
2190 @var{width} and @var{height} specify the size in pixels, and
2191 @var{data} is a string containing the raw bits of the bitmap, row by
2192 row. Each row occupies @math{(@var{width} + 7) / 8} consecutive bytes
2193 in the string (which should be a unibyte string for best results).
2194 This means that each row always occupies at least one whole byte.
2196 If the value is @code{nil}, that means use no stipple pattern.
2198 Normally you do not need to set the stipple attribute, because it is
2199 used automatically to handle certain shades of gray.
2202 The font used to display the face. Its value should be a font object.
2203 @xref{Font Selection}, for information about font objects.
2205 When specifying this attribute using @code{set-face-attribute}
2206 (@pxref{Attribute Functions}), you may also supply a font spec, a font
2207 entity, or a string. Emacs converts such values to an appropriate
2208 font object, and stores that font object as the actual attribute
2209 value. If you specify a string, the contents of the string should be
2210 a font name (@pxref{Fonts,,, emacs, The GNU Emacs Manual}); if the
2211 font name is an XLFD containing wildcards, Emacs chooses the first
2212 font matching those wildcards. Specifying this attribute also changes
2213 the values of the @code{:family}, @code{:foundry}, @code{:width},
2214 @code{:height}, @code{:weight}, and @code{:slant} attributes.
2217 The name of a face from which to inherit attributes, or a list of face
2218 names. Attributes from inherited faces are merged into the face like
2219 an underlying face would be, with higher priority than underlying
2220 faces (@pxref{Displaying Faces}). If a list of faces is used,
2221 attributes from faces earlier in the list override those from later
2225 For compatibility with Emacs 20, you can also specify values for two
2226 ``fake'' face attributes: @code{:bold} and @code{:italic}. Their
2227 values must be either @code{t} or @code{nil}; a value of
2228 @code{unspecified} is not allowed. Setting @code{:bold} to @code{t}
2229 is equivalent to setting the @code{:weight} attribute to @code{bold},
2230 and setting it to @code{nil} is equivalent to setting @code{:weight}
2231 to @code{normal}. Setting @code{:italic} to @code{t} is equivalent to
2232 setting the @code{:slant} attribute to @code{italic}, and setting it
2233 to @code{nil} is equivalent to setting @code{:slant} to @code{normal}.
2235 @defun font-family-list &optional frame
2236 This function returns a list of available font family names. The
2237 optional argument @var{frame} specifies the frame on which the text is
2238 to be displayed; if it is @code{nil}, the selected frame is used.
2241 @defopt underline-minimum-offset
2242 This variable specifies the minimum distance between the baseline and
2243 the underline, in pixels, when displaying underlined text.
2246 @defopt x-bitmap-file-path
2247 This variable specifies a list of directories for searching
2248 for bitmap files, for the @code{:stipple} attribute.
2251 @defun bitmap-spec-p object
2252 This returns @code{t} if @var{object} is a valid bitmap specification,
2253 suitable for use with @code{:stipple} (see above). It returns
2254 @code{nil} otherwise.
2257 @node Attribute Functions
2258 @subsection Face Attribute Functions
2260 This section describes the functions for accessing and modifying the
2261 attributes of an existing face.
2263 @defun set-face-attribute face frame &rest arguments
2264 This function sets one or more attributes of @var{face} for
2265 @var{frame}. The attributes you specify this way override whatever
2266 the @code{defface} says.
2268 The extra arguments @var{arguments} specify the attributes to set, and
2269 the values for them. They should consist of alternating attribute
2270 names (such as @code{:family} or @code{:underline}) and values. Thus,
2273 (set-face-attribute 'foo nil
2279 sets the attribute @code{:width} to @code{extended} and the attribute
2280 @code{:weight} to @code{bold}.
2282 If @var{frame} is @code{t}, this function sets the default attributes
2283 for new frames. Default attribute values specified this way override
2284 the @code{defface} for newly created frames.
2286 If @var{frame} is @code{nil}, this function sets the attributes for
2287 all existing frames, and the default for new frames.
2290 @defun face-attribute face attribute &optional frame inherit
2291 This returns the value of the @var{attribute} attribute of @var{face}
2292 on @var{frame}. If @var{frame} is @code{nil}, that means the selected
2293 frame (@pxref{Input Focus}).
2295 If @var{frame} is @code{t}, this returns whatever new-frames default
2296 value you previously specified with @code{set-face-attribute} for the
2297 @var{attribute} attribute of @var{face}. If you have not specified
2298 one, it returns @code{nil}.
2300 If @var{inherit} is @code{nil}, only attributes directly defined by
2301 @var{face} are considered, so the return value may be
2302 @code{unspecified}, or a relative value. If @var{inherit} is
2303 non-@code{nil}, @var{face}'s definition of @var{attribute} is merged
2304 with the faces specified by its @code{:inherit} attribute; however the
2305 return value may still be @code{unspecified} or relative. If
2306 @var{inherit} is a face or a list of faces, then the result is further
2307 merged with that face (or faces), until it becomes specified and
2310 To ensure that the return value is always specified and absolute, use
2311 a value of @code{default} for @var{inherit}; this will resolve any
2312 unspecified or relative values by merging with the @code{default} face
2313 (which is always completely specified).
2318 (face-attribute 'bold :weight)
2323 @defun face-attribute-relative-p attribute value
2324 This function returns non-@code{nil} if @var{value}, when used as the
2325 value of the face attribute @var{attribute}, is relative. This means
2326 it would modify, rather than completely override, any value that comes
2327 from a subsequent face in the face list or that is inherited from
2330 @code{unspecified} is a relative value for all attributes. For
2331 @code{:height}, floating point and function values are also relative.
2336 (face-attribute-relative-p :height 2.0)
2341 @defun face-all-attributes face &optional frame
2342 This function returns an alist of attributes of @var{face}. The
2343 elements of the result are name-value pairs of the form
2344 @w{@code{(@var{attr-name} . @var{attr-value})}}. Optional argument
2345 @var{frame} specifies the frame whose definition of @var{face} to
2346 return; if omitted or @code{nil}, the returned value describes the
2347 default attributes of @var{face} for newly created frames.
2350 @defun merge-face-attribute attribute value1 value2
2351 If @var{value1} is a relative value for the face attribute
2352 @var{attribute}, returns it merged with the underlying value
2353 @var{value2}; otherwise, if @var{value1} is an absolute value for the
2354 face attribute @var{attribute}, returns @var{value1} unchanged.
2357 The following commands and functions mostly provide compatibility
2358 with old versions of Emacs. They work by calling
2359 @code{set-face-attribute}. Values of @code{t} and @code{nil} for
2360 their @var{frame} argument are handled just like
2361 @code{set-face-attribute} and @code{face-attribute}. The commands
2362 read their arguments using the minibuffer, if called interactively.
2364 @deffn Command set-face-foreground face color &optional frame
2365 @deffnx Command set-face-background face color &optional frame
2366 These set the @code{:foreground} attribute (or @code{:background}
2367 attribute, respectively) of @var{face} to @var{color}.
2370 @deffn Command set-face-stipple face pattern &optional frame
2371 This sets the @code{:stipple} attribute of @var{face} to
2375 @deffn Command set-face-font face font &optional frame
2376 This sets the @code{:font} attribute of @var{face} to @var{font}.
2379 @defun set-face-bold-p face bold-p &optional frame
2380 This sets the @code{:weight} attribute of @var{face} to @var{normal}
2381 if @var{bold-p} is @code{nil}, and to @var{bold} otherwise.
2384 @defun set-face-italic-p face italic-p &optional frame
2385 This sets the @code{:slant} attribute of @var{face} to @var{normal} if
2386 @var{italic-p} is @code{nil}, and to @var{italic} otherwise.
2389 @defun set-face-underline-p face underline &optional frame
2390 This sets the @code{:underline} attribute of @var{face} to
2394 @defun set-face-inverse-video-p face inverse-video-p &optional frame
2395 This sets the @code{:inverse-video} attribute of @var{face} to
2396 @var{inverse-video-p}.
2399 @deffn Command invert-face face &optional frame
2400 This swaps the foreground and background colors of face @var{face}.
2403 The following functions examine the attributes of a face. If you
2404 don't specify @var{frame}, they refer to the selected frame; @code{t}
2405 refers to the default data for new frames. They return the symbol
2406 @code{unspecified} if the face doesn't define any value for that
2409 @defun face-foreground face &optional frame inherit
2410 @defunx face-background face &optional frame inherit
2411 These functions return the foreground color (or background color,
2412 respectively) of face @var{face}, as a string.
2414 If @var{inherit} is @code{nil}, only a color directly defined by the face is
2415 returned. If @var{inherit} is non-@code{nil}, any faces specified by its
2416 @code{:inherit} attribute are considered as well, and if @var{inherit}
2417 is a face or a list of faces, then they are also considered, until a
2418 specified color is found. To ensure that the return value is always
2419 specified, use a value of @code{default} for @var{inherit}.
2422 @defun face-stipple face &optional frame inherit
2423 This function returns the name of the background stipple pattern of face
2424 @var{face}, or @code{nil} if it doesn't have one.
2426 If @var{inherit} is @code{nil}, only a stipple directly defined by the
2427 face is returned. If @var{inherit} is non-@code{nil}, any faces
2428 specified by its @code{:inherit} attribute are considered as well, and
2429 if @var{inherit} is a face or a list of faces, then they are also
2430 considered, until a specified stipple is found. To ensure that the
2431 return value is always specified, use a value of @code{default} for
2435 @defun face-font face &optional frame
2436 This function returns the name of the font of face @var{face}.
2439 @defun face-bold-p face &optional frame
2440 This function returns a non-@code{nil} value if the @code{:weight}
2441 attribute of @var{face} is bolder than normal (i.e., one of
2442 @code{semi-bold}, @code{bold}, @code{extra-bold}, or
2443 @code{ultra-bold}). Otherwise, it returns @code{nil}.
2446 @defun face-italic-p face &optional frame
2447 This function returns a non-@code{nil} value if the @code{:slant}
2448 attribute of @var{face} is @code{italic} or @code{oblique}, and
2449 @code{nil} otherwise.
2452 @defun face-underline-p face &optional frame
2453 This function returns the @code{:underline} attribute of face @var{face}.
2456 @defun face-inverse-video-p face &optional frame
2457 This function returns the @code{:inverse-video} attribute of face @var{face}.
2460 @node Displaying Faces
2461 @subsection Displaying Faces
2463 Here is how Emacs determines the face to use for displaying any
2464 given piece of text:
2468 If the text consists of a special glyph, the glyph can specify a
2469 particular face. @xref{Glyphs}.
2472 If the text lies within an active region, Emacs highlights it using
2473 the @code{region} face. @xref{Standard Faces,,, emacs, The GNU Emacs
2477 If the text lies within an overlay with a non-@code{nil} @code{face}
2478 property, Emacs applies the face or face attributes specified by that
2479 property. If the overlay has a @code{mouse-face} property and the
2480 mouse is ``near enough'' to the overlay, Emacs applies the face or
2481 face attributes specified by the @code{mouse-face} property instead.
2482 @xref{Overlay Properties}.
2484 When multiple overlays cover one character, an overlay with higher
2485 priority overrides those with lower priority. @xref{Overlays}.
2488 If the text contains a @code{face} or @code{mouse-face} property,
2489 Emacs applies the specified faces and face attributes. @xref{Special
2490 Properties}. (This is how Font Lock mode faces are applied.
2491 @xref{Font Lock Mode}.)
2494 If the text lies within the mode line of the selected window, Emacs
2495 applies the @code{mode-line} face. For the mode line of a
2496 non-selected window, Emacs applies the @code{mode-line-inactive} face.
2497 For a header line, Emacs applies the @code{header-line} face.
2500 If any given attribute has not been specified during the preceding
2501 steps, Emacs applies the attribute of the @code{default} face.
2504 If these various sources together specify more than one face for a
2505 particular character, Emacs merges the attributes of the various faces
2506 specified. For each attribute, Emacs tries using the above order
2507 (i.e.@: first the face of any special glyph; then the face for region
2508 highlighting, if appropriate; and so on).
2510 @node Face Remapping
2511 @subsection Face Remapping
2513 The variable @code{face-remapping-alist} is used for buffer-local or
2514 global changes in the appearance of a face. For instance, it is used
2515 to implement the @code{text-scale-adjust} command (@pxref{Text
2516 Scale,,, emacs, The GNU Emacs Manual}).
2518 @defvar face-remapping-alist
2519 The value of this variable is an alist whose elements have the form
2520 @code{(@var{face} . @var{remapping})}. This causes Emacs to display
2521 any text having the face @var{face} with @var{remapping}, rather than
2522 the ordinary definition of @var{face}. @var{remapping} may be any
2523 face specification suitable for a @code{face} text property: either a
2524 face name, or a property list of attribute/value pairs, or a list in
2525 which each element is either a face name or a property list
2526 (@pxref{Special Properties}).
2528 If @code{face-remapping-alist} is buffer-local, its local value takes
2529 effect only within that buffer.
2531 Two points bear emphasizing:
2535 @var{remapping} serves as the complete specification for the remapped
2536 face---it replaces the normal definition of @var{face}, instead of
2540 If @var{remapping} references the same face name @var{face}, either
2541 directly or via the @code{:inherit} attribute of some other face in
2542 @var{remapping}, that reference uses the normal definition of
2543 @var{face}. In other words, the remapping cannot be recursive.
2545 For instance, if the @code{mode-line} face is remapped using this
2546 entry in @code{face-remapping-alist}:
2548 (mode-line italic mode-line)
2551 then the new definition of the @code{mode-line} face inherits from the
2552 @code{italic} face, and the @emph{normal} (non-remapped) definition of
2553 @code{mode-line} face.
2557 The following functions implement a higher-level interface to
2558 @code{face-remapping-alist}. Most Lisp code should use these
2559 functions instead of setting @code{face-remapping-alist} directly, to
2560 avoid trampling on remappings applied elsewhere. These functions are
2561 intended for buffer-local remappings, so they all make
2562 @code{face-remapping-alist} buffer-local as a side-effect. They manage
2563 @code{face-remapping-alist} entries of the form
2566 (@var{face} @var{relative-spec-1} @var{relative-spec-2} @var{...} @var{base-spec})
2570 where, as explained above, each of the @var{relative-spec-N} and
2571 @var{base-spec} is either a face name, or a property list of
2572 attribute/value pairs. Each of the @dfn{relative remapping} entries,
2573 @var{relative-spec-N}, is managed by the
2574 @code{face-remap-add-relative} and @code{face-remap-remove-relative}
2575 functions; these are intended for simple modifications like changing
2576 the text size. The @dfn{base remapping} entry, @var{base-spec}, has
2577 the lowest priority and is managed by the @code{face-remap-set-base}
2578 and @code{face-remap-reset-base} functions; it is intended for major
2579 modes to remap faces in the buffers they control.
2581 @defun face-remap-add-relative face &rest specs
2582 This functions adds the face specifications in @var{specs} as relative
2583 remappings for face @var{face} in the current buffer. The remaining
2584 arguments, @var{specs}, should form either a list of face names, or a
2585 property list of attribute/value pairs.
2587 The return value is a Lisp object that serves as a ``cookie''; you can
2588 pass this object as an argument to @code{face-remap-remove-relative}
2589 if you need to remove the remapping later.
2592 ;; Remap the `escape-glyph' face into a combination
2593 ;; of the `highlight' and `italic' faces:
2594 (face-remap-add-relative 'escape-glyph 'highlight 'italic)
2596 ;; Increase the size of the `default' face by 50%:
2597 (face-remap-add-relative 'default :height 1.5)
2601 @defun face-remap-remove-relative cookie
2602 This function removes a relative remapping previously added by
2603 @code{face-remap-add-relative}. @var{cookie} should be the Lisp
2604 object returned by @code{face-remap-add-relative} when the remapping
2608 @defun face-remap-set-base face &rest specs
2609 This function sets the base remapping of @var{face} in the current
2610 buffer to @var{specs}. If @var{specs} is empty, the default base
2611 remapping is restored, similar to calling @code{face-remap-reset-base}
2612 (see below); note that this is different from @var{specs} containing a
2613 single value @code{nil}, which has the opposite result (the global
2614 definition of @var{face} is ignored).
2616 This overwrites the default @var{base-spec}, which inherits the global
2617 face definition, so it is up to the caller to add such inheritance if
2621 @defun face-remap-reset-base face
2622 This function sets the base remapping of @var{face} to its default
2623 value, which inherits from @var{face}'s global definition.
2626 @node Face Functions
2627 @subsection Functions for Working with Faces
2629 Here are additional functions for creating and working with faces.
2632 This function returns a list of all defined face names.
2636 This function returns the @dfn{face number} of face @var{face}. This
2637 is a number that uniquely identifies a face at low levels within
2638 Emacs. It is seldom necessary to refer to a face by its face number.
2641 @defun face-documentation face
2642 This function returns the documentation string of face @var{face}, or
2643 @code{nil} if none was specified for it.
2646 @defun face-equal face1 face2 &optional frame
2647 This returns @code{t} if the faces @var{face1} and @var{face2} have the
2648 same attributes for display.
2651 @defun face-differs-from-default-p face &optional frame
2652 This returns non-@code{nil} if the face @var{face} displays
2653 differently from the default face.
2657 A @dfn{face alias} provides an equivalent name for a face. You can
2658 define a face alias by giving the alias symbol the @code{face-alias}
2659 property, with a value of the target face name. The following example
2660 makes @code{modeline} an alias for the @code{mode-line} face.
2663 (put 'modeline 'face-alias 'mode-line)
2666 @defmac define-obsolete-face-alias obsolete-face current-face when
2667 This macro defines @code{obsolete-face} as an alias for
2668 @var{current-face}, and also marks it as obsolete, indicating that it
2669 may be removed in future. @var{when} should be a string indicating
2670 when @code{obsolete-face} was made obsolete (usually a version number
2675 @subsection Automatic Face Assignment
2676 @cindex automatic face assignment
2677 @cindex faces, automatic choice
2679 This hook is used for automatically assigning faces to text in the
2680 buffer. It is part of the implementation of Jit-Lock mode, used by
2683 @defvar fontification-functions
2684 This variable holds a list of functions that are called by Emacs
2685 redisplay as needed, just before doing redisplay. They are called even
2686 when Font Lock Mode isn't enabled. When Font Lock Mode is enabled, this
2687 variable usually holds just one function, @code{jit-lock-function}.
2689 The functions are called in the order listed, with one argument, a
2690 buffer position @var{pos}. Collectively they should attempt to assign
2691 faces to the text in the current buffer starting at @var{pos}.
2693 The functions should record the faces they assign by setting the
2694 @code{face} property. They should also add a non-@code{nil}
2695 @code{fontified} property to all the text they have assigned faces to.
2696 That property tells redisplay that faces have been assigned to that text
2699 It is probably a good idea for the functions to do nothing if the
2700 character after @var{pos} already has a non-@code{nil} @code{fontified}
2701 property, but this is not required. If one function overrides the
2702 assignments made by a previous one, the properties after the last
2703 function finishes are the ones that really matter.
2705 For efficiency, we recommend writing these functions so that they
2706 usually assign faces to around 400 to 600 characters at each call.
2710 @subsection Basic Faces
2712 If your Emacs Lisp program needs to assign some faces to text, it is
2713 often a good idea to use certain existing faces or inherit from them,
2714 rather than defining entirely new faces. This way, if other users
2715 have customized the basic faces to give Emacs a certain look, your
2716 program will ``fit in'' without additional customization.
2718 Some of the basic faces defined in Emacs are listed below. In
2719 addition to these, you might want to make use of the Font Lock faces
2720 for syntactic highlighting, if highlighting is not already handled by
2721 Font Lock mode, or if some Font Lock faces are not in use.
2722 @xref{Faces for Font Lock}.
