2 @c This is part of the GNU Emacs Lisp Reference Manual.
3 @c Copyright (C) 1990-1995, 1998-2014 Free Software Foundation, Inc.
4 @c See the file elisp.texi for copying conditions.
8 This chapter describes a number of features related to the display
9 that Emacs presents to the user.
12 * Refresh Screen:: Clearing the screen and redrawing everything on it.
13 * Forcing Redisplay:: Forcing redisplay.
14 * Truncation:: Folding or wrapping long text lines.
15 * The Echo Area:: Displaying messages at the bottom of the screen.
16 * Warnings:: Displaying warning messages for the user.
17 * Invisible Text:: Hiding part of the buffer text.
18 * Selective Display:: Hiding part of the buffer text (the old way).
19 * Temporary Displays:: Displays that go away automatically.
20 * Overlays:: Use overlays to highlight parts of the buffer.
21 * Size of Displayed Text:: How large displayed text is.
22 * Line Height:: Controlling the height of lines.
23 * Faces:: A face defines a graphics style for text characters:
25 * Fringes:: Controlling window fringes.
26 * Scroll Bars:: Controlling vertical scroll bars.
27 * Window Dividers:: Separating windows visually.
28 * Display Property:: Enabling special display features.
29 * Images:: Displaying images in Emacs buffers.
30 * Buttons:: Adding clickable buttons to Emacs buffers.
31 * Abstract Display:: Emacs's Widget for Object Collections.
32 * Blinking:: How Emacs shows the matching open parenthesis.
33 * Character Display:: How Emacs displays individual characters.
34 * Beeping:: Audible signal to the user.
35 * Window Systems:: Which window system is being used.
36 * Bidirectional Display:: Display of bidirectional scripts, such as
41 @section Refreshing the Screen
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 @defvar pre-redisplay-function
122 A function run just before redisplay. It is called with one argument,
123 the set of windows to redisplay.
126 Although @code{redisplay} tries immediately to redisplay, it does
127 not change how Emacs decides which parts of its frame(s) to redisplay.
128 By contrast, the following function adds certain windows to the
129 pending redisplay work (as if their contents had completely changed),
130 but does not immediately try to perform redisplay.
132 @defun force-window-update &optional object
133 This function forces some or all windows to be updated the next time
134 Emacs does a redisplay. If @var{object} is a window, that window is
135 to be updated. If @var{object} is a buffer or buffer name, all
136 windows displaying that buffer are to be updated. If @var{object} is
137 @code{nil} (or omitted), all windows are to be updated.
139 This function does not do a redisplay immediately; Emacs does that as
140 it waits for input, or when the function @code{redisplay} is called.
145 @cindex line wrapping
146 @cindex line truncation
147 @cindex continuation lines
148 @cindex @samp{$} in display
149 @cindex @samp{\} in display
151 When a line of text extends beyond the right edge of a window, Emacs
152 can @dfn{continue} the line (make it ``wrap'' to the next screen
153 line), or @dfn{truncate} the line (limit it to one screen line). The
154 additional screen lines used to display a long text line are called
155 @dfn{continuation} lines. Continuation is not the same as filling;
156 continuation happens on the screen only, not in the buffer contents,
157 and it breaks a line precisely at the right margin, not at a word
158 boundary. @xref{Filling}.
160 On a graphical display, tiny arrow images in the window fringes
161 indicate truncated and continued lines (@pxref{Fringes}). On a text
162 terminal, a @samp{$} in the rightmost column of the window indicates
163 truncation; a @samp{\} on the rightmost column indicates a line that
164 ``wraps''. (The display table can specify alternate characters to use
165 for this; @pxref{Display Tables}).
167 @defopt truncate-lines
168 If this buffer-local variable is non-@code{nil}, lines that extend
169 beyond the right edge of the window are truncated; otherwise, they are
170 continued. As a special exception, the variable
171 @code{truncate-partial-width-windows} takes precedence in
172 @dfn{partial-width} windows (i.e., windows that do not occupy the
176 @defopt truncate-partial-width-windows
177 @cindex partial-width windows
178 This variable controls line truncation in @dfn{partial-width} windows.
179 A partial-width window is one that does not occupy the entire frame
180 width (@pxref{Splitting Windows}). If the value is @code{nil}, line
181 truncation is determined by the variable @code{truncate-lines} (see
182 above). If the value is an integer @var{n}, lines are truncated if
183 the partial-width window has fewer than @var{n} columns, regardless of
184 the value of @code{truncate-lines}; if the partial-width window has
185 @var{n} or more columns, line truncation is determined by
186 @code{truncate-lines}. For any other non-@code{nil} value, lines are
187 truncated in every partial-width window, regardless of the value of
188 @code{truncate-lines}.
191 When horizontal scrolling (@pxref{Horizontal Scrolling}) is in use in
192 a window, that forces truncation.
195 If this buffer-local variable is non-@code{nil}, it defines a
196 @dfn{wrap prefix} which Emacs displays at the start of every
197 continuation line. (If lines are truncated, @code{wrap-prefix} is
198 never used.) Its value may be a string or an image (@pxref{Other
199 Display Specs}), or a stretch of whitespace such as specified by the
200 @code{:width} or @code{:align-to} display properties (@pxref{Specified
201 Space}). The value is interpreted in the same way as a @code{display}
202 text property. @xref{Display Property}.
204 A wrap prefix may also be specified for regions of text, using the
205 @code{wrap-prefix} text or overlay property. This takes precedence
206 over the @code{wrap-prefix} variable. @xref{Special Properties}.
210 If this buffer-local variable is non-@code{nil}, it defines a
211 @dfn{line prefix} which Emacs displays at the start of every
212 non-continuation line. Its value may be a string or an image
213 (@pxref{Other Display Specs}), or a stretch of whitespace such as
214 specified by the @code{:width} or @code{:align-to} display properties
215 (@pxref{Specified Space}). The value is interpreted in the same way
216 as a @code{display} text property. @xref{Display Property}.
218 A line prefix may also be specified for regions of text using the
219 @code{line-prefix} text or overlay property. This takes precedence
220 over the @code{line-prefix} variable. @xref{Special Properties}.
224 If your buffer contains only very short lines, you might find it
225 advisable to set @code{cache-long-scans} to @code{nil}.
227 @defvar cache-long-scans
228 If this variable is non-@code{nil} (the default), various indentation
229 and motion functions, and Emacs redisplay, cache the results of
230 scanning the buffer, and consult the cache to avoid rescanning regions
231 of the buffer unless they are modified.
233 Turning off the cache speeds up processing of short lines somewhat.
235 This variable is automatically buffer-local in every buffer.
240 @section The Echo Area
241 @cindex error display
244 @c FIXME: Why not use @xref{Minibuffers} directly? --xfq
245 The @dfn{echo area} is used for displaying error messages
246 (@pxref{Errors}), for messages made with the @code{message} primitive,
247 and for echoing keystrokes. It is not the same as the minibuffer,
248 despite the fact that the minibuffer appears (when active) in the same
249 place on the screen as the echo area. @xref{Minibuffer,, The
250 Minibuffer, emacs, The GNU Emacs Manual}.
252 Apart from the functions documented in this section, you can print
253 Lisp objects to the echo area by specifying @code{t} as the output
254 stream. @xref{Output Streams}.
257 * Displaying Messages:: Explicitly displaying text in the echo area.
258 * Progress:: Informing user about progress of a long operation.
259 * Logging Messages:: Echo area messages are logged for the user.
260 * Echo Area Customization:: Controlling the echo area.
263 @node Displaying Messages
264 @subsection Displaying Messages in the Echo Area
265 @cindex display message in echo area
267 This section describes the standard functions for displaying
268 messages in the echo area.
270 @defun message format-string &rest arguments
271 This function displays a message in the echo area.
272 @var{format-string} is a format string, and @var{arguments} are the
273 objects for its format specifications, like in the @code{format}
274 function (@pxref{Formatting Strings}). The resulting formatted string
275 is displayed in the echo area; if it contains @code{face} text
276 properties, it is displayed with the specified faces (@pxref{Faces}).
277 The string is also added to the @file{*Messages*} buffer, but without
278 text properties (@pxref{Logging Messages}).
280 In batch mode, the message is printed to the standard error stream,
281 followed by a newline.
283 If @var{format-string} is @code{nil} or the empty string,
284 @code{message} clears the echo area; if the echo area has been
285 expanded automatically, this brings it back to its normal size. If
286 the minibuffer is active, this brings the minibuffer contents back
287 onto the screen immediately.
291 (message "Minibuffer depth is %d."
293 @print{} Minibuffer depth is 0.
294 @result{} "Minibuffer depth is 0."
298 ---------- Echo Area ----------
299 Minibuffer depth is 0.
300 ---------- Echo Area ----------
304 To automatically display a message in the echo area or in a pop-buffer,
305 depending on its size, use @code{display-message-or-buffer} (see below).
308 @defmac with-temp-message message &rest body
309 This construct displays a message in the echo area temporarily, during
310 the execution of @var{body}. It displays @var{message}, executes
311 @var{body}, then returns the value of the last body form while restoring
312 the previous echo area contents.
315 @defun message-or-box format-string &rest arguments
316 This function displays a message like @code{message}, but may display it
317 in a dialog box instead of the echo area. If this function is called in
318 a command that was invoked using the mouse---more precisely, if
319 @code{last-nonmenu-event} (@pxref{Command Loop Info}) is either
320 @code{nil} or a list---then it uses a dialog box or pop-up menu to
321 display the message. Otherwise, it uses the echo area. (This is the
322 same criterion that @code{y-or-n-p} uses to make a similar decision; see
323 @ref{Yes-or-No Queries}.)
325 You can force use of the mouse or of the echo area by binding
326 @code{last-nonmenu-event} to a suitable value around the call.
329 @defun message-box format-string &rest arguments
331 This function displays a message like @code{message}, but uses a dialog
332 box (or a pop-up menu) whenever that is possible. If it is impossible
333 to use a dialog box or pop-up menu, because the terminal does not
334 support them, then @code{message-box} uses the echo area, like
338 @defun display-message-or-buffer message &optional buffer-name not-this-window frame
339 This function displays the message @var{message}, which may be either a
340 string or a buffer. If it is shorter than the maximum height of the
341 echo area, as defined by @code{max-mini-window-height}, it is displayed
342 in the echo area, using @code{message}. Otherwise,
343 @code{display-buffer} is used to show it in a pop-up buffer.
345 Returns either the string shown in the echo area, or when a pop-up
346 buffer is used, the window used to display it.
348 If @var{message} is a string, then the optional argument
349 @var{buffer-name} is the name of the buffer used to display it when a
350 pop-up buffer is used, defaulting to @file{*Message*}. In the case
351 where @var{message} is a string and displayed in the echo area, it is
352 not specified whether the contents are inserted into the buffer anyway.
354 The optional arguments @var{not-this-window} and @var{frame} are as for
355 @code{display-buffer}, and only used if a buffer is displayed.
358 @defun current-message
359 This function returns the message currently being displayed in the
360 echo area, or @code{nil} if there is none.
364 @subsection Reporting Operation Progress
365 @cindex progress reporting
367 When an operation can take a while to finish, you should inform the
368 user about the progress it makes. This way the user can estimate
369 remaining time and clearly see that Emacs is busy working, not hung.
370 A convenient way to do this is to use a @dfn{progress reporter}.
372 Here is a working example that does nothing useful:
375 (let ((progress-reporter
376 (make-progress-reporter "Collecting mana for Emacs..."
380 (progress-reporter-update progress-reporter k))
381 (progress-reporter-done progress-reporter))
384 @defun make-progress-reporter message &optional min-value max-value current-value min-change min-time
385 This function creates and returns a progress reporter object, which
386 you will use as an argument for the other functions listed below. The
387 idea is to precompute as much data as possible to make progress
390 When this progress reporter is subsequently used, it will display
391 @var{message} in the echo area, followed by progress percentage.
392 @var{message} is treated as a simple string. If you need it to depend
393 on a filename, for instance, use @code{format} before calling this
396 The arguments @var{min-value} and @var{max-value} should be numbers
397 standing for the starting and final states of the operation. For
398 instance, an operation that ``scans'' a buffer should set these to the
399 results of @code{point-min} and @code{point-max} correspondingly.
400 @var{max-value} should be greater than @var{min-value}.
402 Alternatively, you can set @var{min-value} and @var{max-value} to
403 @code{nil}. In that case, the progress reporter does not report
404 process percentages; it instead displays a ``spinner'' that rotates a
405 notch each time you update the progress reporter.
407 If @var{min-value} and @var{max-value} are numbers, you can give the
408 argument @var{current-value} a numerical value specifying the initial
409 progress; if omitted, this defaults to @var{min-value}.
411 The remaining arguments control the rate of echo area updates. The
412 progress reporter will wait for at least @var{min-change} more
413 percents of the operation to be completed before printing next
414 message; the default is one percent. @var{min-time} specifies the
415 minimum time in seconds to pass between successive prints; the default
416 is 0.2 seconds. (On some operating systems, the progress reporter may
417 handle fractions of seconds with varying precision).
419 This function calls @code{progress-reporter-update}, so the first
420 message is printed immediately.
423 @defun progress-reporter-update reporter &optional value
424 This function does the main work of reporting progress of your
425 operation. It displays the message of @var{reporter}, followed by
426 progress percentage determined by @var{value}. If percentage is zero,
427 or close enough according to the @var{min-change} and @var{min-time}
428 arguments, then it is omitted from the output.
430 @var{reporter} must be the result of a call to
431 @code{make-progress-reporter}. @var{value} specifies the current
432 state of your operation and must be between @var{min-value} and
433 @var{max-value} (inclusive) as passed to
434 @code{make-progress-reporter}. For instance, if you scan a buffer,
435 then @var{value} should be the result of a call to @code{point}.
437 This function respects @var{min-change} and @var{min-time} as passed
438 to @code{make-progress-reporter} and so does not output new messages
439 on every invocation. It is thus very fast and normally you should not
440 try to reduce the number of calls to it: resulting overhead will most
441 likely negate your effort.
444 @defun progress-reporter-force-update reporter &optional value new-message
445 This function is similar to @code{progress-reporter-update} except
446 that it prints a message in the echo area unconditionally.
448 The first two arguments have the same meaning as for
449 @code{progress-reporter-update}. Optional @var{new-message} allows
450 you to change the message of the @var{reporter}. Since this function
451 always updates the echo area, such a change will be immediately
452 presented to the user.
455 @defun progress-reporter-done reporter
456 This function should be called when the operation is finished. It
457 prints the message of @var{reporter} followed by word ``done'' in the
460 You should always call this function and not hope for
461 @code{progress-reporter-update} to print ``100%''. Firstly, it may
462 never print it, there are many good reasons for this not to happen.
463 Secondly, ``done'' is more explicit.
466 @defmac dotimes-with-progress-reporter (var count [result]) message body@dots{}
467 This is a convenience macro that works the same way as @code{dotimes}
468 does, but also reports loop progress using the functions described
469 above. It allows you to save some typing.
471 You can rewrite the example in the beginning of this node using
475 (dotimes-with-progress-reporter
477 "Collecting some mana for Emacs..."
482 @node Logging Messages
483 @subsection Logging Messages in @file{*Messages*}
484 @cindex logging echo-area messages
486 Almost all the messages displayed in the echo area are also recorded
487 in the @file{*Messages*} buffer so that the user can refer back to
488 them. This includes all the messages that are output with
489 @code{message}. By default, this buffer is read-only and uses the major
490 mode @code{messages-buffer-mode}. Nothing prevents the user from
491 killing the @file{*Messages*} buffer, but the next display of a message
492 recreates it. Any Lisp code that needs to access the
493 @file{*Messages*} buffer directly and wants to ensure that it exists
494 should use the function @code{messages-buffer}.
496 @defun messages-buffer
497 This function returns the @file{*Messages*} buffer. If it does not
498 exist, it creates it, and switches it to @code{messages-buffer-mode}.
501 @defopt message-log-max
502 This variable specifies how many lines to keep in the @file{*Messages*}
503 buffer. The value @code{t} means there is no limit on how many lines to
504 keep. The value @code{nil} disables message logging entirely. Here's
505 how to display a message and prevent it from being logged:
508 (let (message-log-max)
513 To make @file{*Messages*} more convenient for the user, the logging
514 facility combines successive identical messages. It also combines
515 successive related messages for the sake of two cases: question
516 followed by answer, and a series of progress messages.
518 A ``question followed by an answer'' means two messages like the
519 ones produced by @code{y-or-n-p}: the first is @samp{@var{question}},
520 and the second is @samp{@var{question}...@var{answer}}. The first
521 message conveys no additional information beyond what's in the second,
522 so logging the second message discards the first from the log.
524 A ``series of progress messages'' means successive messages like
525 those produced by @code{make-progress-reporter}. They have the form
526 @samp{@var{base}...@var{how-far}}, where @var{base} is the same each
527 time, while @var{how-far} varies. Logging each message in the series
528 discards the previous one, provided they are consecutive.
530 The functions @code{make-progress-reporter} and @code{y-or-n-p}
531 don't have to do anything special to activate the message log
532 combination feature. It operates whenever two consecutive messages
533 are logged that share a common prefix ending in @samp{...}.
535 @node Echo Area Customization
536 @subsection Echo Area Customization
538 These variables control details of how the echo area works.
540 @defvar cursor-in-echo-area
541 This variable controls where the cursor appears when a message is
542 displayed in the echo area. If it is non-@code{nil}, then the cursor
543 appears at the end of the message. Otherwise, the cursor appears at
544 point---not in the echo area at all.
546 The value is normally @code{nil}; Lisp programs bind it to @code{t}
547 for brief periods of time.
550 @defvar echo-area-clear-hook
551 This normal hook is run whenever the echo area is cleared---either by
552 @code{(message nil)} or for any other reason.
555 @defopt echo-keystrokes
556 This variable determines how much time should elapse before command
557 characters echo. Its value must be a number, and specifies the
558 number of seconds to wait before echoing. If the user types a prefix
559 key (such as @kbd{C-x}) and then delays this many seconds before
560 continuing, the prefix key is echoed in the echo area. (Once echoing
561 begins in a key sequence, all subsequent characters in the same key
562 sequence are echoed immediately.)
564 If the value is zero, then command input is not echoed.
567 @defvar message-truncate-lines
568 Normally, displaying a long message resizes the echo area to display
569 the entire message. But if the variable @code{message-truncate-lines}
570 is non-@code{nil}, the echo area does not resize, and the message is
574 The variable @code{max-mini-window-height}, which specifies the
575 maximum height for resizing minibuffer windows, also applies to the
576 echo area (which is really a special use of the minibuffer window;
577 @pxref{Minibuffer Misc}).
580 @section Reporting Warnings
583 @dfn{Warnings} are a facility for a program to inform the user of a
584 possible problem, but continue running.
587 * Warning Basics:: Warnings concepts and functions to report them.
588 * Warning Variables:: Variables programs bind to customize their warnings.
589 * Warning Options:: Variables users set to control display of warnings.
590 * Delayed Warnings:: Deferring a warning until the end of a command.
594 @subsection Warning Basics
595 @cindex severity level
597 Every warning has a textual message, which explains the problem for
598 the user, and a @dfn{severity level} which is a symbol. Here are the
599 possible severity levels, in order of decreasing severity, and their
604 A problem that will seriously impair Emacs operation soon
605 if you do not attend to it promptly.
607 A report of data or circumstances that are inherently wrong.
609 A report of data or circumstances that are not inherently wrong, but
610 raise suspicion of a possible problem.
612 A report of information that may be useful if you are debugging.
615 When your program encounters invalid input data, it can either
616 signal a Lisp error by calling @code{error} or @code{signal} or report
617 a warning with severity @code{:error}. Signaling a Lisp error is the
618 easiest thing to do, but it means the program cannot continue
619 processing. If you want to take the trouble to implement a way to
620 continue processing despite the bad data, then reporting a warning of
621 severity @code{:error} is the right way to inform the user of the
622 problem. For instance, the Emacs Lisp byte compiler can report an
623 error that way and continue compiling other functions. (If the
624 program signals a Lisp error and then handles it with
625 @code{condition-case}, the user won't see the error message; it could
626 show the message to the user by reporting it as a warning.)
628 @c FIXME: Why use "(bytecomp)" instead of "'bytecomp" or simply
629 @c "bytecomp" here? The parens are part of warning-type-format but
630 @c not part of the warning type. --xfq
632 Each warning has a @dfn{warning type} to classify it. The type is a
633 list of symbols. The first symbol should be the custom group that you
634 use for the program's user options. For example, byte compiler
635 warnings use the warning type @code{(bytecomp)}. You can also
636 subcategorize the warnings, if you wish, by using more symbols in the
639 @defun display-warning type message &optional level buffer-name
640 This function reports a warning, using @var{message} as the message
641 and @var{type} as the warning type. @var{level} should be the
642 severity level, with @code{:warning} being the default.
644 @var{buffer-name}, if non-@code{nil}, specifies the name of the buffer
645 for logging the warning. By default, it is @file{*Warnings*}.
648 @defun lwarn type level message &rest args
649 This function reports a warning using the value of @code{(format
650 @var{message} @var{args}...)} as the message in the @file{*Warnings*}
651 buffer. In other respects it is equivalent to @code{display-warning}.
654 @defun warn message &rest args
655 This function reports a warning using the value of @code{(format
656 @var{message} @var{args}...)} as the message, @code{(emacs)} as the
657 type, and @code{:warning} as the severity level. It exists for
658 compatibility only; we recommend not using it, because you should
659 specify a specific warning type.
662 @node Warning Variables
663 @subsection Warning Variables
665 Programs can customize how their warnings appear by binding
666 the variables described in this section.
668 @defvar warning-levels
669 This list defines the meaning and severity order of the warning
670 severity levels. Each element defines one severity level,
671 and they are arranged in order of decreasing severity.
673 Each element has the form @code{(@var{level} @var{string}
674 @var{function})}, where @var{level} is the severity level it defines.
675 @var{string} specifies the textual description of this level.
676 @var{string} should use @samp{%s} to specify where to put the warning
677 type information, or it can omit the @samp{%s} so as not to include
680 The optional @var{function}, if non-@code{nil}, is a function to call
681 with no arguments, to get the user's attention.
683 Normally you should not change the value of this variable.
686 @defvar warning-prefix-function
687 If non-@code{nil}, the value is a function to generate prefix text for
688 warnings. Programs can bind the variable to a suitable function.
689 @code{display-warning} calls this function with the warnings buffer
690 current, and the function can insert text in it. That text becomes
691 the beginning of the warning message.
693 The function is called with two arguments, the severity level and its
694 entry in @code{warning-levels}. It should return a list to use as the
695 entry (this value need not be an actual member of
696 @code{warning-levels}). By constructing this value, the function can
697 change the severity of the warning, or specify different handling for
698 a given severity level.
700 If the variable's value is @code{nil} then there is no function
704 @defvar warning-series
705 Programs can bind this variable to @code{t} to say that the next
706 warning should begin a series. When several warnings form a series,
707 that means to leave point on the first warning of the series, rather
708 than keep moving it for each warning so that it appears on the last one.
709 The series ends when the local binding is unbound and
710 @code{warning-series} becomes @code{nil} again.
712 The value can also be a symbol with a function definition. That is
713 equivalent to @code{t}, except that the next warning will also call
714 the function with no arguments with the warnings buffer current. The
715 function can insert text which will serve as a header for the series
718 Once a series has begun, the value is a marker which points to the
719 buffer position in the warnings buffer of the start of the series.
721 The variable's normal value is @code{nil}, which means to handle
722 each warning separately.
725 @defvar warning-fill-prefix
726 When this variable is non-@code{nil}, it specifies a fill prefix to
727 use for filling each warning's text.
730 @defvar warning-type-format
731 This variable specifies the format for displaying the warning type
732 in the warning message. The result of formatting the type this way
733 gets included in the message under the control of the string in the
734 entry in @code{warning-levels}. The default value is @code{" (%s)"}.
735 If you bind it to @code{""} then the warning type won't appear at
739 @node Warning Options
740 @subsection Warning Options
742 These variables are used by users to control what happens
743 when a Lisp program reports a warning.
745 @defopt warning-minimum-level
746 This user option specifies the minimum severity level that should be
747 shown immediately to the user. The default is @code{:warning}, which
748 means to immediately display all warnings except @code{:debug}
752 @defopt warning-minimum-log-level
753 This user option specifies the minimum severity level that should be
754 logged in the warnings buffer. The default is @code{:warning}, which
755 means to log all warnings except @code{:debug} warnings.
758 @defopt warning-suppress-types
759 This list specifies which warning types should not be displayed
760 immediately for the user. Each element of the list should be a list
761 of symbols. If its elements match the first elements in a warning
762 type, then that warning is not displayed immediately.
765 @defopt warning-suppress-log-types
766 This list specifies which warning types should not be logged in the
767 warnings buffer. Each element of the list should be a list of
768 symbols. If it matches the first few elements in a warning type, then
769 that warning is not logged.
772 @node Delayed Warnings
773 @subsection Delayed Warnings
775 Sometimes, you may wish to avoid showing a warning while a command is
776 running, and only show it only after the end of the command. You can
777 use the variable @code{delayed-warnings-list} for this.
779 @defvar delayed-warnings-list
780 The value of this variable is a list of warnings to be displayed after
781 the current command has finished. Each element must be a list
784 (@var{type} @var{message} [@var{level} [@var{buffer-name}]])
788 with the same form, and the same meanings, as the argument list of
789 @code{display-warning} (@pxref{Warning Basics}). Immediately after
790 running @code{post-command-hook} (@pxref{Command Overview}), the Emacs
791 command loop displays all the warnings specified by this variable,
792 then resets it to @code{nil}.
795 Programs which need to further customize the delayed warnings
796 mechanism can change the variable @code{delayed-warnings-hook}:
798 @defvar delayed-warnings-hook
799 This is a normal hook which is run by the Emacs command loop, after
800 @code{post-command-hook}, in order to to process and display delayed
803 Its default value is a list of two functions:
806 (collapse-delayed-warnings display-delayed-warnings)
809 @findex collapse-delayed-warnings
810 @findex display-delayed-warnings
812 The function @code{collapse-delayed-warnings} removes repeated entries
813 from @code{delayed-warnings-list}. The function
814 @code{display-delayed-warnings} calls @code{display-warning} on each
815 of the entries in @code{delayed-warnings-list}, in turn, and then sets
816 @code{delayed-warnings-list} to @code{nil}.
820 @section Invisible Text
822 @cindex invisible text
823 You can make characters @dfn{invisible}, so that they do not appear on
824 the screen, with the @code{invisible} property. This can be either a
825 text property (@pxref{Text Properties}) or an overlay property
826 (@pxref{Overlays}). Cursor motion also partly ignores these
827 characters; if the command loop finds that point is inside a range of
828 invisible text after a command, it relocates point to the other side
831 In the simplest case, any non-@code{nil} @code{invisible} property makes
832 a character invisible. This is the default case---if you don't alter
833 the default value of @code{buffer-invisibility-spec}, this is how the
834 @code{invisible} property works. You should normally use @code{t}
835 as the value of the @code{invisible} property if you don't plan
836 to set @code{buffer-invisibility-spec} yourself.
838 More generally, you can use the variable @code{buffer-invisibility-spec}
839 to control which values of the @code{invisible} property make text
840 invisible. This permits you to classify the text into different subsets
841 in advance, by giving them different @code{invisible} values, and
842 subsequently make various subsets visible or invisible by changing the
843 value of @code{buffer-invisibility-spec}.
845 Controlling visibility with @code{buffer-invisibility-spec} is
846 especially useful in a program to display the list of entries in a
847 database. It permits the implementation of convenient filtering
848 commands to view just a part of the entries in the database. Setting
849 this variable is very fast, much faster than scanning all the text in
850 the buffer looking for properties to change.
852 @defvar buffer-invisibility-spec
853 This variable specifies which kinds of @code{invisible} properties
854 actually make a character invisible. Setting this variable makes it
859 A character is invisible if its @code{invisible} property is
860 non-@code{nil}. This is the default.
863 Each element of the list specifies a criterion for invisibility; if a
864 character's @code{invisible} property fits any one of these criteria,
865 the character is invisible. The list can have two kinds of elements:
869 A character is invisible if its @code{invisible} property value is
870 @var{atom} or if it is a list with @var{atom} as a member; comparison
871 is done with @code{eq}.
873 @item (@var{atom} . t)
874 A character is invisible if its @code{invisible} property value is
875 @var{atom} or if it is a list with @var{atom} as a member; comparison
876 is done with @code{eq}. Moreover, a sequence of such characters
877 displays as an ellipsis.
882 Two functions are specifically provided for adding elements to
883 @code{buffer-invisibility-spec} and removing elements from it.
885 @defun add-to-invisibility-spec element
886 This function adds the element @var{element} to
887 @code{buffer-invisibility-spec}. If @code{buffer-invisibility-spec}
888 was @code{t}, it changes to a list, @code{(t)}, so that text whose
889 @code{invisible} property is @code{t} remains invisible.
892 @defun remove-from-invisibility-spec element
893 This removes the element @var{element} from
894 @code{buffer-invisibility-spec}. This does nothing if @var{element}
898 A convention for use of @code{buffer-invisibility-spec} is that a
899 major mode should use the mode's own name as an element of
900 @code{buffer-invisibility-spec} and as the value of the
901 @code{invisible} property:
904 ;; @r{If you want to display an ellipsis:}
905 (add-to-invisibility-spec '(my-symbol . t))
906 ;; @r{If you don't want ellipsis:}
907 (add-to-invisibility-spec 'my-symbol)
909 (overlay-put (make-overlay beginning end)
910 'invisible 'my-symbol)
912 ;; @r{When done with the invisibility:}
913 (remove-from-invisibility-spec '(my-symbol . t))
914 ;; @r{Or respectively:}
915 (remove-from-invisibility-spec 'my-symbol)
918 You can check for invisibility using the following function:
920 @defun invisible-p pos-or-prop
921 If @var{pos-or-prop} is a marker or number, this function returns a
922 non-@code{nil} value if the text at that position is invisible.
924 If @var{pos-or-prop} is any other kind of Lisp object, that is taken
925 to mean a possible value of the @code{invisible} text or overlay
926 property. In that case, this function returns a non-@code{nil} value
927 if that value would cause text to become invisible, based on the
928 current value of @code{buffer-invisibility-spec}.
