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[Emacs-diffs] Changes to emacs/lispref/windows.texi [gnus-5_10-branch]
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From: |
Miles Bader |
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Subject: |
[Emacs-diffs] Changes to emacs/lispref/windows.texi [gnus-5_10-branch] |
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Date: |
Sat, 04 Sep 2004 08:28:38 -0400 |
Index: emacs/lispref/windows.texi
diff -c /dev/null emacs/lispref/windows.texi:1.74.2.1
*** /dev/null Sat Sep 4 12:02:47 2004
--- emacs/lispref/windows.texi Sat Sep 4 12:01:14 2004
***************
*** 0 ****
--- 1,2316 ----
+ @c -*-texinfo-*-
+ @c This is part of the GNU Emacs Lisp Reference Manual.
+ @c Copyright (C) 1990, 1991, 1992, 1993, 1994, 1995, 1998, 1999, 2004
+ @c Free Software Foundation, Inc.
+ @c See the file elisp.texi for copying conditions.
+ @setfilename ../info/windows
+ @node Windows, Frames, Buffers, Top
+ @chapter Windows
+
+ This chapter describes most of the functions and variables related to
+ Emacs windows. See @ref{Display}, for information on how text is
+ displayed in windows.
+
+ @menu
+ * Basic Windows:: Basic information on using windows.
+ * Splitting Windows:: Splitting one window into two windows.
+ * Deleting Windows:: Deleting a window gives its space to other
windows.
+ * Selecting Windows:: The selected window is the one that you edit in.
+ * Cyclic Window Ordering:: Moving around the existing windows.
+ * Buffers and Windows:: Each window displays the contents of a buffer.
+ * Displaying Buffers:: Higher-level functions for displaying a buffer
+ and choosing a window for it.
+ * Choosing Window:: How to choose a window for displaying a buffer.
+ * Window Point:: Each window has its own location of point.
+ * Window Start:: The display-start position controls which text
+ is on-screen in the window.
+ * Textual Scrolling:: Moving text up and down through the window.
+ * Vertical Scrolling:: Moving the contents up and down on the window.
+ * Horizontal Scrolling:: Moving the contents sideways on the window.
+ * Size of Window:: Accessing the size of a window.
+ * Resizing Windows:: Changing the size of a window.
+ * Coordinates and Windows:: Converting coordinates to windows.
+ * Window Configurations:: Saving and restoring the state of the screen.
+ * Window Hooks:: Hooks for scrolling, window size changes,
+ redisplay going past a certain point,
+ or window configuration changes.
+ @end menu
+
+ @node Basic Windows
+ @section Basic Concepts of Emacs Windows
+ @cindex window
+ @cindex selected window
+
+ A @dfn{window} in Emacs is the physical area of the screen in which a
+ buffer is displayed. The term is also used to refer to a Lisp object that
+ represents that screen area in Emacs Lisp. It should be
+ clear from the context which is meant.
+
+ Emacs groups windows into frames. A frame represents an area of
+ screen available for Emacs to use. Each frame always contains at least
+ one window, but you can subdivide it vertically or horizontally into
+ multiple nonoverlapping Emacs windows.
+
+ In each frame, at any time, one and only one window is designated as
+ @dfn{selected within the frame}. The frame's cursor appears in that
+ window. At any time, one frame is the selected frame; and the window
+ selected within that frame is @dfn{the selected window}. The selected
+ window's buffer is usually the current buffer (except when
+ @code{set-buffer} has been used). @xref{Current Buffer}.
+
+ For practical purposes, a window exists only while it is displayed in
+ a frame. Once removed from the frame, the window is effectively deleted
+ and should not be used, @emph{even though there may still be references
+ to it} from other Lisp objects. Restoring a saved window configuration
+ is the only way for a window no longer on the screen to come back to
+ life. (@xref{Deleting Windows}.)
+
+ Each window has the following attributes:
+
+ @itemize @bullet
+ @item
+ containing frame
+
+ @item
+ window height
+
+ @item
+ window width
+
+ @item
+ window edges with respect to the screen or frame
+
+ @item
+ the buffer it displays
+
+ @item
+ position within the buffer at the upper left of the window
+
+ @item
+ amount of horizontal scrolling, in columns
+
+ @item
+ point
+
+ @item
+ the mark
+
+ @item
+ how recently the window was selected
+
+ @item
+ fringe settings
+
+ @item
+ display margins
+
+ @item
+ scroll-bar settings
+ @end itemize
+
+ @cindex multiple windows
+ Users create multiple windows so they can look at several buffers at
+ once. Lisp libraries use multiple windows for a variety of reasons, but
+ most often to display related information. In Rmail, for example, you
+ can move through a summary buffer in one window while the other window
+ shows messages one at a time as they are reached.
+
+ The meaning of ``window'' in Emacs is similar to what it means in the
+ context of general-purpose window systems such as X, but not identical.
+ The X Window System places X windows on the screen; Emacs uses one or
+ more X windows as frames, and subdivides them into
+ Emacs windows. When you use Emacs on a character-only terminal, Emacs
+ treats the whole terminal screen as one frame.
+
+ @cindex terminal screen
+ @cindex screen of terminal
+ @cindex tiled windows
+ Most window systems support arbitrarily located overlapping windows.
+ In contrast, Emacs windows are @dfn{tiled}; they never overlap, and
+ together they fill the whole screen or frame. Because of the way in
+ which Emacs creates new windows and resizes them, not all conceivable
+ tilings of windows on an Emacs frame are actually possible.
+ @xref{Splitting Windows}, and @ref{Size of Window}.
+
+ @xref{Display}, for information on how the contents of the
+ window's buffer are displayed in the window.
+
+ @defun windowp object
+ This function returns @code{t} if @var{object} is a window.
+ @end defun
+
+ @node Splitting Windows
+ @section Splitting Windows
+ @cindex splitting windows
+ @cindex window splitting
+
+ The functions described here are the primitives used to split a window
+ into two windows. Two higher level functions sometimes split a window,
+ but not always: @code{pop-to-buffer} and @code{display-buffer}
+ (@pxref{Displaying Buffers}).
+
+ The functions described here do not accept a buffer as an argument.
+ The two ``halves'' of the split window initially display the same buffer
+ previously visible in the window that was split.
+
+ @deffn Command split-window &optional window size horizontal
+ This function splits @var{window} into two windows. The original
+ window @var{window} remains the selected window, but occupies only
+ part of its former screen area. The rest is occupied by a newly created
+ window which is returned as the value of this function.
+
+ If @var{horizontal} is address@hidden, then @var{window} splits into
+ two side by side windows. The original window @var{window} keeps the
+ leftmost @var{size} columns, and gives the rest of the columns to the
+ new window. Otherwise, it splits into windows one above the other, and
+ @var{window} keeps the upper @var{size} lines and gives the rest of the
+ lines to the new window. The original window is therefore the
+ left-hand or upper of the two, and the new window is the right-hand or
+ lower.
+
+ If @var{window} is omitted or @code{nil}, then the selected window is
+ split. If @var{size} is omitted or @code{nil}, then @var{window} is
+ divided evenly into two parts. (If there is an odd line, it is
+ allocated to the new window.) When @code{split-window} is called
+ interactively, all its arguments are @code{nil}.
+
+ If splitting would result in making a window that is smaller than
+ @code{window-min-height} or @code{window-min-width}, the function
+ signals an error and does not split the window at all.
+
+ The following example starts with one window on a screen that is 50
+ lines high by 80 columns wide; then it splits the window.
+
+ @smallexample
+ @group
+ (setq w (selected-window))
+ @result{} #<window 8 on windows.texi>
+ (window-edges) ; @r{Edges in order:}
+ @result{} (0 0 80 50) ; @r{left--top--right--bottom}
+ @end group
+
+ @group
+ ;; @r{Returns window created}
+ (setq w2 (split-window w 15))
+ @result{} #<window 28 on windows.texi>
+ @end group
+ @group
+ (window-edges w2)
+ @result{} (0 15 80 50) ; @r{Bottom window;}
+ ; @r{top is line 15}
+ @end group
+ @group
+ (window-edges w)
+ @result{} (0 0 80 15) ; @r{Top window}
+ @end group
+ @end smallexample
+
+ The screen looks like this:
+
+ @smallexample
+ @group
+ __________
+ | | line 0
+ | w |
+ |__________|
+ | | line 15
+ | w2 |
+ |__________|
+ line 50
+ column 0 column 80
+ @end group
+ @end smallexample
+
+ Next, split the top window horizontally:
+
+ @smallexample
+ @group
+ (setq w3 (split-window w 35 t))
+ @result{} #<window 32 on windows.texi>
+ @end group
+ @group
+ (window-edges w3)
+ @result{} (35 0 80 15) ; @r{Left edge at column 35}
+ @end group
+ @group
+ (window-edges w)
+ @result{} (0 0 35 15) ; @r{Right edge at column 35}
+ @end group
+ @group
+ (window-edges w2)
+ @result{} (0 15 80 50) ; @r{Bottom window unchanged}
+ @end group
+ @end smallexample
+
+ @need 3000
+ Now the screen looks like this:
+
+ @smallexample
+ @group
+ column 35
+ __________
+ | | | line 0
+ | w | w3 |
+ |___|______|
+ | | line 15
+ | w2 |
+ |__________|
+ line 50
+ column 0 column 80
+ @end group
+ @end smallexample
+
+ Normally, Emacs indicates the border between two side-by-side windows
+ with a scroll bar (@pxref{Window Frame Parameters,Scroll Bars}) or @samp{|}
+ characters. The display table can specify alternative border
+ characters; see @ref{Display Tables}.
+ @end deffn
+
+ @deffn Command split-window-vertically &optional size
+ This function splits the selected window into two windows, one above the
+ other, leaving the upper of the two windows selected, with @var{size}
+ lines. (If @var{size} is negative, then the lower of the two windows
+ gets @minus{} @var{size} lines and the upper window gets the rest, but
+ the upper window is still the one selected.) However, if
+ @code{split-window-keep-point} (see below) is @code{nil}, then either
+ window can be selected.
+
+ In other respects, this function is similar to @code{split-window}.
+ In particular, the upper window is the original one and the return
+ value is the new, lower window.
