2 @c This is part of the GNU Emacs Lisp Reference Manual.
3 @c Copyright (C) 1990, 1991, 1992, 1993, 1994, 1995, 1998, 1999
4 @c Free Software Foundation, Inc.
5 @c See the file elisp.texi for copying conditions.
6 @setfilename ../info/windows
7 @node Windows, Frames, Buffers, Top
10 This chapter describes most of the functions and variables related to
11 Emacs windows. See @ref{Display}, for information on how text is
15 * Basic Windows:: Basic information on using windows.
16 * Splitting Windows:: Splitting one window into two windows.
17 * Deleting Windows:: Deleting a window gives its space to other windows.
18 * Selecting Windows:: The selected window is the one that you edit in.
19 * Cyclic Window Ordering:: Moving around the existing windows.
20 * Buffers and Windows:: Each window displays the contents of a buffer.
21 * Displaying Buffers:: Higher-lever functions for displaying a buffer
22 and choosing a window for it.
23 * Choosing Window:: How to choose a window for displaying a buffer.
24 * Window Point:: Each window has its own location of point.
25 * Window Start:: The display-start position controls which text
26 is on-screen in the window.
27 * Textual Scrolling:: Moving text up and down through the window.
28 * Vertical Scrolling:: Moving the contents up and down on the window.
29 * Horizontal Scrolling:: Moving the contents sideways on the window.
30 * Size of Window:: Accessing the size of a window.
31 * Resizing Windows:: Changing the size of a window.
32 * Coordinates and Windows:: Converting coordinates to windows.
33 * Window Configurations:: Saving and restoring the state of the screen.
34 * Window Hooks:: Hooks for scrolling, window size changes,
35 redisplay going past a certain point,
36 or window configuration changes.
40 @section Basic Concepts of Emacs Windows
42 @cindex selected window
44 A @dfn{window} in Emacs is the physical area of the screen in which a
45 buffer is displayed. The term is also used to refer to a Lisp object that
46 represents that screen area in Emacs Lisp. It should be
47 clear from the context which is meant.
49 Emacs groups windows into frames. A frame represents an area of
50 screen available for Emacs to use. Each frame always contains at least
51 one window, but you can subdivide it vertically or horizontally into
52 multiple nonoverlapping Emacs windows.
54 In each frame, at any time, one and only one window is designated as
55 @dfn{selected within the frame}. The frame's cursor appears in that
56 window. At any time, one frame is the selected frame; and the window
57 selected within that frame is @dfn{the selected window}. The selected
58 window's buffer is usually the current buffer (except when
59 @code{set-buffer} has been used). @xref{Current Buffer}.
61 For practical purposes, a window exists only while it is displayed in
62 a frame. Once removed from the frame, the window is effectively deleted
63 and should not be used, @emph{even though there may still be references
64 to it} from other Lisp objects. Restoring a saved window configuration
65 is the only way for a window no longer on the screen to come back to
66 life. (@xref{Deleting Windows}.)
68 Each window has the following attributes:
81 window edges with respect to the screen or frame
84 the buffer it displays
87 position within the buffer at the upper left of the window
90 amount of horizontal scrolling, in columns
99 how recently the window was selected
102 @cindex multiple windows
103 Users create multiple windows so they can look at several buffers at
104 once. Lisp libraries use multiple windows for a variety of reasons, but
105 most often to display related information. In Rmail, for example, you
106 can move through a summary buffer in one window while the other window
107 shows messages one at a time as they are reached.
109 The meaning of ``window'' in Emacs is similar to what it means in the
110 context of general-purpose window systems such as X, but not identical.
111 The X Window System places X windows on the screen; Emacs uses one or
112 more X windows as frames, and subdivides them into
113 Emacs windows. When you use Emacs on a character-only terminal, Emacs
114 treats the whole terminal screen as one frame.
116 @cindex terminal screen
117 @cindex screen of terminal
118 @cindex tiled windows
119 Most window systems support arbitrarily located overlapping windows.
120 In contrast, Emacs windows are @dfn{tiled}; they never overlap, and
121 together they fill the whole screen or frame. Because of the way in
122 which Emacs creates new windows and resizes them, not all conceivable
123 tilings of windows on an Emacs frame are actually possible.
124 @xref{Splitting Windows}, and @ref{Size of Window}.
126 @xref{Display}, for information on how the contents of the
127 window's buffer are displayed in the window.
129 @defun windowp object
130 This function returns @code{t} if @var{object} is a window.
133 @node Splitting Windows
134 @section Splitting Windows
135 @cindex splitting windows
136 @cindex window splitting
138 The functions described here are the primitives used to split a window
139 into two windows. Two higher level functions sometimes split a window,
140 but not always: @code{pop-to-buffer} and @code{display-buffer}
141 (@pxref{Displaying Buffers}).
143 The functions described here do not accept a buffer as an argument.
144 The two ``halves'' of the split window initially display the same buffer
145 previously visible in the window that was split.
147 @deffn Command split-window &optional window size horizontal
148 This function splits @var{window} into two windows. The original
149 window @var{window} remains the selected window, but occupies only
150 part of its former screen area. The rest is occupied by a newly created
151 window which is returned as the value of this function.
153 If @var{horizontal} is non-@code{nil}, then @var{window} splits into
154 two side by side windows. The original window @var{window} keeps the
155 leftmost @var{size} columns, and gives the rest of the columns to the
156 new window. Otherwise, it splits into windows one above the other, and
157 @var{window} keeps the upper @var{size} lines and gives the rest of the
158 lines to the new window. The original window is therefore the
159 left-hand or upper of the two, and the new window is the right-hand or
162 If @var{window} is omitted or @code{nil}, then the selected window is
163 split. If @var{size} is omitted or @code{nil}, then @var{window} is
164 divided evenly into two parts. (If there is an odd line, it is
165 allocated to the new window.) When @code{split-window} is called
166 interactively, all its arguments are @code{nil}.
168 If splitting would result in making a window that is smaller than
169 @code{window-min-height} or @code{window-min-width}, the function
170 signals an error and does not split the window at all.
172 The following example starts with one window on a screen that is 50
173 lines high by 80 columns wide; then it splits the window.
177 (setq w (selected-window))
178 @result{} #<window 8 on windows.texi>
179 (window-edges) ; @r{Edges in order:}
180 @result{} (0 0 80 50) ; @r{left--top--right--bottom}
184 ;; @r{Returns window created}
185 (setq w2 (split-window w 15))
186 @result{} #<window 28 on windows.texi>
190 @result{} (0 15 80 50) ; @r{Bottom window;}
195 @result{} (0 0 80 15) ; @r{Top window}
199 The screen looks like this:
215 Next, split the top window horizontally:
219 (setq w3 (split-window w 35 t))
220 @result{} #<window 32 on windows.texi>
224 @result{} (35 0 80 15) ; @r{Left edge at column 35}
228 @result{} (0 0 35 15) ; @r{Right edge at column 35}
232 @result{} (0 15 80 50) ; @r{Bottom window unchanged}
237 Now the screen looks like this:
254 Normally, Emacs indicates the border between two side-by-side windows
255 with a scroll bar (@pxref{Window Frame Parameters,Scroll Bars}) or @samp{|}
256 characters. The display table can specify alternative border
257 characters; see @ref{Display Tables}.
260 @deffn Command split-window-vertically &optional size
261 This function splits the selected window into two windows, one above the
262 other, leaving the upper of the two windows selected, with @var{size}
263 lines. (If @var{size} is negative, then the lower of the two windows
264 gets @minus{} @var{size} lines and the upper window gets the rest, but
265 the upper window is still the one selected.)
268 @deffn Command split-window-horizontally &optional size
269 This function splits the selected window into two windows
270 side-by-side, leaving the selected window with @var{size} columns.
272 This function is basically an interface to @code{split-window}.
273 You could define a simplified version of the function like this:
277 (defun split-window-horizontally (&optional arg)
278 "Split selected window into two windows, side by side..."
282 (let ((size (and arg (prefix-numeric-value arg))))
284 (setq size (+ (window-width) size)))
285 (split-window nil size t)))
290 @defun one-window-p &optional no-mini all-frames
291 This function returns non-@code{nil} if there is only one window. The
292 argument @var{no-mini}, if non-@code{nil}, means don't count the
293 minibuffer even if it is active; otherwise, the minibuffer window is
294 included, if active, in the total number of windows, which is compared
297 The argument @var{all-frames} specifies which frames to consider. Here
298 are the possible values and their meanings:
302 Count the windows in the selected frame, plus the minibuffer used
303 by that frame even if it lies in some other frame.
306 Count all windows in all existing frames.
309 Count all windows in all visible frames.
312 Count all windows in all visible or iconified frames.
315 Count precisely the windows in the selected frame, and no others.
319 @node Deleting Windows
320 @section Deleting Windows
321 @cindex deleting windows
323 A window remains visible on its frame unless you @dfn{delete} it by
324 calling certain functions that delete windows. A deleted window cannot
325 appear on the screen, but continues to exist as a Lisp object until
326 there are no references to it. There is no way to cancel the deletion
327 of a window aside from restoring a saved window configuration
328 (@pxref{Window Configurations}). Restoring a window configuration also
329 deletes any windows that aren't part of that configuration.