931 @vindex line-move-ignore-invisible
932 Ordinarily, functions that operate on text or move point do not care
933 whether the text is invisible. The user-level line motion commands
934 ignore invisible newlines if @code{line-move-ignore-invisible} is
935 non-@code{nil} (the default), but only because they are explicitly
938 However, if a command ends with point inside or at the boundary of
939 invisible text, the main editing loop relocates point to one of the
940 two ends of the invisible text. Emacs chooses the direction of
941 relocation so that it is the same as the overall movement direction of
942 the command; if in doubt, it prefers a position where an inserted char
943 would not inherit the @code{invisible} property. Additionally, if the
944 text is not replaced by an ellipsis and the command only moved within
945 the invisible text, then point is moved one extra character so as to
946 try and reflect the command's movement by a visible movement of the
949 Thus, if the command moved point back to an invisible range (with the usual
950 stickiness), Emacs moves point back to the beginning of that range. If the
951 command moved point forward into an invisible range, Emacs moves point forward
952 to the first visible character that follows the invisible text and then forward
955 Incremental search can make invisible overlays visible temporarily
956 and/or permanently when a match includes invisible text. To enable
957 this, the overlay should have a non-@code{nil}
958 @code{isearch-open-invisible} property. The property value should be a
959 function to be called with the overlay as an argument. This function
960 should make the overlay visible permanently; it is used when the match
961 overlaps the overlay on exit from the search.
963 During the search, such overlays are made temporarily visible by
964 temporarily modifying their invisible and intangible properties. If you
965 want this to be done differently for a certain overlay, give it an
966 @code{isearch-open-invisible-temporary} property which is a function.
967 The function is called with two arguments: the first is the overlay, and
968 the second is @code{nil} to make the overlay visible, or @code{t} to
969 make it invisible again.
971 @node Selective Display
972 @section Selective Display
973 @c @cindex selective display Duplicates selective-display
975 @dfn{Selective display} refers to a pair of related features for
976 hiding certain lines on the screen.
978 @cindex explicit selective display
979 The first variant, explicit selective display, was designed for use in a Lisp
980 program: it controls which lines are hidden by altering the text. This kind of
981 hiding is now obsolete; instead you can get the same effect with the
982 @code{invisible} property (@pxref{Invisible Text}).
984 In the second variant, the choice of lines to hide is made
985 automatically based on indentation. This variant is designed to be a
988 The way you control explicit selective display is by replacing a
989 newline (control-j) with a carriage return (control-m). The text that
990 was formerly a line following that newline is now hidden. Strictly
991 speaking, it is temporarily no longer a line at all, since only
992 newlines can separate lines; it is now part of the previous line.
994 Selective display does not directly affect editing commands. For
995 example, @kbd{C-f} (@code{forward-char}) moves point unhesitatingly
996 into hidden text. However, the replacement of newline characters with
997 carriage return characters affects some editing commands. For
998 example, @code{next-line} skips hidden lines, since it searches only
999 for newlines. Modes that use selective display can also define
1000 commands that take account of the newlines, or that control which
1001 parts of the text are hidden.
1003 When you write a selectively displayed buffer into a file, all the
1004 control-m's are output as newlines. This means that when you next read
1005 in the file, it looks OK, with nothing hidden. The selective display
1006 effect is seen only within Emacs.
1008 @defvar selective-display
1009 This buffer-local variable enables selective display. This means that
1010 lines, or portions of lines, may be made hidden.
1014 If the value of @code{selective-display} is @code{t}, then the character
1015 control-m marks the start of hidden text; the control-m, and the rest
1016 of the line following it, are not displayed. This is explicit selective
1020 If the value of @code{selective-display} is a positive integer, then
1021 lines that start with more than that many columns of indentation are not
1025 When some portion of a buffer is hidden, the vertical movement
1026 commands operate as if that portion did not exist, allowing a single
1027 @code{next-line} command to skip any number of hidden lines.
1028 However, character movement commands (such as @code{forward-char}) do
1029 not skip the hidden portion, and it is possible (if tricky) to insert
1030 or delete text in an hidden portion.
1032 In the examples below, we show the @emph{display appearance} of the
1033 buffer @code{foo}, which changes with the value of
1034 @code{selective-display}. The @emph{contents} of the buffer do not
1039 (setq selective-display nil)
1042 ---------- Buffer: foo ----------
1049 ---------- Buffer: foo ----------
1053 (setq selective-display 2)
1056 ---------- Buffer: foo ----------
1061 ---------- Buffer: foo ----------
1066 @defopt selective-display-ellipses
1067 If this buffer-local variable is non-@code{nil}, then Emacs displays
1068 @samp{@dots{}} at the end of a line that is followed by hidden text.
1069 This example is a continuation of the previous one.
1073 (setq selective-display-ellipses t)
1076 ---------- Buffer: foo ----------
1081 ---------- Buffer: foo ----------
1085 You can use a display table to substitute other text for the ellipsis
1086 (@samp{@dots{}}). @xref{Display Tables}.
1089 @node Temporary Displays
1090 @section Temporary Displays
1092 Temporary displays are used by Lisp programs to put output into a
1093 buffer and then present it to the user for perusal rather than for
1094 editing. Many help commands use this feature.
1096 @defmac with-output-to-temp-buffer buffer-name body@dots{}
1097 This function executes the forms in @var{body} while arranging to insert
1098 any output they print into the buffer named @var{buffer-name}, which is
1099 first created if necessary, and put into Help mode. (See the similar
1100 form @code{with-temp-buffer-window} below.) Finally, the buffer is
1101 displayed in some window, but that window is not selected.
1103 If the forms in @var{body} do not change the major mode in the output
1104 buffer, so that it is still Help mode at the end of their execution,
1105 then @code{with-output-to-temp-buffer} makes this buffer read-only at
1106 the end, and also scans it for function and variable names to make them
1107 into clickable cross-references. @xref{Docstring hyperlinks, , Tips for
1108 Documentation Strings}, in particular the item on hyperlinks in
1109 documentation strings, for more details.
1111 The string @var{buffer-name} specifies the temporary buffer, which need
1112 not already exist. The argument must be a string, not a buffer. The
1113 buffer is erased initially (with no questions asked), and it is marked
1114 as unmodified after @code{with-output-to-temp-buffer} exits.
1116 @code{with-output-to-temp-buffer} binds @code{standard-output} to the
1117 temporary buffer, then it evaluates the forms in @var{body}. Output
1118 using the Lisp output functions within @var{body} goes by default to
1119 that buffer (but screen display and messages in the echo area, although
1120 they are ``output'' in the general sense of the word, are not affected).
1121 @xref{Output Functions}.
1123 Several hooks are available for customizing the behavior
1124 of this construct; they are listed below.
1126 The value of the last form in @var{body} is returned.
1130 ---------- Buffer: foo ----------
1131 This is the contents of foo.
1132 ---------- Buffer: foo ----------
1136 (with-output-to-temp-buffer "foo"
1138 (print standard-output))
1139 @result{} #<buffer foo>
1141 ---------- Buffer: foo ----------
1147 ---------- Buffer: foo ----------
1152 @defopt temp-buffer-show-function
1153 If this variable is non-@code{nil}, @code{with-output-to-temp-buffer}
1154 calls it as a function to do the job of displaying a help buffer. The
1155 function gets one argument, which is the buffer it should display.
1157 It is a good idea for this function to run @code{temp-buffer-show-hook}
1158 just as @code{with-output-to-temp-buffer} normally would, inside of
1159 @code{save-selected-window} and with the chosen window and buffer
1163 @defvar temp-buffer-setup-hook
1164 This normal hook is run by @code{with-output-to-temp-buffer} before
1165 evaluating @var{body}. When the hook runs, the temporary buffer is
1166 current. This hook is normally set up with a function to put the
1167 buffer in Help mode.
1170 @defvar temp-buffer-show-hook
1171 This normal hook is run by @code{with-output-to-temp-buffer} after
1172 displaying the temporary buffer. When the hook runs, the temporary buffer
1173 is current, and the window it was displayed in is selected.
1176 @defmac with-temp-buffer-window buffer-or-name action quit-function body@dots{}
1177 This macro is similar to @code{with-output-to-temp-buffer}. Like that
1178 construct, it executes @var{body} while arranging to insert any output
1179 it prints into the buffer named @var{buffer-or-name} and displays that
1180 buffer in some window. Unlike @code{with-output-to-temp-buffer},
1181 however, it does not automatically switch that buffer to Help mode.
1183 Like @code{with-output-to-temp-buffer} it neither makes the buffer
1184 specified by @var{buffer-or-name} current when executing @var{body}.
1185 @findex with-current-buffer-window
1186 The otherwise identical macro @code{with-current-buffer-window} can be
1187 used to execute @var{body} with that buffer current.
1189 The argument @var{buffer-or-name} specifies the temporary buffer. It
1190 can be either a buffer, which must already exist, or a string, in which
1191 case a buffer of that name is created, if necessary. The buffer is
1192 marked as unmodified and read-only when @code{with-temp-buffer-window}
1195 This macro does not call @code{temp-buffer-show-function}. Rather, it
1196 passes the @var{action} argument to @code{display-buffer} in order to
1199 The value of the last form in @var{body} is returned, unless the
1200 argument @var{quit-function} is specified. In that case, it is called
1201 with two arguments: the window showing the buffer and the result of
1202 @var{body}. The final return value is then whatever
1203 @var{quit-function} returns.
1205 @vindex temp-buffer-window-setup-hook
1206 @vindex temp-buffer-window-show-hook
1207 This macro uses the normal hooks @code{temp-buffer-window-setup-hook}
1208 and @code{temp-buffer-window-show-hook} in place of the analogous hooks
1209 run by @code{with-output-to-temp-buffer}.
1212 @defun momentary-string-display string position &optional char message
1213 This function momentarily displays @var{string} in the current buffer at
1214 @var{position}. It has no effect on the undo list or on the buffer's
1215 modification status.
1217 The momentary display remains until the next input event. If the next
1218 input event is @var{char}, @code{momentary-string-display} ignores it
1219 and returns. Otherwise, that event remains buffered for subsequent use
1220 as input. Thus, typing @var{char} will simply remove the string from
1221 the display, while typing (say) @kbd{C-f} will remove the string from
1222 the display and later (presumably) move point forward. The argument
1223 @var{char} is a space by default.
1225 The return value of @code{momentary-string-display} is not meaningful.
1227 If the string @var{string} does not contain control characters, you can
1228 do the same job in a more general way by creating (and then subsequently
1229 deleting) an overlay with a @code{before-string} property.
1230 @xref{Overlay Properties}.
1232 If @var{message} is non-@code{nil}, it is displayed in the echo area
1233 while @var{string} is displayed in the buffer. If it is @code{nil}, a
1234 default message says to type @var{char} to continue.
1236 In this example, point is initially located at the beginning of the
1241 ---------- Buffer: foo ----------
1242 This is the contents of foo.
1243 @point{}Second line.
1244 ---------- Buffer: foo ----------
1248 (momentary-string-display
1249 "**** Important Message! ****"
1251 "Type RET when done reading")
1256 ---------- Buffer: foo ----------
1257 This is the contents of foo.
1258 **** Important Message! ****Second line.
1259 ---------- Buffer: foo ----------
1261 ---------- Echo Area ----------
1262 Type RET when done reading
1263 ---------- Echo Area ----------
1271 @c FIXME: mention intervals in this section?
1273 You can use @dfn{overlays} to alter the appearance of a buffer's text on
1274 the screen, for the sake of presentation features. An overlay is an
1275 object that belongs to a particular buffer, and has a specified
1276 beginning and end. It also has properties that you can examine and set;
1277 these affect the display of the text within the overlay.
1279 @cindex scalability of overlays
1280 The visual effect of an overlay is the same as of the corresponding
1281 text property (@pxref{Text Properties}). However, due to a different
1282 implementation, overlays generally don't scale well (many operations
1283 take a time that is proportional to the number of overlays in the
1284 buffer). If you need to affect the visual appearance of many portions
1285 in the buffer, we recommend using text properties.
1287 An overlay uses markers to record its beginning and end; thus,
1288 editing the text of the buffer adjusts the beginning and end of each
1289 overlay so that it stays with the text. When you create the overlay,
1290 you can specify whether text inserted at the beginning should be
1291 inside the overlay or outside, and likewise for the end of the overlay.
1294 * Managing Overlays:: Creating and moving overlays.
1295 * Overlay Properties:: How to read and set properties.
1296 What properties do to the screen display.
1297 * Finding Overlays:: Searching for overlays.
1300 @node Managing Overlays
1301 @subsection Managing Overlays
1303 This section describes the functions to create, delete and move
1304 overlays, and to examine their contents. Overlay changes are not
1305 recorded in the buffer's undo list, since the overlays are not
1306 part of the buffer's contents.
1308 @defun overlayp object
1309 This function returns @code{t} if @var{object} is an overlay.
1312 @defun make-overlay start end &optional buffer front-advance rear-advance
1313 This function creates and returns an overlay that belongs to
1314 @var{buffer} and ranges from @var{start} to @var{end}. Both @var{start}
1315 and @var{end} must specify buffer positions; they may be integers or
1316 markers. If @var{buffer} is omitted, the overlay is created in the
1319 The arguments @var{front-advance} and @var{rear-advance} specify the
1320 marker insertion type for the start of the overlay and for the end of
1321 the overlay, respectively. @xref{Marker Insertion Types}. If they
1322 are both @code{nil}, the default, then the overlay extends to include
1323 any text inserted at the beginning, but not text inserted at the end.
1324 If @var{front-advance} is non-@code{nil}, text inserted at the
1325 beginning of the overlay is excluded from the overlay. If
1326 @var{rear-advance} is non-@code{nil}, text inserted at the end of the
1327 overlay is included in the overlay.
1330 @defun overlay-start overlay
1331 This function returns the position at which @var{overlay} starts,
1335 @defun overlay-end overlay
1336 This function returns the position at which @var{overlay} ends,
1340 @defun overlay-buffer overlay
1341 This function returns the buffer that @var{overlay} belongs to. It
1342 returns @code{nil} if @var{overlay} has been deleted.
1345 @defun delete-overlay overlay
1346 This function deletes @var{overlay}. The overlay continues to exist as
1347 a Lisp object, and its property list is unchanged, but it ceases to be
1348 attached to the buffer it belonged to, and ceases to have any effect on
1351 A deleted overlay is not permanently disconnected. You can give it a
1352 position in a buffer again by calling @code{move-overlay}.
1355 @defun move-overlay overlay start end &optional buffer
1356 This function moves @var{overlay} to @var{buffer}, and places its bounds
1357 at @var{start} and @var{end}. Both arguments @var{start} and @var{end}
1358 must specify buffer positions; they may be integers or markers.
1360 If @var{buffer} is omitted, @var{overlay} stays in the same buffer it
1361 was already associated with; if @var{overlay} was deleted, it goes into
1364 The return value is @var{overlay}.
1366 This is the only valid way to change the endpoints of an overlay. Do
1367 not try modifying the markers in the overlay by hand, as that fails to
1368 update other vital data structures and can cause some overlays to be
1372 @defun remove-overlays &optional start end name value
1373 This function removes all the overlays between @var{start} and
1374 @var{end} whose property @var{name} has the value @var{value}. It can
1375 move the endpoints of the overlays in the region, or split them.
1377 If @var{name} is omitted or @code{nil}, it means to delete all overlays in
1378 the specified region. If @var{start} and/or @var{end} are omitted or
1379 @code{nil}, that means the beginning and end of the buffer respectively.
1380 Therefore, @code{(remove-overlays)} removes all the overlays in the
1384 @defun copy-overlay overlay
1385 This function returns a copy of @var{overlay}. The copy has the same
1386 endpoints and properties as @var{overlay}. However, the marker
1387 insertion type for the start of the overlay and for the end of the
1388 overlay are set to their default values (@pxref{Marker Insertion
1392 Here are some examples:
1395 ;; @r{Create an overlay.}
1396 (setq foo (make-overlay 1 10))
1397 @result{} #<overlay from 1 to 10 in display.texi>
1402 (overlay-buffer foo)
1403 @result{} #<buffer display.texi>
1404 ;; @r{Give it a property we can check later.}
1405 (overlay-put foo 'happy t)
1407 ;; @r{Verify the property is present.}
1408 (overlay-get foo 'happy)
1410 ;; @r{Move the overlay.}
1411 (move-overlay foo 5 20)
1412 @result{} #<overlay from 5 to 20 in display.texi>
1417 ;; @r{Delete the overlay.}
1418 (delete-overlay foo)
1420 ;; @r{Verify it is deleted.}
1422 @result{} #<overlay in no buffer>
1423 ;; @r{A deleted overlay has no position.}
1428 (overlay-buffer foo)
1430 ;; @r{Undelete the overlay.}
1431 (move-overlay foo 1 20)
1432 @result{} #<overlay from 1 to 20 in display.texi>
1433 ;; @r{Verify the results.}
1438 (overlay-buffer foo)
1439 @result{} #<buffer display.texi>
1440 ;; @r{Moving and deleting the overlay does not change its properties.}
1441 (overlay-get foo 'happy)
1445 Emacs stores the overlays of each buffer in two lists, divided
1446 around an arbitrary ``center position''. One list extends backwards
1447 through the buffer from that center position, and the other extends
1448 forwards from that center position. The center position can be anywhere
1451 @defun overlay-recenter pos
1452 This function recenters the overlays of the current buffer around
1453 position @var{pos}. That makes overlay lookup faster for positions
1454 near @var{pos}, but slower for positions far away from @var{pos}.
1457 A loop that scans the buffer forwards, creating overlays, can run
1458 faster if you do @code{(overlay-recenter (point-max))} first.
1460 @node Overlay Properties
1461 @subsection Overlay Properties
1463 Overlay properties are like text properties in that the properties that
1464 alter how a character is displayed can come from either source. But in
1465 most respects they are different. @xref{Text Properties}, for comparison.
1467 Text properties are considered a part of the text; overlays and
1468 their properties are specifically considered not to be part of the
1469 text. Thus, copying text between various buffers and strings
1470 preserves text properties, but does not try to preserve overlays.
1471 Changing a buffer's text properties marks the buffer as modified,
1472 while moving an overlay or changing its properties does not. Unlike
1473 text property changes, overlay property changes are not recorded in
1474 the buffer's undo list.
1476 Since more than one overlay can specify a property value for the
1477 same character, Emacs lets you specify a priority value of each
1478 overlay. In case two overlays have the same priority value, and one
1479 is nested in the other, then the inner one will have priority over the
1480 outer one. If neither is nested in the other then you should not make
1481 assumptions about which overlay will prevail.
1483 These functions read and set the properties of an overlay:
1485 @defun overlay-get overlay prop
1486 This function returns the value of property @var{prop} recorded in
1487 @var{overlay}, if any. If @var{overlay} does not record any value for
1488 that property, but it does have a @code{category} property which is a
1489 symbol, that symbol's @var{prop} property is used. Otherwise, the value
1493 @defun overlay-put overlay prop value
1494 This function sets the value of property @var{prop} recorded in
1495 @var{overlay} to @var{value}. It returns @var{value}.
1498 @defun overlay-properties overlay
1499 This returns a copy of the property list of @var{overlay}.
1502 See also the function @code{get-char-property} which checks both
1503 overlay properties and text properties for a given character.
1504 @xref{Examining Properties}.
1506 Many overlay properties have special meanings; here is a table
1511 @kindex priority @r{(overlay property)}
1512 This property's value determines the priority of the overlay. No priority, or
1513 @code{nil}, means zero. A non-nil and non-integer value has
1516 The priority matters when two or more overlays cover the same
1517 character and both specify the same property; the one whose
1518 @code{priority} value is larger overrides the other. For the
1519 @code{face} property, the higher priority overlay's value does not
1520 completely override the other value; instead, its face attributes
1521 override the face attributes of the lower priority @code{face}
1524 Currently, all overlays take priority over text properties. Please
1525 avoid using negative priority values, as we have not yet decided just
1526 what they should mean.
1529 @kindex window @r{(overlay property)}
1530 If the @code{window} property is non-@code{nil}, then the overlay
1531 applies only on that window.
1534 @kindex category @r{(overlay property)}
1535 If an overlay has a @code{category} property, we call it the
1536 @dfn{category} of the overlay. It should be a symbol. The properties
1537 of the symbol serve as defaults for the properties of the overlay.
1540 @kindex face @r{(overlay property)}
1541 This property controls the appearance of the text (@pxref{Faces}).
1542 The value of the property can be the following:
1546 A face name (a symbol or string).
1549 An anonymous face: a property list of the form @code{(@var{keyword}
1550 @var{value} @dots{})}, where each @var{keyword} is a face attribute
1551 name and @var{value} is a value for that attribute.
1554 A list of faces. Each list element should be either a face name or an
1555 anonymous face. This specifies a face which is an aggregate of the
1556 attributes of each of the listed faces. Faces occurring earlier in
1557 the list have higher priority.
1560 A cons cell of the form @code{(foreground-color . @var{color-name})}
1561 or @code{(background-color . @var{color-name})}. This specifies the
1562 foreground or background color, similar to @code{(:foreground
1563 @var{color-name})} or @code{(:background @var{color-name})}. This
1564 form is supported for backward compatibility only, and should be
1569 @kindex mouse-face @r{(overlay property)}
1570 This property is used instead of @code{face} when the mouse is within
1571 the range of the overlay. However, Emacs ignores all face attributes
1572 from this property that alter the text size (e.g., @code{:height},
1573 @code{:weight}, and @code{:slant}). Those attributes are always the
1574 same as in the unhighlighted text.
1577 @kindex display @r{(overlay property)}
1578 This property activates various features that change the
1579 way text is displayed. For example, it can make text appear taller
1580 or shorter, higher or lower, wider or narrower, or replaced with an image.
1581 @xref{Display Property}.
1584 @kindex help-echo @r{(overlay property)}
1585 If an overlay has a @code{help-echo} property, then when you move the
1586 mouse onto the text in the overlay, Emacs displays a help string in the
1587 echo area, or in the tooltip window. For details see @ref{Text
1591 @kindex field @r{(overlay property)}
1592 @c Copied from Special Properties.
1593 Consecutive characters with the same @code{field} property constitute a
1594 @emph{field}. Some motion functions including @code{forward-word} and
1595 @code{beginning-of-line} stop moving at a field boundary.
1598 @item modification-hooks
1599 @kindex modification-hooks @r{(overlay property)}
1600 This property's value is a list of functions to be called if any
1601 character within the overlay is changed or if text is inserted strictly
1604 The hook functions are called both before and after each change.
1605 If the functions save the information they receive, and compare notes
1606 between calls, they can determine exactly what change has been made
1609 When called before a change, each function receives four arguments: the
1610 overlay, @code{nil}, and the beginning and end of the text range to be
1613 When called after a change, each function receives five arguments: the
1614 overlay, @code{t}, the beginning and end of the text range just
1615 modified, and the length of the pre-change text replaced by that range.
1616 (For an insertion, the pre-change length is zero; for a deletion, that
1617 length is the number of characters deleted, and the post-change
1618 beginning and end are equal.)
1620 If these functions modify the buffer, they should bind
1621 @code{inhibit-modification-hooks} to @code{t} around doing so, to
1622 avoid confusing the internal mechanism that calls these hooks.
1624 Text properties also support the @code{modification-hooks} property,
1625 but the details are somewhat different (@pxref{Special Properties}).
1627 @item insert-in-front-hooks
1628 @kindex insert-in-front-hooks @r{(overlay property)}
1629 This property's value is a list of functions to be called before and
1630 after inserting text right at the beginning of the overlay. The calling
1631 conventions are the same as for the @code{modification-hooks} functions.
1633 @item insert-behind-hooks
1634 @kindex insert-behind-hooks @r{(overlay property)}
1635 This property's value is a list of functions to be called before and
1636 after inserting text right at the end of the overlay. The calling
1637 conventions are the same as for the @code{modification-hooks} functions.
1640 @kindex invisible @r{(overlay property)}
1641 The @code{invisible} property can make the text in the overlay
1642 invisible, which means that it does not appear on the screen.
1643 @xref{Invisible Text}, for details.
1646 @kindex intangible @r{(overlay property)}
1647 The @code{intangible} property on an overlay works just like the
1648 @code{intangible} text property. @xref{Special Properties}, for details.
1650 @item isearch-open-invisible
1651 This property tells incremental search how to make an invisible overlay
1652 visible, permanently, if the final match overlaps it. @xref{Invisible
1655 @item isearch-open-invisible-temporary
1656 This property tells incremental search how to make an invisible overlay
1657 visible, temporarily, during the search. @xref{Invisible Text}.
1660 @kindex before-string @r{(overlay property)}
1661 This property's value is a string to add to the display at the beginning
1662 of the overlay. The string does not appear in the buffer in any
1663 sense---only on the screen.
1666 @kindex after-string @r{(overlay property)}
1667 This property's value is a string to add to the display at the end of
1668 the overlay. The string does not appear in the buffer in any
1669 sense---only on the screen.
1672 This property specifies a display spec to prepend to each
1673 non-continuation line at display-time. @xref{Truncation}.
1676 This property specifies a display spec to prepend to each continuation
1677 line at display-time. @xref{Truncation}.
1680 @kindex evaporate @r{(overlay property)}
1681 If this property is non-@code{nil}, the overlay is deleted automatically
1682 if it becomes empty (i.e., if its length becomes zero). If you give
1683 an empty overlay a non-@code{nil} @code{evaporate} property, that deletes
1687 @cindex keymap of character (and overlays)
1688 @kindex keymap @r{(overlay property)}
1689 If this property is non-@code{nil}, it specifies a keymap for a portion of the
1690 text. This keymap is used when the character after point is within the
1691 overlay, and takes precedence over most other keymaps. @xref{Active Keymaps}.
1694 @kindex local-map @r{(overlay property)}
1695 The @code{local-map} property is similar to @code{keymap} but replaces the
1696 buffer's local map rather than augmenting existing keymaps. This also means it
1697 has lower precedence than minor mode keymaps.
1700 The @code{keymap} and @code{local-map} properties do not affect a
1701 string displayed by the @code{before-string}, @code{after-string}, or
1702 @code{display} properties. This is only relevant for mouse clicks and
1703 other mouse events that fall on the string, since point is never on
1704 the string. To bind special mouse events for the string, assign it a
1705 @code{keymap} or @code{local-map} text property. @xref{Special
1708 @node Finding Overlays
1709 @subsection Searching for Overlays
1711 @defun overlays-at pos &optional sorted
1712 This function returns a list of all the overlays that cover the character at
1713 position @var{pos} in the current buffer. If @var{sorted} is non-nil, the list
1714 is in decreasing order of priority, otherwise it is in no particular order.
1715 An overlay contains position @var{pos} if it begins at or before @var{pos}, and
1716 ends after @var{pos}.
1718 To illustrate usage, here is a Lisp function that returns a list of the
1719 overlays that specify property @var{prop} for the character at point:
1722 (defun find-overlays-specifying (prop)
1723 (let ((overlays (overlays-at (point)))
1726 (let ((overlay (car overlays)))
1727 (if (overlay-get overlay prop)
1728 (setq found (cons overlay found))))
1729 (setq overlays (cdr overlays)))
1734 @defun overlays-in beg end
1735 This function returns a list of the overlays that overlap the region
1736 @var{beg} through @var{end}. ``Overlap'' means that at least one
1737 character is contained within the overlay and also contained within the
1738 specified region; however, empty overlays are included in the result if
1739 they are located at @var{beg}, strictly between @var{beg} and @var{end},
1740 or at @var{end} when @var{end} denotes the position at the end of the
1744 @defun next-overlay-change pos
1745 This function returns the buffer position of the next beginning or end
1746 of an overlay, after @var{pos}. If there is none, it returns
1750 @defun previous-overlay-change pos
1751 This function returns the buffer position of the previous beginning or
1752 end of an overlay, before @var{pos}. If there is none, it returns
1756 As an example, here's a simplified (and inefficient) version of the
1757 primitive function @code{next-single-char-property-change}
1758 (@pxref{Property Search}). It searches forward from position
1759 @var{pos} for the next position where the value of a given property
1760 @code{prop}, as obtained from either overlays or text properties,
1764 (defun next-single-char-property-change (position prop)
1766 (goto-char position)
1767 (let ((propval (get-char-property (point) prop)))
1768 (while (and (not (eobp))
1769 (eq (get-char-property (point) prop) propval))
1770 (goto-char (min (next-overlay-change (point))
1771 (next-single-property-change (point) prop)))))
1775 @node Size of Displayed Text
1776 @section Size of Displayed Text
1778 Since not all characters have the same width, these functions let you
1779 check the width of a character. @xref{Primitive Indent}, and
1780 @ref{Screen Lines}, for related functions.
1782 @defun char-width char
1783 This function returns the width in columns of the character
1784 @var{char}, if it were displayed in the current buffer (i.e., taking
1785 into account the buffer's display table, if any; @pxref{Display
1786 Tables}). The width of a tab character is usually @code{tab-width}
1787 (@pxref{Usual Display}).
1790 @defun string-width string
1791 This function returns the width in columns of the string @var{string},
1792 if it were displayed in the current buffer and the selected window.
1795 @defun truncate-string-to-width string width &optional start-column padding ellipsis
1796 This function returns the part of @var{string} that fits within
1797 @var{width} columns, as a new string.
1799 If @var{string} does not reach @var{width}, then the result ends where
1800 @var{string} ends. If one multi-column character in @var{string}
1801 extends across the column @var{width}, that character is not included in
1802 the result. Thus, the result can fall short of @var{width} but cannot
1805 The optional argument @var{start-column} specifies the starting column.
1806 If this is non-@code{nil}, then the first @var{start-column} columns of
1807 the string are omitted from the value. If one multi-column character in
1808 @var{string} extends across the column @var{start-column}, that
1809 character is not included.
1811 The optional argument @var{padding}, if non-@code{nil}, is a padding
1812 character added at the beginning and end of the result string, to extend
1813 it to exactly @var{width} columns. The padding character is used at the
1814 end of the result if it falls short of @var{width}. It is also used at
1815 the beginning of the result if one multi-column character in
1816 @var{string} extends across the column @var{start-column}.
1818 If @var{ellipsis} is non-@code{nil}, it should be a string which will
1819 replace the end of @var{string} (including any padding) if it extends
1820 beyond @var{width}, unless the display width of @var{string} is equal
1821 to or less than the display width of @var{ellipsis}. If
1822 @var{ellipsis} is non-@code{nil} and not a string, it stands for
1826 (truncate-string-to-width "\tab\t" 12 4)
1828 (truncate-string-to-width "\tab\t" 12 4 ?\s)
1833 The following function returns the size in pixels of text as if it were
1834 displayed in a given window. This function is used by
1835 @code{fit-window-to-buffer} (@pxref{Resizing Windows}) and
1836 @code{fit-frame-to-buffer} (@pxref{Size and Position}) to make a window
1837 exactly as large as the text it contains.