+ @end deffn
+
+ @defopt split-window-keep-point
+ If this variable is address@hidden (the default), then
+ @code{split-window-vertically} behaves as described above.
+
+ If it is @code{nil}, then @code{split-window-vertically} adjusts point
+ in each of the two windows to avoid scrolling. (This is useful on
+ slow terminals.) It selects whichever window contains the screen line
+ that point was previously on.
+
+ This variable only affects the behavior of @code{split-window-vertically}.
+ It has no effect on the other functions described here.
+ @end defopt
+
+ @deffn Command split-window-horizontally &optional size
+ This function splits the selected window into two windows
+ side-by-side, leaving the selected window on the left with @var{size}
+ columns. If @var{size} is negative, the rightmost window gets
+ @minus{} @var{size} columns, but the leftmost window still remains
+ selected.
+
+ This function is basically an interface to @code{split-window}.
+ You could define a simplified version of the function like this:
+
+ @smallexample
+ @group
+ (defun split-window-horizontally (&optional arg)
+ "Split selected window into two windows, side by side..."
+ (interactive "P")
+ @end group
+ @group
+ (let ((size (and arg (prefix-numeric-value arg))))
+ (and size (< size 0)
+ (setq size (+ (window-width) size)))
+ (split-window nil size t)))
+ @end group
+ @end smallexample
+ @end deffn
+
+ @defun one-window-p &optional no-mini all-frames
+ This function returns address@hidden if there is only one window. The
+ argument @var{no-mini}, if address@hidden, means don't count the
+ minibuffer even if it is active; otherwise, the minibuffer window is
+ counted when it is active.
+
+ The argument @var{all-frames} specifies which frames to consider. Here
+ are the possible values and their meanings:
+
+ @table @asis
+ @item @code{nil}
+ Count the windows in the selected frame, plus the minibuffer used
+ by that frame even if it lies in some other frame.
+
+ @item @code{t}
+ Count all windows in all existing frames.
+
+ @item @code{visible}
+ Count all windows in all visible frames.
+
+ @item 0
+ Count all windows in all visible or iconified frames.
+
+ @item anything else
+ Count precisely the windows in the selected frame, and no others.
+ @end table
+ @end defun
+
+ @node Deleting Windows
+ @section Deleting Windows
+ @cindex deleting windows
+
+ A window remains visible on its frame unless you @dfn{delete} it by
+ calling certain functions that delete windows. A deleted window cannot
+ appear on the screen, but continues to exist as a Lisp object until
+ there are no references to it. There is no way to cancel the deletion
+ of a window aside from restoring a saved window configuration
+ (@pxref{Window Configurations}). Restoring a window configuration also
+ deletes any windows that aren't part of that configuration.
+
+ When you delete a window, the space it took up is given to one
+ adjacent sibling.
+
+ @c Emacs 19 feature
+ @defun window-live-p window
+ This function returns @code{nil} if @var{window} is deleted, and
+ @code{t} otherwise.
+
+ @strong{Warning:} Erroneous information or fatal errors may result from
+ using a deleted window as if it were live.
+ @end defun
+
+ @deffn Command delete-window &optional window
+ This function removes @var{window} from display, and returns @code{nil}.
+ If @var{window} is omitted, then the selected window is deleted. An
+ error is signaled if there is only one window when @code{delete-window}
+ is called.
+ @end deffn
+
+ @deffn Command delete-other-windows &optional window
+ This function makes @var{window} the only window on its frame, by
+ deleting the other windows in that frame. If @var{window} is omitted or
+ @code{nil}, then the selected window is used by default.
+
+ The return value is @code{nil}.
+ @end deffn
+
+ @deffn Command delete-windows-on buffer-or-name &optional frame
+ This function deletes all windows showing @var{buffer-or-name}. If
+ there are no windows showing @var{buffer-or-name}, it does nothing.
+ @var{buffer-or-name} must be a buffer or the name of an existing
+ buffer.
+
+ @code{delete-windows-on} operates frame by frame. If a frame has
+ several windows showing different buffers, then those showing
+ @var{buffer-or-name} are removed, and the others expand to fill the
+ space. If all windows in some frame are showing @var{buffer-or-name}
+ (including the case where there is only one window), then the frame
+ winds up with a single window showing another buffer chosen with
+ @code{other-buffer}. @xref{The Buffer List}.
+
+ The argument @var{frame} controls which frames to operate on. This
+ function does not use it in quite the same way as the other functions
+ which scan all windows; specifically, the values @code{t} and @code{nil}
+ have the opposite of their meanings in other functions. Here are the
+ full details:
+
+ @itemize @bullet
+ @item
+ If it is @code{nil}, operate on all frames.
+ @item
+ If it is @code{t}, operate on the selected frame.
+ @item
+ If it is @code{visible}, operate on all visible frames.
+ @item
+ If it is 0, operate on all visible or iconified frames.
+ @item
+ If it is a frame, operate on that frame.
+ @end itemize
+
+ This function always returns @code{nil}.
+ @end deffn
+
+ @node Selecting Windows
+ @section Selecting Windows
+ @cindex selecting windows
+
+ When a window is selected, the buffer in the window becomes the current
+ buffer, and the cursor will appear in it.
+
+ @defun selected-window
+ This function returns the selected window. This is the window in
+ which the cursor appears and to which many commands apply.
+ @end defun
+
+ @defun select-window window &optional norecord
+ This function makes @var{window} the selected window. The cursor then
+ appears in @var{window} (on redisplay). Unless @var{window} was
+ already selected, @code{select-window} makes @var{window}'s buffer the
+ current buffer.
+
+ Normally @var{window}'s selected buffer is moved to the front of the
+ buffer list, but if @var{norecord} is address@hidden, the buffer list
+ order is unchanged.
+
+ The return value is @var{window}.
+
+ @example
+ @group
+ (setq w (next-window))
+ (select-window w)
+ @result{} #<window 65 on windows.texi>
+ @end group
+ @end example
+ @end defun
+
+ @defmac save-selected-window address@hidden
+ This macro records the selected window, as well as the selected window
+ of each frame, executes @var{forms} in sequence, then restores the
+ earlier selected windows. It returns the value of the last form in
+ @var{forms}.
+
+ This macro does not save or restore anything about the sizes,
+ arrangement or contents of windows; therefore, if the @var{forms}
+ change them, the change persists. If the previously selected window
+ of some frame is no longer live at the time of exit from @var{forms},
+ that frame's selected window is left alone. If the previously
+ selected window is no longer live, then whatever window is selected at
+ the end of @var{forms} remains selected.
+ @end defmac
+
+ @defmac with-selected-window window address@hidden
+ This macro selects @var{window} (without changing the buffer list),
+ executes @var{forms} in sequence, then restores the previously
+ selected window (unless that window is no longer alive). It is similar
+ to @code{save-selected-window} except that it explicitly selects
+ @var{window}, without altering the buffer list sequence.
+ @end defmac
+
+ @cindex finding windows
+ The following functions choose one of the windows on the screen,
+ offering various criteria for the choice.
+
+ @defun get-lru-window &optional frame
+ This function returns the window least recently ``used'' (that is,
+ selected). If any full-width windows are present, it only considers
+ these. The selected window is always the most recently used window.
+
+ The selected window can be the least recently used window if it is the
+ only window. A newly created window becomes the least recently used
+ window until it is selected. A minibuffer window is never a candidate.
+
+ The argument @var{frame} controls which windows are considered.
+
+ @itemize @bullet
+ @item
+ If it is @code{nil}, consider windows on the selected frame.
+ @item
+ If it is @code{t}, consider windows on all frames.
+ @item
+ If it is @code{visible}, consider windows on all visible frames.
+ @item
+ If it is 0, consider windows on all visible or iconified frames.
+ @item
+ If it is a frame, consider windows on that frame.
+ @end itemize
+ @end defun
+
+ @defun get-largest-window &optional frame
+ This function returns the window with the largest area (height times
+ width). If there are no side-by-side windows, then this is the window
+ with the most lines. A minibuffer window is never a candidate.
+
+ If there are two windows of the same size, then the function returns
+ the window that is first in the cyclic ordering of windows (see
+ following section), starting from the selected window.
+
+ The argument @var{frame} controls which set of windows to
+ consider. See @code{get-lru-window}, above.
+ @end defun
+
+ @cindex window that satisfies a predicate
+ @cindex conditional selection of windows
+ @defun get-window-with-predicate predicate &optional minibuf all-frames
default
+ This function returns a window satisfying @var{predicate}. It cycles
+ through all visible windows using @code{walk-windows} (@pxref{Cyclic
+ Window Ordering}), calling @var{predicate} on each one of them
+ with that window as its argument. The function returns the first
+ window for which @var{predicate} returns a address@hidden value; if
+ that never happens, it returns @var{default}.
+
+ The optional arguments @var{minibuf} and @var{all-frames} specify the
+ set of windows to include in the scan. See the description of
+ @code{next-window} in @ref{Cyclic Window Ordering}, for details.
+ @end defun
+
+ @node Cyclic Window Ordering
+ @comment node-name, next, previous, up
+ @section Cyclic Ordering of Windows
+ @cindex cyclic ordering of windows
+ @cindex ordering of windows, cyclic
+ @cindex window ordering, cyclic
+
+ When you use the command @kbd{C-x o} (@code{other-window}) to select
+ the next window, it moves through all the windows on the screen in a
+ specific cyclic order. For any given configuration of windows, this
+ order never varies. It is called the @dfn{cyclic ordering of windows}.
+
+ This ordering generally goes from top to bottom, and from left to
+ right. But it may go down first or go right first, depending on the
+ order in which the windows were split.
+
+ If the first split was vertical (into windows one above each other),
+ and then the subwindows were split horizontally, then the ordering is
+ left to right in the top of the frame, and then left to right in the
+ next lower part of the frame, and so on. If the first split was
+ horizontal, the ordering is top to bottom in the left part, and so on.
+ In general, within each set of siblings at any level in the window tree,
+ the order is left to right, or top to bottom.
+
+ @defun next-window &optional window minibuf all-frames
+ @cindex minibuffer window
+ This function returns the window following @var{window} in the cyclic
+ ordering of windows. This is the window that @kbd{C-x o} would select
+ if typed when @var{window} is selected. If @var{window} is the only
+ window visible, then this function returns @var{window}. If omitted,
+ @var{window} defaults to the selected window.