331 When you delete a window, the space it took up is given to one
335 @defun window-live-p window
336 This function returns @code{nil} if @var{window} is deleted, and
339 @strong{Warning:} Erroneous information or fatal errors may result from
340 using a deleted window as if it were live.
343 @deffn Command delete-window &optional window
344 This function removes @var{window} from display, and returns @code{nil}.
345 If @var{window} is omitted, then the selected window is deleted. An
346 error is signaled if there is only one window when @code{delete-window}
350 @deffn Command delete-other-windows &optional window
351 This function makes @var{window} the only window on its frame, by
352 deleting the other windows in that frame. If @var{window} is omitted or
353 @code{nil}, then the selected window is used by default.
355 The return value is @code{nil}.
358 @deffn Command delete-windows-on buffer &optional frame
359 This function deletes all windows showing @var{buffer}. If there are
360 no windows showing @var{buffer}, it does nothing.
362 @code{delete-windows-on} operates frame by frame. If a frame has
363 several windows showing different buffers, then those showing
364 @var{buffer} are removed, and the others expand to fill the space. If
365 all windows in some frame are showing @var{buffer} (including the case
366 where there is only one window), then the frame reverts to having a
367 single window showing another buffer chosen with @code{other-buffer}.
368 @xref{The Buffer List}.
370 The argument @var{frame} controls which frames to operate on. This
371 function does not use it in quite the same way as the other functions
372 which scan all windows; specifically, the values @code{t} and @code{nil}
373 have the opposite of their meanings in other functions. Here are the
378 If it is @code{nil}, operate on all frames.
380 If it is @code{t}, operate on the selected frame.
382 If it is @code{visible}, operate on all visible frames.
384 If it is 0, operate on all visible or iconified frames.
386 If it is a frame, operate on that frame.
389 This function always returns @code{nil}.
392 @node Selecting Windows
393 @section Selecting Windows
394 @cindex selecting windows
396 When a window is selected, the buffer in the window becomes the current
397 buffer, and the cursor will appear in it.
399 @defun selected-window
400 This function returns the selected window. This is the window in
401 which the cursor appears and to which many commands apply.
404 @defun select-window window &optional norecord
405 This function makes @var{window} the selected window. The cursor then
406 appears in @var{window} (on redisplay). The buffer being displayed in
407 @var{window} is immediately designated the current buffer.
409 Normally @var{window}'s selected buffer is moved to the front of the
410 buffer list, but if @var{norecord} is non-@code{nil}, the buffer list
413 The return value is @var{window}.
417 (setq w (next-window))
419 @result{} #<window 65 on windows.texi>
424 @defmac save-selected-window forms@dots{}
425 This macro records the selected window, executes @var{forms}
426 in sequence, then restores the earlier selected window (unless that
427 window is no longer alive).
429 This macro does not save or restore anything about the sizes, arrangement
430 or contents of windows; therefore, if the @var{forms} change them,
433 Each frame, at any time, has a window selected within the frame. This
434 macro saves only @emph{the} selected window; it does not save anything
435 about other frames. If the @var{forms} select some other frame and
436 alter the window selected within it, the change persists.
439 @defmac with-selected-window window forms@dots{}
440 This macro selects @var{window} (without changing the buffer list),
441 executes @var{forms} in sequence, then restores the previously
442 selected window (unless that window is no longer alive). It is similar
443 to @code{save-selected-window} except that it explicitly selects
444 @var{window} and that it does not alter the buffer list sequence.
447 @cindex finding windows
448 The following functions choose one of the windows on the screen,
449 offering various criteria for the choice.
451 @defun get-lru-window &optional frame
452 This function returns the window least recently ``used'' (that is,
453 selected). The selected window is always the most recently used window.
455 The selected window can be the least recently used window if it is the
456 only window. A newly created window becomes the least recently used
457 window until it is selected. A minibuffer window is never a candidate.
459 The argument @var{frame} controls which windows are considered.
463 If it is @code{nil}, consider windows on the selected frame.
465 If it is @code{t}, consider windows on all frames.
467 If it is @code{visible}, consider windows on all visible frames.
469 If it is 0, consider windows on all visible or iconified frames.
471 If it is a frame, consider windows on that frame.
475 @defun get-largest-window &optional frame
476 This function returns the window with the largest area (height times
477 width). If there are no side-by-side windows, then this is the window
478 with the most lines. A minibuffer window is never a candidate.
480 If there are two windows of the same size, then the function returns
481 the window that is first in the cyclic ordering of windows (see
482 following section), starting from the selected window.
484 The argument @var{frame} controls which set of windows to
485 consider. See @code{get-lru-window}, above.
488 @cindex window that satisfies a predicate
489 @cindex conditional selection of windows
490 @defun get-window-with-predicate predicate &optional minibuf all-frames default
491 This function returns a window satisfying @var{predicate}. It cycles
492 through all visible windows using @code{walk-windows} (@pxref{Cyclic
493 Window Ordering}), calling @var{predicate} on each one of them
494 with that window as its argument. The function returns the first
495 window for which @var{predicate} returns a non-@code{nil} value; if
496 that never happens, it returns @var{default}.
498 The optional arguments @var{minibuf} and @var{all-frames} specify the
499 set of windows to include in the scan. See the description of
500 @code{next-window} in @ref{Cyclic Window Ordering}, for details.
503 @node Cyclic Window Ordering
504 @comment node-name, next, previous, up
505 @section Cyclic Ordering of Windows
506 @cindex cyclic ordering of windows
507 @cindex ordering of windows, cyclic
508 @cindex window ordering, cyclic
510 When you use the command @kbd{C-x o} (@code{other-window}) to select
511 the next window, it moves through all the windows on the screen in a
512 specific cyclic order. For any given configuration of windows, this
513 order never varies. It is called the @dfn{cyclic ordering of windows}.
515 This ordering generally goes from top to bottom, and from left to
516 right. But it may go down first or go right first, depending on the
517 order in which the windows were split.
519 If the first split was vertical (into windows one above each other),
520 and then the subwindows were split horizontally, then the ordering is
521 left to right in the top of the frame, and then left to right in the
522 next lower part of the frame, and so on. If the first split was
523 horizontal, the ordering is top to bottom in the left part, and so on.
524 In general, within each set of siblings at any level in the window tree,
525 the order is left to right, or top to bottom.
527 @defun next-window &optional window minibuf all-frames
528 @cindex minibuffer window
529 This function returns the window following @var{window} in the cyclic
530 ordering of windows. This is the window that @kbd{C-x o} would select
531 if typed when @var{window} is selected. If @var{window} is the only
532 window visible, then this function returns @var{window}. If omitted,
533 @var{window} defaults to the selected window.
535 The value of the argument @var{minibuf} determines whether the
536 minibuffer is included in the window order. Normally, when
537 @var{minibuf} is @code{nil}, the minibuffer is included if it is
538 currently active; this is the behavior of @kbd{C-x o}. (The minibuffer
539 window is active while the minibuffer is in use. @xref{Minibuffers}.)
541 If @var{minibuf} is @code{t}, then the cyclic ordering includes the
542 minibuffer window even if it is not active.
544 If @var{minibuf} is neither @code{t} nor @code{nil}, then the minibuffer
545 window is not included even if it is active.
547 The argument @var{all-frames} specifies which frames to consider. Here
548 are the possible values and their meanings:
552 Consider all the windows in @var{window}'s frame, plus the minibuffer
553 used by that frame even if it lies in some other frame.
556 Consider all windows in all existing frames.
559 Consider all windows in all visible frames. (To get useful results, you
560 must ensure @var{window} is in a visible frame.)
563 Consider all windows in all visible or iconified frames.
566 Consider precisely the windows in @var{window}'s frame, and no others.
569 This example assumes there are two windows, both displaying the
570 buffer @samp{windows.texi}:
575 @result{} #<window 56 on windows.texi>
578 (next-window (selected-window))
579 @result{} #<window 52 on windows.texi>
582 (next-window (next-window (selected-window)))
583 @result{} #<window 56 on windows.texi>
588 @defun previous-window &optional window minibuf all-frames
589 This function returns the window preceding @var{window} in the cyclic
590 ordering of windows. The other arguments specify which windows to
591 include in the cycle, as in @code{next-window}.
594 @deffn Command other-window count &optional all-frames
595 This function selects the @var{count}th following window in the cyclic
596 order. If count is negative, then it moves back @minus{}@var{count}
597 windows in the cycle, rather than forward. It returns @code{nil}.
599 The argument @var{all-frames} has the same meaning as in
600 @code{next-window}, but the @var{minibuf} argument of @code{next-window}
601 is always effectively @code{nil}.