1839 @defun window-text-pixel-size &optional window from to x-limit y-limit mode-and-header-line
1840 This function returns the size of the text of @var{window}'s buffer in
1841 pixels. @var{window} must be a live window and defaults to the selected
1842 one. The return value is a cons of the maximum pixel-width of any text
1843 line and the maximum pixel-height of all text lines.
1845 The optional argument @var{from}, if non-@code{nil}, specifies the first
1846 text position to consider and defaults to the minimum accessible
1847 position of the buffer. If @var{from} is @code{t}, it uses the minimum
1848 accessible position that is not a newline character. The optional
1849 argument @var{to}, if non-@code{nil}, specifies the last text position
1850 to consider and defaults to the maximum accessible position of the
1851 buffer. If @var{to} is @code{t}, it uses the maximum accessible
1852 position that is not a newline character.
1854 The optional argument @var{x-limit}, if non-@code{nil}, specifies the
1855 maximum pixel-width that can be returned. @var{x-limit} @code{nil} or
1856 omitted, means to use the pixel-width of @var{window}'s body
1857 (@pxref{Window Sizes}); this is useful when the caller does not intend
1858 to change the width of @var{window}. Otherwise, the caller should
1859 specify here the maximum width @var{window}'s body may assume. Text
1860 whose x-coordinate is beyond @var{x-limit} is ignored. Since
1861 calculating the width of long lines can take some time, it's always a
1862 good idea to make this argument as small as needed; in particular, if
1863 the buffer might contain long lines that will be truncated anyway.
1865 The optional argument @var{y-limit}, if non-@code{nil}, specifies the
1866 maximum pixel-height that can be returned. Text lines whose
1867 y-coordinate is beyond @var{y-limit} are ignored. Since calculating the
1868 pixel-height of a large buffer can take some time, it makes sense to
1869 specify this argument; in particular, if the caller does not know the
1872 The optional argument @var{mode-and-header-line} @code{nil} or omitted
1873 means to not include the height of the mode- or header-line of
1874 @var{window} in the return value. If it is either the symbol
1875 @code{mode-line} or @code{header-line}, include only the height of that
1876 line, if present, in the return value. If it is @code{t}, include the
1877 height of both, if present, in the return value.
1882 @section Line Height
1884 @cindex height of a line
1886 The total height of each display line consists of the height of the
1887 contents of the line, plus optional additional vertical line spacing
1888 above or below the display line.
1890 The height of the line contents is the maximum height of any
1891 character or image on that display line, including the final newline
1892 if there is one. (A display line that is continued doesn't include a
1893 final newline.) That is the default line height, if you do nothing to
1894 specify a greater height. (In the most common case, this equals the
1895 height of the default frame font.)
1897 There are several ways to explicitly specify a larger line height,
1898 either by specifying an absolute height for the display line, or by
1899 specifying vertical space. However, no matter what you specify, the
1900 actual line height can never be less than the default.
1902 @kindex line-height @r{(text property)}
1903 A newline can have a @code{line-height} text or overlay property
1904 that controls the total height of the display line ending in that
1907 If the property value is @code{t}, the newline character has no
1908 effect on the displayed height of the line---the visible contents
1909 alone determine the height. This is useful for tiling small images
1910 (or image slices) without adding blank areas between the images.
1912 If the property value is a list of the form @code{(@var{height}
1913 @var{total})}, that adds extra space @emph{below} the display line.
1914 First Emacs uses @var{height} as a height spec to control extra space
1915 @emph{above} the line; then it adds enough space @emph{below} the line
1916 to bring the total line height up to @var{total}. In this case, the
1917 other ways to specify the line spacing are ignored.
1920 Any other kind of property value is a height spec, which translates
1921 into a number---the specified line height. There are several ways to
1922 write a height spec; here's how each of them translates into a number:
1926 If the height spec is a positive integer, the height value is that integer.
1928 If the height spec is a float, @var{float}, the numeric height value
1929 is @var{float} times the frame's default line height.
1930 @item (@var{face} . @var{ratio})
1931 If the height spec is a cons of the format shown, the numeric height
1932 is @var{ratio} times the height of face @var{face}. @var{ratio} can
1933 be any type of number, or @code{nil} which means a ratio of 1.
1934 If @var{face} is @code{t}, it refers to the current face.
1935 @item (nil . @var{ratio})
1936 If the height spec is a cons of the format shown, the numeric height
1937 is @var{ratio} times the height of the contents of the line.
1940 Thus, any valid height spec determines the height in pixels, one way
1941 or another. If the line contents' height is less than that, Emacs
1942 adds extra vertical space above the line to achieve the specified
1945 If you don't specify the @code{line-height} property, the line's
1946 height consists of the contents' height plus the line spacing.
1947 There are several ways to specify the line spacing for different
1948 parts of Emacs text.
1950 On graphical terminals, you can specify the line spacing for all
1951 lines in a frame, using the @code{line-spacing} frame parameter
1952 (@pxref{Layout Parameters}). However, if the default value of
1953 @code{line-spacing} is non-@code{nil}, it overrides the
1954 frame's @code{line-spacing} parameter. An integer specifies the
1955 number of pixels put below lines. A floating-point number specifies
1956 the spacing relative to the frame's default line height.
1958 @vindex line-spacing
1959 You can specify the line spacing for all lines in a buffer via the
1960 buffer-local @code{line-spacing} variable. An integer specifies
1961 the number of pixels put below lines. A floating-point number
1962 specifies the spacing relative to the default frame line height. This
1963 overrides line spacings specified for the frame.
1965 @kindex line-spacing @r{(text property)}
1966 Finally, a newline can have a @code{line-spacing} text or overlay
1967 property that overrides the default frame line spacing and the buffer
1968 local @code{line-spacing} variable, for the display line ending in
1971 One way or another, these mechanisms specify a Lisp value for the
1972 spacing of each line. The value is a height spec, and it translates
1973 into a Lisp value as described above. However, in this case the
1974 numeric height value specifies the line spacing, rather than the line
1977 On text terminals, the line spacing cannot be altered.
1983 A @dfn{face} is a collection of graphical attributes for displaying
1984 text: font, foreground color, background color, optional underlining,
1985 etc. Faces control how Emacs displays text in buffers, as well as
1986 other parts of the frame such as the mode line.
1988 @cindex anonymous face
1989 One way to represent a face is as a property list of attributes,
1990 like @code{(:foreground "red" :weight bold)}. Such a list is called
1991 an @dfn{anonymous face}. For example, you can assign an anonymous
1992 face as the value of the @code{face} text property, and Emacs will
1993 display the underlying text with the specified attributes.
1994 @xref{Special Properties}.
1997 More commonly, a face is referred to via a @dfn{face name}: a Lisp
1998 symbol associated with a set of face attributes@footnote{For backward
1999 compatibility, you can also use a string to specify a face name; that
2000 is equivalent to a Lisp symbol with the same name.}. Named faces are
2001 defined using the @code{defface} macro (@pxref{Defining Faces}).
2002 Emacs comes with several standard named faces (@pxref{Basic Faces}).
2004 Many parts of Emacs required named faces, and do not accept
2005 anonymous faces. These include the functions documented in
2006 @ref{Attribute Functions}, and the variable @code{font-lock-keywords}
2007 (@pxref{Search-based Fontification}). Unless otherwise stated, we
2008 will use the term @dfn{face} to refer only to named faces.
2011 This function returns a non-@code{nil} value if @var{object} is a
2012 named face: a Lisp symbol or string which serves as a face name.
2013 Otherwise, it returns @code{nil}.
2017 * Face Attributes:: What is in a face?
2018 * Defining Faces:: How to define a face.
2019 * Attribute Functions:: Functions to examine and set face attributes.
2020 * Displaying Faces:: How Emacs combines the faces specified for a character.
2021 * Face Remapping:: Remapping faces to alternative definitions.
2022 * Face Functions:: How to define and examine faces.
2023 * Auto Faces:: Hook for automatic face assignment.
2024 * Basic Faces:: Faces that are defined by default.
2025 * Font Selection:: Finding the best available font for a face.
2026 * Font Lookup:: Looking up the names of available fonts
2027 and information about them.
2028 * Fontsets:: A fontset is a collection of fonts
2029 that handle a range of character sets.
2030 * Low-Level Font:: Lisp representation for character display fonts.
2033 @node Face Attributes
2034 @subsection Face Attributes
2035 @cindex face attributes
2037 @dfn{Face attributes} determine the visual appearance of a face.
2038 The following table lists all the face attributes, their possible
2039 values, and their effects.
2041 Apart from the values given below, each face attribute can have the
2042 value @code{unspecified}. This special value means that the face
2043 doesn't specify that attribute directly. An @code{unspecified}
2044 attribute tells Emacs to refer instead to a parent face (see the
2045 description @code{:inherit} attribute below); or, failing that, to an
2046 underlying face (@pxref{Displaying Faces}). The @code{default} face
2047 must specify all attributes.
2049 Some of these attributes are meaningful only on certain kinds of
2050 displays. If your display cannot handle a certain attribute, the
2051 attribute is ignored.
2055 Font family or fontset (a string). @xref{Fonts,,, emacs, The GNU
2056 Emacs Manual}, for more information about font families. The function
2057 @code{font-family-list} (see below) returns a list of available family
2058 names. @xref{Fontsets}, for information about fontsets.
2061 The name of the @dfn{font foundry} for the font family specified by
2062 the @code{:family} attribute (a string). @xref{Fonts,,, emacs, The
2066 Relative character width. This should be one of the symbols
2067 @code{ultra-condensed}, @code{extra-condensed}, @code{condensed},
2068 @code{semi-condensed}, @code{normal}, @code{semi-expanded},
2069 @code{expanded}, @code{extra-expanded}, or @code{ultra-expanded}.
2072 The height of the font. In the simplest case, this is an integer in
2073 units of 1/10 point.
2075 The value can also be floating point or a function, which
2076 specifies the height relative to an @dfn{underlying face}
2077 (@pxref{Displaying Faces}). A floating-point value
2078 specifies the amount by which to scale the height of the
2079 underlying face. A function value is called
2080 with one argument, the height of the underlying face, and returns the
2081 height of the new face. If the function is passed an integer
2082 argument, it must return an integer.
2084 The height of the default face must be specified using an integer;
2085 floating point and function values are not allowed.
2088 Font weight---one of the symbols (from densest to faintest)
2089 @code{ultra-bold}, @code{extra-bold}, @code{bold}, @code{semi-bold},
2090 @code{normal}, @code{semi-light}, @code{light}, @code{extra-light}, or
2091 @code{ultra-light}. On text terminals which support
2092 variable-brightness text, any weight greater than normal is displayed
2093 as extra bright, and any weight less than normal is displayed as
2098 Font slant---one of the symbols @code{italic}, @code{oblique},
2099 @code{normal}, @code{reverse-italic}, or @code{reverse-oblique}. On
2100 text terminals that support variable-brightness text, slanted text is
2101 displayed as half-bright.
2104 Foreground color, a string. The value can be a system-defined color
2105 name, or a hexadecimal color specification. @xref{Color Names}. On
2106 black-and-white displays, certain shades of gray are implemented by
2109 @item :distant-foreground
2110 Alternative foreground color, a string. This is like @code{:foreground}
2111 but the color is only used as a foreground when the background color is
2112 near to the foreground that would have been used. This is useful for
2113 example when marking text (i.e. the region face). If the text has a foreground
2114 that is visible with the region face, that foreground is used.
2115 If the foreground is near the region face background,
2116 @code{:distant-foreground} is used instead so the text is readable.
2119 Background color, a string. The value can be a system-defined color
2120 name, or a hexadecimal color specification. @xref{Color Names}.
2122 @cindex underlined text
2124 Whether or not characters should be underlined, and in what
2125 way. The possible values of the @code{:underline} attribute are:
2132 Underline with the foreground color of the face.
2135 Underline in color @var{color}, a string specifying a color.
2137 @item @code{(:color @var{color} :style @var{style})}
2138 @var{color} is either a string, or the symbol @code{foreground-color},
2139 meaning the foreground color of the face. Omitting the attribute
2140 @code{:color} means to use the foreground color of the face.
2141 @var{style} should be a symbol @code{line} or @code{wave}, meaning to
2142 use a straight or wavy line. Omitting the attribute @code{:style}
2143 means to use a straight line.
2146 @cindex overlined text
2148 Whether or not characters should be overlined, and in what color.
2149 If the value is @code{t}, overlining uses the foreground color of the
2150 face. If the value is a string, overlining uses that color. The
2151 value @code{nil} means do not overline.
2153 @cindex strike-through text
2154 @item :strike-through
2155 Whether or not characters should be strike-through, and in what
2156 color. The value is used like that of @code{:overline}.
2161 Whether or not a box should be drawn around characters, its color, the
2162 width of the box lines, and 3D appearance. Here are the possible
2163 values of the @code{:box} attribute, and what they mean:
2170 Draw a box with lines of width 1, in the foreground color.
2173 Draw a box with lines of width 1, in color @var{color}.
2175 @item @code{(:line-width @var{width} :color @var{color} :style @var{style})}
2176 This way you can explicitly specify all aspects of the box. The value
2177 @var{width} specifies the width of the lines to draw; it defaults to
2178 1. A negative width @var{-n} means to draw a line of width @var{n}
2179 that occupies the space of the underlying text, thus avoiding any
2180 increase in the character height or width.
2182 The value @var{color} specifies the color to draw with. The default is
2183 the foreground color of the face for simple boxes, and the background
2184 color of the face for 3D boxes.
2186 The value @var{style} specifies whether to draw a 3D box. If it is
2187 @code{released-button}, the box looks like a 3D button that is not being
2188 pressed. If it is @code{pressed-button}, the box looks like a 3D button
2189 that is being pressed. If it is @code{nil} or omitted, a plain 2D box
2193 @item :inverse-video
2194 Whether or not characters should be displayed in inverse video. The
2195 value should be @code{t} (yes) or @code{nil} (no).
2198 The background stipple, a bitmap.
2200 The value can be a string; that should be the name of a file containing
2201 external-format X bitmap data. The file is found in the directories
2202 listed in the variable @code{x-bitmap-file-path}.
2204 Alternatively, the value can specify the bitmap directly, with a list
2205 of the form @code{(@var{width} @var{height} @var{data})}. Here,
2206 @var{width} and @var{height} specify the size in pixels, and
2207 @var{data} is a string containing the raw bits of the bitmap, row by
2208 row. Each row occupies @math{(@var{width} + 7) / 8} consecutive bytes
2209 in the string (which should be a unibyte string for best results).
2210 This means that each row always occupies at least one whole byte.
2212 If the value is @code{nil}, that means use no stipple pattern.
2214 Normally you do not need to set the stipple attribute, because it is
2215 used automatically to handle certain shades of gray.
2218 The font used to display the face. Its value should be a font object.
2219 @xref{Low-Level Font}, for information about font objects, font specs,
2222 When specifying this attribute using @code{set-face-attribute}
2223 (@pxref{Attribute Functions}), you may also supply a font spec, a font
2224 entity, or a string. Emacs converts such values to an appropriate
2225 font object, and stores that font object as the actual attribute
2226 value. If you specify a string, the contents of the string should be
2227 a font name (@pxref{Fonts,,, emacs, The GNU Emacs Manual}); if the
2228 font name is an XLFD containing wildcards, Emacs chooses the first
2229 font matching those wildcards. Specifying this attribute also changes
2230 the values of the @code{:family}, @code{:foundry}, @code{:width},
2231 @code{:height}, @code{:weight}, and @code{:slant} attributes.
2233 @cindex inheritance, for faces
2235 The name of a face from which to inherit attributes, or a list of face
2236 names. Attributes from inherited faces are merged into the face like
2237 an underlying face would be, with higher priority than underlying
2238 faces (@pxref{Displaying Faces}). If a list of faces is used,
2239 attributes from faces earlier in the list override those from later
2243 @defun font-family-list &optional frame
2244 This function returns a list of available font family names. The
2245 optional argument @var{frame} specifies the frame on which the text is
2246 to be displayed; if it is @code{nil}, the selected frame is used.
2249 @defopt underline-minimum-offset
2250 This variable specifies the minimum distance between the baseline and
2251 the underline, in pixels, when displaying underlined text.
2254 @defopt x-bitmap-file-path
2255 This variable specifies a list of directories for searching
2256 for bitmap files, for the @code{:stipple} attribute.
2259 @defun bitmap-spec-p object
2260 This returns @code{t} if @var{object} is a valid bitmap specification,
2261 suitable for use with @code{:stipple} (see above). It returns
2262 @code{nil} otherwise.
2265 @node Defining Faces
2266 @subsection Defining Faces
2269 The usual way to define a face is through the @code{defface} macro.
2270 This macro associates a face name (a symbol) with a default @dfn{face
2271 spec}. A face spec is a construct which specifies what attributes a
2272 face should have on any given terminal; for example, a face spec might
2273 specify one foreground color on high-color terminals, and a different
2274 foreground color on low-color terminals.
2276 People are sometimes tempted to create a variable whose value is a
2277 face name. In the vast majority of cases, this is not necessary; the
2278 usual procedure is to define a face with @code{defface}, and then use
2281 @defmac defface face spec doc [keyword value]@dots{}
2282 This macro declares @var{face} as a named face whose default face spec
2283 is given by @var{spec}. You should not quote the symbol @var{face},
2284 and it should not end in @samp{-face} (that would be redundant). The
2285 argument @var{doc} is a documentation string for the face. The
2286 additional @var{keyword} arguments have the same meanings as in
2287 @code{defgroup} and @code{defcustom} (@pxref{Common Keywords}).
2289 If @var{face} already has a default face spec, this macro does
2292 The default face spec determines @var{face}'s appearance when no
2293 customizations are in effect (@pxref{Customization}). If @var{face}
2294 has already been customized (via Custom themes or via customizations
2295 read from the init file), its appearance is determined by the custom
2296 face spec(s), which override the default face spec @var{spec}.
2297 However, if the customizations are subsequently removed, the
2298 appearance of @var{face} will again be determined by its default face
2301 As an exception, if you evaluate a @code{defface} form with
2302 @kbd{C-M-x} in Emacs Lisp mode (@code{eval-defun}), a special feature
2303 of @code{eval-defun} overrides any custom face specs on the face,
2304 causing the face to reflect exactly what the @code{defface} says.
2306 The @var{spec} argument is a @dfn{face spec}, which states how the
2307 face should appear on different kinds of terminals. It should be an
2308 alist whose elements each have the form
2311 (@var{display} . @var{plist})
2315 @var{display} specifies a class of terminals (see below). @var{plist}
2316 is a property list of face attributes and their values, specifying how
2317 the face appears on such terminals. For backward compatibility, you
2318 can also write an element as @code{(@var{display} @var{plist})}.
2320 The @var{display} part of an element of @var{spec} determines which
2321 terminals the element matches. If more than one element of @var{spec}
2322 matches a given terminal, the first element that matches is the one
2323 used for that terminal. There are three possibilities for
2327 @item @code{default}
2328 This element of @var{spec} doesn't match any terminal; instead, it
2329 specifies defaults that apply to all terminals. This element, if
2330 used, must be the first element of @var{spec}. Each of the following
2331 elements can override any or all of these defaults.
2334 This element of @var{spec} matches all terminals. Therefore, any
2335 subsequent elements of @var{spec} are never used. Normally @code{t}
2336 is used in the last (or only) element of @var{spec}.
2339 If @var{display} is a list, each element should have the form
2340 @code{(@var{characteristic} @var{value}@dots{})}. Here
2341 @var{characteristic} specifies a way of classifying terminals, and the
2342 @var{value}s are possible classifications which @var{display} should
2343 apply to. Here are the possible values of @var{characteristic}:
2347 The kind of window system the terminal uses---either @code{graphic}
2348 (any graphics-capable display), @code{x}, @code{pc} (for the MS-DOS
2349 console), @code{w32} (for MS Windows 9X/NT/2K/XP), or @code{tty} (a
2350 non-graphics-capable display). @xref{Window Systems, window-system}.
2353 What kinds of colors the terminal supports---either @code{color},
2354 @code{grayscale}, or @code{mono}.
2357 The kind of background---either @code{light} or @code{dark}.
2360 An integer that represents the minimum number of colors the terminal
2361 should support. This matches a terminal if its
2362 @code{display-color-cells} value is at least the specified integer.
2365 Whether or not the terminal can display the face attributes given in
2366 @var{value}@dots{} (@pxref{Face Attributes}). @xref{Display Face
2367 Attribute Testing}, for more information on exactly how this testing
2371 If an element of @var{display} specifies more than one @var{value} for
2372 a given @var{characteristic}, any of those values is acceptable. If
2373 @var{display} has more than one element, each element should specify a
2374 different @var{characteristic}; then @emph{each} characteristic of the
2375 terminal must match one of the @var{value}s specified for it in
2380 For example, here's the definition of the standard face
2385 '((((class color) (min-colors 88) (background light))
2386 :background "darkseagreen2")
2387 (((class color) (min-colors 88) (background dark))
2388 :background "darkolivegreen")
2389 (((class color) (min-colors 16) (background light))
2390 :background "darkseagreen2")
2391 (((class color) (min-colors 16) (background dark))
2392 :background "darkolivegreen")
2393 (((class color) (min-colors 8))
2394 :background "green" :foreground "black")
2395 (t :inverse-video t))
2396 "Basic face for highlighting."
2397 :group 'basic-faces)
2400 Internally, Emacs stores each face's default spec in its
2401 @code{face-defface-spec} symbol property (@pxref{Symbol Properties}).
2402 The @code{saved-face} property stores any face spec saved by the user
2403 using the customization buffer; the @code{customized-face} property
2404 stores the face spec customized for the current session, but not
2405 saved; and the @code{theme-face} property stores an alist associating
2406 the active customization settings and Custom themes with the face
2407 specs for that face. The face's documentation string is stored in the
2408 @code{face-documentation} property.
2410 Normally, a face is declared just once, using @code{defface}, and
2411 any further changes to its appearance are applied using the Customize
2412 framework (e.g., via the Customize user interface or via the
2413 @code{custom-set-faces} function; @pxref{Applying Customizations}), or
2414 by face remapping (@pxref{Face Remapping}). In the rare event that
2415 you need to change a face spec directly from Lisp, you can use the
2416 @code{face-spec-set} function.
2418 @defun face-spec-set face spec &optional spec-type
2419 This function applies @var{spec} as a face spec for @code{face}.
2420 @var{spec} should be a face spec, as described in the above
2421 documentation for @code{defface}.
2423 This function also defines @var{face} as a valid face name if it is
2424 not already one, and (re)calculates its attributes on existing frames.
2426 @cindex override spec @r{(for a face)}
2427 The argument @var{spec-type} determines which spec to set. If it is
2428 @code{nil} or @code{face-override-spec}, this function sets the
2429 @dfn{override spec}, which overrides over all other face specs on
2430 @var{face}. If it is @code{customized-face} or @code{saved-face},
2431 this function sets the customized spec or the saved custom spec. If
2432 it is @code{face-defface-spec}, this function sets the default face
2433 spec (the same one set by @code{defface}). If it is @code{reset},
2434 this function clears out all customization specs and override specs
2435 from @var{face} (in this case, the value of @var{spec} is ignored).
2436 Any other value of @var{spec-type} is reserved for internal use.
2439 @node Attribute Functions
2440 @subsection Face Attribute Functions
2442 This section describes functions for directly accessing and
2443 modifying the attributes of a named face.
2445 @defun face-attribute face attribute &optional frame inherit
2446 This function returns the value of the @var{attribute} attribute for
2447 @var{face} on @var{frame}.
2449 If @var{frame} is @code{nil}, that means the selected frame
2450 (@pxref{Input Focus}). If @var{frame} is @code{t}, this function
2451 returns the value of the specified attribute for newly-created frames
2452 (this is normally @code{unspecified}, unless you have specified some
2453 value using @code{set-face-attribute}; see below).
2455 If @var{inherit} is @code{nil}, only attributes directly defined by
2456 @var{face} are considered, so the return value may be
2457 @code{unspecified}, or a relative value. If @var{inherit} is
2458 non-@code{nil}, @var{face}'s definition of @var{attribute} is merged
2459 with the faces specified by its @code{:inherit} attribute; however the
2460 return value may still be @code{unspecified} or relative. If
2461 @var{inherit} is a face or a list of faces, then the result is further
2462 merged with that face (or faces), until it becomes specified and
2465 To ensure that the return value is always specified and absolute, use
2466 a value of @code{default} for @var{inherit}; this will resolve any
2467 unspecified or relative values by merging with the @code{default} face
2468 (which is always completely specified).
2473 (face-attribute 'bold :weight)
2478 @c FIXME: Add an index for "relative face attribute", maybe here? --xfq
2479 @defun face-attribute-relative-p attribute value
2480 This function returns non-@code{nil} if @var{value}, when used as the
2481 value of the face attribute @var{attribute}, is relative. This means
2482 it would modify, rather than completely override, any value that comes
2483 from a subsequent face in the face list or that is inherited from
2486 @code{unspecified} is a relative value for all attributes. For
2487 @code{:height}, floating point and function values are also relative.
2492 (face-attribute-relative-p :height 2.0)
2497 @defun face-all-attributes face &optional frame
2498 This function returns an alist of attributes of @var{face}. The
2499 elements of the result are name-value pairs of the form
2500 @w{@code{(@var{attr-name} . @var{attr-value})}}. Optional argument
2501 @var{frame} specifies the frame whose definition of @var{face} to
2502 return; if omitted or @code{nil}, the returned value describes the
2503 default attributes of @var{face} for newly created frames.
2506 @defun merge-face-attribute attribute value1 value2
2507 If @var{value1} is a relative value for the face attribute
2508 @var{attribute}, returns it merged with the underlying value
2509 @var{value2}; otherwise, if @var{value1} is an absolute value for the
2510 face attribute @var{attribute}, returns @var{value1} unchanged.
2513 Normally, Emacs uses the face specs of each face to automatically
2514 calculate its attributes on each frame (@pxref{Defining Faces}). The
2515 function @code{set-face-attribute} can override this calculation by
2516 directly assigning attributes to a face, either on a specific frame or
2517 for all frames. This function is mostly intended for internal usage.
2519 @defun set-face-attribute face frame &rest arguments
2520 This function sets one or more attributes of @var{face} for
2521 @var{frame}. The attributes specifies in this way override the face
2522 spec(s) belonging to @var{face}.
2524 The extra arguments @var{arguments} specify the attributes to set, and
2525 the values for them. They should consist of alternating attribute
2526 names (such as @code{:family} or @code{:underline}) and values. Thus,
2529 (set-face-attribute 'foo nil :weight 'bold :slant 'italic)
2533 sets the attribute @code{:weight} to @code{bold} and the attribute
2534 @code{:slant} to @code{italic}.
2537 If @var{frame} is @code{t}, this function sets the default attributes
2538 for newly created frames. If @var{frame} is @code{nil}, this function
2539 sets the attributes for all existing frames, as well as for newly
2543 The following commands and functions mostly provide compatibility
2544 with old versions of Emacs. They work by calling
2545 @code{set-face-attribute}. Values of @code{t} and @code{nil} for
2546 their @var{frame} argument are handled just like
2547 @code{set-face-attribute} and @code{face-attribute}. The commands
2548 read their arguments using the minibuffer, if called interactively.
2550 @deffn Command set-face-foreground face color &optional frame
2551 @deffnx Command set-face-background face color &optional frame
2552 These set the @code{:foreground} attribute (or @code{:background}
2553 attribute, respectively) of @var{face} to @var{color}.
2556 @deffn Command set-face-stipple face pattern &optional frame
2557 This sets the @code{:stipple} attribute of @var{face} to
2561 @deffn Command set-face-font face font &optional frame
2562 This sets the @code{:font} attribute of @var{face} to @var{font}.
2565 @defun set-face-bold face bold-p &optional frame
2566 This sets the @code{:weight} attribute of @var{face} to @var{normal}
2567 if @var{bold-p} is @code{nil}, and to @var{bold} otherwise.
2570 @defun set-face-italic face italic-p &optional frame
2571 This sets the @code{:slant} attribute of @var{face} to @var{normal} if
2572 @var{italic-p} is @code{nil}, and to @var{italic} otherwise.
2575 @defun set-face-underline face underline &optional frame
2576 This sets the @code{:underline} attribute of @var{face} to
2580 @defun set-face-inverse-video face inverse-video-p &optional frame
2581 This sets the @code{:inverse-video} attribute of @var{face} to
2582 @var{inverse-video-p}.
2585 @deffn Command invert-face face &optional frame
2586 This swaps the foreground and background colors of face @var{face}.
2589 The following functions examine the attributes of a face. They
2590 mostly provide compatibility with old versions of Emacs. If you don't
2591 specify @var{frame}, they refer to the selected frame; @code{t} refers
2592 to the default data for new frames. They return @code{unspecified} if
2593 the face doesn't define any value for that attribute. If
2594 @var{inherit} is @code{nil}, only an attribute directly defined by the
2595 face is returned. If @var{inherit} is non-@code{nil}, any faces
2596 specified by its @code{:inherit} attribute are considered as well, and
2597 if @var{inherit} is a face or a list of faces, then they are also
2598 considered, until a specified attribute is found. To ensure that the
2599 return value is always specified, use a value of @code{default} for
2602 @defun face-font face &optional frame
2603 This function returns the name of the font of face @var{face}.
2606 @defun face-foreground face &optional frame inherit
2607 @defunx face-background face &optional frame inherit
2608 These functions return the foreground color (or background color,
2609 respectively) of face @var{face}, as a string.
2612 @defun face-stipple face &optional frame inherit
2613 This function returns the name of the background stipple pattern of face
2614 @var{face}, or @code{nil} if it doesn't have one.
2617 @defun face-bold-p face &optional frame inherit
2618 This function returns a non-@code{nil} value if the @code{:weight}
2619 attribute of @var{face} is bolder than normal (i.e., one of
2620 @code{semi-bold}, @code{bold}, @code{extra-bold}, or
2621 @code{ultra-bold}). Otherwise, it returns @code{nil}.
2624 @defun face-italic-p face &optional frame inherit
2625 This function returns a non-@code{nil} value if the @code{:slant}
2626 attribute of @var{face} is @code{italic} or @code{oblique}, and
2627 @code{nil} otherwise.
2630 @defun face-underline-p face &optional frame inherit
2631 This function returns non-@code{nil} if face @var{face} specifies
2632 a non-@code{nil} @code{:underline} attribute.
2635 @defun face-inverse-video-p face &optional frame inherit
2636 This function returns non-@code{nil} if face @var{face} specifies
2637 a non-@code{nil} @code{:inverse-video} attribute.