+
+ The value of the argument @var{minibuf} determines whether the
+ minibuffer is included in the window order. Normally, when
+ @var{minibuf} is @code{nil}, the minibuffer is included if it is
+ currently active; this is the behavior of @kbd{C-x o}. (The minibuffer
+ window is active while the minibuffer is in use. @xref{Minibuffers}.)
+
+ If @var{minibuf} is @code{t}, then the cyclic ordering includes the
+ minibuffer window even if it is not active.
+
+ If @var{minibuf} is neither @code{t} nor @code{nil}, then the minibuffer
+ window is not included even if it is active.
+
+ The argument @var{all-frames} specifies which frames to consider. Here
+ are the possible values and their meanings:
+
+ @table @asis
+ @item @code{nil}
+ Consider all the windows in @var{window}'s frame, plus the minibuffer
+ used by that frame even if it lies in some other frame. If the
+ minibuffer counts (as determined by @var{minibuf}), then all windows on
+ all frames that share that minibuffer count too.
+
+ @item @code{t}
+ Consider all windows in all existing frames.
+
+ @item @code{visible}
+ Consider all windows in all visible frames. (To get useful results, you
+ must ensure @var{window} is in a visible frame.)
+
+ @item 0
+ Consider all windows in all visible or iconified frames.
+
+ @item a frame
+ Consider all windows on that frame.
+
+ @item anything else
+ Consider precisely the windows in @var{window}'s frame, and no others.
+ @end table
+
+ This example assumes there are two windows, both displaying the
+ buffer @samp{windows.texi}:
+
+ @example
+ @group
+ (selected-window)
+ @result{} #<window 56 on windows.texi>
+ @end group
+ @group
+ (next-window (selected-window))
+ @result{} #<window 52 on windows.texi>
+ @end group
+ @group
+ (next-window (next-window (selected-window)))
+ @result{} #<window 56 on windows.texi>
+ @end group
+ @end example
+ @end defun
+
+ @defun previous-window &optional window minibuf all-frames
+ This function returns the window preceding @var{window} in the cyclic
+ ordering of windows. The other arguments specify which windows to
+ include in the cycle, as in @code{next-window}.
+ @end defun
+
+ @deffn Command other-window count &optional all-frames
+ This function selects the @var{count}th following window in the cyclic
+ order. If count is negative, then it moves back @address@hidden
+ windows in the cycle, rather than forward. It returns @code{nil}.
+
+ The argument @var{all-frames} has the same meaning as in
+ @code{next-window}, but the @var{minibuf} argument of @code{next-window}
+ is always effectively @code{nil}.
+
+ In an interactive call, @var{count} is the numeric prefix argument.
+ @end deffn
+
+ @c Emacs 19 feature
+ @defun walk-windows proc &optional minibuf all-frames
+ This function cycles through all windows, calling @code{proc}
+ once for each window with the window as its sole argument.
+
+ The optional arguments @var{minibuf} and @var{all-frames} specify the
+ set of windows to include in the scan. See @code{next-window}, above,
+ for details.
+ @end defun
+
+ @defun window-list &optional frame minibuf window
+ This function returns a list of the windows on @var{frame}, starting
+ with @var{window}. If @var{frame} is @code{nil} or omitted, the
+ selected frame is used instead; if @var{window} is @code{nil} or
+ omitted, the selected window is used instead.
+
+ The value of @var{minibuf} determines if the minibuffer window will be
+ included in the result list. If @var{minibuf} is @code{t}, the
+ minibuffer window will be included, even if it isn't active. If
+ @var{minibuf} is @code{nil} or omitted, the minibuffer window will
+ only be included in the list if it is active. If @var{minibuf} is
+ neither @code{nil} nor @code{t}, the minibuffer window is not
+ included, whether or not it is active.
+ @end defun
+
+ @node Buffers and Windows
+ @section Buffers and Windows
+ @cindex examining windows
+ @cindex windows, controlling precisely
+ @cindex buffers, controlled in windows
+
+ This section describes low-level functions to examine windows or to
+ display buffers in windows in a precisely controlled fashion.
+ @iftex
+ See the following section for
+ @end iftex
+ @ifnottex
+ @xref{Displaying Buffers}, for
+ @end ifnottex
+ related functions that find a window to use and specify a buffer for it.
+ The functions described there are easier to use than these, but they
+ employ heuristics in choosing or creating a window; use these functions
+ when you need complete control.
+
+ @defun set-window-buffer window buffer-or-name &optional keep-margins
+ This function makes @var{window} display @var{buffer-or-name} as its
+ contents. It returns @code{nil}. @var{buffer-or-name} must be a
+ buffer, or the name of an existing buffer. This is the fundamental
+ primitive for changing which buffer is displayed in a window, and all
+ ways of doing that call this function.
+
+ @example
+ @group
+ (set-window-buffer (selected-window) "foo")
+ @result{} nil
+ @end group
+ @end example
+
+ Normally, displaying @var{buffer} in @var{window} resets the window's
+ display margins, fringe widths, scroll bar settings, and position
+ based on the local variables of @var{buffer}. However, if
+ @var{keep-margins} is address@hidden, the display margins and fringe
+ widths of @var{window} remain unchanged. @xref{Fringes}.
+ @end defun
+
+ @defun window-buffer &optional window
+ This function returns the buffer that @var{window} is displaying. If
+ @var{window} is omitted, this function returns the buffer for the
+ selected window.
+
+ @example
+ @group
+ (window-buffer)
+ @result{} #<buffer windows.texi>
+ @end group
+ @end example
+ @end defun
+
+ @defun get-buffer-window buffer-or-name &optional all-frames
+ This function returns a window currently displaying
+ @var{buffer-or-name}, or @code{nil} if there is none. If there are
+ several such windows, then the function returns the first one in the
+ cyclic ordering of windows, starting from the selected window.
+ @xref{Cyclic Window Ordering}.
+
+ The argument @var{all-frames} controls which windows to consider.
+
+ @itemize @bullet
+ @item
+ If it is @code{nil}, consider windows on the selected frame.
+ @item
+ If it is @code{t}, consider windows on all frames.
+ @item
+ If it is @code{visible}, consider windows on all visible frames.
+ @item
+ If it is 0, consider windows on all visible or iconified frames.
+ @item
+ If it is a frame, consider windows on that frame.
+ @end itemize
+ @end defun
+
+ @defun get-buffer-window-list buffer-or-name &optional minibuf all-frames
+ This function returns a list of all the windows currently displaying
+ @var{buffer-or-name}.
+
+ The two optional arguments work like the optional arguments of
+ @code{next-window} (@pxref{Cyclic Window Ordering}); they are @emph{not}
+ like the single optional argument of @code{get-buffer-window}. Perhaps
+ we should change @code{get-buffer-window} in the future to make it
+ compatible with the other functions.
+ @end defun
+
+ @defvar buffer-display-time
+ This variable records the time at which a buffer was last made visible
+ in a window. It is always local in each buffer; each time
+ @code{set-window-buffer} is called, it sets this variable to
+ @code{(current-time)} in the specified buffer (@pxref{Time of Day}).
+ When a buffer is first created, @code{buffer-display-time} starts out
+ with the value @code{nil}.
+ @end defvar
+
+ @node Displaying Buffers
+ @section Displaying Buffers in Windows
+ @cindex switching to a buffer
+ @cindex displaying a buffer
+
+ In this section we describe convenient functions that choose a window
+ automatically and use it to display a specified buffer. These functions
+ can also split an existing window in certain circumstances. We also
+ describe variables that parameterize the heuristics used for choosing a
+ window.
+ @iftex
+ See the preceding section for
+ @end iftex
+ @ifnottex
+ @xref{Buffers and Windows}, for
+ @end ifnottex
+ low-level functions that give you more precise control. All of these
+ functions work by calling @code{set-window-buffer}.
+
+ Do not use the functions in this section in order to make a buffer
+ current so that a Lisp program can access or modify it; they are too
+ drastic for that purpose, since they change the display of buffers in
+ windows, which would be gratuitous and surprise the user. Instead, use
+ @code{set-buffer} and @code{save-current-buffer} (@pxref{Current
+ Buffer}), which designate buffers as current for programmed access
+ without affecting the display of buffers in windows.
+
+ @deffn Command switch-to-buffer buffer-or-name &optional norecord
+ This function makes @var{buffer-or-name} the current buffer, and also
+ displays the buffer in the selected window. This means that a human can
+ see the buffer and subsequent keyboard commands will apply to it.
+ Contrast this with @code{set-buffer}, which makes @var{buffer-or-name}
+ the current buffer but does not display it in the selected window.
+ @xref{Current Buffer}.
+
+ If @var{buffer-or-name} does not identify an existing buffer, then a new
+ buffer by that name is created. The major mode for the new buffer is
+ set according to the variable @code{default-major-mode}. @xref{Auto
+ Major Mode}. If @var{buffer-or-name} is @code{nil},
+ @code{switch-to-buffer} chooses a buffer using @code{other-buffer}.
+
+ Normally the specified buffer is put at the front of the buffer list
+ (both the selected frame's buffer list and the frame-independent buffer
+ list). This affects the operation of @code{other-buffer}. However, if
+ @var{norecord} is address@hidden, this is not done. @xref{The Buffer
+ List}.
+
+ The @code{switch-to-buffer} function is often used interactively, as
+ the binding of @kbd{C-x b}. It is also used frequently in programs. It
+ returns the buffer that it switched to.
+ @end deffn
+
+ The next two functions are similar to @code{switch-to-buffer}, except
+ for the described features.
+
+ @deffn Command switch-to-buffer-other-window buffer-or-name &optional norecord
+ This function makes @var{buffer-or-name} the current buffer and
+ displays it in a window not currently selected. It then selects that
+ window. The handling of the buffer is the same as in
+ @code{switch-to-buffer}.
+
+ The currently selected window is absolutely never used to do the job.
+ If it is the only window, then it is split to make a distinct window for
+ this purpose. If the selected window is already displaying the buffer,
+ then it continues to do so, but another window is nonetheless found to
+ display it in as well.