2726 The default face, whose attributes are all specified. All other faces
2727 implicitly inherit from it: any unspecified attribute defaults to the
2728 attribute on this face (@pxref{Face Attributes}).
2735 @itemx variable-pitch
2736 These have the attributes indicated by their names (e.g. @code{bold}
2737 has a bold @code{:weight} attribute), with all other attributes
2738 unspecified (and so given by @code{default}).
2741 For ``dimmed out'' text. For example, it is used for the ignored
2742 part of a filename in the minibuffer (@pxref{Minibuffer File,,
2743 Minibuffers for File Names, emacs, The GNU Emacs Manual}).
2747 For clickable text buttons that send the user to a different
2748 buffer or ``location''.
2751 For stretches of text that should temporarily stand out. For example,
2752 it is commonly assigned to the @code{mouse-face} property for cursor
2753 highlighting (@pxref{Special Properties}).
2756 For text matching a search command.
2761 For text concerning errors, warnings, or successes. For example,
2762 these are used for messages in @file{*Compilation*} buffers.
2765 @node Font Selection
2766 @subsection Font Selection
2768 Before Emacs can draw a character on a graphical display, it must
2769 select a @dfn{font} for that character@footnote{In this context, the
2770 term @dfn{font} has nothing to do with Font Lock (@pxref{Font Lock
2771 Mode}).}. @xref{Fonts,,, emacs, The GNU Emacs Manual}. Normally,
2772 Emacs automatically chooses a font based on the faces assigned to that
2773 character---specifically, the face attributes @code{:family},
2774 @code{:weight}, @code{:slant}, and @code{:width} (@pxref{Face
2775 Attributes}). The choice of font also depends on the character to be
2776 displayed; some fonts can only display a limited set of characters.
2777 If no available font exactly fits the requirements, Emacs looks for
2778 the @dfn{closest matching font}. The variables in this section
2779 control how Emacs makes this selection.
2781 @defopt face-font-family-alternatives
2782 If a given family is specified but does not exist, this variable
2783 specifies alternative font families to try. Each element should have
2787 (@var{family} @var{alternate-families}@dots{})
2790 If @var{family} is specified but not available, Emacs will try the other
2791 families given in @var{alternate-families}, one by one, until it finds a
2792 family that does exist.
2795 @defopt face-font-selection-order
2796 If there is no font that exactly matches all desired face attributes
2797 (@code{:width}, @code{:height}, @code{:weight}, and @code{:slant}),
2798 this variable specifies the order in which these attributes should be
2799 considered when selecting the closest matching font. The value should
2800 be a list containing those four attribute symbols, in order of
2801 decreasing importance. The default is @code{(:width :height :weight
2804 Font selection first finds the best available matches for the first
2805 attribute in the list; then, among the fonts which are best in that
2806 way, it searches for the best matches in the second attribute, and so
2809 The attributes @code{:weight} and @code{:width} have symbolic values in
2810 a range centered around @code{normal}. Matches that are more extreme
2811 (farther from @code{normal}) are somewhat preferred to matches that are
2812 less extreme (closer to @code{normal}); this is designed to ensure that
2813 non-normal faces contrast with normal ones, whenever possible.
2815 One example of a case where this variable makes a difference is when the
2816 default font has no italic equivalent. With the default ordering, the
2817 @code{italic} face will use a non-italic font that is similar to the
2818 default one. But if you put @code{:slant} before @code{:height}, the
2819 @code{italic} face will use an italic font, even if its height is not
2823 @defopt face-font-registry-alternatives
2824 This variable lets you specify alternative font registries to try, if a
2825 given registry is specified and doesn't exist. Each element should have
2829 (@var{registry} @var{alternate-registries}@dots{})
2832 If @var{registry} is specified but not available, Emacs will try the
2833 other registries given in @var{alternate-registries}, one by one,
2834 until it finds a registry that does exist.
2837 Emacs can make use of scalable fonts, but by default it does not use
2840 @defopt scalable-fonts-allowed
2841 This variable controls which scalable fonts to use. A value of
2842 @code{nil}, the default, means do not use scalable fonts. @code{t}
2843 means to use any scalable font that seems appropriate for the text.
2845 Otherwise, the value must be a list of regular expressions. Then a
2846 scalable font is enabled for use if its name matches any regular
2847 expression in the list. For example,
2850 (setq scalable-fonts-allowed '("muleindian-2$"))
2854 allows the use of scalable fonts with registry @code{muleindian-2}.
2857 @defvar face-font-rescale-alist
2858 This variable specifies scaling for certain faces. Its value should
2859 be a list of elements of the form
2862 (@var{fontname-regexp} . @var{scale-factor})
2865 If @var{fontname-regexp} matches the font name that is about to be
2866 used, this says to choose a larger similar font according to the
2867 factor @var{scale-factor}. You would use this feature to normalize
2868 the font size if certain fonts are bigger or smaller than their
2869 nominal heights and widths would suggest.
2873 @subsection Looking Up Fonts
2875 @defun x-list-fonts name &optional reference-face frame maximum width
2876 This function returns a list of available font names that match
2877 @var{name}. @var{name} should be a string containing a font name in
2878 either the Fontconfig, GTK, or XLFD format (@pxref{Fonts,,, emacs, The
2879 GNU Emacs Manual}). Within an XLFD string, wildcard characters may be
2880 used: the @samp{*} character matches any substring, and the @samp{?}
2881 character matches any single character. Case is ignored when matching
2884 If the optional arguments @var{reference-face} and @var{frame} are
2885 specified, the returned list includes only fonts that are the same
2886 size as @var{reference-face} (a face name) currently is on the frame
2889 The optional argument @var{maximum} sets a limit on how many fonts to
2890 return. If it is non-@code{nil}, then the return value is truncated
2891 after the first @var{maximum} matching fonts. Specifying a small
2892 value for @var{maximum} can make this function much faster, in cases
2893 where many fonts match the pattern.
2895 The optional argument @var{width} specifies a desired font width. If
2896 it is non-@code{nil}, the function only returns those fonts whose
2897 characters are (on average) @var{width} times as wide as
2898 @var{reference-face}.
2901 @defun x-family-fonts &optional family frame
2902 This function returns a list describing the available fonts for family
2903 @var{family} on @var{frame}. If @var{family} is omitted or @code{nil},
2904 this list applies to all families, and therefore, it contains all
2905 available fonts. Otherwise, @var{family} must be a string; it may
2906 contain the wildcards @samp{?} and @samp{*}.
2908 The list describes the display that @var{frame} is on; if @var{frame} is
2909 omitted or @code{nil}, it applies to the selected frame's display
2910 (@pxref{Input Focus}).
2912 Each element in the list is a vector of the following form:
2915 [@var{family} @var{width} @var{point-size} @var{weight} @var{slant}
2916 @var{fixed-p} @var{full} @var{registry-and-encoding}]
2919 The first five elements correspond to face attributes; if you
2920 specify these attributes for a face, it will use this font.
2922 The last three elements give additional information about the font.
2923 @var{fixed-p} is non-@code{nil} if the font is fixed-pitch.
2924 @var{full} is the full name of the font, and
2925 @var{registry-and-encoding} is a string giving the registry and
2926 encoding of the font.
2929 @defvar font-list-limit
2930 This variable specifies maximum number of fonts to consider in font
2931 matching. The function @code{x-family-fonts} will not return more than
2932 that many fonts, and font selection will consider only that many fonts
2933 when searching a matching font for face attributes. The default is
2938 @subsection Fontsets
2940 A @dfn{fontset} is a list of fonts, each assigned to a range of
2941 character codes. An individual font cannot display the whole range of
2942 characters that Emacs supports, but a fontset can. Fontsets have names,
2943 just as fonts do, and you can use a fontset name in place of a font name
2944 when you specify the ``font'' for a frame or a face. Here is
2945 information about defining a fontset under Lisp program control.
2947 @defun create-fontset-from-fontset-spec fontset-spec &optional style-variant-p noerror
2948 This function defines a new fontset according to the specification
2949 string @var{fontset-spec}. The string should have this format:
2952 @var{fontpattern}, @r{[}@var{charset}:@var{font}@r{]@dots{}}
2956 Whitespace characters before and after the commas are ignored.
2958 The first part of the string, @var{fontpattern}, should have the form of
2959 a standard X font name, except that the last two fields should be
2960 @samp{fontset-@var{alias}}.
2962 The new fontset has two names, one long and one short. The long name is
2963 @var{fontpattern} in its entirety. The short name is
2964 @samp{fontset-@var{alias}}. You can refer to the fontset by either
2965 name. If a fontset with the same name already exists, an error is
2966 signaled, unless @var{noerror} is non-@code{nil}, in which case this
2967 function does nothing.
2969 If optional argument @var{style-variant-p} is non-@code{nil}, that says
2970 to create bold, italic and bold-italic variants of the fontset as well.
2971 These variant fontsets do not have a short name, only a long one, which
2972 is made by altering @var{fontpattern} to indicate the bold or italic
2975 The specification string also says which fonts to use in the fontset.
2976 See below for the details.
2979 The construct @samp{@var{charset}:@var{font}} specifies which font to
2980 use (in this fontset) for one particular character set. Here,
2981 @var{charset} is the name of a character set, and @var{font} is the font
2982 to use for that character set. You can use this construct any number of
2983 times in the specification string.
2985 For the remaining character sets, those that you don't specify
2986 explicitly, Emacs chooses a font based on @var{fontpattern}: it replaces
2987 @samp{fontset-@var{alias}} with a value that names one character set.
2988 For the @acronym{ASCII} character set, @samp{fontset-@var{alias}} is replaced
2989 with @samp{ISO8859-1}.
2991 In addition, when several consecutive fields are wildcards, Emacs
2992 collapses them into a single wildcard. This is to prevent use of
2993 auto-scaled fonts. Fonts made by scaling larger fonts are not usable
2994 for editing, and scaling a smaller font is not useful because it is
2995 better to use the smaller font in its own size, which Emacs does.
2997 Thus if @var{fontpattern} is this,
3000 -*-fixed-medium-r-normal-*-24-*-*-*-*-*-fontset-24
3004 the font specification for @acronym{ASCII} characters would be this:
3007 -*-fixed-medium-r-normal-*-24-*-ISO8859-1
3011 and the font specification for Chinese GB2312 characters would be this:
3014 -*-fixed-medium-r-normal-*-24-*-gb2312*-*
3017 You may not have any Chinese font matching the above font
3018 specification. Most X distributions include only Chinese fonts that
3019 have @samp{song ti} or @samp{fangsong ti} in the @var{family} field. In
3020 such a case, @samp{Fontset-@var{n}} can be specified as below:
3023 Emacs.Fontset-0: -*-fixed-medium-r-normal-*-24-*-*-*-*-*-fontset-24,\
3024 chinese-gb2312:-*-*-medium-r-normal-*-24-*-gb2312*-*
3028 Then, the font specifications for all but Chinese GB2312 characters have
3029 @samp{fixed} in the @var{family} field, and the font specification for
3030 Chinese GB2312 characters has a wild card @samp{*} in the @var{family}
3033 @defun set-fontset-font name character font-spec &optional frame add
3034 This function modifies the existing fontset @var{name} to use the font
3035 matching with @var{font-spec} for the character @var{character}.
3037 If @var{name} is @code{nil}, this function modifies the fontset of the
3038 selected frame or that of @var{frame} if @var{frame} is not
3041 If @var{name} is @code{t}, this function modifies the default
3042 fontset, whose short name is @samp{fontset-default}.
3044 @var{character} may be a cons; @code{(@var{from} . @var{to})}, where
3045 @var{from} and @var{to} are character codepoints. In that case, use
3046 @var{font-spec} for all characters in the range @var{from} and @var{to}
3049 @var{character} may be a charset. In that case, use
3050 @var{font-spec} for all character in the charsets.
3052 @var{character} may be a script name. In that case, use
3053 @var{font-spec} for all character in the charsets.
3055 @var{font-spec} may be a cons; @code{(@var{family} . @var{registry})},
3056 where @var{family} is a family name of a font (possibly including a
3057 foundry name at the head), @var{registry} is a registry name of a font
3058 (possibly including an encoding name at the tail).
3060 @var{font-spec} may be a font name string.
3062 The optional argument @var{add}, if non-@code{nil}, specifies how to
3063 add @var{font-spec} to the font specifications previously set. If it
3064 is @code{prepend}, @var{font-spec} is prepended. If it is
3065 @code{append}, @var{font-spec} is appended. By default,
3066 @var{font-spec} overrides the previous settings.
3068 For instance, this changes the default fontset to use a font of which
3069 family name is @samp{Kochi Gothic} for all characters belonging to
3070 the charset @code{japanese-jisx0208}.
3073 (set-fontset-font t 'japanese-jisx0208
3074 (font-spec :family "Kochi Gothic"))
3078 @defun char-displayable-p char
3079 This function returns @code{t} if Emacs ought to be able to display
3080 @var{char}. More precisely, if the selected frame's fontset has a
3081 font to display the character set that @var{char} belongs to.
3083 Fontsets can specify a font on a per-character basis; when the fontset
3084 does that, this function's value may not be accurate.
3087 @node Low-Level Font
3088 @subsection Low-Level Font Representation
3090 Normally, it is not necessary to manipulate fonts directly. In case
3091 you need to do so, this section explains how.
3093 In Emacs Lisp, fonts are represented using three different Lisp
3094 object types: @dfn{font objects}, @dfn{font specs}, and @dfn{font
3097 @defun fontp object &optional type
3098 Return @code{t} if @var{object} is a font object, font spec, or font
3099 entity. Otherwise, return @code{nil}.
3101 The optional argument @var{type}, if non-@code{nil}, determines the
3102 exact type of Lisp object to check for. In that case, @var{type}
3103 should be one of @code{font-object}, @code{font-spec}, or
3107 A font object is a Lisp object that represents a font that Emacs has
3108 @dfn{opened}. Font objects cannot be modified in Lisp, but they can
3111 @defun font-at position &optional window string
3112 Return the font object that is being used to display the character at
3113 position @var{position} in the window @var{window}. If @var{window}
3114 is @code{nil}, it defaults to the selected window. If @var{string} is
3115 @code{nil}, @var{position} specifies a position in the current buffer;
3116 otherwise, @var{string} should be a string, and @var{position}
3117 specifies a position in that string.
3120 A font spec is a Lisp object that contains a set of specifications
3121 that can be used to find a font. More than one font may match the
3122 specifications in a font spec.
3124 @defun font-spec &rest arguments
3125 Return a new font spec using the specifications in @var{arguments},
3126 which should come in @code{property}-@code{value} pairs. The possible
3127 specifications are as follows:
3131 The font name (a string), in either XLFD, Fontconfig, or GTK format.
3132 @xref{Fonts,,, emacs, The GNU Emacs Manual}.
3139 These have the same meanings as the face attributes of the same name.
3140 @xref{Face Attributes}.
3143 The font size---either a non-negative integer that specifies the pixel
3144 size, or a floating point number that specifies the point size.
3147 Additional typographic style information for the font, such as
3148 @samp{sans}. The value should be a string or a symbol.
3151 The charset registry and encoding of the font, such as
3152 @samp{iso8859-1}. The value should be a string or a symbol.
3155 The script that the font must support (a symbol).
3158 The font must be an OpenType font that supports these OpenType
3159 features, provided Emacs is compiled with support for @samp{libotf} (a
3160 library for performing complex text layout in certain scripts). The
3161 value must be a list of the form
3164 @code{(@var{script-tag} @var{langsys-tag} @var{gsub} @var{gpos})}
3167 where @var{script-tag} is the OpenType script tag symbol;
3168 @var{langsys-tag} is the OpenType language system tag symbol, or
3169 @code{nil} to use the default language system; @code{gsub} is a list
3170 of OpenType GSUB feature tag symbols, or @code{nil} if none is
3171 required; and @code{gpos} is a list of OpenType GPOS feature tag
3172 symbols, or @code{nil} if none is required. If @code{gsub} or
3173 @code{gpos} is a list, a @code{nil} element in that list means that
3174 the font must not match any of the remaining tag symbols. The
3175 @code{gpos} element may be omitted.
3179 @defun font-put font-spec property value
3180 Set the font property @var{property} in the font-spec @var{font-spec}
3184 A font entity is a reference to a font that need not be open. Its
3185 properties are intermediate between a font object and a font spec:
3186 like a font object, and unlike a font spec, it refers to a single,
3187 specific font. Unlike a font object, creating a font entity does not
3188 load the contents of that font into computer memory.
3190 @defun find-font font-spec &optional frame
3191 This function returns a font entity that best matches the font spec
3192 @var{font-spec} on frame @var{frame}. If @var{frame} is @code{nil},
3193 it defaults to the selected frame.
3196 @defun list-fonts font-spec &optional frame num prefer
3197 This function returns a list of all font entities that match the font
3198 spec @var{font-spec}.
3200 The optional argument @var{frame}, if non-@code{nil}, specifies the
3201 frame on which the fonts are to be displayed. The optional argument
3202 @var{num}, if non-@code{nil}, should be an integer that specifies the
3203 maximum length of the returned list. The optional argument
3204 @var{prefer}, if non-@code{nil}, should be another font spec, which is
3205 used to control the order of the returned list; the returned font
3206 entities are sorted in order of decreasing ``closeness'' to that font
3210 If you call @code{set-face-attribute} and pass a font spec, font
3211 entity, or font name string as the value of the @code{:font}
3212 attribute, Emacs opens the best ``matching'' font that is available
3213 for display. It then stores the corresponding font object as the
3214 actual value of the @code{:font} attribute for that face.
3216 The following functions can be used to obtain information about a
3217 font. For these functions, the @var{font} argument can be a font
3218 object, a font entity, or a font spec.
3220 @defun font-get font property
3221 This function returns the value of the font property @var{property}
3224 If @var{font} is a font spec and the font spec does not specify
3225 @var{property}, the return value is @code{nil}. If @var{font} is a
3226 font object or font entity, the value for the @var{:script} property
3227 may be a list of scripts supported by the font.
3230 @defun font-face-attributes font &optional frame
3231 This function returns a list of face attributes corresponding to
3232 @var{font}. The optional argument @var{frame} specifies the frame on
3233 which the font is to be displayed. If it is @code{nil}, the selected
3234 frame is used. The return value has the form
3237 (:family @var{family} :height @var{height} :weight @var{weight}
3238 :slant @var{slant} :width @var{width})
3241 where the values of @var{family}, @var{height}, @var{weight},
3242 @var{slant}, and @var{width} are face attribute values. Some of these
3243 key-attribute pairs may be omitted from the list if they are not
3244 specified by @var{font}.
3247 @defun font-xlfd-name font &optional fold-wildcards
3248 This function returns the XLFD (X Logical Font Descriptor), a string,
3249 matching @var{font}. @xref{Fonts,,, emacs, The GNU Emacs Manual}, for
3250 information about XLFDs. If the name is too long for an XLFD (which
3251 can contain at most 255 characters), the function returns @code{nil}.
3253 If the optional argument @var{fold-wildcards} is non-@code{nil},
3254 consecutive wildcards in the XLFD are folded into one.
3261 On graphical displays, Emacs draws @dfn{fringes} next to each
3262 window: thin vertical strips down the sides which can display bitmaps
3263 indicating truncation, continuation, horizontal scrolling, and so on.
3266 * Fringe Size/Pos:: Specifying where to put the window fringes.
3267 * Fringe Indicators:: Displaying indicator icons in the window fringes.
3268 * Fringe Cursors:: Displaying cursors in the right fringe.
3269 * Fringe Bitmaps:: Specifying bitmaps for fringe indicators.
3270 * Customizing Bitmaps:: Specifying your own bitmaps to use in the fringes.