2640 @node Displaying Faces
2641 @subsection Displaying Faces
2643 When Emacs displays a given piece of text, the visual appearance of
2644 the text may be determined by faces drawn from different sources. If
2645 these various sources together specify more than one face for a
2646 particular character, Emacs merges the attributes of the various
2647 faces. Here is the order in which Emacs merges the faces, from
2648 highest to lowest priority:
2652 If the text consists of a special glyph, the glyph can specify a
2653 particular face. @xref{Glyphs}.
2656 If the text lies within an active region, Emacs highlights it using
2657 the @code{region} face. @xref{Standard Faces,,, emacs, The GNU Emacs
2661 If the text lies within an overlay with a non-@code{nil} @code{face}
2662 property, Emacs applies the face(s) specified by that property. If
2663 the overlay has a @code{mouse-face} property and the mouse is ``near
2664 enough'' to the overlay, Emacs applies the face or face attributes
2665 specified by the @code{mouse-face} property instead. @xref{Overlay
2668 When multiple overlays cover one character, an overlay with higher
2669 priority overrides those with lower priority. @xref{Overlays}.
2672 If the text contains a @code{face} or @code{mouse-face} property,
2673 Emacs applies the specified faces and face attributes. @xref{Special
2674 Properties}. (This is how Font Lock mode faces are applied.
2675 @xref{Font Lock Mode}.)
2678 If the text lies within the mode line of the selected window, Emacs
2679 applies the @code{mode-line} face. For the mode line of a
2680 non-selected window, Emacs applies the @code{mode-line-inactive} face.
2681 For a header line, Emacs applies the @code{header-line} face.
2684 If any given attribute has not been specified during the preceding
2685 steps, Emacs applies the attribute of the @code{default} face.
2688 At each stage, if a face has a valid @code{:inherit} attribute,
2689 Emacs treats any attribute with an @code{unspecified} value as having
2690 the corresponding value drawn from the parent face(s). @pxref{Face
2691 Attributes}. Note that the parent face(s) may also leave the
2692 attribute unspecified; in that case, the attribute remains unspecified
2693 at the next level of face merging.
2695 @node Face Remapping
2696 @subsection Face Remapping
2698 The variable @code{face-remapping-alist} is used for buffer-local or
2699 global changes in the appearance of a face. For instance, it is used
2700 to implement the @code{text-scale-adjust} command (@pxref{Text
2701 Scale,,, emacs, The GNU Emacs Manual}).
2703 @defvar face-remapping-alist
2704 The value of this variable is an alist whose elements have the form
2705 @code{(@var{face} . @var{remapping})}. This causes Emacs to display
2706 any text having the face @var{face} with @var{remapping}, rather than
2707 the ordinary definition of @var{face}.
2709 @var{remapping} may be any face spec suitable for a @code{face} text
2710 property: either a face (i.e., a face name or a property list of
2711 attribute/value pairs), or a list of faces. For details, see the
2712 description of the @code{face} text property in @ref{Special
2713 Properties}. @var{remapping} serves as the complete specification for
2714 the remapped face---it replaces the normal definition of @var{face},
2715 instead of modifying it.
2717 If @code{face-remapping-alist} is buffer-local, its local value takes
2718 effect only within that buffer.
2720 Note: face remapping is non-recursive. If @var{remapping} references
2721 the same face name @var{face}, either directly or via the
2722 @code{:inherit} attribute of some other face in @var{remapping}, that
2723 reference uses the normal definition of @var{face}. For instance, if
2724 the @code{mode-line} face is remapped using this entry in
2725 @code{face-remapping-alist}:
2728 (mode-line italic mode-line)
2732 then the new definition of the @code{mode-line} face inherits from the
2733 @code{italic} face, and the @emph{normal} (non-remapped) definition of
2734 @code{mode-line} face.
2737 @cindex relative remapping, faces
2738 @cindex base remapping, faces
2739 The following functions implement a higher-level interface to
2740 @code{face-remapping-alist}. Most Lisp code should use these
2741 functions instead of setting @code{face-remapping-alist} directly, to
2742 avoid trampling on remappings applied elsewhere. These functions are
2743 intended for buffer-local remappings, so they all make
2744 @code{face-remapping-alist} buffer-local as a side-effect. They manage
2745 @code{face-remapping-alist} entries of the form
2748 (@var{face} @var{relative-spec-1} @var{relative-spec-2} @var{...} @var{base-spec})
2752 where, as explained above, each of the @var{relative-spec-N} and
2753 @var{base-spec} is either a face name, or a property list of
2754 attribute/value pairs. Each of the @dfn{relative remapping} entries,
2755 @var{relative-spec-N}, is managed by the
2756 @code{face-remap-add-relative} and @code{face-remap-remove-relative}
2757 functions; these are intended for simple modifications like changing
2758 the text size. The @dfn{base remapping} entry, @var{base-spec}, has
2759 the lowest priority and is managed by the @code{face-remap-set-base}
2760 and @code{face-remap-reset-base} functions; it is intended for major
2761 modes to remap faces in the buffers they control.
2763 @defun face-remap-add-relative face &rest specs
2764 This function adds the face spec in @var{specs} as relative
2765 remappings for face @var{face} in the current buffer. The remaining
2766 arguments, @var{specs}, should form either a list of face names, or a
2767 property list of attribute/value pairs.
2769 The return value is a Lisp object that serves as a ``cookie''; you can
2770 pass this object as an argument to @code{face-remap-remove-relative}
2771 if you need to remove the remapping later.
2774 ;; Remap the `escape-glyph' face into a combination
2775 ;; of the `highlight' and `italic' faces:
2776 (face-remap-add-relative 'escape-glyph 'highlight 'italic)
2778 ;; Increase the size of the `default' face by 50%:
2779 (face-remap-add-relative 'default :height 1.5)
2783 @defun face-remap-remove-relative cookie
2784 This function removes a relative remapping previously added by
2785 @code{face-remap-add-relative}. @var{cookie} should be the Lisp
2786 object returned by @code{face-remap-add-relative} when the remapping
2790 @defun face-remap-set-base face &rest specs
2791 This function sets the base remapping of @var{face} in the current
2792 buffer to @var{specs}. If @var{specs} is empty, the default base
2793 remapping is restored, similar to calling @code{face-remap-reset-base}
2794 (see below); note that this is different from @var{specs} containing a
2795 single value @code{nil}, which has the opposite result (the global
2796 definition of @var{face} is ignored).
2798 This overwrites the default @var{base-spec}, which inherits the global
2799 face definition, so it is up to the caller to add such inheritance if
2803 @defun face-remap-reset-base face
2804 This function sets the base remapping of @var{face} to its default
2805 value, which inherits from @var{face}'s global definition.
2808 @node Face Functions
2809 @subsection Functions for Working with Faces
2811 Here are additional functions for creating and working with faces.
2814 This function returns a list of all defined face names.
2818 This function returns the @dfn{face number} of face @var{face}. This
2819 is a number that uniquely identifies a face at low levels within
2820 Emacs. It is seldom necessary to refer to a face by its face number.
2823 @defun face-documentation face
2824 This function returns the documentation string of face @var{face}, or
2825 @code{nil} if none was specified for it.
2828 @defun face-equal face1 face2 &optional frame
2829 This returns @code{t} if the faces @var{face1} and @var{face2} have the
2830 same attributes for display.
2833 @defun face-differs-from-default-p face &optional frame
2834 This returns non-@code{nil} if the face @var{face} displays
2835 differently from the default face.
2839 @cindex alias, for faces
2840 A @dfn{face alias} provides an equivalent name for a face. You can
2841 define a face alias by giving the alias symbol the @code{face-alias}
2842 property, with a value of the target face name. The following example
2843 makes @code{modeline} an alias for the @code{mode-line} face.
2846 (put 'modeline 'face-alias 'mode-line)
2849 @defmac define-obsolete-face-alias obsolete-face current-face when
2850 This macro defines @code{obsolete-face} as an alias for
2851 @var{current-face}, and also marks it as obsolete, indicating that it
2852 may be removed in future. @var{when} should be a string indicating
2853 when @code{obsolete-face} was made obsolete (usually a version number
2858 @subsection Automatic Face Assignment
2859 @cindex automatic face assignment
2860 @cindex faces, automatic choice
2862 This hook is used for automatically assigning faces to text in the
2863 buffer. It is part of the implementation of Jit-Lock mode, used by
2866 @defvar fontification-functions
2867 This variable holds a list of functions that are called by Emacs
2868 redisplay as needed, just before doing redisplay. They are called even
2869 when Font Lock Mode isn't enabled. When Font Lock Mode is enabled, this
2870 variable usually holds just one function, @code{jit-lock-function}.
2872 The functions are called in the order listed, with one argument, a
2873 buffer position @var{pos}. Collectively they should attempt to assign
2874 faces to the text in the current buffer starting at @var{pos}.
2876 The functions should record the faces they assign by setting the
2877 @code{face} property. They should also add a non-@code{nil}
2878 @code{fontified} property to all the text they have assigned faces to.
2879 That property tells redisplay that faces have been assigned to that text
2882 It is probably a good idea for the functions to do nothing if the
2883 character after @var{pos} already has a non-@code{nil} @code{fontified}
2884 property, but this is not required. If one function overrides the
2885 assignments made by a previous one, the properties after the last
2886 function finishes are the ones that really matter.
2888 For efficiency, we recommend writing these functions so that they
2889 usually assign faces to around 400 to 600 characters at each call.
2893 @subsection Basic Faces
2895 If your Emacs Lisp program needs to assign some faces to text, it is
2896 often a good idea to use certain existing faces or inherit from them,
2897 rather than defining entirely new faces. This way, if other users
2898 have customized the basic faces to give Emacs a certain look, your
2899 program will ``fit in'' without additional customization.
2901 Some of the basic faces defined in Emacs are listed below. In
2902 addition to these, you might want to make use of the Font Lock faces
2903 for syntactic highlighting, if highlighting is not already handled by
2904 Font Lock mode, or if some Font Lock faces are not in use.
2905 @xref{Faces for Font Lock}.
2909 The default face, whose attributes are all specified. All other faces
2910 implicitly inherit from it: any unspecified attribute defaults to the
2911 attribute on this face (@pxref{Face Attributes}).
2918 @itemx variable-pitch
2919 These have the attributes indicated by their names (e.g., @code{bold}
2920 has a bold @code{:weight} attribute), with all other attributes
2921 unspecified (and so given by @code{default}).
2924 For ``dimmed out'' text. For example, it is used for the ignored
2925 part of a filename in the minibuffer (@pxref{Minibuffer File,,
2926 Minibuffers for File Names, emacs, The GNU Emacs Manual}).
2930 For clickable text buttons that send the user to a different
2931 buffer or ``location''.
2934 For stretches of text that should temporarily stand out. For example,
2935 it is commonly assigned to the @code{mouse-face} property for cursor
2936 highlighting (@pxref{Special Properties}).
2939 For text matching a search command.
2944 For text concerning errors, warnings, or successes. For example,
2945 these are used for messages in @file{*Compilation*} buffers.
2948 @node Font Selection
2949 @subsection Font Selection
2950 @cindex font selection
2951 @cindex selecting a font
2953 Before Emacs can draw a character on a graphical display, it must
2954 select a @dfn{font} for that character@footnote{In this context, the
2955 term @dfn{font} has nothing to do with Font Lock (@pxref{Font Lock
2956 Mode}).}. @xref{Fonts,,, emacs, The GNU Emacs Manual}. Normally,
2957 Emacs automatically chooses a font based on the faces assigned to that
2958 character---specifically, the face attributes @code{:family},
2959 @code{:weight}, @code{:slant}, and @code{:width} (@pxref{Face
2960 Attributes}). The choice of font also depends on the character to be
2961 displayed; some fonts can only display a limited set of characters.
2962 If no available font exactly fits the requirements, Emacs looks for
2963 the @dfn{closest matching font}. The variables in this section
2964 control how Emacs makes this selection.
2966 @defopt face-font-family-alternatives
2967 If a given family is specified but does not exist, this variable
2968 specifies alternative font families to try. Each element should have
2972 (@var{family} @var{alternate-families}@dots{})
2975 If @var{family} is specified but not available, Emacs will try the other
2976 families given in @var{alternate-families}, one by one, until it finds a
2977 family that does exist.
2980 @defopt face-font-selection-order
2981 If there is no font that exactly matches all desired face attributes
2982 (@code{:width}, @code{:height}, @code{:weight}, and @code{:slant}),
2983 this variable specifies the order in which these attributes should be
2984 considered when selecting the closest matching font. The value should
2985 be a list containing those four attribute symbols, in order of
2986 decreasing importance. The default is @code{(:width :height :weight
2989 Font selection first finds the best available matches for the first
2990 attribute in the list; then, among the fonts which are best in that
2991 way, it searches for the best matches in the second attribute, and so
2994 The attributes @code{:weight} and @code{:width} have symbolic values in
2995 a range centered around @code{normal}. Matches that are more extreme
2996 (farther from @code{normal}) are somewhat preferred to matches that are
2997 less extreme (closer to @code{normal}); this is designed to ensure that
2998 non-normal faces contrast with normal ones, whenever possible.
3000 One example of a case where this variable makes a difference is when the
3001 default font has no italic equivalent. With the default ordering, the
3002 @code{italic} face will use a non-italic font that is similar to the
3003 default one. But if you put @code{:slant} before @code{:height}, the
3004 @code{italic} face will use an italic font, even if its height is not
3008 @defopt face-font-registry-alternatives
3009 This variable lets you specify alternative font registries to try, if a
3010 given registry is specified and doesn't exist. Each element should have
3014 (@var{registry} @var{alternate-registries}@dots{})
3017 If @var{registry} is specified but not available, Emacs will try the
3018 other registries given in @var{alternate-registries}, one by one,
3019 until it finds a registry that does exist.
3022 @cindex scalable fonts
3023 Emacs can make use of scalable fonts, but by default it does not use
3026 @defopt scalable-fonts-allowed
3027 This variable controls which scalable fonts to use. A value of
3028 @code{nil}, the default, means do not use scalable fonts. @code{t}
3029 means to use any scalable font that seems appropriate for the text.
3031 Otherwise, the value must be a list of regular expressions. Then a
3032 scalable font is enabled for use if its name matches any regular
3033 expression in the list. For example,
3036 (setq scalable-fonts-allowed '("iso10646-1$"))
3040 allows the use of scalable fonts with registry @code{iso10646-1}.
3043 @defvar face-font-rescale-alist
3044 This variable specifies scaling for certain faces. Its value should
3045 be a list of elements of the form
3048 (@var{fontname-regexp} . @var{scale-factor})
3051 If @var{fontname-regexp} matches the font name that is about to be
3052 used, this says to choose a larger similar font according to the
3053 factor @var{scale-factor}. You would use this feature to normalize
3054 the font size if certain fonts are bigger or smaller than their
3055 nominal heights and widths would suggest.
3059 @subsection Looking Up Fonts
3061 @defun x-list-fonts name &optional reference-face frame maximum width
3062 This function returns a list of available font names that match
3063 @var{name}. @var{name} should be a string containing a font name in
3064 either the Fontconfig, GTK, or XLFD format (@pxref{Fonts,,, emacs, The
3065 GNU Emacs Manual}). Within an XLFD string, wildcard characters may be
3066 used: the @samp{*} character matches any substring, and the @samp{?}
3067 character matches any single character. Case is ignored when matching
3070 If the optional arguments @var{reference-face} and @var{frame} are
3071 specified, the returned list includes only fonts that are the same
3072 size as @var{reference-face} (a face name) currently is on the frame
3075 The optional argument @var{maximum} sets a limit on how many fonts to
3076 return. If it is non-@code{nil}, then the return value is truncated
3077 after the first @var{maximum} matching fonts. Specifying a small
3078 value for @var{maximum} can make this function much faster, in cases
3079 where many fonts match the pattern.
3081 The optional argument @var{width} specifies a desired font width. If
3082 it is non-@code{nil}, the function only returns those fonts whose
3083 characters are (on average) @var{width} times as wide as
3084 @var{reference-face}.
3087 @defun x-family-fonts &optional family frame
3088 This function returns a list describing the available fonts for family
3089 @var{family} on @var{frame}. If @var{family} is omitted or @code{nil},
3090 this list applies to all families, and therefore, it contains all
3091 available fonts. Otherwise, @var{family} must be a string; it may
3092 contain the wildcards @samp{?} and @samp{*}.
3094 The list describes the display that @var{frame} is on; if @var{frame} is
3095 omitted or @code{nil}, it applies to the selected frame's display
3096 (@pxref{Input Focus}).
3098 Each element in the list is a vector of the following form:
3101 [@var{family} @var{width} @var{point-size} @var{weight} @var{slant}
3102 @var{fixed-p} @var{full} @var{registry-and-encoding}]
3105 The first five elements correspond to face attributes; if you
3106 specify these attributes for a face, it will use this font.
3108 The last three elements give additional information about the font.
3109 @var{fixed-p} is non-@code{nil} if the font is fixed-pitch.
3110 @var{full} is the full name of the font, and
3111 @var{registry-and-encoding} is a string giving the registry and
3112 encoding of the font.
3116 @subsection Fontsets
3118 A @dfn{fontset} is a list of fonts, each assigned to a range of
3119 character codes. An individual font cannot display the whole range of
3120 characters that Emacs supports, but a fontset can. Fontsets have names,
3121 just as fonts do, and you can use a fontset name in place of a font name
3122 when you specify the ``font'' for a frame or a face. Here is
3123 information about defining a fontset under Lisp program control.
3125 @defun create-fontset-from-fontset-spec fontset-spec &optional style-variant-p noerror
3126 This function defines a new fontset according to the specification
3127 string @var{fontset-spec}. The string should have this format:
3130 @var{fontpattern}, @r{[}@var{charset}:@var{font}@r{]@dots{}}
3134 Whitespace characters before and after the commas are ignored.
3136 The first part of the string, @var{fontpattern}, should have the form of
3137 a standard X font name, except that the last two fields should be
3138 @samp{fontset-@var{alias}}.
3140 The new fontset has two names, one long and one short. The long name is
3141 @var{fontpattern} in its entirety. The short name is
3142 @samp{fontset-@var{alias}}. You can refer to the fontset by either
3143 name. If a fontset with the same name already exists, an error is
3144 signaled, unless @var{noerror} is non-@code{nil}, in which case this
3145 function does nothing.
3147 If optional argument @var{style-variant-p} is non-@code{nil}, that says
3148 to create bold, italic and bold-italic variants of the fontset as well.
3149 These variant fontsets do not have a short name, only a long one, which
3150 is made by altering @var{fontpattern} to indicate the bold and/or italic
3153 The specification string also says which fonts to use in the fontset.
3154 See below for the details.
3157 The construct @samp{@var{charset}:@var{font}} specifies which font to
3158 use (in this fontset) for one particular character set. Here,
3159 @var{charset} is the name of a character set, and @var{font} is the font
3160 to use for that character set. You can use this construct any number of
3161 times in the specification string.
3163 For the remaining character sets, those that you don't specify
3164 explicitly, Emacs chooses a font based on @var{fontpattern}: it replaces
3165 @samp{fontset-@var{alias}} with a value that names one character set.
3166 For the @acronym{ASCII} character set, @samp{fontset-@var{alias}} is replaced
3167 with @samp{ISO8859-1}.
3169 In addition, when several consecutive fields are wildcards, Emacs
3170 collapses them into a single wildcard. This is to prevent use of
3171 auto-scaled fonts. Fonts made by scaling larger fonts are not usable
3172 for editing, and scaling a smaller font is not useful because it is
3173 better to use the smaller font in its own size, which Emacs does.
3175 Thus if @var{fontpattern} is this,
3178 -*-fixed-medium-r-normal-*-24-*-*-*-*-*-fontset-24
3182 the font specification for @acronym{ASCII} characters would be this:
3185 -*-fixed-medium-r-normal-*-24-*-ISO8859-1
3189 and the font specification for Chinese GB2312 characters would be this:
3192 -*-fixed-medium-r-normal-*-24-*-gb2312*-*
3195 You may not have any Chinese font matching the above font
3196 specification. Most X distributions include only Chinese fonts that
3197 have @samp{song ti} or @samp{fangsong ti} in the @var{family} field. In
3198 such a case, @samp{Fontset-@var{n}} can be specified as below:
3201 Emacs.Fontset-0: -*-fixed-medium-r-normal-*-24-*-*-*-*-*-fontset-24,\
3202 chinese-gb2312:-*-*-medium-r-normal-*-24-*-gb2312*-*
3206 Then, the font specifications for all but Chinese GB2312 characters have
3207 @samp{fixed} in the @var{family} field, and the font specification for
3208 Chinese GB2312 characters has a wild card @samp{*} in the @var{family}
3211 @defun set-fontset-font name character font-spec &optional frame add
3212 This function modifies the existing fontset @var{name} to use the font
3213 matching with @var{font-spec} for the character @var{character}.
3215 If @var{name} is @code{nil}, this function modifies the fontset of the
3216 selected frame or that of @var{frame} if @var{frame} is not
3219 If @var{name} is @code{t}, this function modifies the default
3220 fontset, whose short name is @samp{fontset-default}.
3222 @var{character} may be a cons; @code{(@var{from} . @var{to})}, where
3223 @var{from} and @var{to} are character codepoints. In that case, use
3224 @var{font-spec} for all characters in the range @var{from} and @var{to}
3227 @var{character} may be a charset. In that case, use
3228 @var{font-spec} for all character in the charsets.
3230 @var{character} may be a script name. In that case, use
3231 @var{font-spec} for all character in the charsets.
3233 @var{font-spec} may be a cons; @code{(@var{family} . @var{registry})},
3234 where @var{family} is a family name of a font (possibly including a
3235 foundry name at the head), @var{registry} is a registry name of a font
3236 (possibly including an encoding name at the tail).
3238 @var{font-spec} may be a font name string.
3240 The optional argument @var{add}, if non-@code{nil}, specifies how to
3241 add @var{font-spec} to the font specifications previously set. If it
3242 is @code{prepend}, @var{font-spec} is prepended. If it is
3243 @code{append}, @var{font-spec} is appended. By default,
3244 @var{font-spec} overrides the previous settings.
3246 For instance, this changes the default fontset to use a font of which
3247 family name is @samp{Kochi Gothic} for all characters belonging to
3248 the charset @code{japanese-jisx0208}.
3251 (set-fontset-font t 'japanese-jisx0208
3252 (font-spec :family "Kochi Gothic"))
3256 @defun char-displayable-p char
3257 This function returns @code{t} if Emacs ought to be able to display
3258 @var{char}. More precisely, if the selected frame's fontset has a
3259 font to display the character set that @var{char} belongs to.
3261 Fontsets can specify a font on a per-character basis; when the fontset
3262 does that, this function's value may not be accurate.
3265 @node Low-Level Font
3266 @subsection Low-Level Font Representation
3267 @cindex font property
3269 Normally, it is not necessary to manipulate fonts directly. In case
3270 you need to do so, this section explains how.
3272 In Emacs Lisp, fonts are represented using three different Lisp
3273 object types: @dfn{font objects}, @dfn{font specs}, and @dfn{font
3276 @defun fontp object &optional type
3277 Return @code{t} if @var{object} is a font object, font spec, or font
3278 entity. Otherwise, return @code{nil}.
3280 The optional argument @var{type}, if non-@code{nil}, determines the
3281 exact type of Lisp object to check for. In that case, @var{type}
3282 should be one of @code{font-object}, @code{font-spec}, or
3287 A font object is a Lisp object that represents a font that Emacs has
3288 @dfn{opened}. Font objects cannot be modified in Lisp, but they can
3291 @defun font-at position &optional window string
3292 Return the font object that is being used to display the character at
3293 position @var{position} in the window @var{window}. If @var{window}
3294 is @code{nil}, it defaults to the selected window. If @var{string} is
3295 @code{nil}, @var{position} specifies a position in the current buffer;
3296 otherwise, @var{string} should be a string, and @var{position}
3297 specifies a position in that string.
3301 A font spec is a Lisp object that contains a set of specifications
3302 that can be used to find a font. More than one font may match the
3303 specifications in a font spec.
3305 @defun font-spec &rest arguments
3306 Return a new font spec using the specifications in @var{arguments},
3307 which should come in @code{property}-@code{value} pairs. The possible
3308 specifications are as follows:
3312 The font name (a string), in either XLFD, Fontconfig, or GTK format.
3313 @xref{Fonts,,, emacs, The GNU Emacs Manual}.
3320 These have the same meanings as the face attributes of the same name.
3321 @xref{Face Attributes}.
3324 The font size---either a non-negative integer that specifies the pixel
3325 size, or a floating-point number that specifies the point size.
3328 Additional typographic style information for the font, such as
3329 @samp{sans}. The value should be a string or a symbol.
3331 @cindex font registry
3333 The charset registry and encoding of the font, such as
3334 @samp{iso8859-1}. The value should be a string or a symbol.
3337 The script that the font must support (a symbol).
3340 @cindex OpenType font
3341 The font must be an OpenType font that supports these OpenType
3342 features, provided Emacs is compiled with support for @samp{libotf} (a
3343 library for performing complex text layout in certain scripts). The
3344 value must be a list of the form
3347 @code{(@var{script-tag} @var{langsys-tag} @var{gsub} @var{gpos})}
3350 where @var{script-tag} is the OpenType script tag symbol;
3351 @var{langsys-tag} is the OpenType language system tag symbol, or
3352 @code{nil} to use the default language system; @code{gsub} is a list
3353 of OpenType GSUB feature tag symbols, or @code{nil} if none is
3354 required; and @code{gpos} is a list of OpenType GPOS feature tag
3355 symbols, or @code{nil} if none is required. If @code{gsub} or
3356 @code{gpos} is a list, a @code{nil} element in that list means that
3357 the font must not match any of the remaining tag symbols. The
3358 @code{gpos} element may be omitted.
3362 @defun font-put font-spec property value
3363 Set the font property @var{property} in the font-spec @var{font-spec}
3368 A font entity is a reference to a font that need not be open. Its
3369 properties are intermediate between a font object and a font spec:
3370 like a font object, and unlike a font spec, it refers to a single,
3371 specific font. Unlike a font object, creating a font entity does not
3372 load the contents of that font into computer memory. Emacs may open
3373 multiple font objects of different sizes from a single font entity
3374 referring to a scalable font.
3376 @defun find-font font-spec &optional frame
3377 This function returns a font entity that best matches the font spec
3378 @var{font-spec} on frame @var{frame}. If @var{frame} is @code{nil},
3379 it defaults to the selected frame.
3382 @defun list-fonts font-spec &optional frame num prefer
3383 This function returns a list of all font entities that match the font
3384 spec @var{font-spec}.
3386 The optional argument @var{frame}, if non-@code{nil}, specifies the
3387 frame on which the fonts are to be displayed. The optional argument
3388 @var{num}, if non-@code{nil}, should be an integer that specifies the
3389 maximum length of the returned list. The optional argument
3390 @var{prefer}, if non-@code{nil}, should be another font spec, which is
3391 used to control the order of the returned list; the returned font
3392 entities are sorted in order of decreasing ``closeness'' to that font
3396 If you call @code{set-face-attribute} and pass a font spec, font
3397 entity, or font name string as the value of the @code{:font}
3398 attribute, Emacs opens the best ``matching'' font that is available
3399 for display. It then stores the corresponding font object as the
3400 actual value of the @code{:font} attribute for that face.
3402 The following functions can be used to obtain information about a
3403 font. For these functions, the @var{font} argument can be a font
3404 object, a font entity, or a font spec.
3406 @defun font-get font property
3407 This function returns the value of the font property @var{property}
3410 If @var{font} is a font spec and the font spec does not specify
3411 @var{property}, the return value is @code{nil}. If @var{font} is a
3412 font object or font entity, the value for the @var{:script} property
3413 may be a list of scripts supported by the font.
3416 @defun font-face-attributes font &optional frame
3417 This function returns a list of face attributes corresponding to
3418 @var{font}. The optional argument @var{frame} specifies the frame on
3419 which the font is to be displayed. If it is @code{nil}, the selected
3420 frame is used. The return value has the form
3423 (:family @var{family} :height @var{height} :weight @var{weight}
3424 :slant @var{slant} :width @var{width})
3427 where the values of @var{family}, @var{height}, @var{weight},
3428 @var{slant}, and @var{width} are face attribute values. Some of these
3429 key-attribute pairs may be omitted from the list if they are not
3430 specified by @var{font}.
3433 @defun font-xlfd-name font &optional fold-wildcards
3434 This function returns the XLFD (X Logical Font Descriptor), a string,
3435 matching @var{font}. @xref{Fonts,,, emacs, The GNU Emacs Manual}, for
3436 information about XLFDs. If the name is too long for an XLFD (which
3437 can contain at most 255 characters), the function returns @code{nil}.
3439 If the optional argument @var{fold-wildcards} is non-@code{nil},
3440 consecutive wildcards in the XLFD are folded into one.
3447 On graphical displays, Emacs draws @dfn{fringes} next to each
3448 window: thin vertical strips down the sides which can display bitmaps
3449 indicating truncation, continuation, horizontal scrolling, and so on.
3452 * Fringe Size/Pos:: Specifying where to put the window fringes.
3453 * Fringe Indicators:: Displaying indicator icons in the window fringes.
3454 * Fringe Cursors:: Displaying cursors in the right fringe.
3455 * Fringe Bitmaps:: Specifying bitmaps for fringe indicators.
3456 * Customizing Bitmaps:: Specifying your own bitmaps to use in the fringes.
3457 * Overlay Arrow:: Display of an arrow to indicate position.
3460 @node Fringe Size/Pos
3461 @subsection Fringe Size and Position
3463 The following buffer-local variables control the position and width
3464 of fringes in windows showing that buffer.
3466 @defvar fringes-outside-margins
3467 The fringes normally appear between the display margins and the window
3468 text. If the value is non-@code{nil}, they appear outside the display
3469 margins. @xref{Display Margins}.
3472 @defvar left-fringe-width
3473 This variable, if non-@code{nil}, specifies the width of the left
3474 fringe in pixels. A value of @code{nil} means to use the left fringe
3475 width from the window's frame.
3478 @defvar right-fringe-width
3479 This variable, if non-@code{nil}, specifies the width of the right
3480 fringe in pixels. A value of @code{nil} means to use the right fringe
3481 width from the window's frame.
3484 Any buffer which does not specify values for these variables uses
3485 the values specified by the @code{left-fringe} and @code{right-fringe}
3486 frame parameters (@pxref{Layout Parameters}).