+
+ This function updates the buffer list just like @code{switch-to-buffer}
+ unless @var{norecord} is address@hidden
+ @end deffn
+
+ @defun pop-to-buffer buffer-or-name &optional other-window norecord
+ This function makes @var{buffer-or-name} the current buffer and
+ switches to it in some window, preferably not the window previously
+ selected. The ``popped-to'' window becomes the selected window within
+ its frame. The return value is the buffer that was switched to.
+ If @var{buffer-or-name} is @code{nil}, that means to choose some
+ other buffer, but you don't specify which.
+
+ If the variable @code{pop-up-frames} is address@hidden,
+ @code{pop-to-buffer} looks for a window in any visible frame already
+ displaying the buffer; if there is one, it returns that window and makes
+ it be selected within its frame. If there is none, it creates a new
+ frame and displays the buffer in it.
+
+ If @code{pop-up-frames} is @code{nil}, then @code{pop-to-buffer}
+ operates entirely within the selected frame. (If the selected frame has
+ just a minibuffer, @code{pop-to-buffer} operates within the most
+ recently selected frame that was not just a minibuffer.)
+
+ If the variable @code{pop-up-windows} is address@hidden, windows may
+ be split to create a new window that is different from the original
+ window. For details, see @ref{Choosing Window}.
+
+ If @var{other-window} is address@hidden, @code{pop-to-buffer} finds or
+ creates another window even if @var{buffer-or-name} is already visible
+ in the selected window. Thus @var{buffer-or-name} could end up
+ displayed in two windows. On the other hand, if @var{buffer-or-name} is
+ already displayed in the selected window and @var{other-window} is
+ @code{nil}, then the selected window is considered sufficient display
+ for @var{buffer-or-name}, so that nothing needs to be done.
+
+ All the variables that affect @code{display-buffer} affect
+ @code{pop-to-buffer} as well. @xref{Choosing Window}.
+
+ If @var{buffer-or-name} is a string that does not name an existing
+ buffer, a buffer by that name is created. The major mode for the new
+ buffer is set according to the variable @code{default-major-mode}.
+ @xref{Auto Major Mode}.
+
+ This function updates the buffer list just like @code{switch-to-buffer}
+ unless @var{norecord} is address@hidden
+ @end defun
+
+ @deffn Command replace-buffer-in-windows buffer-or-name
+ This function replaces @var{buffer-or-name} with some other buffer in all
+ windows displaying it. It chooses the other buffer with
+ @code{other-buffer}. In the usual applications of this function, you
+ don't care which other buffer is used; you just want to make sure that
+ @var{buffer-or-name} is no longer displayed.
+
+ This function returns @code{nil}.
+ @end deffn
+
+ @node Choosing Window
+ @section Choosing a Window for Display
+
+ This section describes the basic facility that chooses a window to
+ display a buffer address@hidden All the higher-level
+ functions and commands use this subroutine. Here we describe how to use
+ @code{display-buffer} and how to customize it.
+
+ @deffn Command display-buffer buffer-or-name &optional not-this-window frame
+ This command makes @var{buffer-or-name} appear in some window, like
+ @code{pop-to-buffer}, but it does not select that window and does not
+ make the buffer current. The identity of the selected window is
+ unaltered by this function. @var{buffer-or-name} must be a buffer, or
+ the name of an existing buffer.
+
+ If @var{not-this-window} is address@hidden, it means to display the
+ specified buffer in a window other than the selected one, even if it is
+ already on display in the selected window. This can cause the buffer to
+ appear in two windows at once. Otherwise, if @var{buffer-or-name} is
+ already being displayed in any window, that is good enough, so this
+ function does nothing.
+
+ @code{display-buffer} returns the window chosen to display
+ @var{buffer-or-name}.
+
+ If the argument @var{frame} is address@hidden, it specifies which frames
+ to check when deciding whether the buffer is already displayed. If the
+ buffer is already displayed in some window on one of these frames,
+ @code{display-buffer} simply returns that window. Here are the possible
+ values of @var{frame}:
+
+ @itemize @bullet
+ @item
+ If it is @code{nil}, consider windows on the selected frame.
+ (Actually, the last non-minibuffer frame.)
+ @item
+ If it is @code{t}, consider windows on all frames.
+ @item
+ If it is @code{visible}, consider windows on all visible frames.
+ @item
+ If it is 0, consider windows on all visible or iconified frames.
+ @item
+ If it is a frame, consider windows on that frame.
+ @end itemize
+
+ Precisely how @code{display-buffer} finds or creates a window depends on
+ the variables described below.
+ @end deffn
+
+ @defopt display-buffer-reuse-frames
+ If this variable is address@hidden, @code{display-buffer} searches
+ existing frames for a window displaying the buffer. If the buffer is
+ already displayed in a window in some frame, @code{display-buffer} makes
+ the frame visible and raises it, to use that window. If the buffer is
+ not already displayed, or if @code{display-buffer-reuse-frames} is
+ @code{nil}, @code{display-buffer}'s behavior is determined by other
+ variables, described below.
+ @end defopt
+
+ @defopt pop-up-windows
+ This variable controls whether @code{display-buffer} makes new windows.
+ If it is address@hidden and there is only one window, then that window
+ is split. If it is @code{nil}, then @code{display-buffer} does not
+ split the single window, but uses it whole.
+ @end defopt
+
+ @defopt split-height-threshold
+ This variable determines when @code{display-buffer} may split a window,
+ if there are multiple windows. @code{display-buffer} always splits the
+ largest window if it has at least this many lines. If the largest
+ window is not this tall, it is split only if it is the sole window and
+ @code{pop-up-windows} is address@hidden
+ @end defopt
+
+ @defopt even-window-heights
+ This variable determines if @code{display-buffer} should even out window
+ heights if the buffer gets displayed in an existing window, above or
+ beneath another existing window. If @code{even-window-heights} is
+ @code{t}, the default, window heights will be evened out. If
+ @code{even-window-heights} is @code{nil}, the original window heights
+ will be left alone.
+ @end defopt
+
+ @c Emacs 19 feature
+ @defopt pop-up-frames
+ This variable controls whether @code{display-buffer} makes new frames.
+ If it is address@hidden, @code{display-buffer} looks for an existing
+ window already displaying the desired buffer, on any visible frame. If
+ it finds one, it returns that window. Otherwise it makes a new frame.
+ The variables @code{pop-up-windows} and @code{split-height-threshold} do
+ not matter if @code{pop-up-frames} is address@hidden
+
+ If @code{pop-up-frames} is @code{nil}, then @code{display-buffer} either
+ splits a window or reuses one.
+
+ @xref{Frames}, for more information.
+ @end defopt
+
+ @c Emacs 19 feature
+ @defopt pop-up-frame-function
+ This variable specifies how to make a new frame if @code{pop-up-frames}
+ is address@hidden
+
+ Its value should be a function of no arguments. When
+ @code{display-buffer} makes a new frame, it does so by calling that
+ function, which should return a frame. The default value of the
+ variable is a function that creates a frame using parameters from
+ @code{pop-up-frame-alist}.
+ @end defopt
+
+ @defopt pop-up-frame-alist
+ This variable holds an alist specifying frame parameters used when
+ @code{display-buffer} makes a new frame. @xref{Frame Parameters}, for
+ more information about frame parameters.
+ @end defopt
+
+ @defopt special-display-buffer-names
+ A list of buffer names for buffers that should be displayed specially.
+ If the buffer's name is in this list, @code{display-buffer} handles the
+ buffer specially.
+
+ By default, special display means to give the buffer a dedicated frame.
+
+ If an element is a list, instead of a string, then the @sc{car} of the
+ list is the buffer name, and the rest of the list says how to create
+ the frame. There are two possibilities for the rest of the list (its
+ @sc{cdr}). It can be an alist, specifying frame parameters, or it can
+ contain a function and arguments to give to it. (The function's first
+ argument is always the buffer to be displayed; the arguments from the
+ list come after that.)
+
+ For example:
+
+ @example
+ (("myfile" (minibuffer) (menu-bar-lines . 0)))
+ @end example
+
+ @noindent
+ specifies to display a buffer named @samp{myfile} in a dedicated frame
+ with specified @code{minibuffer} and @code{menu-bar-lines} parameters.
+
+ The list of frame parameters can also use the phony frame parameters
+ @code{same-frame} and @code{same-window}. If the specified frame
+ parameters include @code{(same-window . @var{value})} and @var{value}
+ is address@hidden, that means to display the buffer in the current
+ selected window. Otherwise, if they include @code{(same-frame .
+ @var{value})} and @var{value} is address@hidden, that means to display
+ the buffer in a new window in the currently selected frame.
+ @end defopt
+
+ @defopt special-display-regexps
+ A list of regular expressions that specify buffers that should be
+ displayed specially. If the buffer's name matches any of the regular
+ expressions in this list, @code{display-buffer} handles the buffer
+ specially.
+
+ By default, special display means to give the buffer a dedicated frame.
+
+ If an element is a list, instead of a string, then the @sc{car} of the
+ list is the regular expression, and the rest of the list says how to
+ create the frame. See above, under @code{special-display-buffer-names}.
+ @end defopt
+
+ @defun special-display-p buffer-name
+ This function returns address@hidden if displaying a buffer
+ named @var{buffer-name} with @code{display-buffer} would
+ create a special frame. The value is @code{t} if it would
+ use the default frame parameters, or else the specified list
+ of frame parameters.
+ @end defun
+
+ @defvar special-display-function
+ This variable holds the function to call to display a buffer specially.
+ It receives the buffer as an argument, and should return the window in
+ which it is displayed.
+
+ The default value of this variable is
+ @code{special-display-popup-frame}.
+ @end defvar
+
+ @defun special-display-popup-frame buffer &optional args
+ This function makes @var{buffer} visible in a frame of its own. If
+ @var{buffer} is already displayed in a window in some frame, it makes
+ the frame visible and raises it, to use that window. Otherwise, it
+ creates a frame that will be dedicated to @var{buffer}. This
+ function returns the window it used.
+
+ If @var{args} is an alist, it specifies frame parameters for the new
+ frame.
+
+ If @var{args} is a list whose @sc{car} is a symbol, then @code{(car
+ @var{args})} is called as a function to actually create and set up the
+ frame; it is called with @var{buffer} as first argument, and @code{(cdr
+ @var{args})} as additional arguments.