3271 * Overlay Arrow:: Display of an arrow to indicate position.
3274 @node Fringe Size/Pos
3275 @subsection Fringe Size and Position
3277 The following buffer-local variables control the position and width
3278 of fringes in windows showing that buffer.
3280 @defvar fringes-outside-margins
3281 The fringes normally appear between the display margins and the window
3282 text. If the value is non-@code{nil}, they appear outside the display
3283 margins. @xref{Display Margins}.
3286 @defvar left-fringe-width
3287 This variable, if non-@code{nil}, specifies the width of the left
3288 fringe in pixels. A value of @code{nil} means to use the left fringe
3289 width from the window's frame.
3292 @defvar right-fringe-width
3293 This variable, if non-@code{nil}, specifies the width of the right
3294 fringe in pixels. A value of @code{nil} means to use the right fringe
3295 width from the window's frame.
3298 Any buffer which does not specify values for these variables uses
3299 the values specified by the @code{left-fringe} and @code{right-fringe}
3300 frame parameters (@pxref{Layout Parameters}).
3302 The above variables actually take effect via the function
3303 @code{set-window-buffer} (@pxref{Buffers and Windows}), which calls
3304 @code{set-window-fringes} as a subroutine. If you change one of these
3305 variables, the fringe display is not updated in existing windows
3306 showing the buffer, unless you call @code{set-window-buffer} again in
3307 each affected window. You can also use @code{set-window-fringes} to
3308 control the fringe display in individual windows.
3310 @defun set-window-fringes window left &optional right outside-margins
3311 This function sets the fringe widths of window @var{window}.
3312 If @var{window} is @code{nil}, the selected window is used.
3314 The argument @var{left} specifies the width in pixels of the left
3315 fringe, and likewise @var{right} for the right fringe. A value of
3316 @code{nil} for either one stands for the default width. If
3317 @var{outside-margins} is non-@code{nil}, that specifies that fringes
3318 should appear outside of the display margins.
3321 @defun window-fringes &optional window
3322 This function returns information about the fringes of a window
3323 @var{window}. If @var{window} is omitted or @code{nil}, the selected
3324 window is used. The value has the form @code{(@var{left-width}
3325 @var{right-width} @var{outside-margins})}.
3329 @node Fringe Indicators
3330 @subsection Fringe Indicators
3331 @cindex fringe indicators
3332 @cindex indicators, fringe
3334 @dfn{Fringe indicators} are tiny icons displayed in the window
3335 fringe to indicate truncated or continued lines, buffer boundaries,
3338 @defopt indicate-empty-lines
3339 @cindex fringes, and empty line indication
3340 When this is non-@code{nil}, Emacs displays a special glyph in the
3341 fringe of each empty line at the end of the buffer, on graphical
3342 displays. @xref{Fringes}. This variable is automatically
3343 buffer-local in every buffer.
3346 @defopt indicate-buffer-boundaries
3347 This buffer-local variable controls how the buffer boundaries and
3348 window scrolling are indicated in the window fringes.
3350 Emacs can indicate the buffer boundaries---that is, the first and last
3351 line in the buffer---with angle icons when they appear on the screen.
3352 In addition, Emacs can display an up-arrow in the fringe to show
3353 that there is text above the screen, and a down-arrow to show
3354 there is text below the screen.
3356 There are three kinds of basic values:
3360 Don't display any of these fringe icons.
3362 Display the angle icons and arrows in the left fringe.
3364 Display the angle icons and arrows in the right fringe.
3366 Display the angle icons in the left fringe
3367 and don't display the arrows.
3370 Otherwise the value should be an alist that specifies which fringe
3371 indicators to display and where. Each element of the alist should
3372 have the form @code{(@var{indicator} . @var{position})}. Here,
3373 @var{indicator} is one of @code{top}, @code{bottom}, @code{up},
3374 @code{down}, and @code{t} (which covers all the icons not yet
3375 specified), while @var{position} is one of @code{left}, @code{right}
3378 For example, @code{((top . left) (t . right))} places the top angle
3379 bitmap in left fringe, and the bottom angle bitmap as well as both
3380 arrow bitmaps in right fringe. To show the angle bitmaps in the left
3381 fringe, and no arrow bitmaps, use @code{((top . left) (bottom . left))}.
3384 @defvar fringe-indicator-alist
3385 This buffer-local variable specifies the mapping from logical fringe
3386 indicators to the actual bitmaps displayed in the window fringes. The
3387 value is an alist of elements @code{(@var{indicator}
3388 . @var{bitmaps})}, where @var{indicator} specifies a logical indicator
3389 type and @var{bitmaps} specifies the fringe bitmaps to use for that
3392 Each @var{indicator} should be one of the following symbols:
3395 @item @code{truncation}, @code{continuation}.
3396 Used for truncation and continuation lines.
3398 @item @code{up}, @code{down}, @code{top}, @code{bottom}, @code{top-bottom}
3399 Used when @code{indicate-buffer-boundaries} is non-@code{nil}:
3400 @code{up} and @code{down} indicate a buffer boundary lying above or
3401 below the window edge; @code{top} and @code{bottom} indicate the
3402 topmost and bottommost buffer text line; and @code{top-bottom}
3403 indicates where there is just one line of text in the buffer.
3405 @item @code{empty-line}
3406 Used to indicate empty lines when @code{indicate-empty-lines} is
3409 @item @code{overlay-arrow}
3410 Used for overlay arrows (@pxref{Overlay Arrow}).
3411 @c Is this used anywhere?
3412 @c @item Unknown bitmap indicator:
3416 Each @var{bitmaps} value may be a list of symbols @code{(@var{left}
3417 @var{right} [@var{left1} @var{right1}])}. The @var{left} and
3418 @var{right} symbols specify the bitmaps shown in the left and/or right
3419 fringe, for the specific indicator. @var{left1} and @var{right1} are
3420 specific to the @code{bottom} and @code{top-bottom} indicators, and
3421 are used to indicate that the last text line has no final newline.
3422 Alternatively, @var{bitmaps} may be a single symbol which is used in
3423 both left and right fringes.
3425 @xref{Fringe Bitmaps}, for a list of standard bitmap symbols and how
3426 to define your own. In addition, @code{nil} represents the empty
3427 bitmap (i.e.@: an indicator that is not shown).
3429 When @code{fringe-indicator-alist} has a buffer-local value, and
3430 there is no bitmap defined for a logical indicator, or the bitmap is
3431 @code{t}, the corresponding value from the default value of
3432 @code{fringe-indicator-alist} is used.
3435 @node Fringe Cursors
3436 @subsection Fringe Cursors
3437 @cindex fringe cursors
3438 @cindex cursor, fringe
3440 When a line is exactly as wide as the window, Emacs displays the
3441 cursor in the right fringe instead of using two lines. Different
3442 bitmaps are used to represent the cursor in the fringe depending on
3443 the current buffer's cursor type.
3445 @defopt overflow-newline-into-fringe
3446 If this is non-@code{nil}, lines exactly as wide as the window (not
3447 counting the final newline character) are not continued. Instead,
3448 when point is at the end of the line, the cursor appears in the right
3452 @defvar fringe-cursor-alist
3453 This variable specifies the mapping from logical cursor type to the
3454 actual fringe bitmaps displayed in the right fringe. The value is an
3455 alist where each element has the form @code{(@var{cursor-type}
3456 . @var{bitmap})}, which means to use the fringe bitmap @var{bitmap} to
3457 display cursors of type @var{cursor-type}.
3459 Each @var{cursor-type} should be one of @code{box}, @code{hollow},
3460 @code{bar}, @code{hbar}, or @code{hollow-small}. The first four have
3461 the same meanings as in the @code{cursor-type} frame parameter
3462 (@pxref{Cursor Parameters}). The @code{hollow-small} type is used
3463 instead of @code{hollow} when the normal @code{hollow-rectangle}
3464 bitmap is too tall to fit on a specific display line.
3466 Each @var{bitmap} should be a symbol specifying the fringe bitmap to
3467 be displayed for that logical cursor type.
3469 See the next subsection for details.
3472 @xref{Fringe Bitmaps}.
3475 When @code{fringe-cursor-alist} has a buffer-local value, and there is
3476 no bitmap defined for a cursor type, the corresponding value from the
3477 default value of @code{fringes-indicator-alist} is used.
3480 @node Fringe Bitmaps
3481 @subsection Fringe Bitmaps
3482 @cindex fringe bitmaps
3483 @cindex bitmaps, fringe
3485 The @dfn{fringe bitmaps} are the actual bitmaps which represent the
3486 logical fringe indicators for truncated or continued lines, buffer
3487 boundaries, overlay arrows, etc. Each bitmap is represented by a
3490 These symbols are referred to by the variables
3491 @code{fringe-indicator-alist} and @code{fringe-cursor-alist},
3492 described in the previous subsections.
3495 These symbols are referred to by the variable
3496 @code{fringe-indicator-alist}, which maps fringe indicators to bitmaps
3497 (@pxref{Fringe Indicators}), and the variable
3498 @code{fringe-cursor-alist}, which maps fringe cursors to bitmaps
3499 (@pxref{Fringe Cursors}).
3502 Lisp programs can also directly display a bitmap in the left or
3503 right fringe, by using a @code{display} property for one of the
3504 characters appearing in the line (@pxref{Other Display Specs}). Such
3505 a display specification has the form
3508 (@var{fringe} @var{bitmap} [@var{face}])
3512 @var{fringe} is either the symbol @code{left-fringe} or
3513 @code{right-fringe}. @var{bitmap} is a symbol identifying the bitmap
3514 to display. The optional @var{face} names a face whose foreground
3515 color is used to display the bitmap; this face is automatically merged
3516 with the @code{fringe} face.
3518 Here is a list of the standard fringe bitmaps defined in Emacs, and
3519 how they are currently used in Emacs (via
3520 @code{fringe-indicator-alist} and @code{fringe-cursor-alist}):
3523 @item @code{left-arrow}, @code{right-arrow}
3524 Used to indicate truncated lines.
3526 @item @code{left-curly-arrow}, @code{right-curly-arrow}
3527 Used to indicate continued lines.
3529 @item @code{right-triangle}, @code{left-triangle}
3530 The former is used by overlay arrows. The latter is unused.
3532 @item @code{up-arrow}, @code{down-arrow}, @code{top-left-angle} @code{top-right-angle}
3533 @itemx @code{bottom-left-angle}, @code{bottom-right-angle}
3534 @itemx @code{top-right-angle}, @code{top-left-angle}
3535 @itemx @code{left-bracket}, @code{right-bracket}, @code{top-right-angle}, @code{top-left-angle}
3536 Used to indicate buffer boundaries.
3538 @item @code{filled-rectangle}, @code{hollow-rectangle}
3539 @itemx @code{filled-square}, @code{hollow-square}
3540 @itemx @code{vertical-bar}, @code{horizontal-bar}
3541 Used for different types of fringe cursors.
3543 @item @code{empty-line}, @code{question-mark}
3548 The next subsection describes how to define your own fringe bitmaps.
3550 @defun fringe-bitmaps-at-pos &optional pos window
3551 This function returns the fringe bitmaps of the display line
3552 containing position @var{pos} in window @var{window}. The return
3553 value has the form @code{(@var{left} @var{right} @var{ov})}, where @var{left}
3554 is the symbol for the fringe bitmap in the left fringe (or @code{nil}
3555 if no bitmap), @var{right} is similar for the right fringe, and @var{ov}
3556 is non-@code{nil} if there is an overlay arrow in the left fringe.
3558 The value is @code{nil} if @var{pos} is not visible in @var{window}.
3559 If @var{window} is @code{nil}, that stands for the selected window.
3560 If @var{pos} is @code{nil}, that stands for the value of point in
3564 @node Customizing Bitmaps
3565 @subsection Customizing Fringe Bitmaps
3567 @defun define-fringe-bitmap bitmap bits &optional height width align
3568 This function defines the symbol @var{bitmap} as a new fringe bitmap,
3569 or replaces an existing bitmap with that name.
3571 The argument @var{bits} specifies the image to use. It should be
3572 either a string or a vector of integers, where each element (an
3573 integer) corresponds to one row of the bitmap. Each bit of an integer
3574 corresponds to one pixel of the bitmap, where the low bit corresponds
3575 to the rightmost pixel of the bitmap.
3577 The height is normally the length of @var{bits}. However, you
3578 can specify a different height with non-@code{nil} @var{height}. The width
3579 is normally 8, but you can specify a different width with non-@code{nil}
3580 @var{width}. The width must be an integer between 1 and 16.
3582 The argument @var{align} specifies the positioning of the bitmap
3583 relative to the range of rows where it is used; the default is to
3584 center the bitmap. The allowed values are @code{top}, @code{center},
3587 The @var{align} argument may also be a list @code{(@var{align}
3588 @var{periodic})} where @var{align} is interpreted as described above.
3589 If @var{periodic} is non-@code{nil}, it specifies that the rows in
3590 @code{bits} should be repeated enough times to reach the specified
3594 @defun destroy-fringe-bitmap bitmap
3595 This function destroy the fringe bitmap identified by @var{bitmap}.
3596 If @var{bitmap} identifies a standard fringe bitmap, it actually
3597 restores the standard definition of that bitmap, instead of
3598 eliminating it entirely.
3601 @defun set-fringe-bitmap-face bitmap &optional face
3602 This sets the face for the fringe bitmap @var{bitmap} to @var{face}.
3603 If @var{face} is @code{nil}, it selects the @code{fringe} face. The
3604 bitmap's face controls the color to draw it in.
3606 @var{face} is merged with the @code{fringe} face, so normally
3607 @var{face} should specify only the foreground color.
3611 @subsection The Overlay Arrow
3612 @c @cindex overlay arrow Duplicates variable names
3614 The @dfn{overlay arrow} is useful for directing the user's attention
3615 to a particular line in a buffer. For example, in the modes used for
3616 interface to debuggers, the overlay arrow indicates the line of code
3617 about to be executed. This feature has nothing to do with
3618 @dfn{overlays} (@pxref{Overlays}).
3620 @defvar overlay-arrow-string
3621 This variable holds the string to display to call attention to a
3622 particular line, or @code{nil} if the arrow feature is not in use.
3623 On a graphical display the contents of the string are ignored; instead a
3624 glyph is displayed in the fringe area to the left of the display area.
3627 @defvar overlay-arrow-position
3628 This variable holds a marker that indicates where to display the overlay
3629 arrow. It should point at the beginning of a line. On a non-graphical
3630 display the arrow text
3631 appears at the beginning of that line, overlaying any text that would
3632 otherwise appear. Since the arrow is usually short, and the line
3633 usually begins with indentation, normally nothing significant is
3636 The overlay-arrow string is displayed in any given buffer if the value
3637 of @code{overlay-arrow-position} in that buffer points into that
3638 buffer. Thus, it is possible to display multiple overlay arrow strings
3639 by creating buffer-local bindings of @code{overlay-arrow-position}.
3640 However, it is usually cleaner to use
3641 @code{overlay-arrow-variable-list} to achieve this result.
3642 @c !!! overlay-arrow-position: but the overlay string may remain in the display
3643 @c of some other buffer until an update is required. This should be fixed
3647 You can do a similar job by creating an overlay with a
3648 @code{before-string} property. @xref{Overlay Properties}.
3650 You can define multiple overlay arrows via the variable
3651 @code{overlay-arrow-variable-list}.
3653 @defvar overlay-arrow-variable-list
3654 This variable's value is a list of variables, each of which specifies
3655 the position of an overlay arrow. The variable
3656 @code{overlay-arrow-position} has its normal meaning because it is on
3660 Each variable on this list can have properties
3661 @code{overlay-arrow-string} and @code{overlay-arrow-bitmap} that
3662 specify an overlay arrow string (for text terminals) or fringe bitmap
3663 (for graphical terminals) to display at the corresponding overlay
3664 arrow position. If either property is not set, the default
3665 @code{overlay-arrow-string} or @code{overlay-arrow} fringe indicator
3669 @section Scroll Bars
3672 Normally the frame parameter @code{vertical-scroll-bars} controls
3673 whether the windows in the frame have vertical scroll bars, and
3674 whether they are on the left or right. The frame parameter
3675 @code{scroll-bar-width} specifies how wide they are (@code{nil}
3676 meaning the default). @xref{Layout Parameters}.
3678 @defun frame-current-scroll-bars &optional frame
3679 This function reports the scroll bar type settings for frame
3680 @var{frame}. The value is a cons cell
3681 @code{(@var{vertical-type} .@: @var{horizontal-type})}, where
3682 @var{vertical-type} is either @code{left}, @code{right}, or @code{nil}
3683 (which means no scroll bar.) @var{horizontal-type} is meant to
3684 specify the horizontal scroll bar type, but since they are not
3685 implemented, it is always @code{nil}.
3688 @vindex vertical-scroll-bar
3689 You can enable or disable scroll bars for a particular buffer,
3690 by setting the variable @code{vertical-scroll-bar}. This variable
3691 automatically becomes buffer-local when set. The possible values are
3692 @code{left}, @code{right}, @code{t}, which means to use the
3693 frame's default, and @code{nil} for no scroll bar.
3695 You can also control this for individual windows. Call the function
3696 @code{set-window-scroll-bars} to specify what to do for a specific window:
3698 @defun set-window-scroll-bars window width &optional vertical-type horizontal-type
3699 This function sets the width and type of scroll bars for window
3702 @var{width} specifies the scroll bar width in pixels (@code{nil} means
3703 use the width specified for the frame). @var{vertical-type} specifies
3704 whether to have a vertical scroll bar and, if so, where. The possible
3705 values are @code{left}, @code{right} and @code{nil}, just like the
3706 values of the @code{vertical-scroll-bars} frame parameter.
3708 The argument @var{horizontal-type} is meant to specify whether and
3709 where to have horizontal scroll bars, but since they are not
3710 implemented, it has no effect. If @var{window} is @code{nil}, the
3711 selected window is used.
3714 @defun window-scroll-bars &optional window
3715 Report the width and type of scroll bars specified for @var{window}.
3716 If @var{window} is omitted or @code{nil}, the selected window is used.
3717 The value is a list of the form @code{(@var{width}
3718 @var{cols} @var{vertical-type} @var{horizontal-type})}. The value
3719 @var{width} is the value that was specified for the width (which may
3720 be @code{nil}); @var{cols} is the number of columns that the scroll
3721 bar actually occupies.
3723 @var{horizontal-type} is not actually meaningful.
3726 If you don't specify these values for a window with
3727 @code{set-window-scroll-bars}, the buffer-local variables
3728 @code{scroll-bar-mode} and @code{scroll-bar-width} in the buffer being
3729 displayed control the window's vertical scroll bars. The function
3730 @code{set-window-buffer} examines these variables. If you change them
3731 in a buffer that is already visible in a window, you can make the
3732 window take note of the new values by calling @code{set-window-buffer}
3733 specifying the same buffer that is already displayed.
3735 @defopt scroll-bar-mode
3736 This variable, always local in all buffers, controls whether and where
3737 to put scroll bars in windows displaying the buffer. The possible values
3738 are @code{nil} for no scroll bar, @code{left} to put a scroll bar on
3739 the left, and @code{right} to put a scroll bar on the right.
3742 @defun window-current-scroll-bars &optional window
3743 This function reports the scroll bar type for window @var{window}.
3744 If @var{window} is omitted or @code{nil}, the selected window is used.
3745 The value is a cons cell
3746 @code{(@var{vertical-type} .@: @var{horizontal-type})}. Unlike
3747 @code{window-scroll-bars}, this reports the scroll bar type actually
3748 used, once frame defaults and @code{scroll-bar-mode} are taken into
3752 @defvar scroll-bar-width
3753 This variable, always local in all buffers, specifies the width of the
3754 buffer's scroll bars, measured in pixels. A value of @code{nil} means
3755 to use the value specified by the frame.