3488 The above variables actually take effect via the function
3489 @code{set-window-buffer} (@pxref{Buffers and Windows}), which calls
3490 @code{set-window-fringes} as a subroutine. If you change one of these
3491 variables, the fringe display is not updated in existing windows
3492 showing the buffer, unless you call @code{set-window-buffer} again in
3493 each affected window. You can also use @code{set-window-fringes} to
3494 control the fringe display in individual windows.
3496 @defun set-window-fringes window left &optional right outside-margins
3497 This function sets the fringe widths of window @var{window}.
3498 If @var{window} is @code{nil}, the selected window is used.
3500 The argument @var{left} specifies the width in pixels of the left
3501 fringe, and likewise @var{right} for the right fringe. A value of
3502 @code{nil} for either one stands for the default width. If
3503 @var{outside-margins} is non-@code{nil}, that specifies that fringes
3504 should appear outside of the display margins.
3507 @defun window-fringes &optional window
3508 This function returns information about the fringes of a window
3509 @var{window}. If @var{window} is omitted or @code{nil}, the selected
3510 window is used. The value has the form @code{(@var{left-width}
3511 @var{right-width} @var{outside-margins})}.
3515 @node Fringe Indicators
3516 @subsection Fringe Indicators
3517 @cindex fringe indicators
3518 @cindex indicators, fringe
3520 @dfn{Fringe indicators} are tiny icons displayed in the window
3521 fringe to indicate truncated or continued lines, buffer boundaries,
3524 @defopt indicate-empty-lines
3525 @cindex fringes, and empty line indication
3526 @cindex empty lines, indicating
3527 When this is non-@code{nil}, Emacs displays a special glyph in the
3528 fringe of each empty line at the end of the buffer, on graphical
3529 displays. @xref{Fringes}. This variable is automatically
3530 buffer-local in every buffer.
3533 @defopt indicate-buffer-boundaries
3534 @cindex buffer boundaries, indicating
3535 This buffer-local variable controls how the buffer boundaries and
3536 window scrolling are indicated in the window fringes.
3538 Emacs can indicate the buffer boundaries---that is, the first and last
3539 line in the buffer---with angle icons when they appear on the screen.
3540 In addition, Emacs can display an up-arrow in the fringe to show
3541 that there is text above the screen, and a down-arrow to show
3542 there is text below the screen.
3544 There are three kinds of basic values:
3548 Don't display any of these fringe icons.
3550 Display the angle icons and arrows in the left fringe.
3552 Display the angle icons and arrows in the right fringe.
3554 Display the angle icons in the left fringe
3555 and don't display the arrows.
3558 Otherwise the value should be an alist that specifies which fringe
3559 indicators to display and where. Each element of the alist should
3560 have the form @code{(@var{indicator} . @var{position})}. Here,
3561 @var{indicator} is one of @code{top}, @code{bottom}, @code{up},
3562 @code{down}, and @code{t} (which covers all the icons not yet
3563 specified), while @var{position} is one of @code{left}, @code{right}
3566 For example, @code{((top . left) (t . right))} places the top angle
3567 bitmap in left fringe, and the bottom angle bitmap as well as both
3568 arrow bitmaps in right fringe. To show the angle bitmaps in the left
3569 fringe, and no arrow bitmaps, use @code{((top . left) (bottom . left))}.
3572 @defvar fringe-indicator-alist
3573 This buffer-local variable specifies the mapping from logical fringe
3574 indicators to the actual bitmaps displayed in the window fringes. The
3575 value is an alist of elements @code{(@var{indicator}
3576 . @var{bitmaps})}, where @var{indicator} specifies a logical indicator
3577 type and @var{bitmaps} specifies the fringe bitmaps to use for that
3580 Each @var{indicator} should be one of the following symbols:
3583 @item @code{truncation}, @code{continuation}.
3584 Used for truncation and continuation lines.
3586 @item @code{up}, @code{down}, @code{top}, @code{bottom}, @code{top-bottom}
3587 Used when @code{indicate-buffer-boundaries} is non-@code{nil}:
3588 @code{up} and @code{down} indicate a buffer boundary lying above or
3589 below the window edge; @code{top} and @code{bottom} indicate the
3590 topmost and bottommost buffer text line; and @code{top-bottom}
3591 indicates where there is just one line of text in the buffer.
3593 @item @code{empty-line}
3594 Used to indicate empty lines when @code{indicate-empty-lines} is
3597 @item @code{overlay-arrow}
3598 Used for overlay arrows (@pxref{Overlay Arrow}).
3599 @c Is this used anywhere?
3600 @c @item Unknown bitmap indicator:
3604 Each @var{bitmaps} value may be a list of symbols @code{(@var{left}
3605 @var{right} [@var{left1} @var{right1}])}. The @var{left} and
3606 @var{right} symbols specify the bitmaps shown in the left and/or right
3607 fringe, for the specific indicator. @var{left1} and @var{right1} are
3608 specific to the @code{bottom} and @code{top-bottom} indicators, and
3609 are used to indicate that the last text line has no final newline.
3610 Alternatively, @var{bitmaps} may be a single symbol which is used in
3611 both left and right fringes.
3613 @xref{Fringe Bitmaps}, for a list of standard bitmap symbols and how
3614 to define your own. In addition, @code{nil} represents the empty
3615 bitmap (i.e., an indicator that is not shown).
3617 When @code{fringe-indicator-alist} has a buffer-local value, and
3618 there is no bitmap defined for a logical indicator, or the bitmap is
3619 @code{t}, the corresponding value from the default value of
3620 @code{fringe-indicator-alist} is used.
3623 @node Fringe Cursors
3624 @subsection Fringe Cursors
3625 @cindex fringe cursors
3626 @cindex cursor, fringe
3628 When a line is exactly as wide as the window, Emacs displays the
3629 cursor in the right fringe instead of using two lines. Different
3630 bitmaps are used to represent the cursor in the fringe depending on
3631 the current buffer's cursor type.
3633 @defopt overflow-newline-into-fringe
3634 If this is non-@code{nil}, lines exactly as wide as the window (not
3635 counting the final newline character) are not continued. Instead,
3636 when point is at the end of the line, the cursor appears in the right
3640 @defvar fringe-cursor-alist
3641 This variable specifies the mapping from logical cursor type to the
3642 actual fringe bitmaps displayed in the right fringe. The value is an
3643 alist where each element has the form @code{(@var{cursor-type}
3644 . @var{bitmap})}, which means to use the fringe bitmap @var{bitmap} to
3645 display cursors of type @var{cursor-type}.
3647 Each @var{cursor-type} should be one of @code{box}, @code{hollow},
3648 @code{bar}, @code{hbar}, or @code{hollow-small}. The first four have
3649 the same meanings as in the @code{cursor-type} frame parameter
3650 (@pxref{Cursor Parameters}). The @code{hollow-small} type is used
3651 instead of @code{hollow} when the normal @code{hollow-rectangle}
3652 bitmap is too tall to fit on a specific display line.
3654 Each @var{bitmap} should be a symbol specifying the fringe bitmap to
3655 be displayed for that logical cursor type.
3657 See the next subsection for details.
3660 @xref{Fringe Bitmaps}.
3663 @c FIXME: I can't find the fringes-indicator-alist variable. Maybe
3664 @c it should be fringe-indicator-alist or fringe-cursor-alist? --xfq
3665 When @code{fringe-cursor-alist} has a buffer-local value, and there is
3666 no bitmap defined for a cursor type, the corresponding value from the
3667 default value of @code{fringes-indicator-alist} is used.
3670 @node Fringe Bitmaps
3671 @subsection Fringe Bitmaps
3672 @cindex fringe bitmaps
3673 @cindex bitmaps, fringe
3675 The @dfn{fringe bitmaps} are the actual bitmaps which represent the
3676 logical fringe indicators for truncated or continued lines, buffer
3677 boundaries, overlay arrows, etc. Each bitmap is represented by a
3680 These symbols are referred to by the variables
3681 @code{fringe-indicator-alist} and @code{fringe-cursor-alist},
3682 described in the previous subsections.
3685 These symbols are referred to by the variable
3686 @code{fringe-indicator-alist}, which maps fringe indicators to bitmaps
3687 (@pxref{Fringe Indicators}), and the variable
3688 @code{fringe-cursor-alist}, which maps fringe cursors to bitmaps
3689 (@pxref{Fringe Cursors}).
3692 Lisp programs can also directly display a bitmap in the left or
3693 right fringe, by using a @code{display} property for one of the
3694 characters appearing in the line (@pxref{Other Display Specs}). Such
3695 a display specification has the form
3698 (@var{fringe} @var{bitmap} [@var{face}])
3702 @var{fringe} is either the symbol @code{left-fringe} or
3703 @code{right-fringe}. @var{bitmap} is a symbol identifying the bitmap
3704 to display. The optional @var{face} names a face whose foreground
3705 color is used to display the bitmap; this face is automatically merged
3706 with the @code{fringe} face.
3708 Here is a list of the standard fringe bitmaps defined in Emacs, and
3709 how they are currently used in Emacs (via
3710 @code{fringe-indicator-alist} and @code{fringe-cursor-alist}):
3713 @item @code{left-arrow}, @code{right-arrow}
3714 Used to indicate truncated lines.
3716 @item @code{left-curly-arrow}, @code{right-curly-arrow}
3717 Used to indicate continued lines.
3719 @item @code{right-triangle}, @code{left-triangle}
3720 The former is used by overlay arrows. The latter is unused.
3722 @item @code{up-arrow}, @code{down-arrow}, @code{top-left-angle} @code{top-right-angle}
3723 @itemx @code{bottom-left-angle}, @code{bottom-right-angle}
3724 @itemx @code{top-right-angle}, @code{top-left-angle}
3725 @itemx @code{left-bracket}, @code{right-bracket}, @code{top-right-angle}, @code{top-left-angle}
3726 Used to indicate buffer boundaries.
3728 @item @code{filled-rectangle}, @code{hollow-rectangle}
3729 @itemx @code{filled-square}, @code{hollow-square}
3730 @itemx @code{vertical-bar}, @code{horizontal-bar}
3731 Used for different types of fringe cursors.
3733 @item @code{empty-line}, @code{exclamation-mark}, @code{question-mark}, @code{exclamation-mark}
3734 Not used by core Emacs features.
3738 The next subsection describes how to define your own fringe bitmaps.
3740 @defun fringe-bitmaps-at-pos &optional pos window
3741 This function returns the fringe bitmaps of the display line
3742 containing position @var{pos} in window @var{window}. The return
3743 value has the form @code{(@var{left} @var{right} @var{ov})}, where @var{left}
3744 is the symbol for the fringe bitmap in the left fringe (or @code{nil}
3745 if no bitmap), @var{right} is similar for the right fringe, and @var{ov}
3746 is non-@code{nil} if there is an overlay arrow in the left fringe.
3748 The value is @code{nil} if @var{pos} is not visible in @var{window}.
3749 If @var{window} is @code{nil}, that stands for the selected window.
3750 If @var{pos} is @code{nil}, that stands for the value of point in
3754 @node Customizing Bitmaps
3755 @subsection Customizing Fringe Bitmaps
3756 @cindex fringe bitmaps, customizing
3758 @defun define-fringe-bitmap bitmap bits &optional height width align
3759 This function defines the symbol @var{bitmap} as a new fringe bitmap,
3760 or replaces an existing bitmap with that name.
3762 The argument @var{bits} specifies the image to use. It should be
3763 either a string or a vector of integers, where each element (an
3764 integer) corresponds to one row of the bitmap. Each bit of an integer
3765 corresponds to one pixel of the bitmap, where the low bit corresponds
3766 to the rightmost pixel of the bitmap.
3768 The height is normally the length of @var{bits}. However, you
3769 can specify a different height with non-@code{nil} @var{height}. The width
3770 is normally 8, but you can specify a different width with non-@code{nil}
3771 @var{width}. The width must be an integer between 1 and 16.
3773 The argument @var{align} specifies the positioning of the bitmap
3774 relative to the range of rows where it is used; the default is to
3775 center the bitmap. The allowed values are @code{top}, @code{center},
3778 The @var{align} argument may also be a list @code{(@var{align}
3779 @var{periodic})} where @var{align} is interpreted as described above.
3780 If @var{periodic} is non-@code{nil}, it specifies that the rows in
3781 @code{bits} should be repeated enough times to reach the specified
3785 @defun destroy-fringe-bitmap bitmap
3786 This function destroy the fringe bitmap identified by @var{bitmap}.
3787 If @var{bitmap} identifies a standard fringe bitmap, it actually
3788 restores the standard definition of that bitmap, instead of
3789 eliminating it entirely.
3792 @defun set-fringe-bitmap-face bitmap &optional face
3793 This sets the face for the fringe bitmap @var{bitmap} to @var{face}.
3794 If @var{face} is @code{nil}, it selects the @code{fringe} face. The
3795 bitmap's face controls the color to draw it in.
3797 @var{face} is merged with the @code{fringe} face, so normally
3798 @var{face} should specify only the foreground color.
3802 @subsection The Overlay Arrow
3803 @c @cindex overlay arrow Duplicates variable names
3805 The @dfn{overlay arrow} is useful for directing the user's attention
3806 to a particular line in a buffer. For example, in the modes used for
3807 interface to debuggers, the overlay arrow indicates the line of code
3808 about to be executed. This feature has nothing to do with
3809 @dfn{overlays} (@pxref{Overlays}).
3811 @defvar overlay-arrow-string
3812 This variable holds the string to display to call attention to a
3813 particular line, or @code{nil} if the arrow feature is not in use.
3814 On a graphical display the contents of the string are ignored; instead a
3815 glyph is displayed in the fringe area to the left of the display area.
3818 @defvar overlay-arrow-position
3819 This variable holds a marker that indicates where to display the overlay
3820 arrow. It should point at the beginning of a line. On a non-graphical
3821 display the arrow text
3822 appears at the beginning of that line, overlaying any text that would
3823 otherwise appear. Since the arrow is usually short, and the line
3824 usually begins with indentation, normally nothing significant is
3827 The overlay-arrow string is displayed in any given buffer if the value
3828 of @code{overlay-arrow-position} in that buffer points into that
3829 buffer. Thus, it is possible to display multiple overlay arrow strings
3830 by creating buffer-local bindings of @code{overlay-arrow-position}.
3831 However, it is usually cleaner to use
3832 @code{overlay-arrow-variable-list} to achieve this result.
3833 @c !!! overlay-arrow-position: but the overlay string may remain in the display
3834 @c of some other buffer until an update is required. This should be fixed
3838 You can do a similar job by creating an overlay with a
3839 @code{before-string} property. @xref{Overlay Properties}.
3841 You can define multiple overlay arrows via the variable
3842 @code{overlay-arrow-variable-list}.
3844 @defvar overlay-arrow-variable-list
3845 This variable's value is a list of variables, each of which specifies
3846 the position of an overlay arrow. The variable
3847 @code{overlay-arrow-position} has its normal meaning because it is on
3851 Each variable on this list can have properties
3852 @code{overlay-arrow-string} and @code{overlay-arrow-bitmap} that
3853 specify an overlay arrow string (for text terminals) or fringe bitmap
3854 (for graphical terminals) to display at the corresponding overlay
3855 arrow position. If either property is not set, the default
3856 @code{overlay-arrow-string} or @code{overlay-arrow} fringe indicator
3860 @section Scroll Bars
3863 Normally the frame parameter @code{vertical-scroll-bars} controls
3864 whether the windows in the frame have vertical scroll bars, and
3865 whether they are on the left or right. The frame parameter
3866 @code{scroll-bar-width} specifies how wide they are (@code{nil}
3867 meaning the default). @xref{Layout Parameters}.
3869 @defun frame-current-scroll-bars &optional frame
3870 This function reports the scroll bar type settings for frame
3871 @var{frame}. The value is a cons cell
3872 @code{(@var{vertical-type} .@: @var{horizontal-type})}, where
3873 @var{vertical-type} is either @code{left}, @code{right}, or @code{nil}
3874 (which means no scroll bar.) @var{horizontal-type} is meant to
3875 specify the horizontal scroll bar type, but since they are not
3876 implemented, it is always @code{nil}.
3879 @vindex vertical-scroll-bar
3880 You can enable or disable scroll bars for a particular buffer,
3881 by setting the variable @code{vertical-scroll-bar}. This variable
3882 automatically becomes buffer-local when set. The possible values are
3883 @code{left}, @code{right}, @code{t}, which means to use the
3884 frame's default, and @code{nil} for no scroll bar.
3886 You can also control this for individual windows. Call the function
3887 @code{set-window-scroll-bars} to specify what to do for a specific window:
3889 @defun set-window-scroll-bars window width &optional vertical-type horizontal-type
3890 This function sets the width and type of scroll bars for window
3893 @var{width} specifies the scroll bar width in pixels (@code{nil} means
3894 use the width specified for the frame). @var{vertical-type} specifies
3895 whether to have a vertical scroll bar and, if so, where. The possible
3896 values are @code{left}, @code{right} and @code{nil}, just like the
3897 values of the @code{vertical-scroll-bars} frame parameter.
3899 The argument @var{horizontal-type} is meant to specify whether and
3900 where to have horizontal scroll bars, but since they are not
3901 implemented, it has no effect. If @var{window} is @code{nil}, the
3902 selected window is used.
3905 @defun window-scroll-bars &optional window
3906 Report the width and type of scroll bars specified for @var{window}.
3907 If @var{window} is omitted or @code{nil}, the selected window is used.
3908 The value is a list of the form @code{(@var{width}
3909 @var{cols} @var{vertical-type} @var{horizontal-type})}. The value
3910 @var{width} is the value that was specified for the width (which may
3911 be @code{nil}); @var{cols} is the number of columns that the scroll
3912 bar actually occupies.
3914 @var{horizontal-type} is not actually meaningful.
3917 @defun window-scroll-bar-width &optional window
3918 This function returns the width of @var{window}'s vertical scrollbar,
3919 in pixels. @var{window} must be a live window. If @var{window} is
3920 @code{nil} or omitted, it will be the selected window.
3923 If you don't specify these values for a window with
3924 @code{set-window-scroll-bars}, the buffer-local variables
3925 @code{scroll-bar-mode} and @code{scroll-bar-width} in the buffer being
3926 displayed control the window's vertical scroll bars. The function
3927 @code{set-window-buffer} examines these variables. If you change them
3928 in a buffer that is already visible in a window, you can make the
3929 window take note of the new values by calling @code{set-window-buffer}
3930 specifying the same buffer that is already displayed.
3932 @defopt scroll-bar-mode
3933 This variable, always local in all buffers, controls whether and where
3934 to put scroll bars in windows displaying the buffer. The possible values
3935 are @code{nil} for no scroll bar, @code{left} to put a scroll bar on
3936 the left, and @code{right} to put a scroll bar on the right.
3939 @defun window-current-scroll-bars &optional window
3940 This function reports the scroll bar type for window @var{window}.
3941 If @var{window} is omitted or @code{nil}, the selected window is used.
3942 The value is a cons cell
3943 @code{(@var{vertical-type} .@: @var{horizontal-type})}. Unlike
3944 @code{window-scroll-bars}, this reports the scroll bar type actually
3945 used, once frame defaults and @code{scroll-bar-mode} are taken into
3949 @defvar scroll-bar-width
3950 This variable, always local in all buffers, specifies the width of the
3951 buffer's scroll bars, measured in pixels. A value of @code{nil} means
3952 to use the value specified by the frame.
3955 @node Window Dividers
3956 @section Window Dividers
3957 @cindex window dividers
3958 @cindex right dividers
3959 @cindex bottom dividers
3961 Window dividers are bars drawn between a frame's windows. A ``right''
3962 divider is drawn between a window and any adjacent windows on the right.
3963 Its width (thickness) is specified by the frame parameter
3964 @code{right-divider-width}. A ``bottom'' divider is drawn between a
3965 window and adjacent windows on the bottom or the echo area. Its width
3966 is specified by the frame parameter @code{bottom-divider-width}. In
3967 either case, specifying a width of zero means to not draw such dividers.
3968 @xref{Layout Parameters}.
3970 Technically, a right divider ``belongs'' to the window on its left,
3971 which means that its width contributes to the total width of that
3972 window. A bottom divider ``belongs'' to the window above it, which
3973 means that its width contributes to the total height of that window.
3974 @xref{Window Sizes}. When a window has both, a right and a bottom
3975 divider, the bottom divider ``prevails''. This means that a bottom
3976 divider is drawn over the full total width of its window while the right
3977 divider ends above the bottom divider.
3979 Dividers can be dragged with the mouse and are therefore useful for
3980 adjusting the sizes of adjacent windows with the mouse. They also serve
3981 to visually set apart adjacent windows when no scroll bars or mode lines
3982 are present. The following three faces allow to customize the
3983 appearance of dividers:
3986 @item window-divider
3987 When a divider is less than three pixels wide, it is drawn solidly with
3988 the foreground of this face. For larger dividers this face is used for
3989 the inner part only, excluding the first and last pixel.
3991 @item window-divider-first-pixel
3992 This is the face used for drawing the first pixel of a divider that is
3993 at least three pixels wide. To obtain a solid appearance, set this to
3994 the same value used for the @code{window-divider} face.
3996 @item window-divider-last-pixel
3997 This is the face used for drawing the last pixel of a divider that is at
3998 least three pixels wide. To obtain a solid appearance, set this to the
3999 same value used for the @code{window-divider} face.
4002 You can get the sizes of the dividers of a specific window with the
4003 following two functions.
4005 @defun window-right-divider-width &optional window
4006 Return the width (thickness) in pixels of @var{window}'s right divider.
4007 @var{window} must be a live window and defaults to the selected one.
4008 The return value is always zero for a rightmost window.
4011 @defun window-bottom-divider-width &optional window
4012 Return the width (thickness) in pixels of @var{window}'s bottom divider.
4013 @var{window} must be a live window and defaults to the selected one.
4014 The return value is zero for the minibuffer window or a bottommost
4015 window on a minibuffer-less frame.
4019 @node Display Property
4020 @section The @code{display} Property
4021 @cindex display specification
4022 @kindex display @r{(text property)}
4024 The @code{display} text property (or overlay property) is used to
4025 insert images into text, and to control other aspects of how text
4026 displays. The value of the @code{display} property should be a
4027 display specification, or a list or vector containing several display
4028 specifications. Display specifications in the same @code{display}
4029 property value generally apply in parallel to the text they cover.
4031 If several sources (overlays and/or a text property) specify values
4032 for the @code{display} property, only one of the values takes effect,
4033 following the rules of @code{get-char-property}. @xref{Examining
4036 The rest of this section describes several kinds of
4037 display specifications and what they mean.
4040 * Replacing Specs:: Display specs that replace the text.
4041 * Specified Space:: Displaying one space with a specified width.
4042 * Pixel Specification:: Specifying space width or height in pixels.
4043 * Other Display Specs:: Displaying an image; adjusting the height,
4044 spacing, and other properties of text.
4045 * Display Margins:: Displaying text or images to the side of the main text.
4048 @node Replacing Specs
4049 @subsection Display Specs That Replace The Text
4051 Some kinds of display specifications specify something to display
4052 instead of the text that has the property. These are called
4053 @dfn{replacing} display specifications. Emacs does not allow the user
4054 to interactively move point into the middle of buffer text that is
4055 replaced in this way.
4057 If a list of display specifications includes more than one replacing
4058 display specification, the first overrides the rest. Replacing
4059 display specifications make most other display specifications
4060 irrelevant, since those don't apply to the replacement.
4062 For replacing display specifications, ``the text that has the
4063 property'' means all the consecutive characters that have the same
4064 Lisp object as their @code{display} property; these characters are
4065 replaced as a single unit. If two characters have different Lisp
4066 objects as their @code{display} properties (i.e., objects which are
4067 not @code{eq}), they are handled separately.
4069 Here is an example which illustrates this point. A string serves as
4070 a replacing display specification, which replaces the text that has
4071 the property with the specified string (@pxref{Other Display Specs}).
4072 Consider the following function:
4077 (let ((string (concat "A"))
4078 (start (+ i i (point-min))))
4079 (put-text-property start (1+ start) 'display string)
4080 (put-text-property start (+ 2 start) 'display string))))
4084 This function gives each of the first ten characters in the buffer a
4085 @code{display} property which is a string @code{"A"}, but they don't
4086 all get the same string object. The first two characters get the same
4087 string object, so they are replaced with one @samp{A}; the fact that
4088 the display property was assigned in two separate calls to
4089 @code{put-text-property} is irrelevant. Similarly, the next two
4090 characters get a second string (@code{concat} creates a new string
4091 object), so they are replaced with one @samp{A}; and so on. Thus, the
4092 ten characters appear as five A's.
4094 @node Specified Space
4095 @subsection Specified Spaces
4096 @cindex spaces, specified height or width
4097 @cindex variable-width spaces
4099 To display a space of specified width and/or height, use a display
4100 specification of the form @code{(space . @var{props})}, where
4101 @var{props} is a property list (a list of alternating properties and
4102 values). You can put this property on one or more consecutive
4103 characters; a space of the specified height and width is displayed in
4104 place of @emph{all} of those characters. These are the properties you
4105 can use in @var{props} to specify the weight of the space:
4108 @item :width @var{width}
4109 If @var{width} is a number, it specifies
4110 that the space width should be @var{width} times the normal character
4111 width. @var{width} can also be a @dfn{pixel width} specification
4112 (@pxref{Pixel Specification}).
4114 @item :relative-width @var{factor}
4115 Specifies that the width of the stretch should be computed from the
4116 first character in the group of consecutive characters that have the
4117 same @code{display} property. The space width is the width of that
4118 character, multiplied by @var{factor}.
4120 @item :align-to @var{hpos}
4121 Specifies that the space should be wide enough to reach @var{hpos}.
4122 If @var{hpos} is a number, it is measured in units of the normal
4123 character width. @var{hpos} can also be a @dfn{pixel width}
4124 specification (@pxref{Pixel Specification}).
4127 You should use one and only one of the above properties. You can
4128 also specify the height of the space, with these properties:
4131 @item :height @var{height}
4132 Specifies the height of the space.
4133 If @var{height} is a number, it specifies
4134 that the space height should be @var{height} times the normal character
4135 height. The @var{height} may also be a @dfn{pixel height} specification
4136 (@pxref{Pixel Specification}).
4138 @item :relative-height @var{factor}
4139 Specifies the height of the space, multiplying the ordinary height
4140 of the text having this display specification by @var{factor}.
4142 @item :ascent @var{ascent}
4143 If the value of @var{ascent} is a non-negative number no greater than
4144 100, it specifies that @var{ascent} percent of the height of the space
4145 should be considered as the ascent of the space---that is, the part
4146 above the baseline. The ascent may also be specified in pixel units
4147 with a @dfn{pixel ascent} specification (@pxref{Pixel Specification}).
4151 Don't use both @code{:height} and @code{:relative-height} together.
4153 The @code{:width} and @code{:align-to} properties are supported on
4154 non-graphic terminals, but the other space properties in this section
4157 Note that space properties are treated as paragraph separators for
4158 the purposes of reordering bidirectional text for display.
4159 @xref{Bidirectional Display}, for the details.
4161 @node Pixel Specification
4162 @subsection Pixel Specification for Spaces
4163 @cindex spaces, pixel specification
4165 The value of the @code{:width}, @code{:align-to}, @code{:height},
4166 and @code{:ascent} properties can be a special kind of expression that
4167 is evaluated during redisplay. The result of the evaluation is used
4168 as an absolute number of pixels.
4170 The following expressions are supported:
4174 @var{expr} ::= @var{num} | (@var{num}) | @var{unit} | @var{elem} | @var{pos} | @var{image} | @var{form}
4175 @var{num} ::= @var{integer} | @var{float} | @var{symbol}
4176 @var{unit} ::= in | mm | cm | width | height
4179 @var{elem} ::= left-fringe | right-fringe | left-margin | right-margin
4181 @var{pos} ::= left | center | right
4182 @var{form} ::= (@var{num} . @var{expr}) | (@var{op} @var{expr} ...)
4187 The form @var{num} specifies a fraction of the default frame font
4188 height or width. The form @code{(@var{num})} specifies an absolute
4189 number of pixels. If @var{num} is a symbol, @var{symbol}, its
4190 buffer-local variable binding is used.
4192 The @code{in}, @code{mm}, and @code{cm} units specify the number of
4193 pixels per inch, millimeter, and centimeter, respectively. The
4194 @code{width} and @code{height} units correspond to the default width
4195 and height of the current face. An image specification @code{image}
4196 corresponds to the width or height of the image.
4198 The elements @code{left-fringe}, @code{right-fringe},
4199 @code{left-margin}, @code{right-margin}, @code{scroll-bar}, and
4200 @code{text} specify to the width of the corresponding area of the
4203 The @code{left}, @code{center}, and @code{right} positions can be
4204 used with @code{:align-to} to specify a position relative to the left
4205 edge, center, or right edge of the text area.
4207 Any of the above window elements (except @code{text}) can also be
4208 used with @code{:align-to} to specify that the position is relative to
4209 the left edge of the given area. Once the base offset for a relative
4210 position has been set (by the first occurrence of one of these
4211 symbols), further occurrences of these symbols are interpreted as the
4212 width of the specified area. For example, to align to the center of
4213 the left-margin, use
4216 :align-to (+ left-margin (0.5 . left-margin))
4219 If no specific base offset is set for alignment, it is always relative
4220 to the left edge of the text area. For example, @samp{:align-to 0} in a
4221 header-line aligns with the first text column in the text area.
4223 A value of the form @code{(@var{num} . @var{expr})} stands for the
4224 product of the values of @var{num} and @var{expr}. For example,
4225 @code{(2 . in)} specifies a width of 2 inches, while @code{(0.5 .
4226 @var{image})} specifies half the width (or height) of the specified
4229 The form @code{(+ @var{expr} ...)} adds up the value of the
4230 expressions. The form @code{(- @var{expr} ...)} negates or subtracts
4231 the value of the expressions.
4233 @node Other Display Specs
4234 @subsection Other Display Specifications
4236 Here are the other sorts of display specifications that you can use
4237 in the @code{display} text property.
4241 Display @var{string} instead of the text that has this property.
4243 Recursive display specifications are not supported---@var{string}'s
4244 @code{display} properties, if any, are not used.
4246 @item (image . @var{image-props})
4247 This kind of display specification is an image descriptor (@pxref{Images}).
4248 When used as a display specification, it means to display the image
4249 instead of the text that has the display specification.