+
+ This function always uses an existing window displaying @var{buffer},
+ whether or not it is in a frame of its own; but if you set up the above
+ variables in your init file, before @var{buffer} was created, then
+ presumably the window was previously made by this function.
+ @end defun
+
+ @defopt special-display-frame-alist
+ @anchor{Definition of special-display-frame-alist}
+ This variable holds frame parameters for
+ @code{special-display-popup-frame} to use when it creates a frame.
+ @end defopt
+
+ @defopt same-window-buffer-names
+ A list of buffer names for buffers that should be displayed in the
+ selected window. If the buffer's name is in this list,
+ @code{display-buffer} handles the buffer by switching to it in the
+ selected window.
+ @end defopt
+
+ @defopt same-window-regexps
+ A list of regular expressions that specify buffers that should be
+ displayed in the selected window. If the buffer's name matches any of
+ the regular expressions in this list, @code{display-buffer} handles the
+ buffer by switching to it in the selected window.
+ @end defopt
+
+ @defun same-window-p buffer-name
+ This function returns @code{t} if displaying a buffer
+ named @var{buffer-name} with @code{display-buffer} would
+ put it in the selected window.
+ @end defun
+
+ @c Emacs 19 feature
+ @defvar display-buffer-function
+ This variable is the most flexible way to customize the behavior of
+ @code{display-buffer}. If it is address@hidden, it should be a function
+ that @code{display-buffer} calls to do the work. The function should
+ accept two arguments, the first two arguments that @code{display-buffer}
+ received. It should choose or create a window, display the specified
+ buffer in it, and then return the window.
+
+ This hook takes precedence over all the other options and hooks
+ described above.
+ @end defvar
+
+ @c Emacs 19 feature
+ @cindex dedicated window
+ A window can be marked as ``dedicated'' to its buffer. Then
+ @code{display-buffer} will not try to use that window to display any
+ other buffer.
+
+ @defun window-dedicated-p window
+ This function returns address@hidden if @var{window} is marked as
+ dedicated; otherwise @code{nil}.
+ @end defun
+
+ @defun set-window-dedicated-p window flag
+ This function marks @var{window} as dedicated if @var{flag} is
+ address@hidden, and nondedicated otherwise.
+ @end defun
+
+ @node Window Point
+ @section Windows and Point
+ @cindex window position
+ @cindex window point
+ @cindex position in window
+ @cindex point in window
+
+ Each window has its own value of point, independent of the value of
+ point in other windows displaying the same buffer. This makes it useful
+ to have multiple windows showing one buffer.
+
+ @itemize @bullet
+ @item
+ The window point is established when a window is first created; it is
+ initialized from the buffer's point, or from the window point of another
+ window opened on the buffer if such a window exists.
+
+ @item
+ Selecting a window sets the value of point in its buffer from the
+ window's value of point. Conversely, deselecting a window sets the
+ window's value of point from that of the buffer. Thus, when you switch
+ between windows that display a given buffer, the point value for the
+ selected window is in effect in the buffer, while the point values for
+ the other windows are stored in those windows.
+
+ @item
+ As long as the selected window displays the current buffer, the window's
+ point and the buffer's point always move together; they remain equal.
+
+ @item
+ @xref{Positions}, for more details on buffer positions.
+ @end itemize
+
+ As far as the user is concerned, point is where the cursor is, and
+ when the user switches to another buffer, the cursor jumps to the
+ position of point in that buffer.
+
+ @defun window-point &optional window
+ This function returns the current position of point in @var{window}.
+ For a nonselected window, this is the value point would have (in that
+ window's buffer) if that window were selected. If @var{window} is
+ @code{nil}, the selected window is used.
+
+ When @var{window} is the selected window and its buffer is also the
+ current buffer, the value returned is the same as point in that buffer.
+
+ Strictly speaking, it would be more correct to return the
+ ``top-level'' value of point, outside of any @code{save-excursion}
+ forms. But that value is hard to find.
+ @end defun
+
+ @defun set-window-point window position
+ This function positions point in @var{window} at position
+ @var{position} in @var{window}'s buffer. It returns @var{position}.
+ @end defun
+
+ @node Window Start
+ @section The Window Start Position
+
+ Each window contains a marker used to keep track of a buffer position
+ that specifies where in the buffer display should start. This position
+ is called the @dfn{display-start} position of the window (or just the
+ @dfn{start}). The character after this position is the one that appears
+ at the upper left corner of the window. It is usually, but not
+ inevitably, at the beginning of a text line.
+
+ @defun window-start &optional window
+ @cindex window top line
+ This function returns the display-start position of window
+ @var{window}. If @var{window} is @code{nil}, the selected window is
+ used. For example,
+
+ @example
+ @group
+ (window-start)
+ @result{} 7058
+ @end group
+ @end example
+
+ When you create a window, or display a different buffer in it, the
+ display-start position is set to a display-start position recently used
+ for the same buffer, or 1 if the buffer doesn't have any.
+
+ Redisplay updates the window-start position (if you have not specified
+ it explicitly since the previous redisplay)---for example, to make sure
+ point appears on the screen. Nothing except redisplay automatically
+ changes the window-start position; if you move point, do not expect the
+ window-start position to change in response until after the next
+ redisplay.
+
+ For a realistic example of using @code{window-start}, see the
+ description of @code{count-lines}. @xref{Definition of count-lines}.
+ @end defun
+
+ @defun window-end &optional window update
+ This function returns the position of the end of the display in window
+ @var{window}. If @var{window} is @code{nil}, the selected window is
+ used.
+
+ Simply changing the buffer text or moving point does not update the
+ value that @code{window-end} returns. The value is updated only when
+ Emacs redisplays and redisplay completes without being preempted.
+
+ If the last redisplay of @var{window} was preempted, and did not finish,
+ Emacs does not know the position of the end of display in that window.
+ In that case, this function returns @code{nil}.
+
+ If @var{update} is address@hidden, @code{window-end} always returns an
+ up-to-date value for where the window ends, based on the current
+ @code{window-start} value. If the saved value is valid,
+ @code{window-end} returns that; otherwise it computes the correct
+ value by scanning the buffer text.
+
+ Even if @var{update} is address@hidden, @code{window-end} does not
+ attempt to scroll the display if point has moved off the screen, the
+ way real redisplay would do. It does not alter the
+ @code{window-start} value. In effect, it reports where the displayed
+ text will end if scrolling is not required.
+ @end defun
+
+ @defun set-window-start window position &optional noforce
+ This function sets the display-start position of @var{window} to
+ @var{position} in @var{window}'s buffer. It returns @var{position}.
+
+ The display routines insist that the position of point be visible when a
+ buffer is displayed. Normally, they change the display-start position
+ (that is, scroll the window) whenever necessary to make point visible.
+ However, if you specify the start position with this function using
+ @code{nil} for @var{noforce}, it means you want display to start at
+ @var{position} even if that would put the location of point off the
+ screen. If this does place point off screen, the display routines move
+ point to the left margin on the middle line in the window.
+
+ For example, if point @w{is 1} and you set the start of the window @w{to
+ 2}, then point would be ``above'' the top of the window. The display
+ routines will automatically move point if it is still 1 when redisplay
+ occurs. Here is an example:
+
+ @example
+ @group
+ ;; @r{Here is what @samp{foo} looks like before executing}
+ ;; @r{the @code{set-window-start} expression.}
+ @end group
+
+ @group
+ ---------- Buffer: foo ----------
+ @point{}This is the contents of buffer foo.
+ 2
+ 3
+ 4
+ 5
+ 6
+ ---------- Buffer: foo ----------
+ @end group
+
+ @group
+ (set-window-start
+ (selected-window)
+ (1+ (window-start)))
+ @result{} 2
+ @end group
+
+ @group
+ ;; @r{Here is what @samp{foo} looks like after executing}
+ ;; @r{the @code{set-window-start} expression.}
+ ---------- Buffer: foo ----------
+ his is the contents of buffer foo.
+ 2
+ 3
+ @point{}4
+ 5
+ 6
+ ---------- Buffer: foo ----------
+ @end group
+ @end example
+
+ If @var{noforce} is address@hidden, and @var{position} would place point
+ off screen at the next redisplay, then redisplay computes a new window-start
+ position that works well with point, and thus @var{position} is not used.
+ @end defun
+
+ @defun pos-visible-in-window-p &optional position window partially
+ This function returns address@hidden if @var{position} is within the
+ range of text currently visible on the screen in @var{window}. It
+ returns @code{nil} if @var{position} is scrolled vertically out of
+ view. Locations that are partially obscured are not considered
+ visible unless @var{partially} is address@hidden The argument
+ @var{position} defaults to the current position of point in
+ @var{window}; @var{window}, to the selected window.
+
+ The @code{pos-visible-in-window-p} function considers only vertical
+ scrolling. If @var{position} is out of view only because @var{window}
+ has been scrolled horizontally, @code{pos-visible-in-window-p} returns
+ address@hidden anyway. @xref{Horizontal Scrolling}.
+
+ If @var{position} is visible, @code{pos-visible-in-window-p} returns
+ @code{t} if @var{partially} is @code{nil}; if @var{partially} is
+ address@hidden, it returns a list of the form @code{(@var{x} @var{y}
+ @var{fully})}, where @var{x} and @var{y} are the pixel coordinates
+ relative to the top left corner of the window, and @var{fully} is
+ @code{t} if the character after @var{position} is fully visible and
+ @code{nil} otherwise.
+
+ Here is an example:
+
+ @example
+ @group
+ (or (pos-visible-in-window-p
+ (point) (selected-window))
+ (recenter 0))
+ @end group
+ @end example
+ @end defun
+
+ @node Textual Scrolling
+ @section Textual Scrolling
+ @cindex textual scrolling
+ @cindex scrolling textually
+
+ @dfn{Textual scrolling} means moving the text up or down through a
+ window. It works by changing the value of the window's display-start
+ location. It may also change the value of @code{window-point} to keep
+ point on the screen.
+
+ Textual scrolling was formerly called ``vertical scrolling,'' but we
+ changed its name to distinguish it from the new vertical fractional
+ scrolling feature (@pxref{Vertical Scrolling}).