603 In an interactive call, @var{count} is the numeric prefix argument.
607 @defun walk-windows proc &optional minibuf all-frames
608 This function cycles through all windows, calling @code{proc}
609 once for each window with the window as its sole argument.
611 The optional arguments @var{minibuf} and @var{all-frames} specify the
612 set of windows to include in the scan. See @code{next-window}, above,
616 @defun window-list &optional frame minibuf window
617 This function returns a list of the windows on @var{frame}, starting
618 with @var{window}. If @var{frame} is @code{nil} or omitted, the
619 selected frame is used instead; if @var{window} is @code{nil} or
620 omitted, the selected window is used instead.
622 The value of @var{minibuf} determines if the minibuffer window will be
623 included in the result list. If @var{minibuf} is @code{t}, the
624 minibuffer window will be included, even if it isn't active. If
625 @var{minibuf} is @code{nil} or omitted, the minibuffer window will
626 only be included in the list if it is active. If @var{minibuf} is
627 neither @code{nil} nor @code{t}, the minibuffer window is not
628 included, whether or not it is active.
631 @node Buffers and Windows
632 @section Buffers and Windows
633 @cindex examining windows
634 @cindex windows, controlling precisely
635 @cindex buffers, controlled in windows
637 This section describes low-level functions to examine windows or to
638 display buffers in windows in a precisely controlled fashion.
640 See the following section for
643 @xref{Displaying Buffers}, for
645 related functions that find a window to use and specify a buffer for it.
646 The functions described there are easier to use than these, but they
647 employ heuristics in choosing or creating a window; use these functions
648 when you need complete control.
650 @defun set-window-buffer window buffer-or-name
651 This function makes @var{window} display @var{buffer-or-name} as its
652 contents. It returns @code{nil}. This is the fundamental primitive
653 for changing which buffer is displayed in a window, and all ways
654 of doing that call this function.
658 (set-window-buffer (selected-window) "foo")
664 @defun window-buffer &optional window
665 This function returns the buffer that @var{window} is displaying. If
666 @var{window} is omitted, this function returns the buffer for the
672 @result{} #<buffer windows.texi>
677 @defun get-buffer-window buffer-or-name &optional all-frames
678 This function returns a window currently displaying
679 @var{buffer-or-name}, or @code{nil} if there is none. If there are
680 several such windows, then the function returns the first one in the
681 cyclic ordering of windows, starting from the selected window.
682 @xref{Cyclic Window Ordering}.
684 The argument @var{all-frames} controls which windows to consider.
688 If it is @code{nil}, consider windows on the selected frame.
690 If it is @code{t}, consider windows on all frames.
692 If it is @code{visible}, consider windows on all visible frames.
694 If it is 0, consider windows on all visible or iconified frames.
696 If it is a frame, consider windows on that frame.
700 @defun get-buffer-window-list buffer-or-name &optional minibuf all-frames
701 This function returns a list of all the windows currently displaying
702 @var{buffer-or-name}.
704 The two optional arguments work like the optional arguments of
705 @code{next-window} (@pxref{Cyclic Window Ordering}); they are @emph{not}
706 like the single optional argument of @code{get-buffer-window}. Perhaps
707 we should change @code{get-buffer-window} in the future to make it
708 compatible with the other functions.
710 The argument @var{all-frames} controls which windows to consider.
714 If it is @code{nil}, consider windows on the selected frame.
716 If it is @code{t}, consider windows on all frames.
718 If it is @code{visible}, consider windows on all visible frames.
720 If it is 0, consider windows on all visible or iconified frames.
722 If it is a frame, consider windows on that frame.
726 @defvar buffer-display-time
727 This variable records the time at which a buffer was last made visible
728 in a window. It is always local in each buffer; each time
729 @code{set-window-buffer} is called, it sets this variable to
730 @code{(current-time)} in the specified buffer (@pxref{Time of Day}).
731 When a buffer is first created, @code{buffer-display-time} starts out
732 with the value @code{nil}.
735 @node Displaying Buffers
736 @section Displaying Buffers in Windows
737 @cindex switching to a buffer
738 @cindex displaying a buffer
740 In this section we describe convenient functions that choose a window
741 automatically and use it to display a specified buffer. These functions
742 can also split an existing window in certain circumstances. We also
743 describe variables that parameterize the heuristics used for choosing a
746 See the preceding section for
749 @xref{Buffers and Windows}, for
751 low-level functions that give you more precise control. All of these
752 functions work by calling @code{set-window-buffer}.
754 Do not use the functions in this section in order to make a buffer
755 current so that a Lisp program can access or modify it; they are too
756 drastic for that purpose, since they change the display of buffers in
757 windows, which would be gratuitous and surprise the user. Instead, use
758 @code{set-buffer} and @code{save-current-buffer} (@pxref{Current
759 Buffer}), which designate buffers as current for programmed access
760 without affecting the display of buffers in windows.
762 @deffn Command switch-to-buffer buffer-or-name &optional norecord
763 This function makes @var{buffer-or-name} the current buffer, and also
764 displays the buffer in the selected window. This means that a human can
765 see the buffer and subsequent keyboard commands will apply to it.
766 Contrast this with @code{set-buffer}, which makes @var{buffer-or-name}
767 the current buffer but does not display it in the selected window.
768 @xref{Current Buffer}.
770 If @var{buffer-or-name} does not identify an existing buffer, then a new
771 buffer by that name is created. The major mode for the new buffer is
772 set according to the variable @code{default-major-mode}. @xref{Auto
775 Normally the specified buffer is put at the front of the buffer list
776 (both the selected frame's buffer list and the frame-independent buffer
777 list). This affects the operation of @code{other-buffer}. However, if
778 @var{norecord} is non-@code{nil}, this is not done. @xref{The Buffer
781 The @code{switch-to-buffer} function is often used interactively, as
782 the binding of @kbd{C-x b}. It is also used frequently in programs. It
783 returns the buffer that it switched to.
786 @deffn Command switch-to-buffer-other-window buffer-or-name &optional norecord
787 This function makes @var{buffer-or-name} the current buffer and
788 displays it in a window not currently selected. It then selects that
789 window. The handling of the buffer is the same as in
790 @code{switch-to-buffer}.
792 The currently selected window is absolutely never used to do the job.
793 If it is the only window, then it is split to make a distinct window for
794 this purpose. If the selected window is already displaying the buffer,
795 then it continues to do so, but another window is nonetheless found to
796 display it in as well.
798 This function updates the buffer list just like @code{switch-to-buffer}
799 unless @var{norecord} is non-@code{nil}.
802 @defun pop-to-buffer buffer-or-name &optional other-window norecord
803 This function makes @var{buffer-or-name} the current buffer and
804 switches to it in some window, preferably not the window previously
805 selected. The ``popped-to'' window becomes the selected window within
806 its frame. The return value is the buffer that was switched to.
808 If the variable @code{pop-up-frames} is non-@code{nil},
809 @code{pop-to-buffer} looks for a window in any visible frame already
810 displaying the buffer; if there is one, it returns that window and makes
811 it be selected within its frame. If there is none, it creates a new
812 frame and displays the buffer in it.
814 If @code{pop-up-frames} is @code{nil}, then @code{pop-to-buffer}
815 operates entirely within the selected frame. (If the selected frame has
816 just a minibuffer, @code{pop-to-buffer} operates within the most
817 recently selected frame that was not just a minibuffer.)
819 If the variable @code{pop-up-windows} is non-@code{nil}, windows may
820 be split to create a new window that is different from the original
821 window. For details, see @ref{Choosing Window}.
823 If @var{other-window} is non-@code{nil}, @code{pop-to-buffer} finds or
824 creates another window even if @var{buffer-or-name} is already visible
825 in the selected window. Thus @var{buffer-or-name} could end up
826 displayed in two windows. On the other hand, if @var{buffer-or-name} is
827 already displayed in the selected window and @var{other-window} is
828 @code{nil}, then the selected window is considered sufficient display
829 for @var{buffer-or-name}, so that nothing needs to be done.
831 All the variables that affect @code{display-buffer} affect
832 @code{pop-to-buffer} as well. @xref{Choosing Window}.
834 If @var{buffer-or-name} is a string that does not name an existing
835 buffer, a buffer by that name is created. The major mode for the new
836 buffer is set according to the variable @code{default-major-mode}.
837 @xref{Auto Major Mode}.
839 This function updates the buffer list just like @code{switch-to-buffer}
840 unless @var{norecord} is non-@code{nil}.
843 @deffn Command replace-buffer-in-windows buffer
844 This function replaces @var{buffer} with some other buffer in all
845 windows displaying it. The other buffer used is chosen with
846 @code{other-buffer}. In the usual applications of this function, you
847 don't care which other buffer is used; you just want to make sure that
848 @var{buffer} is no longer displayed.
850 This function returns @code{nil}.
853 @node Choosing Window
854 @section Choosing a Window for Display
856 This section describes the basic facility that chooses a window to
857 display a buffer in---@code{display-buffer}. All the higher-level
858 functions and commands use this subroutine. Here we describe how to use
859 @code{display-buffer} and how to customize it.