4251 @item (slice @var{x} @var{y} @var{width} @var{height})
4252 This specification together with @code{image} specifies a @dfn{slice}
4253 (a partial area) of the image to display. The elements @var{y} and
4254 @var{x} specify the top left corner of the slice, within the image;
4255 @var{width} and @var{height} specify the width and height of the
4256 slice. Integers are numbers of pixels. A floating-point number
4257 in the range 0.0--1.0 stands for that fraction of the width or height
4258 of the entire image.
4260 @item ((margin nil) @var{string})
4261 A display specification of this form means to display @var{string}
4262 instead of the text that has the display specification, at the same
4263 position as that text. It is equivalent to using just @var{string},
4264 but it is done as a special case of marginal display (@pxref{Display
4267 @item (left-fringe @var{bitmap} @r{[}@var{face}@r{]})
4268 @itemx (right-fringe @var{bitmap} @r{[}@var{face}@r{]})
4269 This display specification on any character of a line of text causes
4270 the specified @var{bitmap} be displayed in the left or right fringes
4271 for that line, instead of the characters that have the display
4272 specification. The optional @var{face} specifies the colors to be
4273 used for the bitmap. @xref{Fringe Bitmaps}, for the details.
4275 @item (space-width @var{factor})
4276 This display specification affects all the space characters within the
4277 text that has the specification. It displays all of these spaces
4278 @var{factor} times as wide as normal. The element @var{factor} should
4279 be an integer or float. Characters other than spaces are not affected
4280 at all; in particular, this has no effect on tab characters.
4282 @item (height @var{height})
4283 This display specification makes the text taller or shorter.
4284 Here are the possibilities for @var{height}:
4287 @item @code{(+ @var{n})}
4288 @c FIXME: Add an index for "step"? --xfq
4289 This means to use a font that is @var{n} steps larger. A ``step'' is
4290 defined by the set of available fonts---specifically, those that match
4291 what was otherwise specified for this text, in all attributes except
4292 height. Each size for which a suitable font is available counts as
4293 another step. @var{n} should be an integer.
4295 @item @code{(- @var{n})}
4296 This means to use a font that is @var{n} steps smaller.
4298 @item a number, @var{factor}
4299 A number, @var{factor}, means to use a font that is @var{factor} times
4300 as tall as the default font.
4302 @item a symbol, @var{function}
4303 A symbol is a function to compute the height. It is called with the
4304 current height as argument, and should return the new height to use.
4306 @item anything else, @var{form}
4307 If the @var{height} value doesn't fit the previous possibilities, it is
4308 a form. Emacs evaluates it to get the new height, with the symbol
4309 @code{height} bound to the current specified font height.
4312 @item (raise @var{factor})
4313 This kind of display specification raises or lowers the text
4314 it applies to, relative to the baseline of the line.
4316 @var{factor} must be a number, which is interpreted as a multiple of the
4317 height of the affected text. If it is positive, that means to display
4318 the characters raised. If it is negative, that means to display them
4321 If the text also has a @code{height} display specification, that does
4322 not affect the amount of raising or lowering, which is based on the
4323 faces used for the text.
4326 @c We put all the `@code{(when ...)}' on one line to encourage
4327 @c makeinfo's end-of-sentence heuristics to DTRT. Previously, the dot
4328 @c was at eol; the info file ended up w/ two spaces rendered after it.
4329 You can make any display specification conditional. To do that,
4330 package it in another list of the form
4331 @code{(when @var{condition} . @var{spec})}.
4332 Then the specification @var{spec} applies only when
4333 @var{condition} evaluates to a non-@code{nil} value. During the
4334 evaluation, @code{object} is bound to the string or buffer having the
4335 conditional @code{display} property. @code{position} and
4336 @code{buffer-position} are bound to the position within @code{object}
4337 and the buffer position where the @code{display} property was found,
4338 respectively. Both positions can be different when @code{object} is a
4341 @node Display Margins
4342 @subsection Displaying in the Margins
4343 @cindex display margins
4344 @cindex margins, display
4346 A buffer can have blank areas called @dfn{display margins} on the
4347 left and on the right. Ordinary text never appears in these areas,
4348 but you can put things into the display margins using the
4349 @code{display} property. There is currently no way to make text or
4350 images in the margin mouse-sensitive.
4352 The way to display something in the margins is to specify it in a
4353 margin display specification in the @code{display} property of some
4354 text. This is a replacing display specification, meaning that the
4355 text you put it on does not get displayed; the margin display appears,
4356 but that text does not.
4358 A margin display specification looks like @code{((margin
4359 right-margin) @var{spec})} or @code{((margin left-margin) @var{spec})}.
4360 Here, @var{spec} is another display specification that says what to
4361 display in the margin. Typically it is a string of text to display,
4362 or an image descriptor.
4364 To display something in the margin @emph{in association with}
4365 certain buffer text, without altering or preventing the display of
4366 that text, put a @code{before-string} property on the text and put the
4367 margin display specification on the contents of the before-string.
4369 Before the display margins can display anything, you must give
4370 them a nonzero width. The usual way to do that is to set these
4373 @defvar left-margin-width
4374 This variable specifies the width of the left margin, in character
4375 cell (a.k.a.@: ``column'') units. It is buffer-local in all buffers.
4376 A value of @code{nil} means no left marginal area.
4379 @defvar right-margin-width
4380 This variable specifies the width of the right margin, in character
4381 cell units. It is buffer-local in all buffers. A value of @code{nil}
4382 means no right marginal area.
4385 Setting these variables does not immediately affect the window. These
4386 variables are checked when a new buffer is displayed in the window.
4387 Thus, you can make changes take effect by calling
4388 @code{set-window-buffer}.
4390 You can also set the margin widths immediately.
4392 @defun set-window-margins window left &optional right
4393 This function specifies the margin widths for window @var{window}, in
4394 character cell units. The argument @var{left} controls the left
4395 margin, and @var{right} controls the right margin (default @code{0}).
4398 @defun window-margins &optional window
4399 This function returns the width of the left and right margins of
4400 @var{window} as a cons cell of the form @w{@code{(@var{left}
4401 . @var{right})}}. If one of the two marginal areas does not exist,
4402 its width is returned as @code{nil}; if neither of the two margins exist,
4403 the function returns @code{(nil)}. If @var{window} is @code{nil}, the
4404 selected window is used.
4409 @cindex images in buffers
4411 To display an image in an Emacs buffer, you must first create an image
4412 descriptor, then use it as a display specifier in the @code{display}
4413 property of text that is displayed (@pxref{Display Property}).
4415 Emacs is usually able to display images when it is run on a
4416 graphical terminal. Images cannot be displayed in a text terminal, on
4417 certain graphical terminals that lack the support for this, or if
4418 Emacs is compiled without image support. You can use the function
4419 @code{display-images-p} to determine if images can in principle be
4420 displayed (@pxref{Display Feature Testing}).
4423 * Image Formats:: Supported image formats.
4424 * Image Descriptors:: How to specify an image for use in @code{:display}.
4425 * XBM Images:: Special features for XBM format.
4426 * XPM Images:: Special features for XPM format.
4427 * PostScript Images:: Special features for PostScript format.
4428 * ImageMagick Images:: Special features available through ImageMagick.
4429 * Other Image Types:: Various other formats are supported.
4430 * Defining Images:: Convenient ways to define an image for later use.
4431 * Showing Images:: Convenient ways to display an image once it is defined.
4432 * Multi-Frame Images:: Some images contain more than one frame.
4433 * Image Cache:: Internal mechanisms of image display.
4437 @subsection Image Formats
4438 @cindex image formats
4441 Emacs can display a number of different image formats. Some of
4442 these image formats are supported only if particular support libraries
4443 are installed. On some platforms, Emacs can load support libraries on
4444 demand; if so, the variable @code{dynamic-library-alist} can be used
4445 to modify the set of known names for these dynamic libraries.
4446 @xref{Dynamic Libraries}.
4448 Supported image formats (and the required support libraries) include
4449 PBM and XBM (which do not depend on support libraries and are always
4450 available), XPM (@code{libXpm}), GIF (@code{libgif} or
4451 @code{libungif}), PostScript (@code{gs}), JPEG (@code{libjpeg}), TIFF
4452 (@code{libtiff}), PNG (@code{libpng}), and SVG (@code{librsvg}).
4454 Each of these image formats is associated with an @dfn{image type
4455 symbol}. The symbols for the above formats are, respectively,
4456 @code{pbm}, @code{xbm}, @code{xpm}, @code{gif}, @code{postscript},
4457 @code{jpeg}, @code{tiff}, @code{png}, and @code{svg}.
4459 Furthermore, if you build Emacs with ImageMagick
4460 (@code{libMagickWand}) support, Emacs can display any image format
4461 that ImageMagick can. @xref{ImageMagick Images}. All images
4462 displayed via ImageMagick have type symbol @code{imagemagick}.
4465 This variable contains a list of type symbols for image formats which
4466 are potentially supported in the current configuration.
4468 ``Potentially'' means that Emacs knows about the image types, not
4469 necessarily that they can be used (for example, they could depend on
4470 unavailable dynamic libraries). To know which image types are really
4471 available, use @code{image-type-available-p}.
4474 @defun image-type-available-p type
4475 This function returns non-@code{nil} if images of type @var{type} can
4476 be loaded and displayed. @var{type} must be an image type symbol.
4478 For image types whose support libraries are statically linked, this
4479 function always returns @code{t}. For image types whose support
4480 libraries are dynamically loaded, it returns @code{t} if the library
4481 could be loaded and @code{nil} otherwise.
4484 @node Image Descriptors
4485 @subsection Image Descriptors
4486 @cindex image descriptor
4488 An @dfn{image descriptor} is a list which specifies the underlying
4489 data for an image, and how to display it. It is typically used as the
4490 value of a @code{display} overlay or text property (@pxref{Other
4491 Display Specs}); but @xref{Showing Images}, for convenient helper
4492 functions to insert images into buffers.
4494 Each image descriptor has the form @code{(image . @var{props})},
4495 where @var{props} is a property list of alternating keyword symbols
4496 and values, including at least the pair @code{:type @var{TYPE}} which
4497 specifies the image type.
4499 The following is a list of properties that are meaningful for all
4500 image types (there are also properties which are meaningful only for
4501 certain image types, as documented in the following subsections):
4504 @item :type @var{type}
4507 @xref{Image Formats}.
4509 Every image descriptor must include this property.
4511 @item :file @var{file}
4512 This says to load the image from file @var{file}. If @var{file} is
4513 not an absolute file name, it is expanded in @code{data-directory}.
4515 @item :data @var{data}
4516 This specifies the raw image data. Each image descriptor must have
4517 either @code{:data} or @code{:file}, but not both.
4519 For most image types, the value of a @code{:data} property should be a
4520 string containing the image data. Some image types do not support
4521 @code{:data}; for some others, @code{:data} alone is not enough, so
4522 you need to use other image properties along with @code{:data}. See
4523 the following subsections for details.
4525 @item :margin @var{margin}
4526 This specifies how many pixels to add as an extra margin around the
4527 image. The value, @var{margin}, must be a non-negative number, or a
4528 pair @code{(@var{x} . @var{y})} of such numbers. If it is a pair,
4529 @var{x} specifies how many pixels to add horizontally, and @var{y}
4530 specifies how many pixels to add vertically. If @code{:margin} is not
4531 specified, the default is zero.
4533 @item :ascent @var{ascent}
4534 This specifies the amount of the image's height to use for its
4535 ascent---that is, the part above the baseline. The value,
4536 @var{ascent}, must be a number in the range 0 to 100, or the symbol
4539 If @var{ascent} is a number, that percentage of the image's height is
4540 used for its ascent.
4542 If @var{ascent} is @code{center}, the image is vertically centered
4543 around a centerline which would be the vertical centerline of text drawn
4544 at the position of the image, in the manner specified by the text
4545 properties and overlays that apply to the image.
4547 If this property is omitted, it defaults to 50.
4549 @item :relief @var{relief}
4550 This adds a shadow rectangle around the image. The value,
4551 @var{relief}, specifies the width of the shadow lines, in pixels. If
4552 @var{relief} is negative, shadows are drawn so that the image appears
4553 as a pressed button; otherwise, it appears as an unpressed button.
4555 @item :conversion @var{algorithm}
4556 This specifies a conversion algorithm that should be applied to the
4557 image before it is displayed; the value, @var{algorithm}, specifies
4563 Specifies the Laplace edge detection algorithm, which blurs out small
4564 differences in color while highlighting larger differences. People
4565 sometimes consider this useful for displaying the image for a
4566 ``disabled'' button.
4568 @item (edge-detection :matrix @var{matrix} :color-adjust @var{adjust})
4569 @cindex edge detection, images
4570 Specifies a general edge-detection algorithm. @var{matrix} must be
4571 either a nine-element list or a nine-element vector of numbers. A pixel
4572 at position @math{x/y} in the transformed image is computed from
4573 original pixels around that position. @var{matrix} specifies, for each
4574 pixel in the neighborhood of @math{x/y}, a factor with which that pixel
4575 will influence the transformed pixel; element @math{0} specifies the
4576 factor for the pixel at @math{x-1/y-1}, element @math{1} the factor for
4577 the pixel at @math{x/y-1} etc., as shown below:
4580 $$\pmatrix{x-1/y-1 & x/y-1 & x+1/y-1 \cr
4581 x-1/y & x/y & x+1/y \cr
4582 x-1/y+1& x/y+1 & x+1/y+1 \cr}$$
4587 (x-1/y-1 x/y-1 x+1/y-1
4589 x-1/y+1 x/y+1 x+1/y+1)
4593 The resulting pixel is computed from the color intensity of the color
4594 resulting from summing up the RGB values of surrounding pixels,
4595 multiplied by the specified factors, and dividing that sum by the sum
4596 of the factors' absolute values.
4598 Laplace edge-detection currently uses a matrix of
4601 $$\pmatrix{1 & 0 & 0 \cr
4614 Emboss edge-detection uses a matrix of
4617 $$\pmatrix{ 2 & -1 & 0 \cr
4631 Specifies transforming the image so that it looks ``disabled''.
4634 @item :mask @var{mask}
4635 If @var{mask} is @code{heuristic} or @code{(heuristic @var{bg})}, build
4636 a clipping mask for the image, so that the background of a frame is
4637 visible behind the image. If @var{bg} is not specified, or if @var{bg}
4638 is @code{t}, determine the background color of the image by looking at
4639 the four corners of the image, assuming the most frequently occurring
4640 color from the corners is the background color of the image. Otherwise,
4641 @var{bg} must be a list @code{(@var{red} @var{green} @var{blue})}
4642 specifying the color to assume for the background of the image.
4644 If @var{mask} is @code{nil}, remove a mask from the image, if it has
4645 one. Images in some formats include a mask which can be removed by
4646 specifying @code{:mask nil}.
4648 @item :pointer @var{shape}
4649 This specifies the pointer shape when the mouse pointer is over this
4650 image. @xref{Pointer Shape}, for available pointer shapes.
4652 @item :map @var{map}
4654 This associates an image map of @dfn{hot spots} with this image.
4656 An image map is an alist where each element has the format
4657 @code{(@var{area} @var{id} @var{plist})}. An @var{area} is specified
4658 as either a rectangle, a circle, or a polygon.
4660 A rectangle is a cons
4661 @code{(rect . ((@var{x0} . @var{y0}) . (@var{x1} . @var{y1})))}
4662 which specifies the pixel coordinates of the upper left and bottom right
4663 corners of the rectangle area.
4666 @code{(circle . ((@var{x0} . @var{y0}) . @var{r}))}
4667 which specifies the center and the radius of the circle; @var{r} may
4668 be a float or integer.
4671 @code{(poly . [@var{x0} @var{y0} @var{x1} @var{y1} ...])}
4672 where each pair in the vector describes one corner in the polygon.
4674 When the mouse pointer lies on a hot-spot area of an image, the
4675 @var{plist} of that hot-spot is consulted; if it contains a @code{help-echo}
4676 property, that defines a tool-tip for the hot-spot, and if it contains
4677 a @code{pointer} property, that defines the shape of the mouse cursor when
4678 it is on the hot-spot.
4679 @xref{Pointer Shape}, for available pointer shapes.
4681 When you click the mouse when the mouse pointer is over a hot-spot, an
4682 event is composed by combining the @var{id} of the hot-spot with the
4683 mouse event; for instance, @code{[area4 mouse-1]} if the hot-spot's
4684 @var{id} is @code{area4}.
4687 @defun image-mask-p spec &optional frame
4688 This function returns @code{t} if image @var{spec} has a mask bitmap.
4689 @var{frame} is the frame on which the image will be displayed.
4690 @var{frame} @code{nil} or omitted means to use the selected frame
4691 (@pxref{Input Focus}).
4695 @subsection XBM Images
4698 To use XBM format, specify @code{xbm} as the image type. This image
4699 format doesn't require an external library, so images of this type are
4702 Additional image properties supported for the @code{xbm} image type are:
4705 @item :foreground @var{foreground}
4706 The value, @var{foreground}, should be a string specifying the image
4707 foreground color, or @code{nil} for the default color. This color is
4708 used for each pixel in the XBM that is 1. The default is the frame's
4711 @item :background @var{background}
4712 The value, @var{background}, should be a string specifying the image
4713 background color, or @code{nil} for the default color. This color is
4714 used for each pixel in the XBM that is 0. The default is the frame's
4718 If you specify an XBM image using data within Emacs instead of an
4719 external file, use the following three properties:
4722 @item :data @var{data}
4723 The value, @var{data}, specifies the contents of the image.
4724 There are three formats you can use for @var{data}:
4728 A vector of strings or bool-vectors, each specifying one line of the
4729 image. Do specify @code{:height} and @code{:width}.
4732 A string containing the same byte sequence as an XBM file would contain.
4733 You must not specify @code{:height} and @code{:width} in this case,
4734 because omitting them is what indicates the data has the format of an
4735 XBM file. The file contents specify the height and width of the image.
4738 A string or a bool-vector containing the bits of the image (plus perhaps
4739 some extra bits at the end that will not be used). It should contain at
4740 least @var{width} * @code{height} bits. In this case, you must specify
4741 @code{:height} and @code{:width}, both to indicate that the string
4742 contains just the bits rather than a whole XBM file, and to specify the
4746 @item :width @var{width}
4747 The value, @var{width}, specifies the width of the image, in pixels.
4749 @item :height @var{height}
4750 The value, @var{height}, specifies the height of the image, in pixels.
4754 @subsection XPM Images
4757 To use XPM format, specify @code{xpm} as the image type. The
4758 additional image property @code{:color-symbols} is also meaningful with
4759 the @code{xpm} image type:
4762 @item :color-symbols @var{symbols}
4763 The value, @var{symbols}, should be an alist whose elements have the
4764 form @code{(@var{name} . @var{color})}. In each element, @var{name} is
4765 the name of a color as it appears in the image file, and @var{color}
4766 specifies the actual color to use for displaying that name.
4769 @node PostScript Images
4770 @subsection PostScript Images
4771 @cindex postscript images
4773 To use PostScript for an image, specify image type @code{postscript}.
4774 This works only if you have Ghostscript installed. You must always use
4775 these three properties:
4778 @item :pt-width @var{width}
4779 The value, @var{width}, specifies the width of the image measured in
4780 points (1/72 inch). @var{width} must be an integer.
4782 @item :pt-height @var{height}
4783 The value, @var{height}, specifies the height of the image in points
4784 (1/72 inch). @var{height} must be an integer.
4786 @item :bounding-box @var{box}
4787 The value, @var{box}, must be a list or vector of four integers, which
4788 specifying the bounding box of the PostScript image, analogous to the
4789 @samp{BoundingBox} comment found in PostScript files.
4792 %%BoundingBox: 22 171 567 738
4796 @node ImageMagick Images
4797 @subsection ImageMagick Images
4798 @cindex ImageMagick images
4799 @cindex images, support for more formats
4801 If you build Emacs with ImageMagick support, you can use the
4802 ImageMagick library to load many image formats (@pxref{File
4803 Conveniences,,, emacs, The GNU Emacs Manual}). The image type symbol
4804 for images loaded via ImageMagick is @code{imagemagick}, regardless of
4805 the actual underlying image format.
4807 @defun imagemagick-types
4808 This function returns a list of image file extensions supported by the
4809 current ImageMagick installation. Each list element is a symbol
4810 representing an internal ImageMagick name for an image type, such as
4811 @code{BMP} for @file{.bmp} images.
4814 @defopt imagemagick-enabled-types
4815 The value of this variable is a list of ImageMagick image types which
4816 Emacs may attempt to render using ImageMagick. Each list element
4817 should be one of the symbols in the list returned by
4818 @code{imagemagick-types}, or an equivalent string. Alternatively, a
4819 value of @code{t} enables ImageMagick for all possible image types.
4820 Regardless of the value of this variable,
4821 @code{imagemagick-types-inhibit} (see below) takes precedence.
4824 @defopt imagemagick-types-inhibit
4825 The value of this variable lists the ImageMagick image types which
4826 should never be rendered using ImageMagick, regardless of the value of
4827 @code{imagemagick-enabled-types}. A value of @code{t} disables
4828 ImageMagick entirely.
4831 @defvar image-format-suffixes
4832 This variable is an alist mapping image types to file name extensions.
4833 Emacs uses this in conjunction with the @code{:format} image property
4834 (see below) to give a hint to the ImageMagick library as to the type
4835 of an image. Each element has the form @code{(@var{type}
4836 @var{extension})}, where @var{type} is a symbol specifying an image
4837 content-type, and @var{extension} is a string that specifies the
4838 associated file name extension.
4841 Images loaded with ImageMagick support the following additional
4842 image descriptor properties:
4845 @item :background @var{background}
4846 @var{background}, if non-@code{nil}, should be a string specifying a
4847 color, which is used as the image's background color if the image
4848 supports transparency. If the value is @code{nil}, it defaults to the
4849 frame's background color.
4851 @item :width @var{width}, :height @var{height}
4852 The @code{:width} and @code{:height} keywords are used for scaling the
4853 image. If only one of them is specified, the other one will be
4854 calculated so as to preserve the aspect ratio. If both are specified,
4855 aspect ratio may not be preserved.
4857 @item :max-width @var{max-width}, :max-height @var{max-height}
4858 The @code{:max-width} and @code{:max-height} keywords are used for
4859 scaling if the size of the image of the image exceeds these values.
4860 If @code{:width} is set it will have precedence over @code{max-width},
4861 and if @code{:height} is set it will have precedence over
4862 @code{max-height}, but you can otherwise mix these keywords as you
4863 wish. @code{:max-width} and @code{:max-height} will always preserve
4866 @item :format @var{type}
4867 The value, @var{type}, should be a symbol specifying the type of the
4868 image data, as found in @code{image-format-suffixes}. This is used
4869 when the image does not have an associated file name, to provide a
4870 hint to ImageMagick to help it detect the image type.
4872 @item :rotation @var{angle}
4873 Specifies a rotation angle in degrees.
4875 @item :index @var{frame}
4876 @c Doesn't work: http://debbugs.gnu.org/7978
4877 @xref{Multi-Frame Images}.
4880 @node Other Image Types
4881 @subsection Other Image Types
4884 For PBM images, specify image type @code{pbm}. Color, gray-scale and
4885 monochromatic images are supported. For mono PBM images, two additional
4886 image properties are supported.
4889 @item :foreground @var{foreground}
4890 The value, @var{foreground}, should be a string specifying the image
4891 foreground color, or @code{nil} for the default color. This color is
4892 used for each pixel in the PBM that is 1. The default is the frame's
4895 @item :background @var{background}
4896 The value, @var{background}, should be a string specifying the image
4897 background color, or @code{nil} for the default color. This color is
4898 used for each pixel in the PBM that is 0. The default is the frame's
4903 The remaining image types that Emacs can support are:
4907 Image type @code{gif}.
4908 Supports the @code{:index} property. @xref{Multi-Frame Images}.
4911 Image type @code{jpeg}.
4914 Image type @code{png}.
4917 Image type @code{svg}.
4920 Image type @code{tiff}.
4921 Supports the @code{:index} property. @xref{Multi-Frame Images}.
4924 @node Defining Images
4925 @subsection Defining Images
4927 The functions @code{create-image}, @code{defimage} and
4928 @code{find-image} provide convenient ways to create image descriptors.
4930 @defun create-image file-or-data &optional type data-p &rest props
4931 This function creates and returns an image descriptor which uses the
4932 data in @var{file-or-data}. @var{file-or-data} can be a file name or
4933 a string containing the image data; @var{data-p} should be @code{nil}
4934 for the former case, non-@code{nil} for the latter case.
4936 The optional argument @var{type} is a symbol specifying the image type.
4937 If @var{type} is omitted or @code{nil}, @code{create-image} tries to
4938 determine the image type from the file's first few bytes, or else
4939 from the file's name.
4941 The remaining arguments, @var{props}, specify additional image
4942 properties---for example,
4944 @c ':heuristic-mask' is not documented?
4946 (create-image "foo.xpm" 'xpm nil :heuristic-mask t)
4949 The function returns @code{nil} if images of this type are not
4950 supported. Otherwise it returns an image descriptor.
4953 @defmac defimage symbol specs &optional doc
4954 This macro defines @var{symbol} as an image name. The arguments
4955 @var{specs} is a list which specifies how to display the image.
4956 The third argument, @var{doc}, is an optional documentation string.
4958 Each argument in @var{specs} has the form of a property list, and each
4959 one should specify at least the @code{:type} property and either the
4960 @code{:file} or the @code{:data} property. The value of @code{:type}
4961 should be a symbol specifying the image type, the value of
4962 @code{:file} is the file to load the image from, and the value of
4963 @code{:data} is a string containing the actual image data. Here is an
4967 (defimage test-image
4968 ((:type xpm :file "~/test1.xpm")
4969 (:type xbm :file "~/test1.xbm")))
4972 @code{defimage} tests each argument, one by one, to see if it is
4973 usable---that is, if the type is supported and the file exists. The
4974 first usable argument is used to make an image descriptor which is
4975 stored in @var{symbol}.
4977 If none of the alternatives will work, then @var{symbol} is defined
4981 @defun find-image specs
4982 This function provides a convenient way to find an image satisfying one
4983 of a list of image specifications @var{specs}.
4985 Each specification in @var{specs} is a property list with contents
4986 depending on image type. All specifications must at least contain the
4987 properties @code{:type @var{type}} and either @w{@code{:file @var{file}}}
4988 or @w{@code{:data @var{DATA}}}, where @var{type} is a symbol specifying
4989 the image type, e.g., @code{xbm}, @var{file} is the file to load the
4990 image from, and @var{data} is a string containing the actual image data.
4991 The first specification in the list whose @var{type} is supported, and
4992 @var{file} exists, is used to construct the image specification to be
4993 returned. If no specification is satisfied, @code{nil} is returned.
4995 The image is looked for in @code{image-load-path}.
4998 @defvar image-load-path
4999 This variable's value is a list of locations in which to search for
5000 image files. If an element is a string or a variable symbol whose
5001 value is a string, the string is taken to be the name of a directory
5002 to search. If an element is a variable symbol whose value is a list,
5003 that is taken to be a list of directory names to search.
5005 The default is to search in the @file{images} subdirectory of the
5006 directory specified by @code{data-directory}, then the directory
5007 specified by @code{data-directory}, and finally in the directories in
5008 @code{load-path}. Subdirectories are not automatically included in
5009 the search, so if you put an image file in a subdirectory, you have to
5010 supply the subdirectory name explicitly. For example, to find the
5011 image @file{images/foo/bar.xpm} within @code{data-directory}, you
5012 should specify the image as follows:
5015 (defimage foo-image '((:type xpm :file "foo/bar.xpm")))
5019 @defun image-load-path-for-library library image &optional path no-error
5020 This function returns a suitable search path for images used by the
5021 Lisp package @var{library}.
5023 The function searches for @var{image} first using @code{image-load-path},
5024 excluding @file{@code{data-directory}/images}, and then in
5025 @code{load-path}, followed by a path suitable for @var{library}, which
5026 includes @file{../../etc/images} and @file{../etc/images} relative to
5027 the library file itself, and finally in
5028 @file{@code{data-directory}/images}.
5030 Then this function returns a list of directories which contains first
5031 the directory in which @var{image} was found, followed by the value of
5032 @code{load-path}. If @var{path} is given, it is used instead of
5035 If @var{no-error} is non-@code{nil} and a suitable path can't be
5036 found, don't signal an error. Instead, return a list of directories as
5037 before, except that @code{nil} appears in place of the image directory.
5039 Here is an example of using @code{image-load-path-for-library}:
5042 (defvar image-load-path) ; shush compiler
5043 (let* ((load-path (image-load-path-for-library
5044 "mh-e" "mh-logo.xpm"))
5045 (image-load-path (cons (car load-path)
5047 (mh-tool-bar-folder-buttons-init))
5051 @node Showing Images
5052 @subsection Showing Images
5054 You can use an image descriptor by setting up the @code{display}
5055 property yourself, but it is easier to use the functions in this
5058 @defun insert-image image &optional string area slice
5059 This function inserts @var{image} in the current buffer at point. The
5060 value @var{image} should be an image descriptor; it could be a value
5061 returned by @code{create-image}, or the value of a symbol defined with
5062 @code{defimage}. The argument @var{string} specifies the text to put
5063 in the buffer to hold the image. If it is omitted or @code{nil},
5064 @code{insert-image} uses @code{" "} by default.
5066 The argument @var{area} specifies whether to put the image in a margin.
5067 If it is @code{left-margin}, the image appears in the left margin;
5068 @code{right-margin} specifies the right margin. If @var{area} is
5069 @code{nil} or omitted, the image is displayed at point within the
5072 The argument @var{slice} specifies a slice of the image to insert. If
5073 @var{slice} is @code{nil} or omitted the whole image is inserted.
5074 Otherwise, @var{slice} is a list @code{(@var{x} @var{y} @var{width}
5075 @var{height})} which specifies the @var{x} and @var{y} positions and
5076 @var{width} and @var{height} of the image area to insert. Integer
5077 values are in units of pixels. A floating-point number in the range
5078 0.0--1.0 stands for that fraction of the width or height of the entire
5081 Internally, this function inserts @var{string} in the buffer, and gives
5082 it a @code{display} property which specifies @var{image}. @xref{Display
5086 @cindex slice, image
5088 @defun insert-sliced-image image &optional string area rows cols
5089 This function inserts @var{image} in the current buffer at point, like
5090 @code{insert-image}, but splits the image into @var{rows}x@var{cols}
5091 equally sized slices.
5093 If an image is inserted ``sliced'', Emacs displays each slice as a
5094 separate image, and allow more intuitive scrolling up/down, instead of
5095 jumping up/down the entire image when paging through a buffer that
5096 displays (large) images.