+
+ In the commands @code{scroll-up} and @code{scroll-down}, the directions
+ ``up'' and ``down'' refer to the motion of the text in the buffer at which
+ you are looking through the window. Imagine that the text is
+ written on a long roll of paper and that the scrolling commands move the
+ paper up and down. Thus, if you are looking at text in the middle of a
+ buffer and repeatedly call @code{scroll-down}, you will eventually see
+ the beginning of the buffer.
+
+ Some people have urged that the opposite convention be used: they
+ imagine that the window moves over text that remains in place. Then
+ ``down'' commands would take you to the end of the buffer. This view is
+ more consistent with the actual relationship between windows and the
+ text in the buffer, but it is less like what the user sees. The
+ position of a window on the terminal does not move, and short scrolling
+ commands clearly move the text up or down on the screen. We have chosen
+ names that fit the user's point of view.
+
+ The textual scrolling functions (aside from
+ @code{scroll-other-window}) have unpredictable results if the current
+ buffer is different from the buffer that is displayed in the selected
+ window. @xref{Current Buffer}.
+
+ @deffn Command scroll-up &optional count
+ This function scrolls the text in the selected window upward
+ @var{count} lines. If @var{count} is negative, scrolling is actually
+ downward.
+
+ If @var{count} is @code{nil} (or omitted), then the length of scroll
+ is @code{next-screen-context-lines} lines less than the usable height of
+ the window (not counting its mode line).
+
+ @code{scroll-up} returns @code{nil}, unless it gets an error
+ because it can't scroll any further.
+ @end deffn
+
+ @deffn Command scroll-down &optional count
+ This function scrolls the text in the selected window downward
+ @var{count} lines. If @var{count} is negative, scrolling is actually
+ upward.
+
+ If @var{count} is omitted or @code{nil}, then the length of the scroll
+ is @code{next-screen-context-lines} lines less than the usable height of
+ the window (not counting its mode line).
+
+ @code{scroll-down} returns @code{nil}, unless it gets an error because
+ it can't scroll any further.
+ @end deffn
+
+ @deffn Command scroll-other-window &optional count
+ This function scrolls the text in another window upward @var{count}
+ lines. Negative values of @var{count}, or @code{nil}, are handled
+ as in @code{scroll-up}.
+
+ You can specify which buffer to scroll by setting the variable
+ @code{other-window-scroll-buffer} to a buffer. If that buffer isn't
+ already displayed, @code{scroll-other-window} displays it in some
+ window.
+
+ When the selected window is the minibuffer, the next window is normally
+ the one at the top left corner. You can specify a different window to
+ scroll, when the minibuffer is selected, by setting the variable
+ @code{minibuffer-scroll-window}. This variable has no effect when any
+ other window is selected. When it is address@hidden and the
+ minibuffer is selected, it takes precedence over
+ @code{other-window-scroll-buffer}. @xref{Definition of
+ minibuffer-scroll-window}.
+
+ When the minibuffer is active, it is the next window if the selected
+ window is the one at the bottom right corner. In this case,
+ @code{scroll-other-window} attempts to scroll the minibuffer. If the
+ minibuffer contains just one line, it has nowhere to scroll to, so the
+ line reappears after the echo area momentarily displays the message
+ ``Beginning of buffer''.
+ @end deffn
+
+ @c Emacs 19 feature
+ @defvar other-window-scroll-buffer
+ If this variable is address@hidden, it tells @code{scroll-other-window}
+ which buffer to scroll.
+ @end defvar
+
+ @defopt scroll-margin
+ This option specifies the size of the scroll margin---a minimum number
+ of lines between point and the top or bottom of a window. Whenever
+ point gets within this many lines of the top or bottom of the window,
+ redisplay scrolls the text automatically (if possible) to move point
+ out of the margin, closer to the center of the window.
+ @end defopt
+
+ @defopt scroll-conservatively
+ This variable controls how scrolling is done automatically when point
+ moves off the screen (or into the scroll margin). If the value is a
+ positive integer @var{n}, then redisplay scrolls the text up to
+ @var{n} lines in either direction, if that will bring point back into
+ proper view. This action is called @dfn{conservative scrolling}.
+ Otherwise, scrolling happens in the usual way, under the control of
+ other variables such as @code{scroll-up-aggressively} and
+ @code{scroll-down-aggressively}.
+
+ The default value is zero, which means that conservative scrolling
+ never happens.
+ @end defopt
+
+ @defopt scroll-down-aggressively
+ @tindex scroll-down-aggressively
+ The value of this variable should be either @code{nil} or a fraction
+ @var{f} between 0 and 1. If it is a fraction, that specifies where on
+ the screen to put point when scrolling down. More precisely, when a
+ window scrolls down because point is above the window start, the new
+ start position is chosen to put point @var{f} part of the window
+ height from the top. The larger @var{f}, the more aggressive the
+ scrolling.
+
+ A value of @code{nil} is equivalent to .5, since its effect is to center
+ point. This variable automatically becomes buffer-local when set in any
+ fashion.
+ @end defopt
+
+ @defopt scroll-up-aggressively
+ @tindex scroll-up-aggressively
+ Likewise, for scrolling up. The value, @var{f}, specifies how far
+ point should be placed from the bottom of the window; thus, as with
+ @code{scroll-up-aggressively}, a larger value scrolls more aggressively.
+ @end defopt
+
+ @defopt scroll-step
+ This variable is an older variant of @code{scroll-conservatively}. The
+ difference is that it if its value is @var{n}, that permits scrolling
+ only by precisely @var{n} lines, not a smaller number. This feature
+ does not work with @code{scroll-margin}. The default value is zero.
+ @end defopt
+
+ @defopt scroll-preserve-screen-position
+ If this option is address@hidden, the scroll functions move point so
+ that the vertical position of the cursor is unchanged, when that is
+ possible.
+ @end defopt
+
+ @defopt next-screen-context-lines
+ The value of this variable is the number of lines of continuity to
+ retain when scrolling by full screens. For example, @code{scroll-up}
+ with an argument of @code{nil} scrolls so that this many lines at the
+ bottom of the window appear instead at the top. The default value is
+ @code{2}.
+ @end defopt
+
+ @deffn Command recenter &optional count
+ @cindex centering point
+ This function scrolls the text in the selected window so that point is
+ displayed at a specified vertical position within the window. It does
+ not ``move point'' with respect to the text.
+
+ If @var{count} is a nonnegative number, that puts the line containing
+ point @var{count} lines down from the top of the window. If
+ @var{count} is a negative number, then it counts upward from the
+ bottom of the window, so that @minus{}1 stands for the last usable
+ line in the window. If @var{count} is a address@hidden list, then it
+ stands for the line in the middle of the window.
+
+ If @var{count} is @code{nil}, @code{recenter} puts the line containing
+ point in the middle of the window, then clears and redisplays the entire
+ selected frame.
+
+ When @code{recenter} is called interactively, @var{count} is the raw
+ prefix argument. Thus, typing @kbd{C-u} as the prefix sets the
+ @var{count} to a address@hidden list, while typing @kbd{C-u 4} sets
+ @var{count} to 4, which positions the current line four lines from the
+ top.
+
+ With an argument of zero, @code{recenter} positions the current line at
+ the top of the window. This action is so handy that some people make a
+ separate key binding to do this. For example,
+
+ @example
+ @group
+ (defun line-to-top-of-window ()
+ "Scroll current line to top of window.
+ Replaces three keystroke sequence C-u 0 C-l."
+ (interactive)
+ (recenter 0))
+
+ (global-set-key [kp-multiply] 'line-to-top-of-window)
+ @end group
+ @end example
+ @end deffn
+
+ @node Vertical Scrolling
+ @section Vertical Fractional Scrolling
+ @cindex Vertical Fractional Scrolling
+
+ @dfn{Vertical fractional scrolling} means shifting the image in the
+ window up or down by a specified multiple or fraction of a line.
+ Starting in Emacs 21, each window has a @dfn{vertical scroll position},
+ which is a number, never less than zero. It specifies how far to raise
+ the contents of the window. Raising the window contents generally makes
+ all or part of some lines disappear off the top, and all or part of some
+ other lines appear at the bottom. The usual value is zero.
+
+ The vertical scroll position is measured in units of the normal line
+ height, which is the height of the default font. Thus, if the value is
+ .5, that means the window contents are scrolled up half the normal line
+ height. If it is 3.3, that means the window contents are scrolled up
+ somewhat over three times the normal line height.
+
+ What fraction of a line the vertical scrolling covers, or how many
+ lines, depends on what the lines contain. A value of .5 could scroll a
+ line whose height is very short off the screen, while a value of 3.3
+ could scroll just part of the way through a tall line or an image.
+
+ @defun window-vscroll &optional window pixels-p
+ This function returns the current vertical scroll position of
+ @var{window}. If @var{window} is @code{nil}, the selected window is
+ used. If @var{pixels-p} is address@hidden, the return value is
+ measured in pixels, rather than in units of the normal line height.
+
+ @example
+ @group
+ (window-vscroll)
+ @result{} 0
+ @end group
+ @end example
+ @end defun
+
+ @defun set-window-vscroll window lines &optional pixels-p
+ This function sets @var{window}'s vertical scroll position to
+ @var{lines}. The argument @var{lines} should be zero or positive; if
+ not, it is taken as zero.
+
+ If @var{window} is @code{nil}, the selected window is used.
+
+ The actual vertical scroll position must always correspond
+ to an integral number of pixels, so the value you specify
+ is rounded accordingly.
+
+ The return value is the result of this rounding.
+
+ @example
+ @group
+ (set-window-vscroll (selected-window) 1.2)
+ @result{} 1.13
+ @end group
+ @end example
+
+ If @var{pixels-p} is address@hidden, @var{lines} specifies a number of
+ pixels. In this case, the return value is @var{lines}.
+ @end defun
+
+ @node Horizontal Scrolling
+ @section Horizontal Scrolling
+ @cindex horizontal scrolling
+
+ @dfn{Horizontal scrolling} means shifting the image in the window left
+ or right by a specified multiple of the normal character width. Each
+ window has a @dfn{horizontal scroll position}, which is a number, never
+ less than zero. It specifies how far to shift the contents left.
+ Shifting the window contents left generally makes all or part of some
+ characters disappear off the left, and all or part of some other
+ characters appear at the right. The usual value is zero.