861 @deffn Command display-buffer buffer-or-name &optional not-this-window frame
862 This command makes @var{buffer-or-name} appear in some window, like
863 @code{pop-to-buffer}, but it does not select that window and does not
864 make the buffer current. The identity of the selected window is
865 unaltered by this function.
867 If @var{not-this-window} is non-@code{nil}, it means to display the
868 specified buffer in a window other than the selected one, even if it is
869 already on display in the selected window. This can cause the buffer to
870 appear in two windows at once. Otherwise, if @var{buffer-or-name} is
871 already being displayed in any window, that is good enough, so this
872 function does nothing.
874 @code{display-buffer} returns the window chosen to display
875 @var{buffer-or-name}.
877 If the argument @var{frame} is non-@code{nil}, it specifies which frames
878 to check when deciding whether the buffer is already displayed. If the
879 buffer is already displayed in some window on one of these frames,
880 @code{display-buffer} simply returns that window. Here are the possible
881 values of @var{frame}:
885 If it is @code{nil}, consider windows on the selected frame.
887 If it is @code{t}, consider windows on all frames.
889 If it is @code{visible}, consider windows on all visible frames.
891 If it is 0, consider windows on all visible or iconified frames.
893 If it is a frame, consider windows on that frame.
896 Precisely how @code{display-buffer} finds or creates a window depends on
897 the variables described below.
900 @defopt display-buffer-reuse-frames
901 If this variable is non-@code{nil}, @code{display-buffer} searches
902 existing frames for a window displaying the buffer. If the buffer is
903 already displayed in a window in some frame, @code{display-buffer} makes
904 the frame visible and raises it, to use that window. If the buffer is
905 not already displayed, or if @code{display-buffer-reuse-frames} is
906 @code{nil}, @code{display-buffer}'s behavior is determined by other
907 variables, described below.
910 @defopt pop-up-windows
911 This variable controls whether @code{display-buffer} makes new windows.
912 If it is non-@code{nil} and there is only one window, then that window
913 is split. If it is @code{nil}, then @code{display-buffer} does not
914 split the single window, but uses it whole.
917 @defopt split-height-threshold
918 This variable determines when @code{display-buffer} may split a window,
919 if there are multiple windows. @code{display-buffer} always splits the
920 largest window if it has at least this many lines. If the largest
921 window is not this tall, it is split only if it is the sole window and
922 @code{pop-up-windows} is non-@code{nil}.
925 @defopt even-window-heights
926 This variable determines if @code{display-buffer} should even out window
927 heights if the buffer gets displayed in an existing window, above or
928 beneath another existing window. If @code{even-window-heights} is
929 @code{t}, the default, window heights will be evened out. If
930 @code{even-window-heights} is @code{nil}, the original window heights
935 @defopt pop-up-frames
936 This variable controls whether @code{display-buffer} makes new frames.
937 If it is non-@code{nil}, @code{display-buffer} looks for an existing
938 window already displaying the desired buffer, on any visible frame. If
939 it finds one, it returns that window. Otherwise it makes a new frame.
940 The variables @code{pop-up-windows} and @code{split-height-threshold} do
941 not matter if @code{pop-up-frames} is non-@code{nil}.
943 If @code{pop-up-frames} is @code{nil}, then @code{display-buffer} either
944 splits a window or reuses one.
946 @xref{Frames}, for more information.
950 @defvar pop-up-frame-function
951 This variable specifies how to make a new frame if @code{pop-up-frames}
954 Its value should be a function of no arguments. When
955 @code{display-buffer} makes a new frame, it does so by calling that
956 function, which should return a frame. The default value of the
957 variable is a function that creates a frame using parameters from
958 @code{pop-up-frame-alist}.
961 @defopt pop-up-frame-alist
962 This variable holds an alist specifying frame parameters used when
963 @code{display-buffer} makes a new frame. @xref{Frame Parameters}, for
964 more information about frame parameters.
967 @defopt special-display-buffer-names
968 A list of buffer names for buffers that should be displayed specially.
969 If the buffer's name is in this list, @code{display-buffer} handles the
972 By default, special display means to give the buffer a dedicated frame.
974 If an element is a list, instead of a string, then the @sc{car} of the
975 list is the buffer name, and the rest of the list says how to create
976 the frame. There are two possibilities for the rest of the list (its
977 @sc{cdr}). It can be an alist, specifying frame parameters, or it can
978 contain a function and arguments to give to it. (The function's first
979 argument is always the buffer to be displayed; the arguments from the
980 list come after that.)
985 (("myfile" (minibuffer) (menu-bar-lines . 0)))
989 specifies to display a buffer named @samp{myfile} in a dedicated frame
990 with specified @code{minibuffer} and @code{menu-bar-lines} parameters.
993 @defopt special-display-regexps
994 A list of regular expressions that specify buffers that should be
995 displayed specially. If the buffer's name matches any of the regular
996 expressions in this list, @code{display-buffer} handles the buffer
999 By default, special display means to give the buffer a dedicated frame.
1001 If an element is a list, instead of a string, then the @sc{car} of the
1002 list is the regular expression, and the rest of the list says how to
1003 create the frame. See above, under @code{special-display-buffer-names}.
1006 @defvar special-display-function
1007 This variable holds the function to call to display a buffer specially.
1008 It receives the buffer as an argument, and should return the window in
1009 which it is displayed.
1011 The default value of this variable is
1012 @code{special-display-popup-frame}.
1015 @defun special-display-popup-frame buffer &rest args
1016 This function makes @var{buffer} visible in a frame of its own. If
1017 @var{buffer} is already displayed in a window in some frame, it makes
1018 the frame visible and raises it, to use that window. Otherwise, it
1019 creates a frame that will be dedicated to @var{buffer}.
1021 If @var{args} is an alist, it specifies frame parameters for the new
1024 If @var{args} is a list whose @sc{car} is a symbol, then @code{(car
1025 @var{args})} is called as a function to actually create and set up the
1026 frame; it is called with @var{buffer} as first argument, and @code{(cdr
1027 @var{args})} as additional arguments.
1029 This function always uses an existing window displaying @var{buffer},
1030 whether or not it is in a frame of its own; but if you set up the above
1031 variables in your init file, before @var{buffer} was created, then
1032 presumably the window was previously made by this function.
1035 @defopt special-display-frame-alist
1036 This variable holds frame parameters for
1037 @code{special-display-popup-frame} to use when it creates a frame.
1040 @defopt same-window-buffer-names
1041 A list of buffer names for buffers that should be displayed in the
1042 selected window. If the buffer's name is in this list,
1043 @code{display-buffer} handles the buffer by switching to it in the
1047 @defopt same-window-regexps
1048 A list of regular expressions that specify buffers that should be
1049 displayed in the selected window. If the buffer's name matches any of
1050 the regular expressions in this list, @code{display-buffer} handles the
1051 buffer by switching to it in the selected window.
1055 @defvar display-buffer-function
1056 This variable is the most flexible way to customize the behavior of
1057 @code{display-buffer}. If it is non-@code{nil}, it should be a function
1058 that @code{display-buffer} calls to do the work. The function should
1059 accept two arguments, the same two arguments that @code{display-buffer}
1060 received. It should choose or create a window, display the specified
1061 buffer, and then return the window.
1063 This hook takes precedence over all the other options and hooks
1068 @cindex dedicated window
1069 A window can be marked as ``dedicated'' to its buffer. Then
1070 @code{display-buffer} will not try to use that window to display any
1073 @defun window-dedicated-p window
1074 This function returns @code{t} if @var{window} is marked as dedicated;
1075 otherwise @code{nil}.
1078 @defun set-window-dedicated-p window flag
1079 This function marks @var{window} as dedicated if @var{flag} is
1080 non-@code{nil}, and nondedicated otherwise.
1084 @section Windows and Point
1085 @cindex window position
1086 @cindex window point
1087 @cindex position in window
1088 @cindex point in window
1090 Each window has its own value of point, independent of the value of
1091 point in other windows displaying the same buffer. This makes it useful
1092 to have multiple windows showing one buffer.
1096 The window point is established when a window is first created; it is
1097 initialized from the buffer's point, or from the window point of another
1098 window opened on the buffer if such a window exists.
1101 Selecting a window sets the value of point in its buffer from the
1102 window's value of point. Conversely, deselecting a window sets the
1103 window's value of point from that of the buffer. Thus, when you switch
1104 between windows that display a given buffer, the point value for the
1105 selected window is in effect in the buffer, while the point values for
1106 the other windows are stored in those windows.
1109 As long as the selected window displays the current buffer, the window's
1110 point and the buffer's point always move together; they remain equal.
1113 @xref{Positions}, for more details on buffer positions.
1116 As far as the user is concerned, point is where the cursor is, and
1117 when the user switches to another buffer, the cursor jumps to the
1118 position of point in that buffer.
1120 @defun window-point &optional window
1121 This function returns the current position of point in @var{window}.
1122 For a nonselected window, this is the value point would have (in that
1123 window's buffer) if that window were selected. If @var{window} is
1124 @code{nil}, the selected window is used.