5099 @defun put-image image pos &optional string area
5100 This function puts image @var{image} in front of @var{pos} in the
5101 current buffer. The argument @var{pos} should be an integer or a
5102 marker. It specifies the buffer position where the image should appear.
5103 The argument @var{string} specifies the text that should hold the image
5104 as an alternative to the default.
5106 The argument @var{image} must be an image descriptor, perhaps returned
5107 by @code{create-image} or stored by @code{defimage}.
5109 The argument @var{area} specifies whether to put the image in a margin.
5110 If it is @code{left-margin}, the image appears in the left margin;
5111 @code{right-margin} specifies the right margin. If @var{area} is
5112 @code{nil} or omitted, the image is displayed at point within the
5115 Internally, this function creates an overlay, and gives it a
5116 @code{before-string} property containing text that has a @code{display}
5117 property whose value is the image. (Whew!)
5120 @defun remove-images start end &optional buffer
5121 This function removes images in @var{buffer} between positions
5122 @var{start} and @var{end}. If @var{buffer} is omitted or @code{nil},
5123 images are removed from the current buffer.
5125 This removes only images that were put into @var{buffer} the way
5126 @code{put-image} does it, not images that were inserted with
5127 @code{insert-image} or in other ways.
5130 @defun image-size spec &optional pixels frame
5131 @cindex size of image
5132 This function returns the size of an image as a pair
5133 @w{@code{(@var{width} . @var{height})}}. @var{spec} is an image
5134 specification. @var{pixels} non-@code{nil} means return sizes
5135 measured in pixels, otherwise return sizes measured in canonical
5136 character units (fractions of the width/height of the frame's default
5137 font). @var{frame} is the frame on which the image will be displayed.
5138 @var{frame} null or omitted means use the selected frame (@pxref{Input
5142 @defvar max-image-size
5143 This variable is used to define the maximum size of image that Emacs
5144 will load. Emacs will refuse to load (and display) any image that is
5145 larger than this limit.
5147 If the value is an integer, it directly specifies the maximum
5148 image height and width, measured in pixels. If it is floating
5149 point, it specifies the maximum image height and width
5150 as a ratio to the frame height and width. If the value is
5151 non-numeric, there is no explicit limit on the size of images.
5153 The purpose of this variable is to prevent unreasonably large images
5154 from accidentally being loaded into Emacs. It only takes effect the
5155 first time an image is loaded. Once an image is placed in the image
5156 cache, it can always be displayed, even if the value of
5157 @code{max-image-size} is subsequently changed (@pxref{Image Cache}).
5160 @node Multi-Frame Images
5161 @subsection Multi-Frame Images
5162 @cindex multi-frame images
5165 @cindex image animation
5166 @cindex image frames
5167 Some image files can contain more than one image. We say that there
5168 are multiple ``frames'' in the image. At present, Emacs supports
5169 multiple frames for GIF, TIFF, and certain ImageMagick formats such as
5172 The frames can be used either to represent multiple ``pages'' (this is
5173 usually the case with multi-frame TIFF files, for example), or to
5174 create animation (usually the case with multi-frame GIF files).
5176 A multi-frame image has a property @code{:index}, whose value is an
5177 integer (counting from 0) that specifies which frame is being displayed.
5179 @defun image-multi-frame-p image
5180 This function returns non-@code{nil} if @var{image} contains more than
5181 one frame. The actual return value is a cons @code{(@var{nimages}
5182 . @var{delay})}, where @var{nimages} is the number of frames and
5183 @var{delay} is the delay in seconds between them, or @code{nil}
5184 if the image does not specify a delay. Images that are intended to be
5185 animated usually specify a frame delay, whereas ones that are intended
5186 to be treated as multiple pages do not.
5189 @defun image-current-frame image
5190 This function returns the index of the current frame number for
5191 @var{image}, counting from 0.
5194 @defun image-show-frame image n &optional nocheck
5195 This function switches @var{image} to frame number @var{n}. It
5196 replaces a frame number outside the valid range with that of the end
5197 of the range, unless @var{nocheck} is non-@code{nil}. If @var{image}
5198 does not contain a frame with the specified number, the image displays
5202 @defun image-animate image &optional index limit
5203 This function animates @var{image}. The optional integer @var{index}
5204 specifies the frame from which to start (default 0). The optional
5205 argument @var{limit} controls the length of the animation. If omitted
5206 or @code{nil}, the image animates once only; if @code{t} it loops
5207 forever; if a number animation stops after that many seconds.
5210 @vindex image-minimum-frame-delay
5211 @vindex image-default-frame-delay
5212 @noindent Animation operates by means of a timer. Note that Emacs imposes a
5213 minimum frame delay of 0.01 (@code{image-minimum-frame-delay}) seconds.
5214 If the image itself does not specify a delay, Emacs uses
5215 @code{image-default-frame-delay}.
5217 @defun image-animate-timer image
5218 This function returns the timer responsible for animating @var{image},
5224 @subsection Image Cache
5227 Emacs caches images so that it can display them again more
5228 efficiently. When Emacs displays an image, it searches the image
5229 cache for an existing image specification @code{equal} to the desired
5230 specification. If a match is found, the image is displayed from the
5231 cache. Otherwise, Emacs loads the image normally.
5233 @defun image-flush spec &optional frame
5234 This function removes the image with specification @var{spec} from the
5235 image cache of frame @var{frame}. Image specifications are compared
5236 using @code{equal}. If @var{frame} is @code{nil}, it defaults to the
5237 selected frame. If @var{frame} is @code{t}, the image is flushed on
5238 all existing frames.
5240 In Emacs's current implementation, each graphical terminal possesses an
5241 image cache, which is shared by all the frames on that terminal
5242 (@pxref{Multiple Terminals}). Thus, refreshing an image in one frame
5243 also refreshes it in all other frames on the same terminal.
5246 One use for @code{image-flush} is to tell Emacs about a change in an
5247 image file. If an image specification contains a @code{:file}
5248 property, the image is cached based on the file's contents when the
5249 image is first displayed. Even if the file subsequently changes,
5250 Emacs continues displaying the old version of the image. Calling
5251 @code{image-flush} flushes the image from the cache, forcing Emacs to
5252 re-read the file the next time it needs to display that image.
5254 Another use for @code{image-flush} is for memory conservation. If
5255 your Lisp program creates a large number of temporary images over a
5256 period much shorter than @code{image-cache-eviction-delay} (see
5257 below), you can opt to flush unused images yourself, instead of
5258 waiting for Emacs to do it automatically.
5260 @defun clear-image-cache &optional filter
5261 This function clears an image cache, removing all the images stored in
5262 it. If @var{filter} is omitted or @code{nil}, it clears the cache for
5263 the selected frame. If @var{filter} is a frame, it clears the cache
5264 for that frame. If @var{filter} is @code{t}, all image caches are
5265 cleared. Otherwise, @var{filter} is taken to be a file name, and all
5266 images associated with that file name are removed from all image
5270 If an image in the image cache has not been displayed for a specified
5271 period of time, Emacs removes it from the cache and frees the
5274 @defvar image-cache-eviction-delay
5275 This variable specifies the number of seconds an image can remain in
5276 the cache without being displayed. When an image is not displayed for
5277 this length of time, Emacs removes it from the image cache.
5279 Under some circumstances, if the number of images in the cache grows
5280 too large, the actual eviction delay may be shorter than this.
5282 If the value is @code{nil}, Emacs does not remove images from the cache
5283 except when you explicitly clear it. This mode can be useful for
5289 @cindex buttons in buffers
5290 @cindex clickable buttons in buffers
5292 The Button package defines functions for inserting and manipulating
5293 @dfn{buttons} that can be activated with the mouse or via keyboard
5294 commands. These buttons are typically used for various kinds of
5297 A button is essentially a set of text or overlay properties,
5298 attached to a stretch of text in a buffer. These properties are
5299 called @dfn{button properties}. One of these properties, the
5300 @dfn{action property}, specifies a function which is called when the
5301 user invokes the button using the keyboard or the mouse. The action
5302 function may examine the button and use its other properties as
5305 In some ways, the Button package duplicates the functionality in the
5306 Widget package. @xref{Top, , Introduction, widget, The Emacs Widget
5307 Library}. The advantage of the Button package is that it is faster,
5308 smaller, and simpler to program. From the point of view of the user,
5309 the interfaces produced by the two packages are very similar.
5312 * Button Properties:: Button properties with special meanings.
5313 * Button Types:: Defining common properties for classes of buttons.
5314 * Making Buttons:: Adding buttons to Emacs buffers.
5315 * Manipulating Buttons:: Getting and setting properties of buttons.
5316 * Button Buffer Commands:: Buffer-wide commands and bindings for buttons.
5319 @node Button Properties
5320 @subsection Button Properties
5321 @cindex button properties
5323 Each button has an associated list of properties defining its
5324 appearance and behavior, and other arbitrary properties may be used
5325 for application specific purposes. The following properties have
5326 special meaning to the Button package:
5330 @kindex action @r{(button property)}
5331 The function to call when the user invokes the button, which is passed
5332 the single argument @var{button}. By default this is @code{ignore},
5336 @kindex mouse-action @r{(button property)}
5337 This is similar to @code{action}, and when present, will be used
5338 instead of @code{action} for button invocations resulting from
5339 mouse-clicks (instead of the user hitting @key{RET}). If not
5340 present, mouse-clicks use @code{action} instead.
5343 @kindex face @r{(button property)}
5344 This is an Emacs face controlling how buttons of this type are
5345 displayed; by default this is the @code{button} face.
5348 @kindex mouse-face @r{(button property)}
5349 This is an additional face which controls appearance during
5350 mouse-overs (merged with the usual button face); by default this is
5351 the usual Emacs @code{highlight} face.
5354 @kindex keymap @r{(button property)}
5355 The button's keymap, defining bindings active within the button
5356 region. By default this is the usual button region keymap, stored
5357 in the variable @code{button-map}, which defines @key{RET} and
5358 @key{mouse-2} to invoke the button.
5361 @kindex type @r{(button property)}
5362 The button type. @xref{Button Types}.
5365 @kindex help-index @r{(button property)}
5366 A string displayed by the Emacs tool-tip help system; by default,
5367 @code{"mouse-2, RET: Push this button"}.
5370 @kindex follow-link @r{(button property)}
5371 The follow-link property, defining how a @key{Mouse-1} click behaves
5372 on this button, @xref{Clickable Text}.
5375 @kindex button @r{(button property)}
5376 All buttons have a non-@code{nil} @code{button} property, which may be useful
5377 in finding regions of text that comprise buttons (which is what the
5378 standard button functions do).
5381 There are other properties defined for the regions of text in a
5382 button, but these are not generally interesting for typical uses.
5385 @subsection Button Types
5386 @cindex button types
5388 Every button has a @dfn{button type}, which defines default values
5389 for the button's properties. Button types are arranged in a
5390 hierarchy, with specialized types inheriting from more general types,
5391 so that it's easy to define special-purpose types of buttons for
5394 @defun define-button-type name &rest properties
5395 Define a `button type' called @var{name} (a symbol).
5396 The remaining arguments
5397 form a sequence of @var{property value} pairs, specifying default
5398 property values for buttons with this type (a button's type may be set
5399 by giving it a @code{type} property when creating the button, using
5400 the @code{:type} keyword argument).
5402 In addition, the keyword argument @code{:supertype} may be used to
5403 specify a button-type from which @var{name} inherits its default
5404 property values. Note that this inheritance happens only when
5405 @var{name} is defined; subsequent changes to a supertype are not
5406 reflected in its subtypes.
5409 Using @code{define-button-type} to define default properties for
5410 buttons is not necessary---buttons without any specified type use the
5411 built-in button-type @code{button}---but it is encouraged, since
5412 doing so usually makes the resulting code clearer and more efficient.
5414 @node Making Buttons
5415 @subsection Making Buttons
5416 @cindex making buttons
5418 Buttons are associated with a region of text, using an overlay or
5419 text properties to hold button-specific information, all of which are
5420 initialized from the button's type (which defaults to the built-in
5421 button type @code{button}). Like all Emacs text, the appearance of
5422 the button is governed by the @code{face} property; by default (via
5423 the @code{face} property inherited from the @code{button} button-type)
5424 this is a simple underline, like a typical web-page link.
5426 For convenience, there are two sorts of button-creation functions,
5427 those that add button properties to an existing region of a buffer,
5428 called @code{make-...button}, and those that also insert the button
5429 text, called @code{insert-...button}.
5431 The button-creation functions all take the @code{&rest} argument
5432 @var{properties}, which should be a sequence of @var{property value}
5433 pairs, specifying properties to add to the button; see @ref{Button
5434 Properties}. In addition, the keyword argument @code{:type} may be
5435 used to specify a button-type from which to inherit other properties;
5436 see @ref{Button Types}. Any properties not explicitly specified
5437 during creation will be inherited from the button's type (if the type
5438 defines such a property).
5440 The following functions add a button using an overlay
5441 (@pxref{Overlays}) to hold the button properties:
5443 @defun make-button beg end &rest properties
5444 This makes a button from @var{beg} to @var{end} in the
5445 current buffer, and returns it.
5448 @defun insert-button label &rest properties
5449 This insert a button with the label @var{label} at point,
5453 The following functions are similar, but using text properties
5454 (@pxref{Text Properties}) to hold the button properties. Such buttons
5455 do not add markers to the buffer, so editing in the buffer does not
5456 slow down if there is an extremely large numbers of buttons. However,
5457 if there is an existing face text property on the text (e.g., a face
5458 assigned by Font Lock mode), the button face may not be visible. Both
5459 of these functions return the starting position of the new button.
5461 @defun make-text-button beg end &rest properties
5462 This makes a button from @var{beg} to @var{end} in the current buffer,
5463 using text properties.
5466 @defun insert-text-button label &rest properties
5467 This inserts a button with the label @var{label} at point, using text
5471 @node Manipulating Buttons
5472 @subsection Manipulating Buttons
5473 @cindex manipulating buttons
5475 These are functions for getting and setting properties of buttons.
5476 Often these are used by a button's invocation function to determine
5479 Where a @var{button} parameter is specified, it means an object
5480 referring to a specific button, either an overlay (for overlay
5481 buttons), or a buffer-position or marker (for text property buttons).
5482 Such an object is passed as the first argument to a button's
5483 invocation function when it is invoked.
5485 @defun button-start button
5486 Return the position at which @var{button} starts.
5489 @defun button-end button
5490 Return the position at which @var{button} ends.
5493 @defun button-get button prop
5494 Get the property of button @var{button} named @var{prop}.
5497 @defun button-put button prop val
5498 Set @var{button}'s @var{prop} property to @var{val}.
5501 @defun button-activate button &optional use-mouse-action
5502 Call @var{button}'s @code{action} property (i.e., invoke it). If
5503 @var{use-mouse-action} is non-@code{nil}, try to invoke the button's
5504 @code{mouse-action} property instead of @code{action}; if the button
5505 has no @code{mouse-action} property, use @code{action} as normal.
5508 @defun button-label button
5509 Return @var{button}'s text label.
5512 @defun button-type button
5513 Return @var{button}'s button-type.
5516 @defun button-has-type-p button type
5517 Return @code{t} if @var{button} has button-type @var{type}, or one of
5518 @var{type}'s subtypes.
5521 @defun button-at pos
5522 Return the button at position @var{pos} in the current buffer, or
5523 @code{nil}. If the button at @var{pos} is a text property button, the
5524 return value is a marker pointing to @var{pos}.
5527 @defun button-type-put type prop val
5528 Set the button-type @var{type}'s @var{prop} property to @var{val}.
5531 @defun button-type-get type prop
5532 Get the property of button-type @var{type} named @var{prop}.
5535 @defun button-type-subtype-p type supertype
5536 Return @code{t} if button-type @var{type} is a subtype of @var{supertype}.
5539 @node Button Buffer Commands
5540 @subsection Button Buffer Commands
5541 @cindex button buffer commands
5543 These are commands and functions for locating and operating on
5544 buttons in an Emacs buffer.
5546 @code{push-button} is the command that a user uses to actually `push'
5547 a button, and is bound by default in the button itself to @key{RET}
5548 and to @key{mouse-2} using a local keymap in the button's overlay or
5549 text properties. Commands that are useful outside the buttons itself,
5550 such as @code{forward-button} and @code{backward-button} are
5551 additionally available in the keymap stored in
5552 @code{button-buffer-map}; a mode which uses buttons may want to use
5553 @code{button-buffer-map} as a parent keymap for its keymap.
5555 If the button has a non-@code{nil} @code{follow-link} property, and
5556 @code{mouse-1-click-follows-link} is set, a quick @key{Mouse-1} click
5557 will also activate the @code{push-button} command.
5558 @xref{Clickable Text}.
5560 @deffn Command push-button &optional pos use-mouse-action
5561 Perform the action specified by a button at location @var{pos}.
5562 @var{pos} may be either a buffer position or a mouse-event. If
5563 @var{use-mouse-action} is non-@code{nil}, or @var{pos} is a
5564 mouse-event (@pxref{Mouse Events}), try to invoke the button's
5565 @code{mouse-action} property instead of @code{action}; if the button
5566 has no @code{mouse-action} property, use @code{action} as normal.
5567 @var{pos} defaults to point, except when @code{push-button} is invoked
5568 interactively as the result of a mouse-event, in which case, the mouse
5569 event's position is used. If there's no button at @var{pos}, do
5570 nothing and return @code{nil}, otherwise return @code{t}.
5573 @deffn Command forward-button n &optional wrap display-message
5574 Move to the @var{n}th next button, or @var{n}th previous button if
5575 @var{n} is negative. If @var{n} is zero, move to the start of any
5576 button at point. If @var{wrap} is non-@code{nil}, moving past either
5577 end of the buffer continues from the other end. If
5578 @var{display-message} is non-@code{nil}, the button's help-echo string
5579 is displayed. Any button with a non-@code{nil} @code{skip} property
5580 is skipped over. Returns the button found.
5583 @deffn Command backward-button n &optional wrap display-message
5584 Move to the @var{n}th previous button, or @var{n}th next button if
5585 @var{n} is negative. If @var{n} is zero, move to the start of any
5586 button at point. If @var{wrap} is non-@code{nil}, moving past either
5587 end of the buffer continues from the other end. If
5588 @var{display-message} is non-@code{nil}, the button's help-echo string
5589 is displayed. Any button with a non-@code{nil} @code{skip} property
5590 is skipped over. Returns the button found.
5593 @defun next-button pos &optional count-current
5594 @defunx previous-button pos &optional count-current
5595 Return the next button after (for @code{next-button}) or before (for
5596 @code{previous-button}) position @var{pos} in the current buffer. If
5597 @var{count-current} is non-@code{nil}, count any button at @var{pos}
5598 in the search, instead of starting at the next button.
5601 @node Abstract Display
5602 @section Abstract Display
5604 @cindex display, abstract
5605 @cindex display, arbitrary objects
5606 @cindex model/view/controller
5607 @cindex view part, model/view/controller
5609 The Ewoc package constructs buffer text that represents a structure
5610 of Lisp objects, and updates the text to follow changes in that
5611 structure. This is like the ``view'' component in the
5612 ``model/view/controller'' design paradigm. Ewoc means ``Emacs's
5613 Widget for Object Collections''.
5615 An @dfn{ewoc} is a structure that organizes information required to
5616 construct buffer text that represents certain Lisp data. The buffer
5617 text of the ewoc has three parts, in order: first, fixed @dfn{header}
5618 text; next, textual descriptions of a series of data elements (Lisp
5619 objects that you specify); and last, fixed @dfn{footer} text.
5620 Specifically, an ewoc contains information on:
5624 The buffer which its text is generated in.
5627 The text's start position in the buffer.
5630 The header and footer strings.
5634 @c or "@cindex node, abstract display"?
5635 A doubly-linked chain of @dfn{nodes}, each of which contains:
5639 A @dfn{data element}, a single Lisp object.
5642 Links to the preceding and following nodes in the chain.
5646 A @dfn{pretty-printer} function which is responsible for
5647 inserting the textual representation of a data
5648 element value into the current buffer.
5651 Typically, you define an ewoc with @code{ewoc-create}, and then pass
5652 the resulting ewoc structure to other functions in the Ewoc package to
5653 build nodes within it, and display it in the buffer. Once it is
5654 displayed in the buffer, other functions determine the correspondence
5655 between buffer positions and nodes, move point from one node's textual
5656 representation to another, and so forth. @xref{Abstract Display
5659 @cindex encapsulation, ewoc
5660 @c or "@cindex encapsulation, abstract display"?
5661 A node @dfn{encapsulates} a data element much the way a variable
5662 holds a value. Normally, encapsulation occurs as a part of adding a
5663 node to the ewoc. You can retrieve the data element value and place a
5664 new value in its place, like so:
5667 (ewoc-data @var{node})
5670 (ewoc-set-data @var{node} @var{new-value})
5671 @result{} @var{new-value}
5675 You can also use, as the data element value, a Lisp object (list or
5676 vector) that is a container for the ``real'' value, or an index into
5677 some other structure. The example (@pxref{Abstract Display Example})
5678 uses the latter approach.
5680 When the data changes, you will want to update the text in the
5681 buffer. You can update all nodes by calling @code{ewoc-refresh}, or
5682 just specific nodes using @code{ewoc-invalidate}, or all nodes
5683 satisfying a predicate using @code{ewoc-map}. Alternatively, you can
5684 delete invalid nodes using @code{ewoc-delete} or @code{ewoc-filter},
5685 and add new nodes in their place. Deleting a node from an ewoc deletes
5686 its associated textual description from buffer, as well.
5689 * Abstract Display Functions:: Functions in the Ewoc package.
5690 * Abstract Display Example:: Example of using Ewoc.
5693 @node Abstract Display Functions
5694 @subsection Abstract Display Functions
5696 In this subsection, @var{ewoc} and @var{node} stand for the
5697 structures described above (@pxref{Abstract Display}), while
5698 @var{data} stands for an arbitrary Lisp object used as a data element.
5700 @defun ewoc-create pretty-printer &optional header footer nosep
5701 This constructs and returns a new ewoc, with no nodes (and thus no data
5702 elements). @var{pretty-printer} should be a function that takes one
5703 argument, a data element of the sort you plan to use in this ewoc, and
5704 inserts its textual description at point using @code{insert} (and never
5705 @code{insert-before-markers}, because that would interfere with the
5706 Ewoc package's internal mechanisms).
5708 Normally, a newline is automatically inserted after the header,
5709 the footer and every node's textual description. If @var{nosep}
5710 is non-@code{nil}, no newline is inserted. This may be useful for
5711 displaying an entire ewoc on a single line, for example, or for
5712 making nodes ``invisible'' by arranging for @var{pretty-printer}
5713 to do nothing for those nodes.
5715 An ewoc maintains its text in the buffer that is current when
5716 you create it, so switch to the intended buffer before calling
5720 @defun ewoc-buffer ewoc
5721 This returns the buffer where @var{ewoc} maintains its text.
5724 @defun ewoc-get-hf ewoc
5725 This returns a cons cell @code{(@var{header} . @var{footer})}
5726 made from @var{ewoc}'s header and footer.
5729 @defun ewoc-set-hf ewoc header footer
5730 This sets the header and footer of @var{ewoc} to the strings
5731 @var{header} and @var{footer}, respectively.
5734 @defun ewoc-enter-first ewoc data
5735 @defunx ewoc-enter-last ewoc data
5736 These add a new node encapsulating @var{data}, putting it, respectively,
5737 at the beginning or end of @var{ewoc}'s chain of nodes.
5740 @defun ewoc-enter-before ewoc node data
5741 @defunx ewoc-enter-after ewoc node data
5742 These add a new node encapsulating @var{data}, adding it to
5743 @var{ewoc} before or after @var{node}, respectively.
5746 @defun ewoc-prev ewoc node
5747 @defunx ewoc-next ewoc node
5748 These return, respectively, the previous node and the next node of @var{node}
5752 @defun ewoc-nth ewoc n
5753 This returns the node in @var{ewoc} found at zero-based index @var{n}.
5754 A negative @var{n} means count from the end. @code{ewoc-nth} returns
5755 @code{nil} if @var{n} is out of range.
5758 @defun ewoc-data node
5759 This extracts the data encapsulated by @var{node} and returns it.
5762 @defun ewoc-set-data node data
5763 This sets the data encapsulated by @var{node} to @var{data}.
5766 @defun ewoc-locate ewoc &optional pos guess
5767 This determines the node in @var{ewoc} which contains point (or
5768 @var{pos} if specified), and returns that node. If @var{ewoc} has no
5769 nodes, it returns @code{nil}. If @var{pos} is before the first node,
5770 it returns the first node; if @var{pos} is after the last node, it returns
5771 the last node. The optional third arg @var{guess}
5772 should be a node that is likely to be near @var{pos}; this doesn't
5773 alter the result, but makes the function run faster.
5776 @defun ewoc-location node
5777 This returns the start position of @var{node}.
5780 @defun ewoc-goto-prev ewoc arg
5781 @defunx ewoc-goto-next ewoc arg
5782 These move point to the previous or next, respectively, @var{arg}th node
5783 in @var{ewoc}. @code{ewoc-goto-prev} does not move if it is already at
5784 the first node or if @var{ewoc} is empty, whereas @code{ewoc-goto-next}
5785 moves past the last node, returning @code{nil}. Excepting this special
5786 case, these functions return the node moved to.
5789 @defun ewoc-goto-node ewoc node
5790 This moves point to the start of @var{node} in @var{ewoc}.
5793 @defun ewoc-refresh ewoc
5794 This function regenerates the text of @var{ewoc}. It works by
5795 deleting the text between the header and the footer, i.e., all the
5796 data elements' representations, and then calling the pretty-printer
5797 function for each node, one by one, in order.
5800 @defun ewoc-invalidate ewoc &rest nodes
5801 This is similar to @code{ewoc-refresh}, except that only @var{nodes} in
5802 @var{ewoc} are updated instead of the entire set.
5805 @defun ewoc-delete ewoc &rest nodes
5806 This deletes each node in @var{nodes} from @var{ewoc}.
5809 @defun ewoc-filter ewoc predicate &rest args
5810 This calls @var{predicate} for each data element in @var{ewoc} and
5811 deletes those nodes for which @var{predicate} returns @code{nil}.
5812 Any @var{args} are passed to @var{predicate}.
5815 @defun ewoc-collect ewoc predicate &rest args
5816 This calls @var{predicate} for each data element in @var{ewoc}
5817 and returns a list of those elements for which @var{predicate}
5818 returns non-@code{nil}. The elements in the list are ordered
5819 as in the buffer. Any @var{args} are passed to @var{predicate}.
5822 @defun ewoc-map map-function ewoc &rest args
5823 This calls @var{map-function} for each data element in @var{ewoc} and
5824 updates those nodes for which @var{map-function} returns non-@code{nil}.
5825 Any @var{args} are passed to @var{map-function}.
5828 @node Abstract Display Example
5829 @subsection Abstract Display Example
5831 Here is a simple example using functions of the ewoc package to
5832 implement a ``color components display'', an area in a buffer that
5833 represents a vector of three integers (itself representing a 24-bit RGB
5834 value) in various ways.
5837 (setq colorcomp-ewoc nil
5839 colorcomp-mode-map nil
5840 colorcomp-labels ["Red" "Green" "Blue"])
5842 (defun colorcomp-pp (data)
5844 (let ((comp (aref colorcomp-data data)))
5845 (insert (aref colorcomp-labels data) "\t: #x"
5846 (format "%02X" comp) " "
5847 (make-string (ash comp -2) ?#) "\n"))
5848 (let ((cstr (format "#%02X%02X%02X"
5849 (aref colorcomp-data 0)
5850 (aref colorcomp-data 1)
5851 (aref colorcomp-data 2)))
5852 (samp " (sample text) "))
5854 (propertize samp 'face
5855 `(foreground-color . ,cstr))
5856 (propertize samp 'face
5857 `(background-color . ,cstr))
5860 (defun colorcomp (color)
5861 "Allow fiddling with COLOR in a new buffer.
5862 The buffer is in Color Components mode."
5863 (interactive "sColor (name or #RGB or #RRGGBB): ")
5864 (when (string= "" color)
5865 (setq color "green"))
5866 (unless (color-values color)
5867 (error "No such color: %S" color))
5869 (generate-new-buffer (format "originally: %s" color)))
5870 (kill-all-local-variables)
5871 (setq major-mode 'colorcomp-mode
5872 mode-name "Color Components")
5873 (use-local-map colorcomp-mode-map)
5875 (buffer-disable-undo)
5876 (let ((data (apply 'vector (mapcar (lambda (n) (ash n -8))
5877 (color-values color))))
5878 (ewoc (ewoc-create 'colorcomp-pp
5879 "\nColor Components\n\n"
5880 (substitute-command-keys
5881 "\n\\@{colorcomp-mode-map@}"))))
5882 (set (make-local-variable 'colorcomp-data) data)
5883 (set (make-local-variable 'colorcomp-ewoc) ewoc)
5884 (ewoc-enter-last ewoc 0)
5885 (ewoc-enter-last ewoc 1)
5886 (ewoc-enter-last ewoc 2)
5887 (ewoc-enter-last ewoc nil)))
5890 @cindex controller part, model/view/controller
5891 This example can be extended to be a ``color selection widget'' (in
5892 other words, the controller part of the ``model/view/controller''
5893 design paradigm) by defining commands to modify @code{colorcomp-data}
5894 and to ``finish'' the selection process, and a keymap to tie it all
5895 together conveniently.
5898 (defun colorcomp-mod (index limit delta)
5899 (let ((cur (aref colorcomp-data index)))
5900 (unless (= limit cur)
5901 (aset colorcomp-data index (+ cur delta)))
5904 (ewoc-nth colorcomp-ewoc index)
5905 (ewoc-nth colorcomp-ewoc -1))))
5907 (defun colorcomp-R-more () (interactive) (colorcomp-mod 0 255 1))
5908 (defun colorcomp-G-more () (interactive) (colorcomp-mod 1 255 1))
5909 (defun colorcomp-B-more () (interactive) (colorcomp-mod 2 255 1))
5910 (defun colorcomp-R-less () (interactive) (colorcomp-mod 0 0 -1))
5911 (defun colorcomp-G-less () (interactive) (colorcomp-mod 1 0 -1))
5912 (defun colorcomp-B-less () (interactive) (colorcomp-mod 2 0 -1))
5914 (defun colorcomp-copy-as-kill-and-exit ()
5915 "Copy the color components into the kill ring and kill the buffer.