+
+ The horizontal scroll position is measured in units of the normal
+ character width, which is the width of space in the default font. Thus,
+ if the value is 5, that means the window contents are scrolled left by 5
+ times the normal character width. How many characters actually
+ disappear off to the left depends on their width, and could vary from
+ line to line.
+
+ Because we read from side to side in the ``inner loop'', and from top
+ to bottom in the ``outer loop'', the effect of horizontal scrolling is
+ not like that of textual or vertical scrolling. Textual scrolling
+ involves selection of a portion of text to display, and vertical
+ scrolling moves the window contents contiguously; but horizontal
+ scrolling causes part of @emph{each line} to go off screen.
+
+ Usually, no horizontal scrolling is in effect; then the leftmost
+ column is at the left edge of the window. In this state, scrolling to
+ the right is meaningless, since there is no data to the left of the edge
+ to be revealed by it; so this is not allowed. Scrolling to the left is
+ allowed; it scrolls the first columns of text off the edge of the window
+ and can reveal additional columns on the right that were truncated
+ before. Once a window has a nonzero amount of leftward horizontal
+ scrolling, you can scroll it back to the right, but only so far as to
+ reduce the net horizontal scroll to zero. There is no limit to how far
+ left you can scroll, but eventually all the text will disappear off the
+ left edge.
+
+ @vindex auto-hscroll-mode
+ If @code{auto-hscroll-mode} is set, redisplay automatically alters
+ the horizontal scrolling of a window as necessary to ensure that point
+ is always visible. However, you can still set the horizontal
+ scrolling value explicitly. The value you specify serves as a lower
+ bound for automatic scrolling, i.e. automatic scrolling will not
+ scroll a window to a column less than the specified one.
+
+ @deffn Command scroll-left &optional count
+ This function scrolls the selected window @var{count} columns to the
+ left (or to the right if @var{count} is negative). The default
+ for @var{count} is the window width, minus 2.
+
+ The return value is the total amount of leftward horizontal scrolling in
+ effect after the change---just like the value returned by
+ @code{window-hscroll} (below).
+ @end deffn
+
+ @deffn Command scroll-right &optional count
+ This function scrolls the selected window @var{count} columns to the
+ right (or to the left if @var{count} is negative). The default
+ for @var{count} is the window width, minus 2.
+
+ The return value is the total amount of leftward horizontal scrolling in
+ effect after the change---just like the value returned by
+ @code{window-hscroll} (below).
+
+ Once you scroll a window as far right as it can go, back to its normal
+ position where the total leftward scrolling is zero, attempts to scroll
+ any farther right have no effect.
+ @end deffn
+
+ @defun window-hscroll &optional window
+ This function returns the total leftward horizontal scrolling of
+ @var{window}---the number of columns by which the text in @var{window}
+ is scrolled left past the left margin.
+
+ The value is never negative. It is zero when no horizontal scrolling
+ has been done in @var{window} (which is usually the case).
+
+ If @var{window} is @code{nil}, the selected window is used.
+
+ @example
+ @group
+ (window-hscroll)
+ @result{} 0
+ @end group
+ @group
+ (scroll-left 5)
+ @result{} 5
+ @end group
+ @group
+ (window-hscroll)
+ @result{} 5
+ @end group
+ @end example
+ @end defun
+
+ @defun set-window-hscroll window columns
+ This function sets horizontal scrolling of @var{window}. The value of
+ @var{columns} specifies the amount of scrolling, in terms of columns
+ from the left margin. The argument @var{columns} should be zero or
+ positive; if not, it is taken as zero. Fractional values of
+ @var{columns} are not supported at present.
+
+ Note that @code{set-window-hscroll} may appear not to work if you test
+ it by evaluating a call with @kbd{M-:} in a simple way. What happens
+ is that the function sets the horizontal scroll value and returns, but
+ then redisplay adjusts the horizontal scrolling to make point visible,
+ and this overrides what the function did. You can observe the
+ function's effect if you call it while point is sufficiently far from
+ the left margin that it will remain visible.
+
+ The value returned is @var{columns}.
+
+ @example
+ @group
+ (set-window-hscroll (selected-window) 10)
+ @result{} 10
+ @end group
+ @end example
+ @end defun
+
+ Here is how you can determine whether a given position @var{position}
+ is off the screen due to horizontal scrolling:
+
+ @example
+ @group
+ (defun hscroll-on-screen (window position)
+ (save-excursion
+ (goto-char position)
+ (and
+ (>= (- (current-column) (window-hscroll window)) 0)
+ (< (- (current-column) (window-hscroll window))
+ (window-width window)))))
+ @end group
+ @end example
+
+ @node Size of Window
+ @section The Size of a Window
+ @cindex window size
+ @cindex size of window
+
+ An Emacs window is rectangular, and its size information consists of
+ the height (the number of lines) and the width (the number of character
+ positions in each line). The mode line is included in the height. But
+ the width does not count the scroll bar or the column of @samp{|}
+ characters that separates side-by-side windows.
+
+ The following three functions return size information about a window:
+
+ @defun window-height &optional window
+ This function returns the number of lines in @var{window}, including
+ its mode line and header line, if any. If @var{window} fills its
+ entire frame except for the echo area, this is typically one less than
+ the value of @code{frame-height} on that frame.
+
+ If @var{window} is @code{nil}, the function uses the selected window.
+
+ @example
+ @group
+ (window-height)
+ @result{} 23
+ @end group
+ @group
+ (split-window-vertically)
+ @result{} #<window 4 on windows.texi>
+ @end group
+ @group
+ (window-height)
+ @result{} 11
+ @end group
+ @end example
+ @end defun
+
+ @tindex window-body-height
+ @defun window-body-height &optional window
+ Like @code{window-height} but the value does not include the
+ mode line (if any) or the header line (if any).
+ @end defun
+
+ @defun window-width &optional window
+ This function returns the number of columns in @var{window}. If
+ @var{window} fills its entire frame, this is the same as the value of
+ @code{frame-width} on that frame. The width does not include the
+ window's scroll bar or the column of @samp{|} characters that separates
+ side-by-side windows.
+
+ If @var{window} is @code{nil}, the function uses the selected window.
+
+ @example
+ @group
+ (window-width)
+ @result{} 80
+ @end group
+ @end example
+ @end defun
+
+ @defun window-edges &optional window
+ This function returns a list of the edge coordinates of @var{window}.
+ If @var{window} is @code{nil}, the selected window is used.
+
+ The order of the list is @code{(@var{left} @var{top} @var{right}
+ @var{bottom})}, all elements relative to 0, 0 at the top left corner of
+ the frame. The element @var{right} of the value is one more than the
+ rightmost column used by @var{window}, and @var{bottom} is one more than
+ the bottommost row used by @var{window} and its mode-line.
+
+ The edges include the space used by the window's scroll bar, display
+ margins, fringes, header line, and mode line, if it has them. Also,
+ if the window has a neighbor on the right, its right edge value
+ includes the width of the separator line between the window and that
+ neighbor. Since the width of the window does not include this
+ separator, the width does not usually equal the difference between the
+ right and left edges.
+ @end defun
+
+ @defun window-inside-edges &optional window
+ This is similar to @code{window-edges}, but the edge values
+ it returns include only the text area of the window. They
+ do not include the header line, mode line, scroll bar or
+ vertical separator, fringes, or display margins.
+ @end defun
+
+ Here are the results obtained on a typical 24-line terminal with just
+ one window, with menu bar enabled:
+
+ @example
+ @group
+ (window-edges (selected-window))
+ @result{} (0 1 80 23)
+ @end group
+ @group
+ (window-inside-edges (selected-window))
+ @result{} (0 1 80 22)
+ @end group
+ @end example
+
+ @noindent
+ The bottom edge is at line 23 because the last line is the echo area.
+ The bottom inside edge is at line 22, which is the window's mode line.
+
+ If @var{window} is at the upper left corner of its frame, and there is
+ no menu bar, then @var{bottom} returned by @code{window-edges} is the
+ same as the value of @code{(window-height)}, @var{right} is almost the
+ same as the value of @code{(window-width)}, and @var{top} and
+ @var{left} are zero. For example, the edges of the following window
+ are @address@hidden 0 8 5}}. Assuming that the frame has more than 8
+ columns, the last column of the window (column 7) holds a border
+ rather than text. The last row (row 4) holds the mode line, shown
+ here with @samp{xxxxxxxxx}.
+
+ @example
+ @group
+ 0
+ _______
+ 0 | |
+ | |
+ | |
+ | |
+ xxxxxxxxx 4
+
+ 7
+ @end group
+ @end example
+
+ In the following example, let's suppose that the frame is 7
+ columns wide. Then the edges of the left window are @address@hidden 0 4 3}}
+ and the edges of the right window are @address@hidden 0 7 3}}.
+ The inside edges of the left window are @address@hidden 0 3 2}},
+ and the inside edges of the right window are @address@hidden 0 7 2}},
+
+ @example
+ @group
+ ___ ___
+ | | |
+ | | |
+ xxxxxxxxx
+
+ 0 34 7
+ @end group
+ @end example
+
+ @defun window-pixel-edges &optional window
+ This function is like @code{window-edges} except that, on a graphical
+ display, the edge values are measured in pixels instead of in
+ character lines and columns.
+ @end defun
+
+ @defun window-inside-pixel-edges &optional window
+ This function is like @code{window-inside-edges} except that, on a
+ graphical display, the edge values are measured in pixels instead of
+ in character lines and columns.
+ @end defun
+
+ @node Resizing Windows
+ @section Changing the Size of a Window
+ @cindex window resizing
+ @cindex changing window size
+ @cindex window size, changing
+
+ The window size functions fall into two classes: high-level commands
+ that change the size of windows and low-level functions that access
+ window size. Emacs does not permit overlapping windows or gaps between
+ windows, so resizing one window affects other windows.
+
+ @deffn Command enlarge-window size &optional horizontal
+ This function makes the selected window @var{size} lines taller,
+ stealing lines from neighboring windows. It takes the lines from one
+ window at a time until that window is used up, then takes from another.
+ If a window from which lines are stolen shrinks below
+ @code{window-min-height} lines, that window disappears.
+
+ If @var{horizontal} is address@hidden, this function makes
+ @var{window} wider by @var{size} columns, stealing columns instead of
+ lines. If a window from which columns are stolen shrinks below
+ @code{window-min-width} columns, that window disappears.