3758 @node Display Property
3759 @section The @code{display} Property
3760 @cindex display specification
3761 @kindex display @r{(text property)}
3763 The @code{display} text property (or overlay property) is used to
3764 insert images into text, and to control other aspects of how text
3765 displays. The value of the @code{display} property should be a
3766 display specification, or a list or vector containing several display
3767 specifications. Display specifications in the same @code{display}
3768 property value generally apply in parallel to the text they cover.
3770 If several sources (overlays and/or a text property) specify values
3771 for the @code{display} property, only one of the values takes effect,
3772 following the rules of @code{get-char-property}. @xref{Examining
3775 The rest of this section describes several kinds of
3776 display specifications and what they mean.
3779 * Replacing Specs:: Display specs that replace the text.
3780 * Specified Space:: Displaying one space with a specified width.
3781 * Pixel Specification:: Specifying space width or height in pixels.
3782 * Other Display Specs:: Displaying an image; adjusting the height,
3783 spacing, and other properties of text.
3784 * Display Margins:: Displaying text or images to the side of the main text.
3787 @node Replacing Specs
3788 @subsection Display Specs That Replace The Text
3790 Some kinds of display specifications specify something to display
3791 instead of the text that has the property. These are called
3792 @dfn{replacing} display specifications. Emacs does not allow the user
3793 to interactively move point into the middle of buffer text that is
3794 replaced in this way.
3796 If a list of display specifications includes more than one replacing
3797 display specification, the first overrides the rest. Replacing
3798 display specifications make most other display specifications
3799 irrelevant, since those don't apply to the replacement.
3801 For replacing display specifications, ``the text that has the
3802 property'' means all the consecutive characters that have the same
3803 Lisp object as their @code{display} property; these characters are
3804 replaced as a single unit. If two characters have different Lisp
3805 objects as their @code{display} properties (i.e.@: objects which are
3806 not @code{eq}), they are handled separately.
3808 Here is an example which illustrates this point. A string serves as
3809 a replacing display specification, which replaces the text that has
3810 the property with the specified string (@pxref{Other Display Specs}).
3811 Consider the following function:
3816 (let ((string (concat "A"))
3817 (start (+ i i (point-min))))
3818 (put-text-property start (1+ start) 'display string)
3819 (put-text-property start (+ 2 start) 'display string))))
3823 This function gives each of the first ten characters in the buffer a
3824 @code{display} property which is a string @code{"A"}, but they don't
3825 all get the same string object. The first two characters get the same
3826 string object, so they are replaced with one @samp{A}; the fact that
3827 the display property was assigned in two separate calls to
3828 @code{put-text-property} is irrelevant. Similarly, the next two
3829 characters get a second string (@code{concat} creates a new string
3830 object), so they are replaced with one @samp{A}; and so on. Thus, the
3831 ten characters appear as five A's.
3833 @node Specified Space
3834 @subsection Specified Spaces
3835 @cindex spaces, specified height or width
3836 @cindex variable-width spaces
3838 To display a space of specified width and/or height, use a display
3839 specification of the form @code{(space . @var{props})}, where
3840 @var{props} is a property list (a list of alternating properties and
3841 values). You can put this property on one or more consecutive
3842 characters; a space of the specified height and width is displayed in
3843 place of @emph{all} of those characters. These are the properties you
3844 can use in @var{props} to specify the weight of the space:
3847 @item :width @var{width}
3848 If @var{width} is an integer or floating point number, it specifies
3849 that the space width should be @var{width} times the normal character
3850 width. @var{width} can also be a @dfn{pixel width} specification
3851 (@pxref{Pixel Specification}).
3853 @item :relative-width @var{factor}
3854 Specifies that the width of the stretch should be computed from the
3855 first character in the group of consecutive characters that have the
3856 same @code{display} property. The space width is the width of that
3857 character, multiplied by @var{factor}.
3859 @item :align-to @var{hpos}
3860 Specifies that the space should be wide enough to reach @var{hpos}.
3861 If @var{hpos} is a number, it is measured in units of the normal
3862 character width. @var{hpos} can also be a @dfn{pixel width}
3863 specification (@pxref{Pixel Specification}).
3866 You should use one and only one of the above properties. You can
3867 also specify the height of the space, with these properties:
3870 @item :height @var{height}
3871 Specifies the height of the space.
3872 If @var{height} is an integer or floating point number, it specifies
3873 that the space height should be @var{height} times the normal character
3874 height. The @var{height} may also be a @dfn{pixel height} specification
3875 (@pxref{Pixel Specification}).
3877 @item :relative-height @var{factor}
3878 Specifies the height of the space, multiplying the ordinary height
3879 of the text having this display specification by @var{factor}.
3881 @item :ascent @var{ascent}
3882 If the value of @var{ascent} is a non-negative number no greater than
3883 100, it specifies that @var{ascent} percent of the height of the space
3884 should be considered as the ascent of the space---that is, the part
3885 above the baseline. The ascent may also be specified in pixel units
3886 with a @dfn{pixel ascent} specification (@pxref{Pixel Specification}).
3890 Don't use both @code{:height} and @code{:relative-height} together.
3892 The @code{:width} and @code{:align-to} properties are supported on
3893 non-graphic terminals, but the other space properties in this section
3896 Note that space properties are treated as paragraph separators for
3897 the purposes of reordering bidirectional text for display.
3898 @xref{Bidirectional Display}, for the details.
3900 @node Pixel Specification
3901 @subsection Pixel Specification for Spaces
3902 @cindex spaces, pixel specification
3904 The value of the @code{:width}, @code{:align-to}, @code{:height},
3905 and @code{:ascent} properties can be a special kind of expression that
3906 is evaluated during redisplay. The result of the evaluation is used
3907 as an absolute number of pixels.
3909 The following expressions are supported:
3913 @var{expr} ::= @var{num} | (@var{num}) | @var{unit} | @var{elem} | @var{pos} | @var{image} | @var{form}
3914 @var{num} ::= @var{integer} | @var{float} | @var{symbol}
3915 @var{unit} ::= in | mm | cm | width | height
3918 @var{elem} ::= left-fringe | right-fringe | left-margin | right-margin
3920 @var{pos} ::= left | center | right
3921 @var{form} ::= (@var{num} . @var{expr}) | (@var{op} @var{expr} ...)
3926 The form @var{num} specifies a fraction of the default frame font
3927 height or width. The form @code{(@var{num})} specifies an absolute
3928 number of pixels. If @var{num} is a symbol, @var{symbol}, its
3929 buffer-local variable binding is used.
3931 The @code{in}, @code{mm}, and @code{cm} units specify the number of
3932 pixels per inch, millimeter, and centimeter, respectively. The
3933 @code{width} and @code{height} units correspond to the default width
3934 and height of the current face. An image specification @code{image}
3935 corresponds to the width or height of the image.
3937 The elements @code{left-fringe}, @code{right-fringe},
3938 @code{left-margin}, @code{right-margin}, @code{scroll-bar}, and
3939 @code{text} specify to the width of the corresponding area of the
3942 The @code{left}, @code{center}, and @code{right} positions can be
3943 used with @code{:align-to} to specify a position relative to the left
3944 edge, center, or right edge of the text area.
3946 Any of the above window elements (except @code{text}) can also be
3947 used with @code{:align-to} to specify that the position is relative to
3948 the left edge of the given area. Once the base offset for a relative
3949 position has been set (by the first occurrence of one of these
3950 symbols), further occurrences of these symbols are interpreted as the
3951 width of the specified area. For example, to align to the center of
3952 the left-margin, use
3955 :align-to (+ left-margin (0.5 . left-margin))
3958 If no specific base offset is set for alignment, it is always relative
3959 to the left edge of the text area. For example, @samp{:align-to 0} in a
3960 header-line aligns with the first text column in the text area.
3962 A value of the form @code{(@var{num} . @var{expr})} stands for the
3963 product of the values of @var{num} and @var{expr}. For example,
3964 @code{(2 . in)} specifies a width of 2 inches, while @code{(0.5 .
3965 @var{image})} specifies half the width (or height) of the specified
3968 The form @code{(+ @var{expr} ...)} adds up the value of the
3969 expressions. The form @code{(- @var{expr} ...)} negates or subtracts
3970 the value of the expressions.
3972 @node Other Display Specs
3973 @subsection Other Display Specifications
3975 Here are the other sorts of display specifications that you can use
3976 in the @code{display} text property.
3980 Display @var{string} instead of the text that has this property.
3982 Recursive display specifications are not supported---@var{string}'s
3983 @code{display} properties, if any, are not used.
3985 @item (image . @var{image-props})
3986 This kind of display specification is an image descriptor (@pxref{Images}).
3987 When used as a display specification, it means to display the image
3988 instead of the text that has the display specification.
3990 @item (slice @var{x} @var{y} @var{width} @var{height})
3991 This specification together with @code{image} specifies a @dfn{slice}
3992 (a partial area) of the image to display. The elements @var{y} and
3993 @var{x} specify the top left corner of the slice, within the image;
3994 @var{width} and @var{height} specify the width and height of the
3995 slice. Integer values are numbers of pixels. A floating point number
3996 in the range 0.0--1.0 stands for that fraction of the width or height
3997 of the entire image.
3999 @item ((margin nil) @var{string})
4000 A display specification of this form means to display @var{string}
4001 instead of the text that has the display specification, at the same
4002 position as that text. It is equivalent to using just @var{string},
4003 but it is done as a special case of marginal display (@pxref{Display
4006 @item (left-fringe @var{bitmap} @r{[}@var{face}@r{]})
4007 @itemx (right-fringe @var{bitmap} @r{[}@var{face}@r{]})
4008 This display specification on any character of a line of text causes
4009 the specified @var{bitmap} be displayed in the left or right fringes
4010 for that line, instead of the characters that have the display
4011 specification. The optional @var{face} specifies the colors to be
4012 used for the bitmap. @xref{Fringe Bitmaps}, for the details.
4014 @item (space-width @var{factor})
4015 This display specification affects all the space characters within the
4016 text that has the specification. It displays all of these spaces
4017 @var{factor} times as wide as normal. The element @var{factor} should
4018 be an integer or float. Characters other than spaces are not affected
4019 at all; in particular, this has no effect on tab characters.
4021 @item (height @var{height})
4022 This display specification makes the text taller or shorter.
4023 Here are the possibilities for @var{height}:
4026 @item @code{(+ @var{n})}
4027 This means to use a font that is @var{n} steps larger. A ``step'' is
4028 defined by the set of available fonts---specifically, those that match
4029 what was otherwise specified for this text, in all attributes except
4030 height. Each size for which a suitable font is available counts as
4031 another step. @var{n} should be an integer.
4033 @item @code{(- @var{n})}
4034 This means to use a font that is @var{n} steps smaller.
4036 @item a number, @var{factor}
4037 A number, @var{factor}, means to use a font that is @var{factor} times
4038 as tall as the default font.
4040 @item a symbol, @var{function}
4041 A symbol is a function to compute the height. It is called with the
4042 current height as argument, and should return the new height to use.
4044 @item anything else, @var{form}
4045 If the @var{height} value doesn't fit the previous possibilities, it is
4046 a form. Emacs evaluates it to get the new height, with the symbol
4047 @code{height} bound to the current specified font height.
4050 @item (raise @var{factor})
4051 This kind of display specification raises or lowers the text
4052 it applies to, relative to the baseline of the line.
4054 @var{factor} must be a number, which is interpreted as a multiple of the
4055 height of the affected text. If it is positive, that means to display
4056 the characters raised. If it is negative, that means to display them
4059 If the text also has a @code{height} display specification, that does
4060 not affect the amount of raising or lowering, which is based on the
4061 faces used for the text.
4064 @c We put all the `@code{(when ...)}' on one line to encourage
4065 @c makeinfo's end-of-sentence heuristics to DTRT. Previously, the dot
4066 @c was at eol; the info file ended up w/ two spaces rendered after it.
4067 You can make any display specification conditional. To do that,
4068 package it in another list of the form
4069 @code{(when @var{condition} . @var{spec})}.
4070 Then the specification @var{spec} applies only when
4071 @var{condition} evaluates to a non-@code{nil} value. During the
4072 evaluation, @code{object} is bound to the string or buffer having the
4073 conditional @code{display} property. @code{position} and
4074 @code{buffer-position} are bound to the position within @code{object}
4075 and the buffer position where the @code{display} property was found,
4076 respectively. Both positions can be different when @code{object} is a
4079 @node Display Margins
4080 @subsection Displaying in the Margins
4081 @cindex display margins
4082 @cindex margins, display
4084 A buffer can have blank areas called @dfn{display margins} on the
4085 left and on the right. Ordinary text never appears in these areas,
4086 but you can put things into the display margins using the
4087 @code{display} property. There is currently no way to make text or
4088 images in the margin mouse-sensitive.
4090 The way to display something in the margins is to specify it in a
4091 margin display specification in the @code{display} property of some
4092 text. This is a replacing display specification, meaning that the
4093 text you put it on does not get displayed; the margin display appears,
4094 but that text does not.
4096 A margin display specification looks like @code{((margin
4097 right-margin) @var{spec})} or @code{((margin left-margin) @var{spec})}.
4098 Here, @var{spec} is another display specification that says what to
4099 display in the margin. Typically it is a string of text to display,
4100 or an image descriptor.
4102 To display something in the margin @emph{in association with}
4103 certain buffer text, without altering or preventing the display of
4104 that text, put a @code{before-string} property on the text and put the
4105 margin display specification on the contents of the before-string.
4107 Before the display margins can display anything, you must give
4108 them a nonzero width. The usual way to do that is to set these
4111 @defvar left-margin-width
4112 This variable specifies the width of the left margin.
4113 It is buffer-local in all buffers.
4116 @defvar right-margin-width
4117 This variable specifies the width of the right margin.
4118 It is buffer-local in all buffers.
4121 Setting these variables does not immediately affect the window. These
4122 variables are checked when a new buffer is displayed in the window.
4123 Thus, you can make changes take effect by calling
4124 @code{set-window-buffer}.
4126 You can also set the margin widths immediately.
4128 @defun set-window-margins window left &optional right
4129 This function specifies the margin widths for window @var{window}.
4130 The argument @var{left} controls the left margin and
4131 @var{right} controls the right margin (default @code{0}).
4134 @defun window-margins &optional window
4135 This function returns the left and right margins of @var{window}
4136 as a cons cell of the form @code{(@var{left} . @var{right})}.
4137 If @var{window} is @code{nil}, the selected window is used.
4142 @cindex images in buffers
4144 To display an image in an Emacs buffer, you must first create an image
4145 descriptor, then use it as a display specifier in the @code{display}
4146 property of text that is displayed (@pxref{Display Property}).
4148 Emacs is usually able to display images when it is run on a
4149 graphical terminal. Images cannot be displayed in a text terminal, on
4150 certain graphical terminals that lack the support for this, or if
4151 Emacs is compiled without image support. You can use the function
4152 @code{display-images-p} to determine if images can in principle be
4153 displayed (@pxref{Display Feature Testing}).
4156 * Image Formats:: Supported image formats.
4157 * Image Descriptors:: How to specify an image for use in @code{:display}.
4158 * XBM Images:: Special features for XBM format.
4159 * XPM Images:: Special features for XPM format.
4160 * GIF Images:: Special features for GIF format.
4161 * TIFF Images:: Special features for TIFF format.
4162 * PostScript Images:: Special features for PostScript format.
4163 * ImageMagick Images:: Special features available through ImageMagick.
4164 * Other Image Types:: Various other formats are supported.
4165 * Defining Images:: Convenient ways to define an image for later use.
4166 * Showing Images:: Convenient ways to display an image once it is defined.
4167 * Animated Images:: Some image formats can be animated.
4168 * Image Cache:: Internal mechanisms of image display.
4172 @subsection Image Formats
4173 @cindex image formats
4176 Emacs can display a number of different image formats. Some of
4177 these image formats are supported only if particular support libraries
4178 are installed. On some platforms, Emacs can load support libraries on
4179 demand; if so, the variable @code{dynamic-library-alist} can be used
4180 to modify the set of known names for these dynamic libraries.
4181 @xref{Dynamic Libraries}.
4183 Supported image formats (and the required support libraries) include
4184 PBM and XBM (which do not depend on support libraries and are always
4185 available), XPM (@code{libXpm}), GIF (@code{libgif} or
4186 @code{libungif}), PostScript (@code{gs}), JPEG (@code{libjpeg}), TIFF
4187 (@code{libtiff}), PNG (@code{libpng}), and SVG (@code{librsvg}).
4189 Each of these image formats is associated with an @dfn{image type
4190 symbol}. The symbols for the above formats are, respectively,
4191 @code{pbm}, @code{xbm}, @code{xpm}, @code{gif}, @code{postscript},
4192 @code{jpeg}, @code{tiff}, @code{png}, and @code{svg}.
4194 Furthermore, if you build Emacs with ImageMagick
4195 (@code{libMagickWand}) support, Emacs can display any image format
4196 that ImageMagick can. @xref{ImageMagick Images}. All images
4197 displayed via ImageMagick have type symbol @code{imagemagick}.
4200 This variable contains a list of type symbols for image formats which
4201 are potentially supported in the current configuration.
4203 ``Potentially'' means that Emacs knows about the image types, not
4204 necessarily that they can be used (for example, they could depend on
4205 unavailable dynamic libraries). To know which image types are really
4206 available, use @code{image-type-available-p}.
4209 @defun image-type-available-p type
4210 This function returns non-@code{nil} if images of type @var{type} can
4211 be loaded and displayed. @var{type} must be an image type symbol.
4213 For image types whose support libraries are statically linked, this
4214 function always returns @code{t}. For image types whose support
4215 libraries are dynamically loaded, it returns @code{t} if the library
4216 could be loaded and @code{nil} otherwise.
4219 @node Image Descriptors
4220 @subsection Image Descriptors
4221 @cindex image descriptor
4223 An @dfn{image descriptor} is a list which specifies the underlying
4224 data for an image, and how to display it. It is typically used as the
4225 value of a @code{display} overlay or text property (@pxref{Other
4226 Display Specs}); but @xref{Showing Images}, for convenient helper
4227 functions to insert images into buffers.
4229 Each image descriptor has the form @code{(image . @var{props})},
4230 where @var{props} is a property list of alternating keyword symbols
4231 and values, including at least the pair @code{:type @var{TYPE}} which
4232 specifies the image type.
4234 The following is a list of properties that are meaningful for all
4235 image types (there are also properties which are meaningful only for
4236 certain image types, as documented in the following subsections):
4239 @item :type @var{type}
4242 @xref{Image Formats}.
4244 Every image descriptor must include this property.
4246 @item :file @var{file}
4247 This says to load the image from file @var{file}. If @var{file} is
4248 not an absolute file name, it is expanded in @code{data-directory}.
4250 @item :data @var{data}
4251 This specifies the raw image data. Each image descriptor must have
4252 either @code{:data} or @code{:file}, but not both.
4254 For most image types, the value of a @code{:data} property should be a
4255 string containing the image data. Some image types do not support
4256 @code{:data}; for some others, @code{:data} alone is not enough, so
4257 you need to use other image properties along with @code{:data}. See
4258 the following subsections for details.
4260 @item :margin @var{margin}
4261 This specifies how many pixels to add as an extra margin around the
4262 image. The value, @var{margin}, must be a non-negative number, or a
4263 pair @code{(@var{x} . @var{y})} of such numbers. If it is a pair,
4264 @var{x} specifies how many pixels to add horizontally, and @var{y}
4265 specifies how many pixels to add vertically. If @code{:margin} is not
4266 specified, the default is zero.