5916 The string is formatted #RRGGBB (hash followed by six hex digits)."
5918 (kill-new (format "#%02X%02X%02X"
5919 (aref colorcomp-data 0)
5920 (aref colorcomp-data 1)
5921 (aref colorcomp-data 2)))
5924 (setq colorcomp-mode-map
5925 (let ((m (make-sparse-keymap)))
5927 (define-key m "i" 'colorcomp-R-less)
5928 (define-key m "o" 'colorcomp-R-more)
5929 (define-key m "k" 'colorcomp-G-less)
5930 (define-key m "l" 'colorcomp-G-more)
5931 (define-key m "," 'colorcomp-B-less)
5932 (define-key m "." 'colorcomp-B-more)
5933 (define-key m " " 'colorcomp-copy-as-kill-and-exit)
5937 Note that we never modify the data in each node, which is fixed when the
5938 ewoc is created to be either @code{nil} or an index into the vector
5939 @code{colorcomp-data}, the actual color components.
5942 @section Blinking Parentheses
5943 @cindex parenthesis matching
5944 @cindex blinking parentheses
5945 @cindex balancing parentheses
5947 This section describes the mechanism by which Emacs shows a matching
5948 open parenthesis when the user inserts a close parenthesis.
5950 @defvar blink-paren-function
5951 The value of this variable should be a function (of no arguments) to
5952 be called whenever a character with close parenthesis syntax is inserted.
5953 The value of @code{blink-paren-function} may be @code{nil}, in which
5954 case nothing is done.
5957 @defopt blink-matching-paren
5958 If this variable is @code{nil}, then @code{blink-matching-open} does
5962 @defopt blink-matching-paren-distance
5963 This variable specifies the maximum distance to scan for a matching
5964 parenthesis before giving up.
5967 @defopt blink-matching-delay
5968 This variable specifies the number of seconds to keep indicating the
5969 matching parenthesis. A fraction of a second often gives good
5970 results, but the default is 1, which works on all systems.
5973 @deffn Command blink-matching-open
5974 This function is the default value of @code{blink-paren-function}. It
5975 assumes that point follows a character with close parenthesis syntax
5976 and applies the appropriate effect momentarily to the matching opening
5977 character. If that character is not already on the screen, it
5978 displays the character's context in the echo area. To avoid long
5979 delays, this function does not search farther than
5980 @code{blink-matching-paren-distance} characters.
5982 Here is an example of calling this function explicitly.
5986 (defun interactive-blink-matching-open ()
5987 "Indicate momentarily the start of parenthesized sexp before point."
5991 (let ((blink-matching-paren-distance
5993 (blink-matching-paren t))
5994 (blink-matching-open)))
5999 @node Character Display
6000 @section Character Display
6002 This section describes how characters are actually displayed by
6003 Emacs. Typically, a character is displayed as a @dfn{glyph} (a
6004 graphical symbol which occupies one character position on the screen),
6005 whose appearance corresponds to the character itself. For example,
6006 the character @samp{a} (character code 97) is displayed as @samp{a}.
6007 Some characters, however, are displayed specially. For example, the
6008 formfeed character (character code 12) is usually displayed as a
6009 sequence of two glyphs, @samp{^L}, while the newline character
6010 (character code 10) starts a new screen line.
6012 You can modify how each character is displayed by defining a
6013 @dfn{display table}, which maps each character code into a sequence of
6014 glyphs. @xref{Display Tables}.
6017 * Usual Display:: The usual conventions for displaying characters.
6018 * Display Tables:: What a display table consists of.
6019 * Active Display Table:: How Emacs selects a display table to use.
6020 * Glyphs:: How to define a glyph, and what glyphs mean.
6021 * Glyphless Chars:: How glyphless characters are drawn.
6025 @subsection Usual Display Conventions
6027 Here are the conventions for displaying each character code (in the
6028 absence of a display table, which can override these
6033 conventions; @pxref{Display Tables}).
6036 @cindex printable ASCII characters
6039 The @dfn{printable @acronym{ASCII} characters}, character codes 32
6040 through 126 (consisting of numerals, English letters, and symbols like
6041 @samp{#}) are displayed literally.
6044 The tab character (character code 9) displays as whitespace stretching
6045 up to the next tab stop column. @xref{Text Display,,, emacs, The GNU
6046 Emacs Manual}. The variable @code{tab-width} controls the number of
6047 spaces per tab stop (see below).
6050 The newline character (character code 10) has a special effect: it
6051 ends the preceding line and starts a new line.
6053 @cindex ASCII control characters
6055 The non-printable @dfn{@acronym{ASCII} control characters}---character
6056 codes 0 through 31, as well as the @key{DEL} character (character code
6057 127)---display in one of two ways according to the variable
6058 @code{ctl-arrow}. If this variable is non-@code{nil} (the default),
6059 these characters are displayed as sequences of two glyphs, where the
6060 first glyph is @samp{^} (a display table can specify a glyph to use
6061 instead of @samp{^}); e.g., the @key{DEL} character is displayed as
6064 If @code{ctl-arrow} is @code{nil}, these characters are displayed as
6065 octal escapes (see below).
6067 This rule also applies to carriage return (character code 13), if that
6068 character appears in the buffer. But carriage returns usually do not
6069 appear in buffer text; they are eliminated as part of end-of-line
6070 conversion (@pxref{Coding System Basics}).
6072 @cindex octal escapes
6074 @dfn{Raw bytes} are non-@acronym{ASCII} characters with codes 128
6075 through 255 (@pxref{Text Representations}). These characters display
6076 as @dfn{octal escapes}: sequences of four glyphs, where the first
6077 glyph is the @acronym{ASCII} code for @samp{\}, and the others are
6078 digit characters representing the character code in octal. (A display
6079 table can specify a glyph to use instead of @samp{\}.)
6082 Each non-@acronym{ASCII} character with code above 255 is displayed
6083 literally, if the terminal supports it. If the terminal does not
6084 support it, the character is said to be @dfn{glyphless}, and it is
6085 usually displayed using a placeholder glyph. For example, if a
6086 graphical terminal has no font for a character, Emacs usually displays
6087 a box containing the character code in hexadecimal. @xref{Glyphless
6091 The above display conventions apply even when there is a display
6092 table, for any character whose entry in the active display table is
6093 @code{nil}. Thus, when you set up a display table, you need only
6094 specify the characters for which you want special behavior.
6096 The following variables affect how certain characters are displayed
6097 on the screen. Since they change the number of columns the characters
6098 occupy, they also affect the indentation functions. They also affect
6099 how the mode line is displayed; if you want to force redisplay of the
6100 mode line using the new values, call the function
6101 @code{force-mode-line-update} (@pxref{Mode Line Format}).
6104 @cindex control characters in display
6105 This buffer-local variable controls how control characters are
6106 displayed. If it is non-@code{nil}, they are displayed as a caret
6107 followed by the character: @samp{^A}. If it is @code{nil}, they are
6108 displayed as octal escapes: a backslash followed by three octal
6109 digits, as in @samp{\001}.
6113 The value of this buffer-local variable is the spacing between tab
6114 stops used for displaying tab characters in Emacs buffers. The value
6115 is in units of columns, and the default is 8. Note that this feature
6116 is completely independent of the user-settable tab stops used by the
6117 command @code{tab-to-tab-stop}. @xref{Indent Tabs}.
6120 @node Display Tables
6121 @subsection Display Tables
6123 @cindex display table
6124 A display table is a special-purpose char-table
6125 (@pxref{Char-Tables}), with @code{display-table} as its subtype, which
6126 is used to override the usual character display conventions. This
6127 section describes how to make, inspect, and assign elements to a
6128 display table object.
6130 @defun make-display-table
6131 This creates and returns a display table. The table initially has
6132 @code{nil} in all elements.
6135 The ordinary elements of the display table are indexed by character
6136 codes; the element at index @var{c} says how to display the character
6137 code @var{c}. The value should be @code{nil} (which means to display
6138 the character @var{c} according to the usual display conventions;
6139 @pxref{Usual Display}), or a vector of glyph codes (which means to
6140 display the character @var{c} as those glyphs; @pxref{Glyphs}).
6142 @strong{Warning:} if you use the display table to change the display
6143 of newline characters, the whole buffer will be displayed as one long
6146 The display table also has six ``extra slots'' which serve special
6147 purposes. Here is a table of their meanings; @code{nil} in any slot
6148 means to use the default for that slot, as stated below.
6152 The glyph for the end of a truncated screen line (the default for this
6153 is @samp{$}). @xref{Glyphs}. On graphical terminals, Emacs uses
6154 arrows in the fringes to indicate truncation, so the display table has
6158 The glyph for the end of a continued line (the default is @samp{\}).
6159 On graphical terminals, Emacs uses curved arrows in the fringes to
6160 indicate continuation, so the display table has no effect.
6163 The glyph for indicating a character displayed as an octal character
6164 code (the default is @samp{\}).
6167 The glyph for indicating a control character (the default is @samp{^}).
6170 A vector of glyphs for indicating the presence of invisible lines (the
6171 default is @samp{...}). @xref{Selective Display}.
6174 The glyph used to draw the border between side-by-side windows (the
6175 default is @samp{|}). @xref{Splitting Windows}. This takes effect only
6176 when there are no scroll bars; if scroll bars are supported and in use,
6177 a scroll bar separates the two windows.
6180 For example, here is how to construct a display table that mimics
6181 the effect of setting @code{ctl-arrow} to a non-@code{nil} value
6182 (@pxref{Glyphs}, for the function @code{make-glyph-code}):
6185 (setq disptab (make-display-table))
6190 (vector (make-glyph-code ?^ 'escape-glyph)
6191 (make-glyph-code (+ i 64) 'escape-glyph)))))
6193 (vector (make-glyph-code ?^ 'escape-glyph)
6194 (make-glyph-code ?? 'escape-glyph)))))
6197 @defun display-table-slot display-table slot
6198 This function returns the value of the extra slot @var{slot} of
6199 @var{display-table}. The argument @var{slot} may be a number from 0 to
6200 5 inclusive, or a slot name (symbol). Valid symbols are
6201 @code{truncation}, @code{wrap}, @code{escape}, @code{control},
6202 @code{selective-display}, and @code{vertical-border}.
6205 @defun set-display-table-slot display-table slot value
6206 This function stores @var{value} in the extra slot @var{slot} of
6207 @var{display-table}. The argument @var{slot} may be a number from 0 to
6208 5 inclusive, or a slot name (symbol). Valid symbols are
6209 @code{truncation}, @code{wrap}, @code{escape}, @code{control},
6210 @code{selective-display}, and @code{vertical-border}.
6213 @defun describe-display-table display-table
6214 This function displays a description of the display table
6215 @var{display-table} in a help buffer.
6218 @deffn Command describe-current-display-table
6219 This command displays a description of the current display table in a
6223 @node Active Display Table
6224 @subsection Active Display Table
6225 @cindex active display table
6227 Each window can specify a display table, and so can each buffer.
6228 The window's display table, if there is one, takes precedence over the
6229 buffer's display table. If neither exists, Emacs tries to use the
6230 standard display table; if that is @code{nil}, Emacs uses the usual
6231 character display conventions (@pxref{Usual Display}).
6233 Note that display tables affect how the mode line is displayed, so
6234 if you want to force redisplay of the mode line using a new display
6235 table, call @code{force-mode-line-update} (@pxref{Mode Line Format}).
6237 @defun window-display-table &optional window
6238 This function returns @var{window}'s display table, or @code{nil} if
6239 there is none. The default for @var{window} is the selected window.
6242 @defun set-window-display-table window table
6243 This function sets the display table of @var{window} to @var{table}.
6244 The argument @var{table} should be either a display table or
6248 @defvar buffer-display-table
6249 This variable is automatically buffer-local in all buffers; its value
6250 specifies the buffer's display table. If it is @code{nil}, there is
6251 no buffer display table.
6254 @defvar standard-display-table
6255 The value of this variable is the standard display table, which is
6256 used when Emacs is displaying a buffer in a window with neither a
6257 window display table nor a buffer display table defined. Its default
6261 The @file{disp-table} library defines several functions for changing
6262 the standard display table.
6269 A @dfn{glyph} is a graphical symbol which occupies a single
6270 character position on the screen. Each glyph is represented in Lisp
6271 as a @dfn{glyph code}, which specifies a character and optionally a
6272 face to display it in (@pxref{Faces}). The main use of glyph codes is
6273 as the entries of display tables (@pxref{Display Tables}). The
6274 following functions are used to manipulate glyph codes:
6276 @defun make-glyph-code char &optional face
6277 This function returns a glyph code representing char @var{char} with
6278 face @var{face}. If @var{face} is omitted or @code{nil}, the glyph
6279 uses the default face; in that case, the glyph code is an integer. If
6280 @var{face} is non-@code{nil}, the glyph code is not necessarily an
6284 @defun glyph-char glyph
6285 This function returns the character of glyph code @var{glyph}.
6288 @defun glyph-face glyph
6289 This function returns face of glyph code @var{glyph}, or @code{nil} if
6290 @var{glyph} uses the default face.
6294 You can set up a @dfn{glyph table} to change how glyph codes are
6295 actually displayed on text terminals. This feature is semi-obsolete;
6296 use @code{glyphless-char-display} instead (@pxref{Glyphless Chars}).
6299 The value of this variable, if non-@code{nil}, is the current glyph
6300 table. It takes effect only on character terminals; on graphical
6301 displays, all glyphs are displayed literally. The glyph table should
6302 be a vector whose @var{g}th element specifies how to display glyph
6303 code @var{g}, where @var{g} is the glyph code for a glyph whose face
6304 is unspecified. Each element should be one of the following:
6308 Display this glyph literally.
6311 Display this glyph by sending the specified string to the terminal.
6314 Display the specified glyph code instead.
6317 Any integer glyph code greater than or equal to the length of the
6318 glyph table is displayed literally.
6322 @node Glyphless Chars
6323 @subsection Glyphless Character Display
6324 @cindex glyphless characters
6326 @dfn{Glyphless characters} are characters which are displayed in a
6327 special way, e.g., as a box containing a hexadecimal code, instead of
6328 being displayed literally. These include characters which are
6329 explicitly defined to be glyphless, as well as characters for which
6330 there is no available font (on a graphical display), and characters
6331 which cannot be encoded by the terminal's coding system (on a text
6334 @defvar glyphless-char-display
6335 The value of this variable is a char-table which defines glyphless
6336 characters and how they are displayed. Each entry must be one of the
6337 following display methods:
6341 Display the character in the usual way.
6343 @item @code{zero-width}
6344 Don't display the character.
6346 @item @code{thin-space}
6347 Display a thin space, 1-pixel wide on graphical displays, or
6348 1-character wide on text terminals.
6350 @item @code{empty-box}
6351 Display an empty box.
6353 @item @code{hex-code}
6354 Display a box containing the Unicode codepoint of the character, in
6355 hexadecimal notation.
6357 @item an @acronym{ASCII} string
6358 Display a box containing that string.
6360 @item a cons cell @code{(@var{graphical} . @var{text})}
6361 Display with @var{graphical} on graphical displays, and with
6362 @var{text} on text terminals. Both @var{graphical} and @var{text}
6363 must be one of the display methods described above.
6367 The @code{thin-space}, @code{empty-box}, @code{hex-code}, and
6368 @acronym{ASCII} string display methods are drawn with the
6369 @code{glyphless-char} face.
6371 The char-table has one extra slot, which determines how to display any
6372 character that cannot be displayed with any available font, or cannot
6373 be encoded by the terminal's coding system. Its value should be one
6374 of the above display methods, except @code{zero-width} or a cons cell.
6376 If a character has a non-@code{nil} entry in an active display table,
6377 the display table takes effect; in this case, Emacs does not consult
6378 @code{glyphless-char-display} at all.
6381 @defopt glyphless-char-display-control
6382 This user option provides a convenient way to set
6383 @code{glyphless-char-display} for groups of similar characters. Do
6384 not set its value directly from Lisp code; the value takes effect only
6385 via a custom @code{:set} function (@pxref{Variable Definitions}),
6386 which updates @code{glyphless-char-display}.
6388 Its value should be an alist of elements @code{(@var{group}
6389 . @var{method})}, where @var{group} is a symbol specifying a group of
6390 characters, and @var{method} is a symbol specifying how to display
6393 @var{group} should be one of the following:
6397 @acronym{ASCII} control characters @code{U+0000} to @code{U+001F},
6398 excluding the newline and tab characters (normally displayed as escape
6399 sequences like @samp{^A}; @pxref{Text Display,, How Text Is Displayed,
6400 emacs, The GNU Emacs Manual}).
6403 Non-@acronym{ASCII}, non-printing characters @code{U+0080} to
6404 @code{U+009F} (normally displayed as octal escape sequences like
6407 @item format-control
6408 Characters of Unicode General Category `Cf', such as @samp{U+200E}
6409 (Left-to-Right Mark), but excluding characters that have graphic
6410 images, such as @samp{U+00AD} (Soft Hyphen).
6413 Characters for there is no suitable font, or which cannot be encoded
6414 by the terminal's coding system.
6417 @c FIXME: this can also be `acronym', but that's not currently
6418 @c completely implemented; it applies only to the format-control
6419 @c group, and only works if the acronym is in `char-acronym-table'.
6420 The @var{method} symbol should be one of @code{zero-width},
6421 @code{thin-space}, @code{empty-box}, or @code{hex-code}. These have
6422 the same meanings as in @code{glyphless-char-display}, above.
6429 This section describes how to make Emacs ring the bell (or blink the
6430 screen) to attract the user's attention. Be conservative about how
6431 often you do this; frequent bells can become irritating. Also be
6432 careful not to use just beeping when signaling an error is more
6433 appropriate (@pxref{Errors}).
6435 @defun ding &optional do-not-terminate
6436 @cindex keyboard macro termination
6437 This function beeps, or flashes the screen (see @code{visible-bell} below).
6438 It also terminates any keyboard macro currently executing unless
6439 @var{do-not-terminate} is non-@code{nil}.
6442 @defun beep &optional do-not-terminate
6443 This is a synonym for @code{ding}.
6446 @defopt visible-bell
6447 This variable determines whether Emacs should flash the screen to
6448 represent a bell. Non-@code{nil} means yes, @code{nil} means no.
6449 This is effective on graphical displays, and on text terminals
6450 provided the terminal's Termcap entry defines the visible bell
6451 capability (@samp{vb}).
6454 @defvar ring-bell-function
6455 If this is non-@code{nil}, it specifies how Emacs should ``ring the
6456 bell''. Its value should be a function of no arguments. If this is
6457 non-@code{nil}, it takes precedence over the @code{visible-bell}
6461 @node Window Systems
6462 @section Window Systems
6464 Emacs works with several window systems, most notably the X Window
6465 System. Both Emacs and X use the term ``window'', but use it
6466 differently. An Emacs frame is a single window as far as X is
6467 concerned; the individual Emacs windows are not known to X at all.
6469 @defvar window-system
6470 This terminal-local variable tells Lisp programs what window system
6471 Emacs is using for displaying the frame. The possible values are
6475 @cindex X Window System
6476 Emacs is displaying the frame using X.
6478 Emacs is displaying the frame using native MS-Windows GUI.
6480 Emacs is displaying the frame using the Nextstep interface (used on
6481 GNUstep and Mac OS X).
6483 Emacs is displaying the frame using MS-DOS direct screen writes.
6485 Emacs is displaying the frame on a character-based terminal.
6489 @defvar initial-window-system
6490 This variable holds the value of @code{window-system} used for the
6491 first frame created by Emacs during startup. (When Emacs is invoked
6492 with the @option{--daemon} option, it does not create any initial
6493 frames, so @code{initial-window-system} is @code{nil}. @xref{Initial
6494 Options, daemon,, emacs, The GNU Emacs Manual}.)
6497 @defun window-system &optional frame
6498 This function returns a symbol whose name tells what window system is
6499 used for displaying @var{frame} (which defaults to the currently
6500 selected frame). The list of possible symbols it returns is the same
6501 one documented for the variable @code{window-system} above.
6504 Do @emph{not} use @code{window-system} and
6505 @code{initial-window-system} as predicates or boolean flag variables,
6506 if you want to write code that works differently on text terminals and
6507 graphic displays. That is because @code{window-system} is not a good
6508 indicator of Emacs capabilities on a given display type. Instead, use
6509 @code{display-graphic-p} or any of the other @code{display-*-p}
6510 predicates described in @ref{Display Feature Testing}.
6512 @defvar window-setup-hook
6513 This variable is a normal hook which Emacs runs after handling the
6514 initialization files. Emacs runs this hook after it has completed
6515 loading your init file, the default initialization file (if
6516 any), and the terminal-specific Lisp code, and running the hook
6517 @code{emacs-startup-hook}.
6519 This hook is used for internal purposes: setting up communication with
6520 the window system, and creating the initial window. Users should not
6524 @node Bidirectional Display
6525 @section Bidirectional Display
6526 @cindex bidirectional display
6527 @cindex right-to-left text
6529 Emacs can display text written in scripts, such as Arabic, Farsi,
6530 and Hebrew, whose natural ordering for horizontal text display runs
6531 from right to left. Furthermore, segments of Latin script and digits
6532 embedded in right-to-left text are displayed left-to-right, while
6533 segments of right-to-left script embedded in left-to-right text
6534 (e.g., Arabic or Hebrew text in comments or strings in a program
6535 source file) are appropriately displayed right-to-left. We call such
6536 mixtures of left-to-right and right-to-left text @dfn{bidirectional
6537 text}. This section describes the facilities and options for editing
6538 and displaying bidirectional text.
6540 @cindex logical order
6541 @cindex reading order
6542 @cindex visual order
6543 @cindex unicode bidirectional algorithm
6545 @cindex bidirectional reordering
6546 @cindex reordering, of bidirectional text
6547 Text is stored in Emacs buffers and strings in @dfn{logical} (or
6548 @dfn{reading}) order, i.e., the order in which a human would read
6549 each character. In right-to-left and bidirectional text, the order in
6550 which characters are displayed on the screen (called @dfn{visual
6551 order}) is not the same as logical order; the characters' screen
6552 positions do not increase monotonically with string or buffer
6553 position. In performing this @dfn{bidirectional reordering}, Emacs
6554 follows the Unicode Bidirectional Algorithm (a.k.a.@: @acronym{UBA}),
6555 which is described in Annex #9 of the Unicode standard
6556 (@url{http://www.unicode.org/reports/tr9/}). Emacs provides a ``Full
6557 Bidirectionality'' class implementation of the @acronym{UBA}.
6559 @defvar bidi-display-reordering
6560 If the value of this buffer-local variable is non-@code{nil} (the
6561 default), Emacs performs bidirectional reordering for display. The
6562 reordering affects buffer text, as well as display strings and overlay
6563 strings from text and overlay properties in the buffer (@pxref{Overlay
6564 Properties}, and @pxref{Display Property}). If the value is
6565 @code{nil}, Emacs does not perform bidirectional reordering in the
6568 The default value of @code{bidi-display-reordering} controls the
6569 reordering of strings which are not directly supplied by a buffer,
6570 including the text displayed in mode lines (@pxref{Mode Line Format})
6571 and header lines (@pxref{Header Lines}).
6574 @cindex unibyte buffers, and bidi reordering
6575 Emacs never reorders the text of a unibyte buffer, even if
6576 @code{bidi-display-reordering} is non-@code{nil} in the buffer. This
6577 is because unibyte buffers contain raw bytes, not characters, and thus
6578 lack the directionality properties required for reordering.
6579 Therefore, to test whether text in a buffer will be reordered for
6580 display, it is not enough to test the value of
6581 @code{bidi-display-reordering} alone. The correct test is this:
6584 (if (and enable-multibyte-characters
6585 bidi-display-reordering)
6586 ;; Buffer is being reordered for display
6590 However, unibyte display and overlay strings @emph{are} reordered if
6591 their parent buffer is reordered. This is because plain-@sc{ascii}
6592 strings are stored by Emacs as unibyte strings. If a unibyte display
6593 or overlay string includes non-@sc{ascii} characters, these characters
6594 are assumed to have left-to-right direction.
6596 @cindex display properties, and bidi reordering of text
6597 Text covered by @code{display} text properties, by overlays with
6598 @code{display} properties whose value is a string, and by any other
6599 properties that replace buffer text, is treated as a single unit when
6600 it is reordered for display. That is, the entire chunk of text
6601 covered by these properties is reordered together. Moreover, the
6602 bidirectional properties of the characters in such a chunk of text are
6603 ignored, and Emacs reorders them as if they were replaced with a
6604 single character @code{U+FFFC}, known as the @dfn{Object Replacement
6605 Character}. This means that placing a display property over a portion
6606 of text may change the way that the surrounding text is reordered for
6607 display. To prevent this unexpected effect, always place such
6608 properties on text whose directionality is identical with text that
6611 @cindex base direction of a paragraph
6612 Each paragraph of bidirectional text has a @dfn{base direction},
6613 either right-to-left or left-to-right. Left-to-right paragraphs are
6614 displayed beginning at the left margin of the window, and are
6615 truncated or continued when the text reaches the right margin.
6616 Right-to-left paragraphs are displayed beginning at the right margin,
6617 and are continued or truncated at the left margin.
6619 By default, Emacs determines the base direction of each paragraph by
6620 looking at the text at its beginning. The precise method of
6621 determining the base direction is specified by the @acronym{UBA}; in a
6622 nutshell, the first character in a paragraph that has an explicit
6623 directionality determines the base direction of the paragraph.
6624 However, sometimes a buffer may need to force a certain base direction
6625 for its paragraphs. For example, buffers containing program source
6626 code should force all paragraphs to be displayed left-to-right. You
6627 can use following variable to do this:
6629 @defvar bidi-paragraph-direction
6630 If the value of this buffer-local variable is the symbol
6631 @code{right-to-left} or @code{left-to-right}, all paragraphs in the
6632 buffer are assumed to have that specified direction. Any other value
6633 is equivalent to @code{nil} (the default), which means to determine
6634 the base direction of each paragraph from its contents.
6636 @cindex @code{prog-mode}, and @code{bidi-paragraph-direction}
6637 Modes for program source code should set this to @code{left-to-right}.
6638 Prog mode does this by default, so modes derived from Prog mode do not
6639 need to set this explicitly (@pxref{Basic Major Modes}).
6642 @defun current-bidi-paragraph-direction &optional buffer
6643 This function returns the paragraph direction at point in the named
6644 @var{buffer}. The returned value is a symbol, either
6645 @code{left-to-right} or @code{right-to-left}. If @var{buffer} is
6646 omitted or @code{nil}, it defaults to the current buffer. If the
6647 buffer-local value of the variable @code{bidi-paragraph-direction} is
6648 non-@code{nil}, the returned value will be identical to that value;
6649 otherwise, the returned value reflects the paragraph direction
6650 determined dynamically by Emacs. For buffers whose value of
6651 @code{bidi-display-reordering} is @code{nil} as well as unibyte
6652 buffers, this function always returns @code{left-to-right}.
6655 @cindex visual-order cursor motion
6656 Sometimes there's a need to move point in strict visual order,
6657 either to the left or to the right of its current screen position.
6658 Emacs provides a primitive to do that.
6660 @defun move-point-visually direction
6661 This function moves point of the currently selected window to the
6662 buffer position that appears immediately to the right or to the left
6663 of point on the screen. If @var{direction} is positive, point will
6664 move one screen position to the right, otherwise it will move one
6665 screen position to the left. Note that, depending on the surrounding
6666 bidirectional context, this could potentially move point many buffer
6667 positions away. If invoked at the end of a screen line, the function
6668 moves point to the rightmost or leftmost screen position of the next
6669 or previous screen line, as appropriate for the value of
6672 The function returns the new buffer position as its value.
6675 @cindex layout on display, and bidirectional text
6676 @cindex jumbled display of bidirectional text
6677 @cindex concatenating bidirectional strings
6678 Bidirectional reordering can have surprising and unpleasant effects
6679 when two strings with bidirectional content are juxtaposed in a
6680 buffer, or otherwise programmatically concatenated into a string of
6681 text. A typical problematic case is when a buffer consists of
6682 sequences of text ``fields'' separated by whitespace or punctuation
6683 characters, like Buffer Menu mode or Rmail Summary Mode. Because the
6684 punctuation characters used as separators have @dfn{weak
6685 directionality}, they take on the directionality of surrounding text.
6686 As result, a numeric field that follows a field with bidirectional
6687 content can be displayed @emph{to the left} of the preceding field,
6688 messing up the expected layout. There are several ways to avoid this
6693 Append the special character @code{U+200E}, LEFT-TO-RIGHT MARK, or
6694 @acronym{LRM}, to the end of each field that may have bidirectional
6695 content, or prepend it to the beginning of the following field. The
6696 function @code{bidi-string-mark-left-to-right}, described below, comes
6697 in handy for this purpose. (In a right-to-left paragraph, use
6698 @code{U+200F}, RIGHT-TO-LEFT MARK, or @acronym{RLM}, instead.) This
6699 is one of the solutions recommended by the UBA.
6702 Include the tab character in the field separator. The tab character
6703 plays the role of @dfn{segment separator} in bidirectional reordering,
6704 causing the text on either side to be reordered separately.
6706 @cindex @code{space} display spec, and bidirectional text
6708 Separate fields with a @code{display} property or overlay with a
6709 property value of the form @code{(space . PROPS)} (@pxref{Specified
6710 Space}). Emacs treats this display specification as a @dfn{paragraph
6711 separator}, and reorders the text on either side separately.
6714 @defun bidi-string-mark-left-to-right string
6715 This function returns its argument @var{string}, possibly modified,
6716 such that the result can be safely concatenated with another string,
6717 or juxtaposed with another string in a buffer, without disrupting the
6718 relative layout of this string and the next one on display. If the
6719 string returned by this function is displayed as part of a
6720 left-to-right paragraph, it will always appear on display to the left
6721 of the text that follows it. The function works by examining the
6722 characters of its argument, and if any of those characters could cause
6723 reordering on display, the function appends the @acronym{LRM}
6724 character to the string. The appended @acronym{LRM} character is made
6725 invisible by giving it an @code{invisible} text property of @code{t}
6726 (@pxref{Invisible Text}).
6729 The reordering algorithm uses the bidirectional properties of the
6730 characters stored as their @code{bidi-class} property
6731 (@pxref{Character Properties}). Lisp programs can change these
6732 properties by calling the @code{put-char-code-property} function.
6733 However, doing this requires a thorough understanding of the
6734 @acronym{UBA}, and is therefore not recommended. Any changes to the
6735 bidirectional properties of a character have global effect: they
6736 affect all Emacs frames and windows.
6738 Similarly, the @code{mirroring} property is used to display the
6739 appropriate mirrored character in the reordered text. Lisp programs
6740 can affect the mirrored display by changing this property. Again, any
6741 such changes affect all of Emacs display.