1126 When @var{window} is the selected window and its buffer is also the
1127 current buffer, the value returned is the same as point in that buffer.
1129 Strictly speaking, it would be more correct to return the
1130 ``top-level'' value of point, outside of any @code{save-excursion}
1131 forms. But that value is hard to find.
1134 @defun set-window-point window position
1135 This function positions point in @var{window} at position
1136 @var{position} in @var{window}'s buffer.
1140 @section The Window Start Position
1142 Each window contains a marker used to keep track of a buffer position
1143 that specifies where in the buffer display should start. This position
1144 is called the @dfn{display-start} position of the window (or just the
1145 @dfn{start}). The character after this position is the one that appears
1146 at the upper left corner of the window. It is usually, but not
1147 inevitably, at the beginning of a text line.
1149 @defun window-start &optional window
1150 @cindex window top line
1151 This function returns the display-start position of window
1152 @var{window}. If @var{window} is @code{nil}, the selected window is
1162 When you create a window, or display a different buffer in it, the
1163 display-start position is set to a display-start position recently used
1164 for the same buffer, or 1 if the buffer doesn't have any.
1166 Redisplay updates the window-start position (if you have not specified
1167 it explicitly since the previous redisplay)---for example, to make sure
1168 point appears on the screen. Nothing except redisplay automatically
1169 changes the window-start position; if you move point, do not expect the
1170 window-start position to change in response until after the next
1173 For a realistic example of using @code{window-start}, see the
1174 description of @code{count-lines} in @ref{Text Lines}.
1177 @defun window-end &optional window update
1178 This function returns the position of the end of the display in window
1179 @var{window}. If @var{window} is @code{nil}, the selected window is
1182 Simply changing the buffer text or moving point does not update the
1183 value that @code{window-end} returns. The value is updated only when
1184 Emacs redisplays and redisplay completes without being preempted.
1186 If the last redisplay of @var{window} was preempted, and did not finish,
1187 Emacs does not know the position of the end of display in that window.
1188 In that case, this function returns @code{nil}.
1190 If @var{update} is non-@code{nil}, @code{window-end} always returns an
1191 up-to-date value for where the window ends, based on the current
1192 @code{window-start} value. If the saved value is valid,
1193 @code{window-end} returns that; otherwise it computes the correct
1194 value by scanning the buffer text.
1196 Even if @var{update} is non-@code{nil}, @code{window-end} does not
1197 attempt to scroll the display if point has moved off the screen, the
1198 way real redisplay would do. It does not alter the
1199 @code{window-start} value. In effect, it reports where the displayed
1200 text will end if scrolling is not required.
1203 @defun set-window-start window position &optional noforce
1204 This function sets the display-start position of @var{window} to
1205 @var{position} in @var{window}'s buffer. It returns @var{position}.
1207 The display routines insist that the position of point be visible when a
1208 buffer is displayed. Normally, they change the display-start position
1209 (that is, scroll the window) whenever necessary to make point visible.
1210 However, if you specify the start position with this function using
1211 @code{nil} for @var{noforce}, it means you want display to start at
1212 @var{position} even if that would put the location of point off the
1213 screen. If this does place point off screen, the display routines move
1214 point to the left margin on the middle line in the window.
1216 For example, if point @w{is 1} and you set the start of the window @w{to
1217 2}, then point would be ``above'' the top of the window. The display
1218 routines will automatically move point if it is still 1 when redisplay
1219 occurs. Here is an example:
1223 ;; @r{Here is what @samp{foo} looks like before executing}
1224 ;; @r{the @code{set-window-start} expression.}
1228 ---------- Buffer: foo ----------
1229 @point{}This is the contents of buffer foo.
1235 ---------- Buffer: foo ----------
1241 (1+ (window-start)))
1246 ;; @r{Here is what @samp{foo} looks like after executing}
1247 ;; @r{the @code{set-window-start} expression.}
1248 ---------- Buffer: foo ----------
1249 his is the contents of buffer foo.
1255 ---------- Buffer: foo ----------
1259 If @var{noforce} is non-@code{nil}, and @var{position} would place point
1260 off screen at the next redisplay, then redisplay computes a new window-start
1261 position that works well with point, and thus @var{position} is not used.
1264 @defun pos-visible-in-window-p &optional position window partially
1265 This function returns @code{t} if @var{position} is within the range of
1266 text currently visible on the screen in @var{window}. It returns
1267 @code{nil} if @var{position} is scrolled vertically or horizontally out
1268 of view. Locations that are partially obscured are not considered
1269 visible unless @var{partially} is non-@code{nil}. The argument
1270 @var{position} defaults to the current position of point in
1271 @var{window}; @var{window}, to the selected window.
1277 (or (pos-visible-in-window-p
1278 (point) (selected-window))
1284 @node Textual Scrolling
1285 @section Textual Scrolling
1286 @cindex textual scrolling
1287 @cindex scrolling textually
1289 @dfn{Textual scrolling} means moving the text up or down though a
1290 window. It works by changing the value of the window's display-start
1291 location. It may also change the value of @code{window-point} to keep
1292 point on the screen.
1294 Textual scrolling was formerly called ``vertical scrolling,'' but we
1295 changed its name to distinguish it from the new vertical fractional
1296 scrolling feature (@pxref{Vertical Scrolling}).
1298 In the commands @code{scroll-up} and @code{scroll-down}, the directions
1299 ``up'' and ``down'' refer to the motion of the text in the buffer at which
1300 you are looking through the window. Imagine that the text is
1301 written on a long roll of paper and that the scrolling commands move the
1302 paper up and down. Thus, if you are looking at text in the middle of a
1303 buffer and repeatedly call @code{scroll-down}, you will eventually see
1304 the beginning of the buffer.
1306 Some people have urged that the opposite convention be used: they
1307 imagine that the window moves over text that remains in place. Then
1308 ``down'' commands would take you to the end of the buffer. This view is
1309 more consistent with the actual relationship between windows and the
1310 text in the buffer, but it is less like what the user sees. The
1311 position of a window on the terminal does not move, and short scrolling
1312 commands clearly move the text up or down on the screen. We have chosen
1313 names that fit the user's point of view.
1315 The textual scrolling functions (aside from
1316 @code{scroll-other-window}) have unpredictable results if the current
1317 buffer is different from the buffer that is displayed in the selected
1318 window. @xref{Current Buffer}.
1320 @deffn Command scroll-up &optional count
1321 This function scrolls the text in the selected window upward
1322 @var{count} lines. If @var{count} is negative, scrolling is actually
1325 If @var{count} is @code{nil} (or omitted), then the length of scroll
1326 is @code{next-screen-context-lines} lines less than the usable height of
1327 the window (not counting its mode line).
1329 @code{scroll-up} returns @code{nil}.
1332 @deffn Command scroll-down &optional count
1333 This function scrolls the text in the selected window downward
1334 @var{count} lines. If @var{count} is negative, scrolling is actually
1337 If @var{count} is omitted or @code{nil}, then the length of the scroll
1338 is @code{next-screen-context-lines} lines less than the usable height of
1339 the window (not counting its mode line).
1341 @code{scroll-down} returns @code{nil}.
1344 @deffn Command scroll-other-window &optional count
1345 This function scrolls the text in another window upward @var{count}
1346 lines. Negative values of @var{count}, or @code{nil}, are handled
1347 as in @code{scroll-up}.
1349 You can specify which buffer to scroll by setting the variable
1350 @code{other-window-scroll-buffer} to a buffer. If that buffer isn't
1351 already displayed, @code{scroll-other-window} displays it in some
1354 When the selected window is the minibuffer, the next window is normally
1355 the one at the top left corner. You can specify a different window to
1356 scroll, when the minibuffer is selected, by setting the variable
1357 @code{minibuffer-scroll-window}. This variable has no effect when any
1358 other window is selected. @xref{Minibuffer Misc}.
1360 When the minibuffer is active, it is the next window if the selected
1361 window is the one at the bottom right corner. In this case,
1362 @code{scroll-other-window} attempts to scroll the minibuffer. If the
1363 minibuffer contains just one line, it has nowhere to scroll to, so the
1364 line reappears after the echo area momentarily displays the message
1365 ``Beginning of buffer''.
1369 @defvar other-window-scroll-buffer
1370 If this variable is non-@code{nil}, it tells @code{scroll-other-window}
1371 which buffer to scroll.
1374 @defopt scroll-margin
1375 This option specifies the size of the scroll margin---a minimum number
1376 of lines between point and the top or bottom of a window. Whenever
1377 point gets within this many lines of the top or bottom of the window,
1378 redisplay scrolls the text automatically (if possible) to move point
1379 out of the margin, closer to the center of the window.
1382 @defopt scroll-conservatively
1383 This variable controls how scrolling is done automatically when point
1384 moves off the screen (or into the scroll margin). If the value is a
1385 positive integer @var{n}, then redisplay scrolls the text up to
1386 @var{n} lines in either direction, if that will bring point back into
1387 proper view. This action is called @dfn{conservative scrolling}.