4268 @item :ascent @var{ascent}
4269 This specifies the amount of the image's height to use for its
4270 ascent---that is, the part above the baseline. The value,
4271 @var{ascent}, must be a number in the range 0 to 100, or the symbol
4274 If @var{ascent} is a number, that percentage of the image's height is
4275 used for its ascent.
4277 If @var{ascent} is @code{center}, the image is vertically centered
4278 around a centerline which would be the vertical centerline of text drawn
4279 at the position of the image, in the manner specified by the text
4280 properties and overlays that apply to the image.
4282 If this property is omitted, it defaults to 50.
4284 @item :relief @var{relief}
4285 This adds a shadow rectangle around the image. The value,
4286 @var{relief}, specifies the width of the shadow lines, in pixels. If
4287 @var{relief} is negative, shadows are drawn so that the image appears
4288 as a pressed button; otherwise, it appears as an unpressed button.
4290 @item :conversion @var{algorithm}
4291 This specifies a conversion algorithm that should be applied to the
4292 image before it is displayed; the value, @var{algorithm}, specifies
4298 Specifies the Laplace edge detection algorithm, which blurs out small
4299 differences in color while highlighting larger differences. People
4300 sometimes consider this useful for displaying the image for a
4301 ``disabled'' button.
4303 @item (edge-detection :matrix @var{matrix} :color-adjust @var{adjust})
4304 Specifies a general edge-detection algorithm. @var{matrix} must be
4305 either a nine-element list or a nine-element vector of numbers. A pixel
4306 at position @math{x/y} in the transformed image is computed from
4307 original pixels around that position. @var{matrix} specifies, for each
4308 pixel in the neighborhood of @math{x/y}, a factor with which that pixel
4309 will influence the transformed pixel; element @math{0} specifies the
4310 factor for the pixel at @math{x-1/y-1}, element @math{1} the factor for
4311 the pixel at @math{x/y-1} etc., as shown below:
4314 $$\pmatrix{x-1/y-1 & x/y-1 & x+1/y-1 \cr
4315 x-1/y & x/y & x+1/y \cr
4316 x-1/y+1& x/y+1 & x+1/y+1 \cr}$$
4321 (x-1/y-1 x/y-1 x+1/y-1
4323 x-1/y+1 x/y+1 x+1/y+1)
4327 The resulting pixel is computed from the color intensity of the color
4328 resulting from summing up the RGB values of surrounding pixels,
4329 multiplied by the specified factors, and dividing that sum by the sum
4330 of the factors' absolute values.
4332 Laplace edge-detection currently uses a matrix of
4335 $$\pmatrix{1 & 0 & 0 \cr
4348 Emboss edge-detection uses a matrix of
4351 $$\pmatrix{ 2 & -1 & 0 \cr
4365 Specifies transforming the image so that it looks ``disabled''.
4368 @item :mask @var{mask}
4369 If @var{mask} is @code{heuristic} or @code{(heuristic @var{bg})}, build
4370 a clipping mask for the image, so that the background of a frame is
4371 visible behind the image. If @var{bg} is not specified, or if @var{bg}
4372 is @code{t}, determine the background color of the image by looking at
4373 the four corners of the image, assuming the most frequently occurring
4374 color from the corners is the background color of the image. Otherwise,
4375 @var{bg} must be a list @code{(@var{red} @var{green} @var{blue})}
4376 specifying the color to assume for the background of the image.
4378 If @var{mask} is @code{nil}, remove a mask from the image, if it has
4379 one. Images in some formats include a mask which can be removed by
4380 specifying @code{:mask nil}.
4382 @item :pointer @var{shape}
4383 This specifies the pointer shape when the mouse pointer is over this
4384 image. @xref{Pointer Shape}, for available pointer shapes.
4386 @item :map @var{map}
4387 This associates an image map of @dfn{hot spots} with this image.
4389 An image map is an alist where each element has the format
4390 @code{(@var{area} @var{id} @var{plist})}. An @var{area} is specified
4391 as either a rectangle, a circle, or a polygon.
4393 A rectangle is a cons
4394 @code{(rect . ((@var{x0} . @var{y0}) . (@var{x1} . @var{y1})))}
4395 which specifies the pixel coordinates of the upper left and bottom right
4396 corners of the rectangle area.
4399 @code{(circle . ((@var{x0} . @var{y0}) . @var{r}))}
4400 which specifies the center and the radius of the circle; @var{r} may
4401 be a float or integer.
4404 @code{(poly . [@var{x0} @var{y0} @var{x1} @var{y1} ...])}
4405 where each pair in the vector describes one corner in the polygon.
4407 When the mouse pointer lies on a hot-spot area of an image, the
4408 @var{plist} of that hot-spot is consulted; if it contains a @code{help-echo}
4409 property, that defines a tool-tip for the hot-spot, and if it contains
4410 a @code{pointer} property, that defines the shape of the mouse cursor when
4411 it is on the hot-spot.
4412 @xref{Pointer Shape}, for available pointer shapes.
4414 When you click the mouse when the mouse pointer is over a hot-spot, an
4415 event is composed by combining the @var{id} of the hot-spot with the
4416 mouse event; for instance, @code{[area4 mouse-1]} if the hot-spot's
4417 @var{id} is @code{area4}.
4420 @defun image-mask-p spec &optional frame
4421 This function returns @code{t} if image @var{spec} has a mask bitmap.
4422 @var{frame} is the frame on which the image will be displayed.
4423 @var{frame} @code{nil} or omitted means to use the selected frame
4424 (@pxref{Input Focus}).
4428 @subsection XBM Images
4431 To use XBM format, specify @code{xbm} as the image type. This image
4432 format doesn't require an external library, so images of this type are
4435 Additional image properties supported for the @code{xbm} image type are:
4438 @item :foreground @var{foreground}
4439 The value, @var{foreground}, should be a string specifying the image
4440 foreground color, or @code{nil} for the default color. This color is
4441 used for each pixel in the XBM that is 1. The default is the frame's
4444 @item :background @var{background}
4445 The value, @var{background}, should be a string specifying the image
4446 background color, or @code{nil} for the default color. This color is
4447 used for each pixel in the XBM that is 0. The default is the frame's
4451 If you specify an XBM image using data within Emacs instead of an
4452 external file, use the following three properties:
4455 @item :data @var{data}
4456 The value, @var{data}, specifies the contents of the image.
4457 There are three formats you can use for @var{data}:
4461 A vector of strings or bool-vectors, each specifying one line of the
4462 image. Do specify @code{:height} and @code{:width}.
4465 A string containing the same byte sequence as an XBM file would contain.
4466 You must not specify @code{:height} and @code{:width} in this case,
4467 because omitting them is what indicates the data has the format of an
4468 XBM file. The file contents specify the height and width of the image.
4471 A string or a bool-vector containing the bits of the image (plus perhaps
4472 some extra bits at the end that will not be used). It should contain at
4473 least @var{width} * @code{height} bits. In this case, you must specify
4474 @code{:height} and @code{:width}, both to indicate that the string
4475 contains just the bits rather than a whole XBM file, and to specify the
4479 @item :width @var{width}
4480 The value, @var{width}, specifies the width of the image, in pixels.
4482 @item :height @var{height}
4483 The value, @var{height}, specifies the height of the image, in pixels.
4487 @subsection XPM Images
4490 To use XPM format, specify @code{xpm} as the image type. The
4491 additional image property @code{:color-symbols} is also meaningful with
4492 the @code{xpm} image type:
4495 @item :color-symbols @var{symbols}
4496 The value, @var{symbols}, should be an alist whose elements have the
4497 form @code{(@var{name} . @var{color})}. In each element, @var{name} is
4498 the name of a color as it appears in the image file, and @var{color}
4499 specifies the actual color to use for displaying that name.
4503 @subsection GIF Images
4506 For GIF images, specify image type @code{gif}.
4509 @item :index @var{index}
4510 You can use @code{:index} to specify image number @var{index} from a
4511 GIF file that contains more than one image. If the GIF file doesn't
4512 contain an image with the specified index, the image displays as a
4513 hollow box. GIF files with more than one image can be animated,
4514 @pxref{Animated Images}.
4518 @subsection TIFF Images
4521 For TIFF images, specify image type @code{tiff}.
4524 @item :index @var{index}
4525 You can use @code{:index} to specify image number @var{index} from a
4526 TIFF file that contains more than one image. If the TIFF file doesn't
4527 contain an image with the specified index, the image displays as a
4531 @node PostScript Images
4532 @subsection PostScript Images
4533 @cindex postscript images
4535 To use PostScript for an image, specify image type @code{postscript}.
4536 This works only if you have Ghostscript installed. You must always use
4537 these three properties:
4540 @item :pt-width @var{width}
4541 The value, @var{width}, specifies the width of the image measured in
4542 points (1/72 inch). @var{width} must be an integer.
4544 @item :pt-height @var{height}
4545 The value, @var{height}, specifies the height of the image in points
4546 (1/72 inch). @var{height} must be an integer.
4548 @item :bounding-box @var{box}
4549 The value, @var{box}, must be a list or vector of four integers, which
4550 specifying the bounding box of the PostScript image, analogous to the
4551 @samp{BoundingBox} comment found in PostScript files.
4554 %%BoundingBox: 22 171 567 738
4558 @node ImageMagick Images
4559 @subsection ImageMagick Images
4560 @cindex ImageMagick images
4561 @cindex images, support for more formats
4563 If you build Emacs with ImageMagick support, you can use the
4564 ImageMagick library to load many image formats. The image type symbol
4565 for images loaded via ImageMagick is @code{imagemagick}, regardless of
4566 the actual underlying image format.
4568 @defun imagemagick-types
4569 This function returns a list of image file extensions supported by the
4570 current ImageMagick installation.
4573 By default, Emacs does not use ImageMagick to display images in
4574 Image mode, e.g.@: when visiting such files with @kbd{C-x C-f}. This
4575 feature is enabled by calling @code{imagemagick-register-types}.
4577 @defun imagemagick-register-types
4578 This function enables using Image mode to visit image files supported
4579 by ImageMagick. @xref{File Conveniences,,, emacs, The GNU Emacs
4580 Manual}. It also causes @code{create-image} and other helper
4581 functions to associate such file names with the @code{imagemagick}
4582 image type (@pxref{Defining Images}).
4584 All image file extensions supported by ImageMagick are registered,
4585 except those specified in @code{imagemagick-types-inhibit}. If Emacs
4586 was not compiled with ImageMagick support, this function does nothing.
4589 @defopt imagemagick-types-inhibit
4590 This variable specifies a list of image types that should @emph{not}
4591 be registered by @code{imagemagick-register-types}. Each entry in
4592 this list should be one of the symbols returned by
4593 @code{imagemagick-types}. The default value lists several file types
4594 that are considered ``images'' by ImageMagick, but which should not be
4595 considered as images by Emacs, including C files and HTML files.
4599 @c I don't know what this means. I suspect it means eg loading jpg
4600 @c images via libjpeg or ImageMagick. But it doesn't work.
4601 @c If you don't have libjpeg support compiled in, you cannot
4602 @c view jpeg images, even if you have imagemagick support:
4603 @c http://debbugs.gnu.org/9045
4604 @c And if you have both compiled in, then you always get
4605 @c the libjpeg version:
4606 @c http://debbugs.gnu.org/10746
4607 There may be overlap between image loaders in your Emacs installation,
4608 and you may prefer to use a different one for a given image type
4609 (which loader will be used in practice depends on the priority of the
4611 For example, if you never want to use the ImageMagick loader to view
4612 JPEG files, add @code{JPG} to this list.
4615 Images loaded with ImageMagick support the following additional
4616 image descriptor properties:
4619 @item :width, :height
4620 The @code{:width} and @code{:height} keywords are used for scaling the
4621 image. If only one of them is specified, the other one will be
4622 calculated so as to preserve the aspect ratio. If both are specified,
4623 aspect ratio may not be preserved.
4626 Specifies a rotation angle in degrees.
4629 @c Doesn't work: http://debbugs.gnu.org/7978
4630 This has the same meaning as it does for GIF images (@pxref{GIF Images}),
4631 i.e. it specifies which image to view inside an image bundle file format
4632 such as DJVM. You can use the @code{image-metadata} function to
4633 retrieve the total number of images in an image bundle.
4636 @node Other Image Types
4637 @subsection Other Image Types
4640 For PBM images, specify image type @code{pbm}. Color, gray-scale and
4641 monochromatic images are supported. For mono PBM images, two additional
4642 image properties are supported.
4645 @item :foreground @var{foreground}
4646 The value, @var{foreground}, should be a string specifying the image
4647 foreground color, or @code{nil} for the default color. This color is
4648 used for each pixel in the PBM that is 1. The default is the frame's
4651 @item :background @var{background}
4652 The value, @var{background}, should be a string specifying the image
4653 background color, or @code{nil} for the default color. This color is
4654 used for each pixel in the PBM that is 0. The default is the frame's
4658 For JPEG images, specify image type @code{jpeg}.
4660 For TIFF images, specify image type @code{tiff}.
4662 For PNG images, specify image type @code{png}.
4664 For SVG images, specify image type @code{svg}.
4666 @node Defining Images
4667 @subsection Defining Images
4669 The functions @code{create-image}, @code{defimage} and
4670 @code{find-image} provide convenient ways to create image descriptors.
4672 @defun create-image file-or-data &optional type data-p &rest props
4673 This function creates and returns an image descriptor which uses the
4674 data in @var{file-or-data}. @var{file-or-data} can be a file name or
4675 a string containing the image data; @var{data-p} should be @code{nil}
4676 for the former case, non-@code{nil} for the latter case.
4678 The optional argument @var{type} is a symbol specifying the image type.
4679 If @var{type} is omitted or @code{nil}, @code{create-image} tries to
4680 determine the image type from the file's first few bytes, or else
4681 from the file's name.
4683 The remaining arguments, @var{props}, specify additional image
4684 properties---for example,
4687 (create-image "foo.xpm" 'xpm nil :heuristic-mask t)
4690 The function returns @code{nil} if images of this type are not
4691 supported. Otherwise it returns an image descriptor.
4694 @defmac defimage symbol specs &optional doc
4695 This macro defines @var{symbol} as an image name. The arguments
4696 @var{specs} is a list which specifies how to display the image.
4697 The third argument, @var{doc}, is an optional documentation string.
4699 Each argument in @var{specs} has the form of a property list, and each
4700 one should specify at least the @code{:type} property and either the
4701 @code{:file} or the @code{:data} property. The value of @code{:type}
4702 should be a symbol specifying the image type, the value of
4703 @code{:file} is the file to load the image from, and the value of
4704 @code{:data} is a string containing the actual image data. Here is an
4708 (defimage test-image
4709 ((:type xpm :file "~/test1.xpm")
4710 (:type xbm :file "~/test1.xbm")))
4713 @code{defimage} tests each argument, one by one, to see if it is
4714 usable---that is, if the type is supported and the file exists. The
4715 first usable argument is used to make an image descriptor which is
4716 stored in @var{symbol}.
4718 If none of the alternatives will work, then @var{symbol} is defined
4722 @defun find-image specs
4723 This function provides a convenient way to find an image satisfying one
4724 of a list of image specifications @var{specs}.
4726 Each specification in @var{specs} is a property list with contents
4727 depending on image type. All specifications must at least contain the
4728 properties @code{:type @var{type}} and either @w{@code{:file @var{file}}}
4729 or @w{@code{:data @var{DATA}}}, where @var{type} is a symbol specifying
4730 the image type, e.g.@: @code{xbm}, @var{file} is the file to load the
4731 image from, and @var{data} is a string containing the actual image data.
4732 The first specification in the list whose @var{type} is supported, and
4733 @var{file} exists, is used to construct the image specification to be
4734 returned. If no specification is satisfied, @code{nil} is returned.
4736 The image is looked for in @code{image-load-path}.
4739 @defvar image-load-path
4740 This variable's value is a list of locations in which to search for
4741 image files. If an element is a string or a variable symbol whose
4742 value is a string, the string is taken to be the name of a directory
4743 to search. If an element is a variable symbol whose value is a list,
4744 that is taken to be a list of directory names to search.
4746 The default is to search in the @file{images} subdirectory of the
4747 directory specified by @code{data-directory}, then the directory
4748 specified by @code{data-directory}, and finally in the directories in
4749 @code{load-path}. Subdirectories are not automatically included in
4750 the search, so if you put an image file in a subdirectory, you have to
4751 supply the subdirectory name explicitly. For example, to find the
4752 image @file{images/foo/bar.xpm} within @code{data-directory}, you
4753 should specify the image as follows:
4756 (defimage foo-image '((:type xpm :file "foo/bar.xpm")))
4760 @defun image-load-path-for-library library image &optional path no-error
4761 This function returns a suitable search path for images used by the
4762 Lisp package @var{library}.
4764 The function searches for @var{image} first using @code{image-load-path},
4765 excluding @file{@code{data-directory}/images}, and then in
4766 @code{load-path}, followed by a path suitable for @var{library}, which
4767 includes @file{../../etc/images} and @file{../etc/images} relative to
4768 the library file itself, and finally in
4769 @file{@code{data-directory}/images}.
4771 Then this function returns a list of directories which contains first
4772 the directory in which @var{image} was found, followed by the value of
4773 @code{load-path}. If @var{path} is given, it is used instead of
4776 If @var{no-error} is non-@code{nil} and a suitable path can't be
4777 found, don't signal an error. Instead, return a list of directories as
4778 before, except that @code{nil} appears in place of the image directory.
4780 Here is an example of using @code{image-load-path-for-library}:
4783 (defvar image-load-path) ; shush compiler
4784 (let* ((load-path (image-load-path-for-library
4785 "mh-e" "mh-logo.xpm"))
4786 (image-load-path (cons (car load-path)
4788 (mh-tool-bar-folder-buttons-init))
4792 @node Showing Images
4793 @subsection Showing Images
4795 You can use an image descriptor by setting up the @code{display}
4796 property yourself, but it is easier to use the functions in this
4799 @defun insert-image image &optional string area slice
4800 This function inserts @var{image} in the current buffer at point. The
4801 value @var{image} should be an image descriptor; it could be a value
4802 returned by @code{create-image}, or the value of a symbol defined with
4803 @code{defimage}. The argument @var{string} specifies the text to put
4804 in the buffer to hold the image. If it is omitted or @code{nil},
4805 @code{insert-image} uses @code{" "} by default.
4807 The argument @var{area} specifies whether to put the image in a margin.
4808 If it is @code{left-margin}, the image appears in the left margin;
4809 @code{right-margin} specifies the right margin. If @var{area} is
4810 @code{nil} or omitted, the image is displayed at point within the
4813 The argument @var{slice} specifies a slice of the image to insert. If
4814 @var{slice} is @code{nil} or omitted the whole image is inserted.
4815 Otherwise, @var{slice} is a list @code{(@var{x} @var{y} @var{width}
4816 @var{height})} which specifies the @var{x} and @var{y} positions and
4817 @var{width} and @var{height} of the image area to insert. Integer
4818 values are in units of pixels. A floating point number in the range
4819 0.0--1.0 stands for that fraction of the width or height of the entire
4822 Internally, this function inserts @var{string} in the buffer, and gives
4823 it a @code{display} property which specifies @var{image}. @xref{Display
4827 @cindex slice, image
4829 @defun insert-sliced-image image &optional string area rows cols
4830 This function inserts @var{image} in the current buffer at point, like
4831 @code{insert-image}, but splits the image into @var{rows}x@var{cols}
4832 equally sized slices.
4834 If an image is inserted ``sliced'', Emacs displays each slice as a
4835 separate image, and allow more intuitive scrolling up/down, instead of
4836 jumping up/down the entire image when paging through a buffer that
4837 displays (large) images.
4840 @defun put-image image pos &optional string area
4841 This function puts image @var{image} in front of @var{pos} in the
4842 current buffer. The argument @var{pos} should be an integer or a
4843 marker. It specifies the buffer position where the image should appear.
4844 The argument @var{string} specifies the text that should hold the image
4845 as an alternative to the default.
4847 The argument @var{image} must be an image descriptor, perhaps returned
4848 by @code{create-image} or stored by @code{defimage}.
4850 The argument @var{area} specifies whether to put the image in a margin.
4851 If it is @code{left-margin}, the image appears in the left margin;
4852 @code{right-margin} specifies the right margin. If @var{area} is
4853 @code{nil} or omitted, the image is displayed at point within the
4856 Internally, this function creates an overlay, and gives it a
4857 @code{before-string} property containing text that has a @code{display}
4858 property whose value is the image. (Whew!)
4861 @defun remove-images start end &optional buffer
4862 This function removes images in @var{buffer} between positions
4863 @var{start} and @var{end}. If @var{buffer} is omitted or @code{nil},
4864 images are removed from the current buffer.
4866 This removes only images that were put into @var{buffer} the way
4867 @code{put-image} does it, not images that were inserted with
4868 @code{insert-image} or in other ways.
4871 @defun image-size spec &optional pixels frame
4872 This function returns the size of an image as a pair
4873 @w{@code{(@var{width} . @var{height})}}. @var{spec} is an image
4874 specification. @var{pixels} non-@code{nil} means return sizes
4875 measured in pixels, otherwise return sizes measured in canonical
4876 character units (fractions of the width/height of the frame's default
4877 font). @var{frame} is the frame on which the image will be displayed.
4878 @var{frame} null or omitted means use the selected frame (@pxref{Input
4882 @defvar max-image-size
4883 This variable is used to define the maximum size of image that Emacs
4884 will load. Emacs will refuse to load (and display) any image that is
4885 larger than this limit.
4887 If the value is an integer, it directly specifies the maximum
4888 image height and width, measured in pixels. If it is a floating
4889 point number, it specifies the maximum image height and width
4890 as a ratio to the frame height and width. If the value is
4891 non-numeric, there is no explicit limit on the size of images.
4893 The purpose of this variable is to prevent unreasonably large images
4894 from accidentally being loaded into Emacs. It only takes effect the
4895 first time an image is loaded. Once an image is placed in the image
4896 cache, it can always be displayed, even if the value of
4897 @var{max-image-size} is subsequently changed (@pxref{Image Cache}).
4900 @node Animated Images
4901 @subsection Animated Images
4904 @cindex image animation
4905 Some image files can contain more than one image. This can be used to
4906 create animation. Currently, Emacs only supports animated GIF files.
4907 The following functions related to animated images are available.
4909 @defun image-animated-p image
4910 This function returns non-@code{nil} if @var{image} can be animated.
4911 The actual return value is a cons @code{(@var{nimages} . @var{delay})},
4912 where @var{nimages} is the number of frames and @var{delay} is the
4913 delay in seconds between them.
4916 @defun image-animate image &optional index limit
4917 This function animates @var{image}. The optional integer @var{index}
4918 specifies the frame from which to start (default 0). The optional
4919 argument @var{limit} controls the length of the animation. If omitted
4920 or @code{nil}, the image animates once only; if @code{t} it loops
4921 forever; if a number animation stops after that many seconds.
4924 @noindent Animation operates by means of a timer. Note that Emacs imposes a
4925 minimum frame delay of 0.01 seconds.
4927 @defun image-animate-timer image
4928 This function returns the timer responsible for animating @var{image},
4934 @subsection Image Cache
4937 Emacs caches images so that it can display them again more
4938 efficiently. When Emacs displays an image, it searches the image
4939 cache for an existing image specification @code{equal} to the desired
4940 specification. If a match is found, the image is displayed from the
4941 cache. Otherwise, Emacs loads the image normally.
4943 @defun image-flush spec &optional frame
4944 This function removes the image with specification @var{spec} from the
4945 image cache of frame @var{frame}. Image specifications are compared
4946 using @code{equal}. If @var{frame} is @code{nil}, it defaults to the
4947 selected frame. If @var{frame} is @code{t}, the image is flushed on
4948 all existing frames.
4950 In Emacs's current implementation, each graphical terminal possesses an
4951 image cache, which is shared by all the frames on that terminal
4952 (@pxref{Multiple Terminals}). Thus, refreshing an image in one frame
4953 also refreshes it in all other frames on the same terminal.
4956 One use for @code{image-flush} is to tell Emacs about a change in an
4957 image file. If an image specification contains a @code{:file}
4958 property, the image is cached based on the file's contents when the
4959 image is first displayed. Even if the file subsequently changes,
4960 Emacs continues displaying the old version of the image. Calling
4961 @code{image-flush} flushes the image from the cache, forcing Emacs to
4962 re-read the file the next time it needs to display that image.
4964 Another use for @code{image-flush} is for memory conservation. If
4965 your Lisp program creates a large number of temporary images over a
4966 period much shorter than @code{image-cache-eviction-delay} (see
4967 below), you can opt to flush unused images yourself, instead of
4968 waiting for Emacs to do it automatically.
4970 @defun clear-image-cache &optional filter
4971 This function clears an image cache, removing all the images stored in
4972 it. If @var{filter} is omitted or @code{nil}, it clears the cache for
4973 the selected frame. If @var{filter} is a frame, it clears the cache
4974 for that frame. If @var{filter} is @code{t}, all image caches are
4975 cleared. Otherwise, @var{filter} is taken to be a file name, and all
4976 images associated with that file name are removed from all image
4980 If an image in the image cache has not been displayed for a specified
4981 period of time, Emacs removes it from the cache and frees the
4984 @defvar image-cache-eviction-delay
4985 This variable specifies the number of seconds an image can remain in
4986 the cache without being displayed. When an image is not displayed for
4987 this length of time, Emacs removes it from the image cache.
4989 Under some circumstances, if the number of images in the cache grows
4990 too large, the actual eviction delay may be shorter than this.
4992 If the value is @code{nil}, Emacs does not remove images from the cache
4993 except when you explicitly clear it. This mode can be useful for
4999 @cindex buttons in buffers
5000 @cindex clickable buttons in buffers
5002 The Button package defines functions for inserting and manipulating
5003 @dfn{buttons} that can be activated with the mouse or via keyboard
5004 commands. These buttons are typically used for various kinds of
5007 A button is essentially a set of text or overlay properties,
5008 attached to a stretch of text in a buffer. These properties are
5009 called @dfn{button properties}. One of these properties, the
5010 @dfn{action property}, specifies a function which is called when the
5011 user invokes the button using the keyboard or the mouse. The action
5012 function may examine the button and use its other properties as
5015 In some ways, the Button package duplicates the functionality in the
5016 Widget package. @xref{Top, , Introduction, widget, The Emacs Widget
5017 Library}. The advantage of the Button package is that it is faster,
5018 smaller, and simpler to program. From the point of view of the user,
5019 the interfaces produced by the two packages are very similar.
5022 * Button Properties:: Button properties with special meanings.
5023 * Button Types:: Defining common properties for classes of buttons.
5024 * Making Buttons:: Adding buttons to Emacs buffers.
5025 * Manipulating Buttons:: Getting and setting properties of buttons.
5026 * Button Buffer Commands:: Buffer-wide commands and bindings for buttons.
5029 @node Button Properties
5030 @subsection Button Properties
5031 @cindex button properties
5033 Each button has an associated list of properties defining its
5034 appearance and behavior, and other arbitrary properties may be used
5035 for application specific purposes. The following properties have
5036 special meaning to the Button package:
5040 @kindex action @r{(button property)}
5041 The function to call when the user invokes the button, which is passed
5042 the single argument @var{button}. By default this is @code{ignore},
5046 @kindex mouse-action @r{(button property)}
5047 This is similar to @code{action}, and when present, will be used
5048 instead of @code{action} for button invocations resulting from
5049 mouse-clicks (instead of the user hitting @key{RET}). If not
5050 present, mouse-clicks use @code{action} instead.
5053 @kindex face @r{(button property)}
5054 This is an Emacs face controlling how buttons of this type are
5055 displayed; by default this is the @code{button} face.
5058 @kindex mouse-face @r{(button property)}
5059 This is an additional face which controls appearance during
5060 mouse-overs (merged with the usual button face); by default this is
5061 the usual Emacs @code{highlight} face.
5064 @kindex keymap @r{(button property)}
5065 The button's keymap, defining bindings active within the button
5066 region. By default this is the usual button region keymap, stored
5067 in the variable @code{button-map}, which defines @key{RET} and
5068 @key{mouse-2} to invoke the button.
5071 @kindex type @r{(button property)}
5072 The button type. @xref{Button Types}.
5075 @kindex help-index @r{(button property)}
5076 A string displayed by the Emacs tool-tip help system; by default,
5077 @code{"mouse-2, RET: Push this button"}.
5080 @kindex follow-link @r{(button property)}
5081 The follow-link property, defining how a @key{Mouse-1} click behaves
5082 on this button, @xref{Clickable Text}.
5085 @kindex button @r{(button property)}
5086 All buttons have a non-@code{nil} @code{button} property, which may be useful
5087 in finding regions of text that comprise buttons (which is what the
5088 standard button functions do).
5091 There are other properties defined for the regions of text in a
5092 button, but these are not generally interesting for typical uses.
5095 @subsection Button Types
5096 @cindex button types
5098 Every button has a @dfn{button type}, which defines default values
5099 for the button's properties. Button types are arranged in a
5100 hierarchy, with specialized types inheriting from more general types,
5101 so that it's easy to define special-purpose types of buttons for
5104 @defun define-button-type name &rest properties
5105 Define a `button type' called @var{name} (a symbol).
5106 The remaining arguments
5107 form a sequence of @var{property value} pairs, specifying default
5108 property values for buttons with this type (a button's type may be set
5109 by giving it a @code{type} property when creating the button, using
5110 the @code{:type} keyword argument).
5112 In addition, the keyword argument @code{:supertype} may be used to
5113 specify a button-type from which @var{name} inherits its default
5114 property values. Note that this inheritance happens only when
5115 @var{name} is defined; subsequent changes to a supertype are not
5116 reflected in its subtypes.
5119 Using @code{define-button-type} to define default properties for
5120 buttons is not necessary---buttons without any specified type use the
5121 built-in button-type @code{button}---but it is encouraged, since
5122 doing so usually makes the resulting code clearer and more efficient.
5124 @node Making Buttons
5125 @subsection Making Buttons
5126 @cindex making buttons
5128 Buttons are associated with a region of text, using an overlay or
5129 text properties to hold button-specific information, all of which are
5130 initialized from the button's type (which defaults to the built-in
5131 button type @code{button}). Like all Emacs text, the appearance of
5132 the button is governed by the @code{face} property; by default (via
5133 the @code{face} property inherited from the @code{button} button-type)
5134 this is a simple underline, like a typical web-page link.
5136 For convenience, there are two sorts of button-creation functions,
5137 those that add button properties to an existing region of a buffer,
5138 called @code{make-...button}, and those that also insert the button
5139 text, called @code{insert-...button}.
5141 The button-creation functions all take the @code{&rest} argument
5142 @var{properties}, which should be a sequence of @var{property value}
5143 pairs, specifying properties to add to the button; see @ref{Button
5144 Properties}. In addition, the keyword argument @code{:type} may be
5145 used to specify a button-type from which to inherit other properties;
5146 see @ref{Button Types}. Any properties not explicitly specified
5147 during creation will be inherited from the button's type (if the type
5148 defines such a property).
5150 The following functions add a button using an overlay
5151 (@pxref{Overlays}) to hold the button properties:
5153 @defun make-button beg end &rest properties
5154 This makes a button from @var{beg} to @var{end} in the
5155 current buffer, and returns it.
5158 @defun insert-button label &rest properties
5159 This insert a button with the label @var{label} at point,
5163 The following functions are similar, but using text properties
5164 (@pxref{Text Properties}) to hold the button properties. Such buttons
5165 do not add markers to the buffer, so editing in the buffer does not
5166 slow down if there is an extremely large numbers of buttons. However,
5167 if there is an existing face text property on the text (e.g.@: a face
5168 assigned by Font Lock mode), the button face may not be visible. Both
5169 of these functions return the starting position of the new button.
5171 @defun make-text-button beg end &rest properties
5172 This makes a button from @var{beg} to @var{end} in the current buffer,
5173 using text properties.
5176 @defun insert-text-button label &rest properties
5177 This inserts a button with the label @var{label} at point, using text
5181 @node Manipulating Buttons
5182 @subsection Manipulating Buttons
5183 @cindex manipulating buttons
5185 These are functions for getting and setting properties of buttons.
5186 Often these are used by a button's invocation function to determine
5189 Where a @var{button} parameter is specified, it means an object
5190 referring to a specific button, either an overlay (for overlay
5191 buttons), or a buffer-position or marker (for text property buttons).
5192 Such an object is passed as the first argument to a button's
5193 invocation function when it is invoked.
5195 @defun button-start button
5196 Return the position at which @var{button} starts.
5199 @defun button-end button
5200 Return the position at which @var{button} ends.
5203 @defun button-get button prop
5204 Get the property of button @var{button} named @var{prop}.
5207 @defun button-put button prop val
5208 Set @var{button}'s @var{prop} property to @var{val}.
5211 @defun button-activate button &optional use-mouse-action
5212 Call @var{button}'s @code{action} property (i.e., invoke it). If
5213 @var{use-mouse-action} is non-@code{nil}, try to invoke the button's
5214 @code{mouse-action} property instead of @code{action}; if the button
5215 has no @code{mouse-action} property, use @code{action} as normal.
5218 @defun button-label button
5219 Return @var{button}'s text label.
5222 @defun button-type button
5223 Return @var{button}'s button-type.
5226 @defun button-has-type-p button type
5227 Return @code{t} if @var{button} has button-type @var{type}, or one of
5228 @var{type}'s subtypes.
5231 @defun button-at pos
5232 Return the button at position @var{pos} in the current buffer, or
5233 @code{nil}. If the button at @var{pos} is a text property button, the
5234 return value is a marker pointing to @var{pos}.
5237 @defun button-type-put type prop val
5238 Set the button-type @var{type}'s @var{prop} property to @var{val}.
5241 @defun button-type-get type prop
5242 Get the property of button-type @var{type} named @var{prop}.
5245 @defun button-type-subtype-p type supertype
5246 Return @code{t} if button-type @var{type} is a subtype of @var{supertype}.
5249 @node Button Buffer Commands
5250 @subsection Button Buffer Commands
5251 @cindex button buffer commands
5253 These are commands and functions for locating and operating on
5254 buttons in an Emacs buffer.
5256 @code{push-button} is the command that a user uses to actually `push'
5257 a button, and is bound by default in the button itself to @key{RET}
5258 and to @key{mouse-2} using a local keymap in the button's overlay or
5259 text properties. Commands that are useful outside the buttons itself,
5260 such as @code{forward-button} and @code{backward-button} are
5261 additionally available in the keymap stored in
5262 @code{button-buffer-map}; a mode which uses buttons may want to use
5263 @code{button-buffer-map} as a parent keymap for its keymap.
5265 If the button has a non-@code{nil} @code{follow-link} property, and
5266 @var{mouse-1-click-follows-link} is set, a quick @key{Mouse-1} click
5267 will also activate the @code{push-button} command.
5268 @xref{Clickable Text}.
5270 @deffn Command push-button &optional pos use-mouse-action
5271 Perform the action specified by a button at location @var{pos}.
5272 @var{pos} may be either a buffer position or a mouse-event. If
5273 @var{use-mouse-action} is non-@code{nil}, or @var{pos} is a
5274 mouse-event (@pxref{Mouse Events}), try to invoke the button's
5275 @code{mouse-action} property instead of @code{action}; if the button
5276 has no @code{mouse-action} property, use @code{action} as normal.
5277 @var{pos} defaults to point, except when @code{push-button} is invoked
5278 interactively as the result of a mouse-event, in which case, the mouse
5279 event's position is used. If there's no button at @var{pos}, do
5280 nothing and return @code{nil}, otherwise return @code{t}.
5283 @deffn Command forward-button n &optional wrap display-message
5284 Move to the @var{n}th next button, or @var{n}th previous button if
5285 @var{n} is negative. If @var{n} is zero, move to the start of any
5286 button at point. If @var{wrap} is non-@code{nil}, moving past either
5287 end of the buffer continues from the other end. If
5288 @var{display-message} is non-@code{nil}, the button's help-echo string
5289 is displayed. Any button with a non-@code{nil} @code{skip} property
5290 is skipped over. Returns the button found.
5293 @deffn Command backward-button n &optional wrap display-message
5294 Move to the @var{n}th previous button, or @var{n}th next button if
5295 @var{n} is negative. If @var{n} is zero, move to the start of any
5296 button at point. If @var{wrap} is non-@code{nil}, moving past either
5297 end of the buffer continues from the other end. If
5298 @var{display-message} is non-@code{nil}, the button's help-echo string
5299 is displayed. Any button with a non-@code{nil} @code{skip} property
5300 is skipped over. Returns the button found.
5303 @defun next-button pos &optional count-current
5304 @defunx previous-button pos &optional count-current
5305 Return the next button after (for @code{next-button} or before (for
5306 @code{previous-button}) position @var{pos} in the current buffer. If
5307 @var{count-current} is non-@code{nil}, count any button at @var{pos}
5308 in the search, instead of starting at the next button.
5311 @node Abstract Display
5312 @section Abstract Display
5314 @cindex display, abstract
5315 @cindex display, arbitrary objects
5316 @cindex model/view/controller
5317 @cindex view part, model/view/controller
5319 The Ewoc package constructs buffer text that represents a structure
5320 of Lisp objects, and updates the text to follow changes in that
5321 structure. This is like the ``view'' component in the
5322 ``model/view/controller'' design paradigm.
5324 An @dfn{ewoc} is a structure that organizes information required to
5325 construct buffer text that represents certain Lisp data. The buffer
5326 text of the ewoc has three parts, in order: first, fixed @dfn{header}
5327 text; next, textual descriptions of a series of data elements (Lisp
5328 objects that you specify); and last, fixed @dfn{footer} text.
5329 Specifically, an ewoc contains information on:
5333 The buffer which its text is generated in.
5336 The text's start position in the buffer.
5339 The header and footer strings.
5342 A doubly-linked chain of @dfn{nodes}, each of which contains:
5346 A @dfn{data element}, a single Lisp object.
5349 Links to the preceding and following nodes in the chain.
5353 A @dfn{pretty-printer} function which is responsible for
5354 inserting the textual representation of a data
5355 element value into the current buffer.
5358 Typically, you define an ewoc with @code{ewoc-create}, and then pass
5359 the resulting ewoc structure to other functions in the Ewoc package to
5360 build nodes within it, and display it in the buffer. Once it is
5361 displayed in the buffer, other functions determine the correspondence
5362 between buffer positions and nodes, move point from one node's textual
5363 representation to another, and so forth. @xref{Abstract Display
5366 A node @dfn{encapsulates} a data element much the way a variable
5367 holds a value. Normally, encapsulation occurs as a part of adding a
5368 node to the ewoc. You can retrieve the data element value and place a
5369 new value in its place, like so:
5372 (ewoc-data @var{node})
5375 (ewoc-set-data @var{node} @var{new-value})
5376 @result{} @var{new-value}
5380 You can also use, as the data element value, a Lisp object (list or
5381 vector) that is a container for the ``real'' value, or an index into
5382 some other structure. The example (@pxref{Abstract Display Example})
5383 uses the latter approach.