1388 Otherwise, scrolling happens in the usual way, under the control of
1389 other variables such as @code{scroll-up-aggressively} and
1390 @code{scroll-down-aggressively}.
1392 The default value is zero, which means that conservative scrolling
1396 @defopt scroll-down-aggressively
1397 @tindex scroll-down-aggressively
1398 The value of this variable should be either @code{nil} or a fraction
1399 @var{f} between 0 and 1. If it is a fraction, that specifies where on
1400 the screen to put point when scrolling down. More precisely, when a
1401 window scrolls down because point is above the window start, the new
1402 start position is chosen to put point @var{f} part of the window
1403 height from the top. The larger @var{f}, the more aggressive the
1406 A value of @code{nil} is equivalent to .5, since its effect is to center
1407 point. This variable automatically becomes buffer-local when set in any
1411 @defopt scroll-up-aggressively
1412 @tindex scroll-up-aggressively
1413 Likewise, for scrolling up. The value, @var{f}, specifies how far
1414 point should be placed from the bottom of the window; thus, as with
1415 @code{scroll-up-aggressively}, a larger value scrolls more aggressively.
1419 This variable is an older variant of @code{scroll-conservatively}. The
1420 difference is that it if its value is @var{n}, that permits scrolling
1421 only by precisely @var{n} lines, not a smaller number. This feature
1422 does not work with @code{scroll-margin}. The default value is zero.
1425 @defopt scroll-preserve-screen-position
1426 If this option is non-@code{nil}, the scroll functions move point so
1427 that the vertical position of the cursor is unchanged, when that is
1431 @defopt next-screen-context-lines
1432 The value of this variable is the number of lines of continuity to
1433 retain when scrolling by full screens. For example, @code{scroll-up}
1434 with an argument of @code{nil} scrolls so that this many lines at the
1435 bottom of the window appear instead at the top. The default value is
1439 @deffn Command recenter &optional count
1440 @cindex centering point
1441 This function scrolls the text in the selected window so that point is
1442 displayed at a specified vertical position within the window. It does
1443 not ``move point'' with respect to the text.
1445 If @var{count} is a nonnegative number, that puts the line containing
1446 point @var{count} lines down from the top of the window. If
1447 @var{count} is a negative number, then it counts upward from the
1448 bottom of the window, so that @minus{}1 stands for the last usable
1449 line in the window. If @var{count} is a non-@code{nil} list, then it
1450 stands for the line in the middle of the window.
1452 If @var{count} is @code{nil}, @code{recenter} puts the line containing
1453 point in the middle of the window, then clears and redisplays the entire
1456 When @code{recenter} is called interactively, @var{count} is the raw
1457 prefix argument. Thus, typing @kbd{C-u} as the prefix sets the
1458 @var{count} to a non-@code{nil} list, while typing @kbd{C-u 4} sets
1459 @var{count} to 4, which positions the current line four lines from the
1462 With an argument of zero, @code{recenter} positions the current line at
1463 the top of the window. This action is so handy that some people make a
1464 separate key binding to do this. For example,
1468 (defun line-to-top-of-window ()
1469 "Scroll current line to top of window.
1470 Replaces three keystroke sequence C-u 0 C-l."
1474 (global-set-key [kp-multiply] 'line-to-top-of-window)
1479 @node Vertical Scrolling
1480 @section Vertical Fractional Scrolling
1481 @cindex Vertical Fractional Scrolling
1483 @dfn{Vertical fractional scrolling} means shifting the image in the
1484 window up or down by a specified multiple or fraction of a line.
1485 Starting in Emacs 21, each window has a @dfn{vertical scroll position},
1486 which is a number, never less than zero. It specifies how far to raise
1487 the contents of the window. Raising the window contents generally makes
1488 all or part of some lines disappear off the top, and all or part of some
1489 other lines appear at the bottom. The usual value is zero.
1491 The vertical scroll position is measured in units of the normal line
1492 height, which is the height of the default font. Thus, if the value is
1493 .5, that means the window contents are scrolled up half the normal line
1494 height. If it is 3.3, that means the window contents are scrolled up
1495 somewhat over three times the normal line height.
1497 What fraction of a line the vertical scrolling covers, or how many
1498 lines, depends on what the lines contain. A value of .5 could scroll a
1499 line whose height is very short off the screen, while a value of 3.3
1500 could scroll just part of the way through a tall line or an image.
1502 @defun window-vscroll &optional window
1503 This function returns the current vertical scroll position of
1504 @var{window}, If @var{window} is @code{nil}, the selected window is
1515 @defun set-window-vscroll window lines
1516 This function sets @var{window}'s vertical scroll position to
1517 @var{lines}. The argument @var{lines} should be zero or positive; if
1518 not, it is taken as zero.
1520 If @var{window} is @code{nil}, the selected window is used.
1522 The actual vertical scroll position must always correspond
1523 to an integral number of pixels, so the value you specify
1524 is rounded accordingly.
1526 The return value is the result of this rounding.
1530 (set-window-vscroll (selected-window) 1.2)
1536 @node Horizontal Scrolling
1537 @section Horizontal Scrolling
1538 @cindex horizontal scrolling
1540 @dfn{Horizontal scrolling} means shifting the image in the window left
1541 or right by a specified multiple of the normal character width. Each
1542 window has a @dfn{horizontal scroll position}, which is a number, never
1543 less than zero. It specifies how far to shift the contents left.
1544 Shifting the window contents left generally makes all or part of some
1545 characters disappear off the left, and all or part of some other
1546 characters appear at the right. The usual value is zero.
1548 The horizontal scroll position is measured in units of the normal
1549 character width, which is the width of space in the default font. Thus,
1550 if the value is 5, that means the window contents are scrolled left by 5
1551 times the normal character width. How many characters actually
1552 disappear off to the left depends on their width, and could vary from
1555 Because we read from side to side in the ``inner loop'', and from top
1556 to bottom in the ``outer loop'', the effect of horizontal scrolling is
1557 not like that of textual or vertical scrolling. Textual scrolling
1558 involves selection of a portion of text to display, and vertical
1559 scrolling moves the window contents contiguously; but horizontal
1560 scrolling causes part of @emph{each line} to go off screen.
1562 Usually, no horizontal scrolling is in effect; then the leftmost
1563 column is at the left edge of the window. In this state, scrolling to
1564 the right is meaningless, since there is no data to the left of the edge
1565 to be revealed by it; so this is not allowed. Scrolling to the left is
1566 allowed; it scrolls the first columns of text off the edge of the window
1567 and can reveal additional columns on the right that were truncated
1568 before. Once a window has a nonzero amount of leftward horizontal
1569 scrolling, you can scroll it back to the right, but only so far as to
1570 reduce the net horizontal scroll to zero. There is no limit to how far
1571 left you can scroll, but eventually all the text will disappear off the
1574 @vindex auto-hscroll-mode
1575 In Emacs 21, redisplay automatically alters the horizontal scrolling
1576 of a window as necessary to ensure that point is always visible, if
1577 @code{auto-hscroll-mode} is set. However, you can still set the
1578 horizontal scrolling value explicitly. The value you specify serves as
1579 a lower bound for automatic scrolling, i.e. automatic scrolling
1580 will not scroll a window to a column less than the specified one.
1582 @deffn Command scroll-left &optional count
1583 This function scrolls the selected window @var{count} columns to the
1584 left (or to the right if @var{count} is negative). The default
1585 for @var{count} is the window width, minus 2.
1587 The return value is the total amount of leftward horizontal scrolling in
1588 effect after the change---just like the value returned by
1589 @code{window-hscroll} (below).
1592 @deffn Command scroll-right &optional count
1593 This function scrolls the selected window @var{count} columns to the
1594 right (or to the left if @var{count} is negative). The default
1595 for @var{count} is the window width, minus 2.
1597 The return value is the total amount of leftward horizontal scrolling in
1598 effect after the change---just like the value returned by
1599 @code{window-hscroll} (below).
1601 Once you scroll a window as far right as it can go, back to its normal
1602 position where the total leftward scrolling is zero, attempts to scroll
1603 any farther right have no effect.
1606 @defun window-hscroll &optional window
1607 This function returns the total leftward horizontal scrolling of
1608 @var{window}---the number of columns by which the text in @var{window}
1609 is scrolled left past the left margin.
1611 The value is never negative. It is zero when no horizontal scrolling
1612 has been done in @var{window} (which is usually the case).
1614 If @var{window} is @code{nil}, the selected window is used.
1632 @defun set-window-hscroll window columns
1633 This function sets the number of columns from the left margin that
1634 @var{window} is scrolled from the value of @var{columns}. The argument
1635 @var{columns} should be zero or positive; if not, it is taken as zero.