5385 When the data changes, you will want to update the text in the
5386 buffer. You can update all nodes by calling @code{ewoc-refresh}, or
5387 just specific nodes using @code{ewoc-invalidate}, or all nodes
5388 satisfying a predicate using @code{ewoc-map}. Alternatively, you can
5389 delete invalid nodes using @code{ewoc-delete} or @code{ewoc-filter},
5390 and add new nodes in their place. Deleting a node from an ewoc deletes
5391 its associated textual description from buffer, as well.
5394 * Abstract Display Functions:: Functions in the Ewoc package.
5395 * Abstract Display Example:: Example of using Ewoc.
5398 @node Abstract Display Functions
5399 @subsection Abstract Display Functions
5401 In this subsection, @var{ewoc} and @var{node} stand for the
5402 structures described above (@pxref{Abstract Display}), while
5403 @var{data} stands for an arbitrary Lisp object used as a data element.
5405 @defun ewoc-create pretty-printer &optional header footer nosep
5406 This constructs and returns a new ewoc, with no nodes (and thus no data
5407 elements). @var{pretty-printer} should be a function that takes one
5408 argument, a data element of the sort you plan to use in this ewoc, and
5409 inserts its textual description at point using @code{insert} (and never
5410 @code{insert-before-markers}, because that would interfere with the
5411 Ewoc package's internal mechanisms).
5413 Normally, a newline is automatically inserted after the header,
5414 the footer and every node's textual description. If @var{nosep}
5415 is non-@code{nil}, no newline is inserted. This may be useful for
5416 displaying an entire ewoc on a single line, for example, or for
5417 making nodes ``invisible'' by arranging for @var{pretty-printer}
5418 to do nothing for those nodes.
5420 An ewoc maintains its text in the buffer that is current when
5421 you create it, so switch to the intended buffer before calling
5425 @defun ewoc-buffer ewoc
5426 This returns the buffer where @var{ewoc} maintains its text.
5429 @defun ewoc-get-hf ewoc
5430 This returns a cons cell @code{(@var{header} . @var{footer})}
5431 made from @var{ewoc}'s header and footer.
5434 @defun ewoc-set-hf ewoc header footer
5435 This sets the header and footer of @var{ewoc} to the strings
5436 @var{header} and @var{footer}, respectively.
5439 @defun ewoc-enter-first ewoc data
5440 @defunx ewoc-enter-last ewoc data
5441 These add a new node encapsulating @var{data}, putting it, respectively,
5442 at the beginning or end of @var{ewoc}'s chain of nodes.
5445 @defun ewoc-enter-before ewoc node data
5446 @defunx ewoc-enter-after ewoc node data
5447 These add a new node encapsulating @var{data}, adding it to
5448 @var{ewoc} before or after @var{node}, respectively.
5451 @defun ewoc-prev ewoc node
5452 @defunx ewoc-next ewoc node
5453 These return, respectively, the previous node and the next node of @var{node}
5457 @defun ewoc-nth ewoc n
5458 This returns the node in @var{ewoc} found at zero-based index @var{n}.
5459 A negative @var{n} means count from the end. @code{ewoc-nth} returns
5460 @code{nil} if @var{n} is out of range.
5463 @defun ewoc-data node
5464 This extracts the data encapsulated by @var{node} and returns it.
5467 @defun ewoc-set-data node data
5468 This sets the data encapsulated by @var{node} to @var{data}.
5471 @defun ewoc-locate ewoc &optional pos guess
5472 This determines the node in @var{ewoc} which contains point (or
5473 @var{pos} if specified), and returns that node. If @var{ewoc} has no
5474 nodes, it returns @code{nil}. If @var{pos} is before the first node,
5475 it returns the first node; if @var{pos} is after the last node, it returns
5476 the last node. The optional third arg @var{guess}
5477 should be a node that is likely to be near @var{pos}; this doesn't
5478 alter the result, but makes the function run faster.
5481 @defun ewoc-location node
5482 This returns the start position of @var{node}.
5485 @defun ewoc-goto-prev ewoc arg
5486 @defunx ewoc-goto-next ewoc arg
5487 These move point to the previous or next, respectively, @var{arg}th node
5488 in @var{ewoc}. @code{ewoc-goto-prev} does not move if it is already at
5489 the first node or if @var{ewoc} is empty, whereas @code{ewoc-goto-next}
5490 moves past the last node, returning @code{nil}. Excepting this special
5491 case, these functions return the node moved to.
5494 @defun ewoc-goto-node ewoc node
5495 This moves point to the start of @var{node} in @var{ewoc}.
5498 @defun ewoc-refresh ewoc
5499 This function regenerates the text of @var{ewoc}. It works by
5500 deleting the text between the header and the footer, i.e., all the
5501 data elements' representations, and then calling the pretty-printer
5502 function for each node, one by one, in order.
5505 @defun ewoc-invalidate ewoc &rest nodes
5506 This is similar to @code{ewoc-refresh}, except that only @var{nodes} in
5507 @var{ewoc} are updated instead of the entire set.
5510 @defun ewoc-delete ewoc &rest nodes
5511 This deletes each node in @var{nodes} from @var{ewoc}.
5514 @defun ewoc-filter ewoc predicate &rest args
5515 This calls @var{predicate} for each data element in @var{ewoc} and
5516 deletes those nodes for which @var{predicate} returns @code{nil}.
5517 Any @var{args} are passed to @var{predicate}.
5520 @defun ewoc-collect ewoc predicate &rest args
5521 This calls @var{predicate} for each data element in @var{ewoc}
5522 and returns a list of those elements for which @var{predicate}
5523 returns non-@code{nil}. The elements in the list are ordered
5524 as in the buffer. Any @var{args} are passed to @var{predicate}.
5527 @defun ewoc-map map-function ewoc &rest args
5528 This calls @var{map-function} for each data element in @var{ewoc} and
5529 updates those nodes for which @var{map-function} returns non-@code{nil}.
5530 Any @var{args} are passed to @var{map-function}.
5533 @node Abstract Display Example
5534 @subsection Abstract Display Example
5536 Here is a simple example using functions of the ewoc package to
5537 implement a ``color components display'', an area in a buffer that
5538 represents a vector of three integers (itself representing a 24-bit RGB
5539 value) in various ways.
5542 (setq colorcomp-ewoc nil
5544 colorcomp-mode-map nil
5545 colorcomp-labels ["Red" "Green" "Blue"])
5547 (defun colorcomp-pp (data)
5549 (let ((comp (aref colorcomp-data data)))
5550 (insert (aref colorcomp-labels data) "\t: #x"
5551 (format "%02X" comp) " "
5552 (make-string (ash comp -2) ?#) "\n"))
5553 (let ((cstr (format "#%02X%02X%02X"
5554 (aref colorcomp-data 0)
5555 (aref colorcomp-data 1)
5556 (aref colorcomp-data 2)))
5557 (samp " (sample text) "))
5559 (propertize samp 'face
5560 `(foreground-color . ,cstr))
5561 (propertize samp 'face
5562 `(background-color . ,cstr))
5565 (defun colorcomp (color)
5566 "Allow fiddling with COLOR in a new buffer.
5567 The buffer is in Color Components mode."
5568 (interactive "sColor (name or #RGB or #RRGGBB): ")
5569 (when (string= "" color)
5570 (setq color "green"))
5571 (unless (color-values color)
5572 (error "No such color: %S" color))
5574 (generate-new-buffer (format "originally: %s" color)))
5575 (kill-all-local-variables)
5576 (setq major-mode 'colorcomp-mode
5577 mode-name "Color Components")
5578 (use-local-map colorcomp-mode-map)
5580 (buffer-disable-undo)
5581 (let ((data (apply 'vector (mapcar (lambda (n) (ash n -8))
5582 (color-values color))))
5583 (ewoc (ewoc-create 'colorcomp-pp
5584 "\nColor Components\n\n"
5585 (substitute-command-keys
5586 "\n\\@{colorcomp-mode-map@}"))))
5587 (set (make-local-variable 'colorcomp-data) data)
5588 (set (make-local-variable 'colorcomp-ewoc) ewoc)
5589 (ewoc-enter-last ewoc 0)
5590 (ewoc-enter-last ewoc 1)
5591 (ewoc-enter-last ewoc 2)
5592 (ewoc-enter-last ewoc nil)))
5595 @cindex controller part, model/view/controller
5596 This example can be extended to be a ``color selection widget'' (in
5597 other words, the controller part of the ``model/view/controller''
5598 design paradigm) by defining commands to modify @code{colorcomp-data}
5599 and to ``finish'' the selection process, and a keymap to tie it all
5600 together conveniently.
5603 (defun colorcomp-mod (index limit delta)
5604 (let ((cur (aref colorcomp-data index)))
5605 (unless (= limit cur)
5606 (aset colorcomp-data index (+ cur delta)))
5609 (ewoc-nth colorcomp-ewoc index)
5610 (ewoc-nth colorcomp-ewoc -1))))
5612 (defun colorcomp-R-more () (interactive) (colorcomp-mod 0 255 1))
5613 (defun colorcomp-G-more () (interactive) (colorcomp-mod 1 255 1))
5614 (defun colorcomp-B-more () (interactive) (colorcomp-mod 2 255 1))
5615 (defun colorcomp-R-less () (interactive) (colorcomp-mod 0 0 -1))
5616 (defun colorcomp-G-less () (interactive) (colorcomp-mod 1 0 -1))
5617 (defun colorcomp-B-less () (interactive) (colorcomp-mod 2 0 -1))
5619 (defun colorcomp-copy-as-kill-and-exit ()
5620 "Copy the color components into the kill ring and kill the buffer.
5621 The string is formatted #RRGGBB (hash followed by six hex digits)."
5623 (kill-new (format "#%02X%02X%02X"
5624 (aref colorcomp-data 0)
5625 (aref colorcomp-data 1)
5626 (aref colorcomp-data 2)))
5629 (setq colorcomp-mode-map
5630 (let ((m (make-sparse-keymap)))
5632 (define-key m "i" 'colorcomp-R-less)
5633 (define-key m "o" 'colorcomp-R-more)
5634 (define-key m "k" 'colorcomp-G-less)
5635 (define-key m "l" 'colorcomp-G-more)
5636 (define-key m "," 'colorcomp-B-less)
5637 (define-key m "." 'colorcomp-B-more)
5638 (define-key m " " 'colorcomp-copy-as-kill-and-exit)
5642 Note that we never modify the data in each node, which is fixed when the
5643 ewoc is created to be either @code{nil} or an index into the vector
5644 @code{colorcomp-data}, the actual color components.
5647 @section Blinking Parentheses
5648 @cindex parenthesis matching
5649 @cindex blinking parentheses
5650 @cindex balancing parentheses
5652 This section describes the mechanism by which Emacs shows a matching
5653 open parenthesis when the user inserts a close parenthesis.
5655 @defvar blink-paren-function
5656 The value of this variable should be a function (of no arguments) to
5657 be called whenever a character with close parenthesis syntax is inserted.
5658 The value of @code{blink-paren-function} may be @code{nil}, in which
5659 case nothing is done.
5662 @defopt blink-matching-paren
5663 If this variable is @code{nil}, then @code{blink-matching-open} does
5667 @defopt blink-matching-paren-distance
5668 This variable specifies the maximum distance to scan for a matching
5669 parenthesis before giving up.
5672 @defopt blink-matching-delay
5673 This variable specifies the number of seconds for the cursor to remain
5674 at the matching parenthesis. A fraction of a second often gives
5675 good results, but the default is 1, which works on all systems.
5678 @deffn Command blink-matching-open
5679 This function is the default value of @code{blink-paren-function}. It
5680 assumes that point follows a character with close parenthesis syntax and
5681 moves the cursor momentarily to the matching opening character. If that
5682 character is not already on the screen, it displays the character's
5683 context in the echo area. To avoid long delays, this function does not
5684 search farther than @code{blink-matching-paren-distance} characters.
5686 Here is an example of calling this function explicitly.
5690 (defun interactive-blink-matching-open ()
5691 "Indicate momentarily the start of sexp before point."
5695 (let ((blink-matching-paren-distance
5697 (blink-matching-paren t))
5698 (blink-matching-open)))
5703 @node Character Display
5704 @section Character Display
5706 This section describes how characters are actually displayed by
5707 Emacs. Typically, a character is displayed as a @dfn{glyph} (a
5708 graphical symbol which occupies one character position on the screen),
5709 whose appearance corresponds to the character itself. For example,
5710 the character @samp{a} (character code 97) is displayed as @samp{a}.
5711 Some characters, however, are displayed specially. For example, the
5712 formfeed character (character code 12) is usually displayed as a
5713 sequence of two glyphs, @samp{^L}, while the newline character
5714 (character code 10) starts a new screen line.
5716 You can modify how each character is displayed by defining a
5717 @dfn{display table}, which maps each character code into a sequence of
5718 glyphs. @xref{Display Tables}.
5721 * Usual Display:: The usual conventions for displaying characters.
5722 * Display Tables:: What a display table consists of.
5723 * Active Display Table:: How Emacs selects a display table to use.
5724 * Glyphs:: How to define a glyph, and what glyphs mean.
5725 * Glyphless Chars:: How glyphless characters are drawn.
5729 @subsection Usual Display Conventions
5731 Here are the conventions for displaying each character code (in the
5732 absence of a display table, which can override these
5737 conventions; @pxref{Display Tables}).
5740 @cindex printable ASCII characters
5743 The @dfn{printable @acronym{ASCII} characters}, character codes 32
5744 through 126 (consisting of numerals, English letters, and symbols like
5745 @samp{#}) are displayed literally.
5748 The tab character (character code 9) displays as whitespace stretching
5749 up to the next tab stop column. @xref{Text Display,,, emacs, The GNU
5750 Emacs Manual}. The variable @code{tab-width} controls the number of
5751 spaces per tab stop (see below).
5754 The newline character (character code 10) has a special effect: it
5755 ends the preceding line and starts a new line.
5757 @cindex ASCII control characters
5759 The non-printable @dfn{@acronym{ASCII} control characters}---character
5760 codes 0 through 31, as well as the @key{DEL} character (character code
5761 127)---display in one of two ways according to the variable
5762 @code{ctl-arrow}. If this variable is non-@code{nil} (the default),
5763 these characters are displayed as sequences of two glyphs, where the
5764 first glyph is @samp{^} (a display table can specify a glyph to use
5765 instead of @samp{^}); e.g.@: the @key{DEL} character is displayed as
5768 If @code{ctl-arrow} is @code{nil}, these characters are displayed as
5769 octal escapes (see below).
5771 This rule also applies to carriage return (character code 13), if that
5772 character appears in the buffer. But carriage returns usually do not
5773 appear in buffer text; they are eliminated as part of end-of-line
5774 conversion (@pxref{Coding System Basics}).
5776 @cindex octal escapes
5778 @dfn{Raw bytes} are non-@acronym{ASCII} characters with codes 128
5779 through 255 (@pxref{Text Representations}). These characters display
5780 as @dfn{octal escapes}: sequences of four glyphs, where the first
5781 glyph is the @acronym{ASCII} code for @samp{\}, and the others are
5782 digit characters representing the character code in octal. (A display
5783 table can specify a glyph to use instead of @samp{\}.)
5786 Each non-@acronym{ASCII} character with code above 255 is displayed
5787 literally, if the terminal supports it. If the terminal does not
5788 support it, the character is said to be @dfn{glyphless}, and it is
5789 usually displayed using a placeholder glyph. For example, if a
5790 graphical terminal has no font for a character, Emacs usually displays
5791 a box containing the character code in hexadecimal. @xref{Glyphless
5795 The above display conventions apply even when there is a display
5796 table, for any character whose entry in the active display table is
5797 @code{nil}. Thus, when you set up a display table, you need only
5798 specify the characters for which you want special behavior.
5800 The following variables affect how certain characters are displayed
5801 on the screen. Since they change the number of columns the characters
5802 occupy, they also affect the indentation functions. They also affect
5803 how the mode line is displayed; if you want to force redisplay of the
5804 mode line using the new values, call the function
5805 @code{force-mode-line-update} (@pxref{Mode Line Format}).
5808 @cindex control characters in display
5809 This buffer-local variable controls how control characters are
5810 displayed. If it is non-@code{nil}, they are displayed as a caret
5811 followed by the character: @samp{^A}. If it is @code{nil}, they are
5812 displayed as octal escapes: a backslash followed by three octal
5813 digits, as in @samp{\001}.
5817 The value of this buffer-local variable is the spacing between tab
5818 stops used for displaying tab characters in Emacs buffers. The value
5819 is in units of columns, and the default is 8. Note that this feature
5820 is completely independent of the user-settable tab stops used by the
5821 command @code{tab-to-tab-stop}. @xref{Indent Tabs}.
5824 @node Display Tables
5825 @subsection Display Tables
5827 @cindex display table
5828 A display table is a special-purpose char-table
5829 (@pxref{Char-Tables}), with @code{display-table} as its subtype, which
5830 is used to override the usual character display conventions. This
5831 section describes how to make, inspect, and assign elements to a
5832 display table object.
5834 @defun make-display-table
5835 This creates and returns a display table. The table initially has
5836 @code{nil} in all elements.
5839 The ordinary elements of the display table are indexed by character
5840 codes; the element at index @var{c} says how to display the character
5841 code @var{c}. The value should be @code{nil} (which means to display
5842 the character @var{c} according to the usual display conventions;
5843 @pxref{Usual Display}), or a vector of glyph codes (which means to
5844 display the character @var{c} as those glyphs; @pxref{Glyphs}).
5846 @strong{Warning:} if you use the display table to change the display
5847 of newline characters, the whole buffer will be displayed as one long
5850 The display table also has six ``extra slots'' which serve special
5851 purposes. Here is a table of their meanings; @code{nil} in any slot
5852 means to use the default for that slot, as stated below.
5856 The glyph for the end of a truncated screen line (the default for this
5857 is @samp{$}). @xref{Glyphs}. On graphical terminals, Emacs uses
5858 arrows in the fringes to indicate truncation, so the display table has
5862 The glyph for the end of a continued line (the default is @samp{\}).
5863 On graphical terminals, Emacs uses curved arrows in the fringes to
5864 indicate continuation, so the display table has no effect.
5867 The glyph for indicating a character displayed as an octal character
5868 code (the default is @samp{\}).
5871 The glyph for indicating a control character (the default is @samp{^}).
5874 A vector of glyphs for indicating the presence of invisible lines (the
5875 default is @samp{...}). @xref{Selective Display}.
5878 The glyph used to draw the border between side-by-side windows (the
5879 default is @samp{|}). @xref{Splitting Windows}. This takes effect only
5880 when there are no scroll bars; if scroll bars are supported and in use,
5881 a scroll bar separates the two windows.
5884 For example, here is how to construct a display table that mimics
5885 the effect of setting @code{ctl-arrow} to a non-@code{nil} value
5886 (@pxref{Glyphs}, for the function @code{make-glyph-code}):
5889 (setq disptab (make-display-table))
5894 (vector (make-glyph-code ?^ 'escape-glyph)
5895 (make-glyph-code (+ i 64) 'escape-glyph)))))
5897 (vector (make-glyph-code ?^ 'escape-glyph)
5898 (make-glyph-code ?? 'escape-glyph)))))
5901 @defun display-table-slot display-table slot
5902 This function returns the value of the extra slot @var{slot} of
5903 @var{display-table}. The argument @var{slot} may be a number from 0 to
5904 5 inclusive, or a slot name (symbol). Valid symbols are
5905 @code{truncation}, @code{wrap}, @code{escape}, @code{control},
5906 @code{selective-display}, and @code{vertical-border}.
5909 @defun set-display-table-slot display-table slot value
5910 This function stores @var{value} in the extra slot @var{slot} of
5911 @var{display-table}. The argument @var{slot} may be a number from 0 to
5912 5 inclusive, or a slot name (symbol). Valid symbols are
5913 @code{truncation}, @code{wrap}, @code{escape}, @code{control},
5914 @code{selective-display}, and @code{vertical-border}.
5917 @defun describe-display-table display-table
5918 This function displays a description of the display table
5919 @var{display-table} in a help buffer.
5922 @deffn Command describe-current-display-table
5923 This command displays a description of the current display table in a
5927 @node Active Display Table
5928 @subsection Active Display Table
5929 @cindex active display table
5931 Each window can specify a display table, and so can each buffer.
5932 The window's display table, if there is one, takes precedence over the
5933 buffer's display table. If neither exists, Emacs tries to use the
5934 standard display table; if that is @code{nil}, Emacs uses the usual
5935 character display conventions (@pxref{Usual Display}).
5937 Note that display tables affect how the mode line is displayed, so
5938 if you want to force redisplay of the mode line using a new display
5939 table, call @code{force-mode-line-update} (@pxref{Mode Line Format}).
5941 @defun window-display-table &optional window
5942 This function returns @var{window}'s display table, or @code{nil} if
5943 there is none. The default for @var{window} is the selected window.
5946 @defun set-window-display-table window table
5947 This function sets the display table of @var{window} to @var{table}.
5948 The argument @var{table} should be either a display table or
5952 @defvar buffer-display-table
5953 This variable is automatically buffer-local in all buffers; its value
5954 specifies the buffer's display table. If it is @code{nil}, there is
5955 no buffer display table.
5958 @defvar standard-display-table
5959 The value of this variable is the standard display table, which is
5960 used when Emacs is displaying a buffer in a window with neither a
5961 window display table nor a buffer display table defined. Its default
5965 The @file{disp-table} library defines several functions for changing
5966 the standard display table.
5972 A @dfn{glyph} is a graphical symbol which occupies a single
5973 character position on the screen. Each glyph is represented in Lisp
5974 as a @dfn{glyph code}, which specifies a character and optionally a
5975 face to display it in (@pxref{Faces}). The main use of glyph codes is
5976 as the entries of display tables (@pxref{Display Tables}). The
5977 following functions are used to manipulate glyph codes:
5979 @defun make-glyph-code char &optional face
5980 This function returns a glyph code representing char @var{char} with
5981 face @var{face}. If @var{face} is omitted or @code{nil}, the glyph
5982 uses the default face; in that case, the glyph code is an integer. If
5983 @var{face} is non-@code{nil}, the glyph code is not necessarily an
5987 @defun glyph-char glyph
5988 This function returns the character of glyph code @var{glyph}.
5991 @defun glyph-face glyph
5992 This function returns face of glyph code @var{glyph}, or @code{nil} if
5993 @var{glyph} uses the default face.
5997 You can set up a @dfn{glyph table} to change how glyph codes are
5998 actually displayed on text terminals. This feature is semi-obsolete;
5999 use @code{glyphless-char-display} instead (@pxref{Glyphless Chars}).
6002 The value of this variable, if non-@code{nil}, is the current glyph
6003 table. It takes effect only on character terminals; on graphical
6004 displays, all glyphs are displayed literally. The glyph table should
6005 be a vector whose @var{g}th element specifies how to display glyph
6006 code @var{g}, where @var{g} is the glyph code for a glyph whose face
6007 is unspecified. Each element should be one of the following:
6011 Display this glyph literally.
6014 Display this glyph by sending the specified string to the terminal.
6017 Display the specified glyph code instead.
6020 Any integer glyph code greater than or equal to the length of the
6021 glyph table is displayed literally.
6025 @node Glyphless Chars
6026 @subsection Glyphless Character Display
6027 @cindex glyphless characters
6029 @dfn{Glyphless characters} are characters which are displayed in a
6030 special way, e.g.@: as a box containing a hexadecimal code, instead of
6031 being displayed literally. These include characters which are
6032 explicitly defined to be glyphless, as well as characters for which
6033 there is no available font (on a graphical display), and characters
6034 which cannot be encoded by the terminal's coding system (on a text
6037 @defvar glyphless-char-display
6038 The value of this variable is a char-table which defines glyphless
6039 characters and how they are displayed. Each entry must be one of the
6040 following display methods:
6044 Display the character in the usual way.
6046 @item @code{zero-width}
6047 Don't display the character.
6049 @item @code{thin-space}
6050 Display a thin space, 1-pixel wide on graphical displays, or
6051 1-character wide on text terminals.
6053 @item @code{empty-box}
6054 Display an empty box.
6056 @item @code{hex-code}
6057 Display a box containing the Unicode codepoint of the character, in
6058 hexadecimal notation.
6060 @item an @acronym{ASCII} string
6061 Display a box containing that string.
6063 @item a cons cell @code{(@var{graphical} . @var{text})}
6064 Display with @var{graphical} on graphical displays, and with
6065 @var{text} on text terminals. Both @var{graphical} and @var{text}
6066 must be one of the display methods described above.
6070 The @code{thin-space}, @code{empty-box}, @code{hex-code}, and
6071 @acronym{ASCII} string display methods are drawn with the
6072 @code{glyphless-char} face.
6074 The char-table has one extra slot, which determines how to display any
6075 character that cannot be displayed with any available font, or cannot
6076 be encoded by the terminal's coding system. Its value should be one
6077 of the above display methods, except @code{zero-width} or a cons cell.
6079 If a character has a non-@code{nil} entry in an active display table,
6080 the display table takes effect; in this case, Emacs does not consult
6081 @code{glyphless-char-display} at all.
6084 @defopt glyphless-char-display-control
6085 This user option provides a convenient way to set
6086 @code{glyphless-char-display} for groups of similar characters. Do
6087 not set its value directly from Lisp code; the value takes effect only
6088 via a custom @code{:set} function (@pxref{Variable Definitions}),
6089 which updates @code{glyphless-char-display}.
6091 Its value should be an alist of elements @code{(@var{group}
6092 . @var{method})}, where @var{group} is a symbol specifying a group of
6093 characters, and @var{method} is a symbol specifying how to display
6096 @var{group} should be one of the following:
6100 @acronym{ASCII} control characters @code{U+0000} to @code{U+001F},
6101 excluding the newline and tab characters (normally displayed as escape
6102 sequences like @samp{^A}; @pxref{Text Display,, How Text Is Displayed,
6103 emacs, The GNU Emacs Manual}).
6106 Non-@acronym{ASCII}, non-printing characters @code{U+0080} to
6107 @code{U+009F} (normally displayed as octal escape sequences like
6110 @item format-control
6111 Characters of Unicode General Category `Cf', such as @samp{U+200E}
6112 (Left-to-Right Mark), but excluding characters that have graphic
6113 images, such as @samp{U+00AD} (Soft Hyphen).
6116 Characters for there is no suitable font, or which cannot be encoded
6117 by the terminal's coding system.
6120 @c FIXME: this can also be `acronym', but that's not currently
6121 @c completely implemented; it applies only to the format-control
6122 @c group, and only works if the acronym is in `char-acronym-table'.
6123 The @var{method} symbol should be one of @code{zero-width},
6124 @code{thin-space}, @code{empty-box}, or @code{hex-code}. These have
6125 the same meanings as in @code{glyphless-char-display}, above.
6132 This section describes how to make Emacs ring the bell (or blink the
6133 screen) to attract the user's attention. Be conservative about how
6134 often you do this; frequent bells can become irritating. Also be
6135 careful not to use just beeping when signaling an error is more
6136 appropriate (@pxref{Errors}).
6138 @defun ding &optional do-not-terminate
6139 @cindex keyboard macro termination
6140 This function beeps, or flashes the screen (see @code{visible-bell} below).
6141 It also terminates any keyboard macro currently executing unless
6142 @var{do-not-terminate} is non-@code{nil}.
6145 @defun beep &optional do-not-terminate
6146 This is a synonym for @code{ding}.
6149 @defopt visible-bell
6150 This variable determines whether Emacs should flash the screen to
6151 represent a bell. Non-@code{nil} means yes, @code{nil} means no.
6152 This is effective on graphical displays, and on text terminals
6153 provided the terminal's Termcap entry defines the visible bell
6154 capability (@samp{vb}).
6157 @defvar ring-bell-function
6158 If this is non-@code{nil}, it specifies how Emacs should ``ring the
6159 bell''. Its value should be a function of no arguments. If this is
6160 non-@code{nil}, it takes precedence over the @code{visible-bell}
6164 @node Window Systems
6165 @section Window Systems
6167 Emacs works with several window systems, most notably the X Window
6168 System. Both Emacs and X use the term ``window'', but use it
6169 differently. An Emacs frame is a single window as far as X is
6170 concerned; the individual Emacs windows are not known to X at all.
6172 @defvar window-system
6173 This terminal-local variable tells Lisp programs what window system
6174 Emacs is using for displaying the frame. The possible values are
6178 @cindex X Window System
6179 Emacs is displaying the frame using X.
6181 Emacs is displaying the frame using native MS-Windows GUI.
6183 Emacs is displaying the frame using the Nextstep interface (used on
6184 GNUstep and Mac OS X).
6186 Emacs is displaying the frame using MS-DOS direct screen writes.
6188 Emacs is displaying the frame on a character-based terminal.
6192 @defvar initial-window-system
6193 This variable holds the value of @code{window-system} used for the
6194 first frame created by Emacs during startup. (When Emacs is invoked
6195 with the @option{--daemon} option, it does not create any initial
6196 frames, so @code{initial-window-system} is @code{nil}. @xref{Initial
6197 Options, daemon,, emacs, The GNU Emacs Manual}.)
6200 @defun window-system &optional frame
6201 This function returns a symbol whose name tells what window system is
6202 used for displaying @var{frame} (which defaults to the currently
6203 selected frame). The list of possible symbols it returns is the same
6204 one documented for the variable @code{window-system} above.
6207 Do @emph{not} use @code{window-system} and
6208 @code{initial-window-system} as predicates or boolean flag variables,
6209 if you want to write code that works differently on text terminals and
6210 graphic displays. That is because @code{window-system} is not a good
6211 indicator of Emacs capabilities on a given display type. Instead, use
6212 @code{display-graphic-p} or any of the other @code{display-*-p}
6213 predicates described in @ref{Display Feature Testing}.
6215 @defvar window-setup-hook
6216 This variable is a normal hook which Emacs runs after handling the
6217 initialization files. Emacs runs this hook after it has completed
6218 loading your init file, the default initialization file (if
6219 any), and the terminal-specific Lisp code, and running the hook
6220 @code{term-setup-hook}.
6222 This hook is used for internal purposes: setting up communication with
6223 the window system, and creating the initial window. Users should not
6227 @node Bidirectional Display
6228 @section Bidirectional Display
6229 @cindex bidirectional display
6230 @cindex right-to-left text
6232 Emacs can display text written in scripts, such as Arabic, Farsi,
6233 and Hebrew, whose natural ordering for horizontal text display runs
6234 from right to left. Furthermore, segments of Latin script and digits
6235 embedded in right-to-left text are displayed left-to-right, while
6236 segments of right-to-left script embedded in left-to-right text
6237 (e.g.@: Arabic or Hebrew text in comments or strings in a program
6238 source file) are appropriately displayed right-to-left. We call such
6239 mixtures of left-to-right and right-to-left text @dfn{bidirectional
6240 text}. This section describes the facilities and options for editing
6241 and displaying bidirectional text.
6243 @cindex logical order
6244 @cindex reading order
6245 @cindex visual order
6246 @cindex unicode bidirectional algorithm
6247 @cindex bidirectional reordering
6248 Text is stored in Emacs buffers and strings in @dfn{logical} (or
6249 @dfn{reading}) order, i.e.@: the order in which a human would read
6250 each character. In right-to-left and bidirectional text, the order in
6251 which characters are displayed on the screen (called @dfn{visual
6252 order}) is not the same as logical order; the characters' screen
6253 positions do not increase monotonically with string or buffer
6254 position. In performing this @dfn{bidirectional reordering}, Emacs
6255 follows the Unicode Bidirectional Algorithm (a.k.a.@: @acronym{UBA}),
6256 which is described in Annex #9 of the Unicode standard
6257 (@url{http://www.unicode.org/reports/tr9/}). Emacs provides a ``Full
6258 Bidirectionality'' class implementation of the @acronym{UBA}.
6260 @defvar bidi-display-reordering
6261 If the value of this buffer-local variable is non-@code{nil} (the
6262 default), Emacs performs bidirectional reordering for display. The
6263 reordering affects buffer text, as well as display strings and overlay
6264 strings from text and overlay properties in the buffer (@pxref{Overlay
6265 Properties}, and @pxref{Display Property}). If the value is
6266 @code{nil}, Emacs does not perform bidirectional reordering in the
6269 The default value of @code{bidi-display-reordering} controls the
6270 reordering of strings which are not directly supplied by a buffer,
6271 including the text displayed in mode lines (@pxref{Mode Line Format})
6272 and header lines (@pxref{Header Lines}).
6275 @cindex unibyte buffers, and bidi reordering
6276 Emacs never reorders the text of a unibyte buffer, even if
6277 @code{bidi-display-reordering} is non-@code{nil} in the buffer. This
6278 is because unibyte buffers contain raw bytes, not characters, and thus
6279 lack the directionality properties required for reordering.
6280 Therefore, to test whether text in a buffer will be reordered for
6281 display, it is not enough to test the value of
6282 @code{bidi-display-reordering} alone. The correct test is this:
6285 (if (and enable-multibyte-characters
6286 bidi-display-reordering)
6287 ;; Buffer is being reordered for display
6291 However, unibyte display and overlay strings @emph{are} reordered if
6292 their parent buffer is reordered. This is because plain-@sc{ascii}
6293 strings are stored by Emacs as unibyte strings. If a unibyte display
6294 or overlay string includes non-@sc{ascii} characters, these characters
6295 are assumed to have left-to-right direction.
6297 @cindex display properties, and bidi reordering of text
6298 Text covered by @code{display} text properties, by overlays with
6299 @code{display} properties whose value is a string, and by any other
6300 properties that replace buffer text, is treated as a single unit when
6301 it is reordered for display. That is, the entire chunk of text
6302 covered by these properties is reordered together. Moreover, the
6303 bidirectional properties of the characters in such a chunk of text are
6304 ignored, and Emacs reorders them as if they were replaced with a
6305 single character @code{U+FFFC}, known as the @dfn{Object Replacement
6306 Character}. This means that placing a display property over a portion
6307 of text may change the way that the surrounding text is reordered for
6308 display. To prevent this unexpected effect, always place such
6309 properties on text whose directionality is identical with text that
6312 @cindex base direction of a paragraph
6313 Each paragraph of bidirectional text has a @dfn{base direction},
6314 either right-to-left or left-to-right. Left-to-right paragraphs are
6315 displayed beginning at the left margin of the window, and are
6316 truncated or continued when the text reaches the right margin.
6317 Right-to-left paragraphs are displayed beginning at the right margin,
6318 and are continued or truncated at the left margin.
6320 By default, Emacs determines the base direction of each paragraph by
6321 looking at the text at its beginning. The precise method of
6322 determining the base direction is specified by the @acronym{UBA}; in a
6323 nutshell, the first character in a paragraph that has an explicit
6324 directionality determines the base direction of the paragraph.
6325 However, sometimes a buffer may need to force a certain base direction
6326 for its paragraphs. For example, buffers containing program source
6327 code should force all paragraphs to be displayed left-to-right. You
6328 can use following variable to do this:
6330 @defvar bidi-paragraph-direction
6331 If the value of this buffer-local variable is the symbol
6332 @code{right-to-left} or @code{left-to-right}, all paragraphs in the
6333 buffer are assumed to have that specified direction. Any other value
6334 is equivalent to @code{nil} (the default), which means to determine
6335 the base direction of each paragraph from its contents.
6337 @cindex @code{prog-mode}, and @code{bidi-paragraph-direction}
6338 Modes for program source code should set this to @code{left-to-right}.
6339 Prog mode does this by default, so modes derived from Prog mode do not
6340 need to set this explicitly (@pxref{Basic Major Modes}).
6343 @defun current-bidi-paragraph-direction &optional buffer
6344 This function returns the paragraph direction at point in the named
6345 @var{buffer}. The returned value is a symbol, either
6346 @code{left-to-right} or @code{right-to-left}. If @var{buffer} is
6347 omitted or @code{nil}, it defaults to the current buffer. If the
6348 buffer-local value of the variable @code{bidi-paragraph-direction} is
6349 non-@code{nil}, the returned value will be identical to that value;
6350 otherwise, the returned value reflects the paragraph direction
6351 determined dynamically by Emacs. For buffers whose value of
6352 @code{bidi-display-reordering} is @code{nil} as well as unibyte
6353 buffers, this function always returns @code{left-to-right}.
6356 @cindex layout on display, and bidirectional text
6357 @cindex jumbled display of bidirectional text
6358 @cindex concatenating bidirectional strings
6359 Bidirectional reordering can have surprising and unpleasant effects
6360 when two strings with bidirectional content are juxtaposed in a
6361 buffer, or otherwise programmatically concatenated into a string of
6362 text. A typical problematic case is when a buffer consists of
6363 sequences of text ``fields'' separated by whitespace or punctuation
6364 characters, like Buffer Menu mode or Rmail Summary Mode. Because the
6365 punctuation characters used as separators have @dfn{weak
6366 directionality}, they take on the directionality of surrounding text.
6367 As result, a numeric field that follows a field with bidirectional
6368 content can be displayed @emph{to the left} of the preceding field,
6369 messing up the expected layout. There are several ways to avoid this
6374 Append the special character @code{U+200E}, LEFT-TO-RIGHT MARK, or
6375 @acronym{LRM}, to the end of each field that may have bidirectional
6376 content, or prepend it to the beginning of the following field. The
6377 function @code{bidi-string-mark-left-to-right}, described below, comes
6378 in handy for this purpose. (In a right-to-left paragraph, use
6379 @code{U+200F}, RIGHT-TO-LEFT MARK, or @acronym{RLM}, instead.) This
6380 is one of the solutions recommended by the UBA.
6383 Include the tab character in the field separator. The tab character
6384 plays the role of @dfn{segment separator} in bidirectional reordering,
6385 causing the text on either side to be reordered separately.
6387 @cindex @code{space} display spec, and bidirectional text
6389 Separate fields with a @code{display} property or overlay with a
6390 property value of the form @code{(space . PROPS)} (@pxref{Specified
6391 Space}). Emacs treats this display specification as a @dfn{paragraph
6392 separator}, and reorders the text on either side separately.
6395 @defun bidi-string-mark-left-to-right string
6396 This function returns its argument @var{string}, possibly modified,
6397 such that the result can be safely concatenated with another string,
6398 or juxtaposed with another string in a buffer, without disrupting the
6399 relative layout of this string and the next one on display. If the
6400 string returned by this function is displayed as part of a
6401 left-to-right paragraph, it will always appear on display to the left
6402 of the text that follows it. The function works by examining the
6403 characters of its argument, and if any of those characters could cause
6404 reordering on display, the function appends the @acronym{LRM}
6405 character to the string. The appended @acronym{LRM} character is made
6406 invisible by giving it an @code{invisible} text property of @code{t}
6407 (@pxref{Invisible Text}).
6410 The reordering algorithm uses the bidirectional properties of the
6411 characters stored as their @code{bidi-class} property
6412 (@pxref{Character Properties}). Lisp programs can change these
6413 properties by calling the @code{put-char-code-property} function.
6414 However, doing this requires a thorough understanding of the
6415 @acronym{UBA}, and is therefore not recommended. Any changes to the
6416 bidirectional properties of a character have global effect: they
6417 affect all Emacs frames and windows.
6419 Similarly, the @code{mirroring} property is used to display the
6420 appropriate mirrored character in the reordered text. Lisp programs
6421 can affect the mirrored display by changing this property. Again, any
6422 such changes affect all of Emacs display.