1636 Fractional values of @var{columns} are not supported at present.
1638 Note that @code{set-window-hscroll} may appear not to work if you test
1639 it by evaluating a call with @kbd{M-:} in a simple way. What happens
1640 is that the function sets the horizontal scroll value and returns, but
1641 then redisplay adjusts the horizontal scrolling to make point visible,
1642 and this overrides what the function did. You can observe the
1643 function's effect if you call it while point is sufficiently far from
1644 the left margin that it will remain visible.
1646 The value returned is @var{columns}.
1650 (set-window-hscroll (selected-window) 10)
1656 Here is how you can determine whether a given position @var{position}
1657 is off the screen due to horizontal scrolling:
1661 (defun hscroll-on-screen (window position)
1663 (goto-char position)
1665 (>= (- (current-column) (window-hscroll window)) 0)
1666 (< (- (current-column) (window-hscroll window))
1667 (window-width window)))))
1671 @node Size of Window
1672 @section The Size of a Window
1674 @cindex size of window
1676 An Emacs window is rectangular, and its size information consists of
1677 the height (the number of lines) and the width (the number of character
1678 positions in each line). The mode line is included in the height. But
1679 the width does not count the scroll bar or the column of @samp{|}
1680 characters that separates side-by-side windows.
1682 The following three functions return size information about a window:
1684 @defun window-height &optional window
1685 This function returns the number of lines in @var{window}, including
1686 its mode line and header line, if any. If @var{window} fills its
1687 entire frame except for the echo area, and there is no tool bar, this
1688 is typically one less than the value of @code{frame-height} on that
1691 If @var{window} is @code{nil}, the function uses the selected window.
1699 (split-window-vertically)
1700 @result{} #<window 4 on windows.texi>
1709 @tindex window-body-height
1710 @defun window-body-height &optional window
1711 Like @code{window-height} but the value does not include the
1712 mode line (if any) or the header line (if any).
1715 @defun window-width &optional window
1716 This function returns the number of columns in @var{window}. If
1717 @var{window} fills its entire frame, this is the same as the value of
1718 @code{frame-width} on that frame. The width does not include the
1719 window's scroll bar or the column of @samp{|} characters that separates
1720 side-by-side windows.
1722 If @var{window} is @code{nil}, the function uses the selected window.
1732 @defun window-edges &optional window
1733 This function returns a list of the edge coordinates of @var{window}.
1734 If @var{window} is @code{nil}, the selected window is used.
1736 The order of the list is @code{(@var{left} @var{top} @var{right}
1737 @var{bottom})}, all elements relative to 0, 0 at the top left corner of
1738 the frame. The element @var{right} of the value is one more than the
1739 rightmost column used by @var{window}, and @var{bottom} is one more than
1740 the bottommost row used by @var{window} and its mode-line.
1742 If a window has a scroll bar, the right edge value includes the width of
1743 the scroll bar. Otherwise, if the window has a neighbor on the right,
1744 its right edge value includes the width of the separator line between
1745 the window and that neighbor. Since the width of the window does not
1746 include this separator, the width does not usually equal the difference
1747 between the right and left edges.
1750 @defun window-inside-edges window
1751 This is similar to @code{window-edges}, but the edge values
1752 it returns include only the text area of the window. They
1753 do not include the header line, mode line, scroll bar or
1754 vertical separator, fringes, or display margins.
1757 Here are the results obtained on a typical 24-line terminal with just
1758 one window, with menu bar enabled:
1762 (window-edges (selected-window))
1763 @result{} (0 1 80 23)
1766 (window-inside-edges (selected-window))
1767 @result{} (0 1 80 22)
1772 The bottom edge is at line 23 because the last line is the echo area.
1773 The bottom inside edge is at line 22, which is the window's mode line.
1775 If @var{window} is at the upper left corner of its frame, and there is
1776 no menu bar, then @var{bottom} returned by @code{window-edges} is the
1777 same as the value of @code{(window-height)}, @var{right} is almost the
1778 same as the value of @code{(window-width)}, and @var{top} and
1779 @var{left} are zero. For example, the edges of the following window
1780 are @w{@samp{0 0 8 5}}. Assuming that the frame has more than 8
1781 columns, the last column of the window (column 7) holds a border
1782 rather than text. The last row (row 4) holds the mode line, shown
1783 here with @samp{xxxxxxxxx}.
1799 In the following example, let's suppose that the frame is 7
1800 columns wide. Then the edges of the left window are @w{@samp{0 0 4 3}}
1801 and the edges of the right window are @w{@samp{4 0 7 3}}.
1802 The inside edges of the left window are @w{@samp{0 0 3 2}},
1803 and the inside edges of the right window are @w{@samp{4 0 7 2}},
1816 @defun window-pixel-edges window
1817 This function is like @code{window-edges} except that, on a graphical
1818 display, the edge values are measured in pixels instead of in
1819 character lines and columns.
1822 @defun window-inside-pixel-edges window
1823 This function is like @code{window-inside-edges} except that, on a
1824 graphical display, the edge values are measured in pixels instead of
1825 in character lines and columns.
1828 @node Resizing Windows
1829 @section Changing the Size of a Window
1830 @cindex window resizing
1831 @cindex changing window size
1832 @cindex window size, changing
1834 The window size functions fall into two classes: high-level commands
1835 that change the size of windows and low-level functions that access
1836 window size. Emacs does not permit overlapping windows or gaps between
1837 windows, so resizing one window affects other windows.
1839 @deffn Command enlarge-window size &optional horizontal
1840 This function makes the selected window @var{size} lines taller,
1841 stealing lines from neighboring windows. It takes the lines from one
1842 window at a time until that window is used up, then takes from another.
1843 If a window from which lines are stolen shrinks below
1844 @code{window-min-height} lines, that window disappears.
1846 If @var{horizontal} is non-@code{nil}, this function makes
1847 @var{window} wider by @var{size} columns, stealing columns instead of
1848 lines. If a window from which columns are stolen shrinks below
1849 @code{window-min-width} columns, that window disappears.
1851 If the requested size would exceed that of the window's frame, then the
1852 function makes the window occupy the entire height (or width) of the
1855 If there are various other windows from which lines or columns can be
1856 stolen, and some of them specify fixed size (using
1857 @code{window-size-fixed}, see below), they are left untouched while
1858 other windows are ``robbed.'' If it would be necessary to alter the
1859 size of a fixed-size window, @code{enlarge-window} gets an error
1862 If @var{size} is negative, this function shrinks the window by
1863 @minus{}@var{size} lines or columns. If that makes the window smaller
1864 than the minimum size (@code{window-min-height} and
1865 @code{window-min-width}), @code{enlarge-window} deletes the window.
1867 @code{enlarge-window} returns @code{nil}.
1870 @deffn Command enlarge-window-horizontally columns
1871 This function makes the selected window @var{columns} wider.
1872 It could be defined as follows:
1876 (defun enlarge-window-horizontally (columns)
1877 (enlarge-window columns t))
1882 @deffn Command shrink-window size &optional horizontal
1883 This function is like @code{enlarge-window} but negates the argument
1884 @var{size}, making the selected window smaller by giving lines (or
1885 columns) to the other windows. If the window shrinks below
1886 @code{window-min-height} or @code{window-min-width}, then it disappears.
1888 If @var{size} is negative, the window is enlarged by @minus{}@var{size}
1892 @deffn Command shrink-window-horizontally columns
1893 This function makes the selected window @var{columns} narrower.
1894 It could be defined as follows:
1898 (defun shrink-window-horizontally (columns)
1899 (shrink-window columns t))
1904 @deffn Command shrink-window-if-larger-than-buffer &optional window
1905 This command shrinks @var{window} to be as small as possible while still
1906 showing the full contents of its buffer---but not less than
1907 @code{window-min-height} lines. If @var{window} is not given,
1908 it defaults to the selected window.
1910 However, the command does nothing if the window is already too small to
1911 display the whole text of the buffer, or if part of the contents are
1912 currently scrolled off screen, or if the window is not the full width of
1913 its frame, or if the window is the only window in its frame.
1916 @tindex window-size-fixed
1917 @defvar window-size-fixed
1918 If this variable is non-@code{nil}, in any given buffer,
1919 then the size of any window displaying the buffer remains fixed
1920 unless you explicitly change it or Emacs has no other choice.
1921 (This feature is new in Emacs 21.)
1923 If the value is @code{height}, then only the window's height is fixed;
1924 if the value is @code{width}, then only the window's width is fixed.
1925 Any other non-@code{nil} value fixes both the width and the height.
1927 The usual way to use this variable is to give it a buffer-local value in
1928 a particular buffer. That way, the windows (but usually there is only
1929 one) displaying that buffer have fixed size.
1931 Explicit size-change functions such as @code{enlarge-window}
1932 get an error if they would have to change a window size which is fixed.
1933 Therefore, when you want to change the size of such a window,
1934 you should bind @code{window-size-fixed} to @code{nil}, like this:
1937 (let ((window-size-fixed nil))
1938 (enlarge-window 10))
1941 Note that changing the frame size will change the size of a
1942 fixed-size window, if there is no other alternative.
1945 @cindex minimum window size
1946 The following two variables constrain the window-structure-changing
1947 functions to a minimum height and width.
1949 @defopt window-min-height
1950 The value of this variable determines how short a window may become
1951 before it is automatically deleted. Making a window smaller than
1952 @code{window-min-height} automatically deletes it, and no window may
1953 be created shorter than this. The default value is 4.
1955 The absolute minimum window height is one; actions that change window
1956 sizes reset this variable to one if it is less than one.
1959 @defopt window-min-width
1960 The value of this variable determines how narrow a window may become
1961 before it is automatically deleted. Making a window smaller than
1962 @code{window-min-width} automatically deletes it, and no window may be
1963 created narrower than this. The default value is 10.
1965 The absolute minimum window width is two; actions that change window
1966 sizes reset this variable to two if it is less than two.
1969 @node Coordinates and Windows
1970 @section Coordinates and Windows
1972 This section describes how to relate screen coordinates to windows.
1974 @defun window-at x y &optional frame
1975 This function returns the window containing the specified cursor
1976 position in the frame @var{frame}. The coordinates @var{x} and @var{y}
1977 are measured in characters and count from the top left corner of the
1978 frame. If they are out of range, @code{window-at} returns @code{nil}.
1980 If you omit @var{frame}, the selected frame is used.
1983 @defun coordinates-in-window-p coordinates window
1984 This function checks whether a particular frame position falls within
1985 the window @var{window}.
1987 The argument @var{coordinates} is a cons cell of the form @code{(@var{x}
1988 . @var{y})}. The coordinates @var{x} and @var{y} are measured in
1989 characters, and count from the top left corner of the screen or frame.
1991 The value returned by @code{coordinates-in-window-p} is non-@code{nil}
1992 if the coordinates are inside @var{window}. The value also indicates
1993 what part of the window the position is in, as follows:
1996 @item (@var{relx} . @var{rely})
1997 The coordinates are inside @var{window}. The numbers @var{relx} and
1998 @var{rely} are the equivalent window-relative coordinates for the
1999 specified position, counting from 0 at the top left corner of the
2003 The coordinates are in the mode line of @var{window}.
2006 The coordinates are in the header line of @var{window}.
2009 The coordinates are in the vertical line between @var{window} and its
2010 neighbor to the right. This value occurs only if the window doesn't
2011 have a scroll bar; positions in a scroll bar are considered outside the
2012 window for these purposes.
2015 The coordinates are not in any part of @var{window}.
2018 The function @code{coordinates-in-window-p} does not require a frame as
2019 argument because it always uses the frame that @var{window} is on.
2022 @node Window Configurations
2023 @section Window Configurations
2024 @cindex window configurations
2025 @cindex saving window information
2027 A @dfn{window configuration} records the entire layout of one
2028 frame---all windows, their sizes, which buffers they contain, what
2029 part of each buffer is displayed, and the values of point and the
2030 mark. It also includes the values of @code{window-min-height},
2031 @code{window-min-width} and @code{minibuffer-scroll-window}. An
2032 exception is made for point in the selected window for the current
2033 buffer; its value is not saved in the window configuration.
2035 You can bring back an entire previous layout by restoring a window
2036 configuration previously saved. If you want to record all frames
2037 instead of just one, use a frame configuration instead of a window
2038 configuration. @xref{Frame Configurations}.
2040 @defun current-window-configuration &optional frame
2041 This function returns a new object representing @var{frame}'s current
2042 window configuration. If @var{frame} is omitted, the selected frame
2046 @defun set-window-configuration configuration
2047 This function restores the configuration of windows and buffers as
2048 specified by @var{configuration}, for the frame that @var{configuration}
2051 The argument @var{configuration} must be a value that was previously
2052 returned by @code{current-window-configuration}. This configuration is
2053 restored in the frame from which @var{configuration} was made, whether
2054 that frame is selected or not. This always counts as a window size
2055 change and triggers execution of the @code{window-size-change-functions}
2056 (@pxref{Window Hooks}), because @code{set-window-configuration} doesn't
2057 know how to tell whether the new configuration actually differs from the
2060 If the frame which @var{configuration} was saved from is dead, all this
2061 function does is restore the three variables @code{window-min-height},
2062 @code{window-min-width} and @code{minibuffer-scroll-window}.
2064 Here is a way of using this function to get the same effect
2065 as @code{save-window-excursion}:
2069 (let ((config (current-window-configuration)))
2071 (progn (split-window-vertically nil)
2073 (set-window-configuration config)))
2078 @defspec save-window-excursion forms@dots{}
2079 This special form records the window configuration, executes @var{forms}
2080 in sequence, then restores the earlier window configuration. The window
2081 configuration includes the value of point and the portion of the buffer
2082 that is visible. It also includes the choice of selected window.
2083 However, it does not include the value of point in the current buffer;
2084 use @code{save-excursion} also, if you wish to preserve that.
2086 Don't use this construct when @code{save-selected-window} is all you need.
2088 Exit from @code{save-window-excursion} always triggers execution of the
2089 @code{window-size-change-functions}. (It doesn't know how to tell
2090 whether the restored configuration actually differs from the one in
2091 effect at the end of the @var{forms}.)
2093 The return value is the value of the final form in @var{forms}.
2099 @result{} #<window 25 on control.texi>
2102 (setq w (selected-window))
2103 @result{} #<window 19 on control.texi>
2106 (save-window-excursion
2107 (delete-other-windows w)
2108 (switch-to-buffer "foo")
2110 @result{} do-something
2111 ;; @r{The screen is now split again.}
2116 @defun window-configuration-p object
2117 This function returns @code{t} if @var{object} is a window configuration.
2120 @defun compare-window-configurations config1 config2
2121 This function compares two window configurations as regards the
2122 structure of windows, but ignores the values of point and mark and the
2123 saved scrolling positions---it can return @code{t} even if those
2126 The function @code{equal} can also compare two window configurations; it
2127 regards configurations as unequal if they differ in any respect, even a
2128 saved point or mark.
2131 Primitives to look inside of window configurations would make sense,
2132 but none are implemented. It is not clear they are useful enough to
2133 be worth implementing. See the file @file{winner.el} for some more
2134 operations on windows configurations.
2137 @section Hooks for Window Scrolling and Changes
2139 This section describes how a Lisp program can take action whenever a
2140 window displays a different part of its buffer or a different buffer.
2141 There are three actions that can change this: scrolling the window,
2142 switching buffers in the window, and changing the size of the window.
2143 The first two actions run @code{window-scroll-functions}; the last runs
2144 @code{window-size-change-functions}. The paradigmatic use of these
2145 hooks is in the implementation of Lazy Lock mode; see @file{lazy-lock.el}.
2147 @defvar window-scroll-functions
2148 This variable holds a list of functions that Emacs should call before
2149 redisplaying a window with scrolling. It is not a normal hook, because
2150 each function is called with two arguments: the window, and its new
2151 display-start position.
2153 Displaying a different buffer in the window also runs these functions.
2155 These functions must be careful in using @code{window-end}
2156 (@pxref{Window Start}); if you need an up-to-date value, you must use
2157 the @var{update} argument to ensure you get it.
2160 @defvar window-size-change-functions
2161 This variable holds a list of functions to be called if the size of any
2162 window changes for any reason. The functions are called just once per
2163 redisplay, and just once for each frame on which size changes have
2166 Each function receives the frame as its sole argument. There is no
2167 direct way to find out which windows on that frame have changed size, or
2168 precisely how. However, if a size-change function records, at each
2169 call, the existing windows and their sizes, it can also compare the
2170 present sizes and the previous sizes.
2172 Creating or deleting windows counts as a size change, and therefore
2173 causes these functions to be called. Changing the frame size also
2174 counts, because it changes the sizes of the existing windows.
2176 It is not a good idea to use @code{save-window-excursion} (@pxref{Window
2177 Configurations}) in these functions, because that always counts as a
2178 size change, and it would cause these functions to be called over and
2179 over. In most cases, @code{save-selected-window} (@pxref{Selecting
2180 Windows}) is what you need here.
2183 @defvar redisplay-end-trigger-functions
2184 This abnormal hook is run whenever redisplay in a window uses text that
2185 extends past a specified end trigger position. You set the end trigger
2186 position with the function @code{set-window-redisplay-end-trigger}. The
2187 functions are called with two arguments: the window, and the end trigger
2188 position. Storing @code{nil} for the end trigger position turns off the
2189 feature, and the trigger value is automatically reset to @code{nil} just
2190 after the hook is run.
2193 @defun set-window-redisplay-end-trigger window position
2194 This function sets @var{window}'s end trigger position at
2198 @defun window-redisplay-end-trigger &optional window
2199 This function returns @var{window}'s current end trigger position.
2202 @defvar window-configuration-change-hook
2203 A normal hook that is run every time you change the window configuration
2204 of an existing frame. This includes splitting or deleting windows,
2205 changing the sizes of windows, or displaying a different buffer in a
2206 window. The frame whose window configuration has changed is the
2207 selected frame when this hook runs.