+
+ If the requested size would exceed that of the window's frame, then the
+ function makes the window occupy the entire height (or width) of the
+ frame.
+
+ If there are various other windows from which lines or columns can be
+ stolen, and some of them specify fixed size (using
+ @code{window-size-fixed}, see below), they are left untouched while
+ other windows are ``robbed.'' If it would be necessary to alter the
+ size of a fixed-size window, @code{enlarge-window} gets an error
+ instead.
+
+ If @var{size} is negative, this function shrinks the window by
+ @address@hidden lines or columns. If that makes the window smaller
+ than the minimum size (@code{window-min-height} and
+ @code{window-min-width}), @code{enlarge-window} deletes the window.
+
+ @code{enlarge-window} returns @code{nil}.
+ @end deffn
+
+ @deffn Command enlarge-window-horizontally columns
+ This function makes the selected window @var{columns} wider.
+ It could be defined as follows:
+
+ @example
+ @group
+ (defun enlarge-window-horizontally (columns)
+ (enlarge-window columns t))
+ @end group
+ @end example
+ @end deffn
+
+ @deffn Command shrink-window size &optional horizontal
+ This function is like @code{enlarge-window} but negates the argument
+ @var{size}, making the selected window smaller by giving lines (or
+ columns) to the other windows. If the window shrinks below
+ @code{window-min-height} or @code{window-min-width}, then it disappears.
+
+ If @var{size} is negative, the window is enlarged by @address@hidden
+ lines or columns.
+ @end deffn
+
+ @deffn Command shrink-window-horizontally columns
+ This function makes the selected window @var{columns} narrower.
+ It could be defined as follows:
+
+ @example
+ @group
+ (defun shrink-window-horizontally (columns)
+ (shrink-window columns t))
+ @end group
+ @end example
+ @end deffn
+
+ @deffn Command shrink-window-if-larger-than-buffer &optional window
+ This command shrinks @var{window} to be as small as possible while still
+ showing the full contents of its buffer---but not less than
+ @code{window-min-height} lines. If @var{window} is not given,
+ it defaults to the selected window.
+
+ However, the command does nothing if the window is already too small to
+ display the whole text of the buffer, or if part of the contents are
+ currently scrolled off screen, or if the window is not the full width of
+ its frame, or if the window is the only window in its frame.
+
+ This command returns address@hidden if it actually shrank the window
+ and @code{nil} otherwise.
+ @end deffn
+
+ @tindex window-size-fixed
+ @defvar window-size-fixed
+ If this variable is address@hidden, in any given buffer,
+ then the size of any window displaying the buffer remains fixed
+ unless you explicitly change it or Emacs has no other choice.
+ (This feature is new in Emacs 21.)
+
+ If the value is @code{height}, then only the window's height is fixed;
+ if the value is @code{width}, then only the window's width is fixed.
+ Any other address@hidden value fixes both the width and the height.
+
+ This variable automatically becomes buffer-local when set.
+
+ Explicit size-change functions such as @code{enlarge-window}
+ get an error if they would have to change a window size which is fixed.
+ Therefore, when you want to change the size of such a window,
+ you should bind @code{window-size-fixed} to @code{nil}, like this:
+
+ @example
+ (let ((window-size-fixed nil))
+ (enlarge-window 10))
+ @end example
+
+ Note that changing the frame size will change the size of a
+ fixed-size window, if there is no other alternative.
+ @end defvar
+
+ @cindex minimum window size
+ The following two variables constrain the window-structure-changing
+ functions to a minimum height and width.
+
+ @defopt window-min-height
+ The value of this variable determines how short a window may become
+ before it is automatically deleted. Making a window smaller than
+ @code{window-min-height} automatically deletes it, and no window may
+ be created shorter than this. The default value is 4.
+
+ The absolute minimum window height is one; actions that change window
+ sizes reset this variable to one if it is less than one.
+ @end defopt
+
+ @defopt window-min-width
+ The value of this variable determines how narrow a window may become
+ before it is automatically deleted. Making a window smaller than
+ @code{window-min-width} automatically deletes it, and no window may be
+ created narrower than this. The default value is 10.
+
+ The absolute minimum window width is two; actions that change window
+ sizes reset this variable to two if it is less than two.
+ @end defopt
+
+ @node Coordinates and Windows
+ @section Coordinates and Windows
+
+ This section describes how to relate screen coordinates to windows.
+
+ @defun window-at x y &optional frame
+ This function returns the window containing the specified cursor
+ position in the frame @var{frame}. The coordinates @var{x} and @var{y}
+ are measured in characters and count from the top left corner of the
+ frame. If they are out of range, @code{window-at} returns @code{nil}.
+
+ If you omit @var{frame}, the selected frame is used.
+ @end defun
+
+ @defun coordinates-in-window-p coordinates window
+ This function checks whether a particular frame position falls within
+ the window @var{window}.
+
+ The argument @var{coordinates} is a cons cell of the form @code{(@var{x}
+ . @var{y})}. The coordinates @var{x} and @var{y} are measured in
+ characters, and count from the top left corner of the screen or frame.
+
+ The value returned by @code{coordinates-in-window-p} is address@hidden
+ if the coordinates are inside @var{window}. The value also indicates
+ what part of the window the position is in, as follows:
+
+ @table @code
+ @item (@var{relx} . @var{rely})
+ The coordinates are inside @var{window}. The numbers @var{relx} and
+ @var{rely} are the equivalent window-relative coordinates for the
+ specified position, counting from 0 at the top left corner of the
+ window.
+
+ @item mode-line
+ The coordinates are in the mode line of @var{window}.
+
+ @item header-line
+ The coordinates are in the header line of @var{window}.
+
+ @item vertical-line
+ The coordinates are in the vertical line between @var{window} and its
+ neighbor to the right. This value occurs only if the window doesn't
+ have a scroll bar; positions in a scroll bar are considered outside the
+ window for these purposes.
+
+ @item left-fringe
+ @itemx right-fringe
+ The coordinates are in the left or right fringe of the window.
+
+ @item left-margin
+ @itemx right-margin
+ The coordinates are in the left or right margin of the window.
+
+ @item nil
+ The coordinates are not in any part of @var{window}.
+ @end table
+
+ The function @code{coordinates-in-window-p} does not require a frame as
+ argument because it always uses the frame that @var{window} is on.
+ @end defun
+
+ @node Window Configurations
+ @section Window Configurations
+ @cindex window configurations
+ @cindex saving window information
+
+ A @dfn{window configuration} records the entire layout of one
+ frame---all windows, their sizes, which buffers they contain, what
+ part of each buffer is displayed, and the values of point and the
+ mark; also their fringes, margins, and scroll bar settings. It also
+ includes the values of @code{window-min-height},
+ @code{window-min-width} and @code{minibuffer-scroll-window}. An
+ exception is made for point in the selected window for the current
+ buffer; its value is not saved in the window configuration.
+
+ You can bring back an entire previous layout by restoring a window
+ configuration previously saved. If you want to record all frames
+ instead of just one, use a frame configuration instead of a window
+ configuration. @xref{Frame Configurations}.
+
+ @defun current-window-configuration &optional frame
+ This function returns a new object representing @var{frame}'s current
+ window configuration. If @var{frame} is omitted, the selected frame
+ is used.
+ @end defun
+
+ @defun set-window-configuration configuration
+ This function restores the configuration of windows and buffers as
+ specified by @var{configuration}, for the frame that @var{configuration}
+ was created for.
+
+ The argument @var{configuration} must be a value that was previously
+ returned by @code{current-window-configuration}. This configuration is
+ restored in the frame from which @var{configuration} was made, whether
+ that frame is selected or not. This always counts as a window size
+ change and triggers execution of the @code{window-size-change-functions}
+ (@pxref{Window Hooks}), because @code{set-window-configuration} doesn't
+ know how to tell whether the new configuration actually differs from the
+ old one.
+
+ If the frame which @var{configuration} was saved from is dead, all this
+ function does is restore the three variables @code{window-min-height},
+ @code{window-min-width} and @code{minibuffer-scroll-window}. In this
+ case, the function returns @code{nil}. Otherwise, it returns @code{t}.
+
+ Here is a way of using this function to get the same effect
+ as @code{save-window-excursion}:
+
+ @example
+ @group
+ (let ((config (current-window-configuration)))
+ (unwind-protect
+ (progn (split-window-vertically nil)
+ @dots{})
+ (set-window-configuration config)))
+ @end group
+ @end example
+ @end defun
+
+ @defspec save-window-excursion address@hidden
+ This special form records the window configuration, executes @var{forms}
+ in sequence, then restores the earlier window configuration. The window
+ configuration includes, for each window, the value of point and the
+ portion of the buffer that is visible. It also includes the choice of
+ selected window. However, it does not include the value of point in
+ the current buffer; use @code{save-excursion} also, if you wish to
+ preserve that.
+
+ Don't use this construct when @code{save-selected-window} is sufficient.
+
+ Exit from @code{save-window-excursion} always triggers execution of the
+ @code{window-size-change-functions}. (It doesn't know how to tell
+ whether the restored configuration actually differs from the one in
+ effect at the end of the @var{forms}.)
+
+ The return value is the value of the final form in @var{forms}.
+ For example:
+
+ @example
+ @group
+ (split-window)
+ @result{} #<window 25 on control.texi>
+ @end group
+ @group
+ (setq w (selected-window))
+ @result{} #<window 19 on control.texi>
+ @end group
+ @group
+ (save-window-excursion
+ (delete-other-windows w)
+ (switch-to-buffer "foo")
+ 'do-something)
+ @result{} do-something
+ ;; @r{The screen is now split again.}
+ @end group
+ @end example
+ @end defspec
+
+ @defun window-configuration-p object
+ This function returns @code{t} if @var{object} is a window configuration.
+ @end defun
+
+ @defun compare-window-configurations config1 config2
+ This function compares two window configurations as regards the
+ structure of windows, but ignores the values of point and mark and the
+ saved scrolling positions---it can return @code{t} even if those
+ aspects differ.
+
+ The function @code{equal} can also compare two window configurations; it
+ regards configurations as unequal if they differ in any respect, even a
+ saved point or mark.
+ @end defun
+
+ @defun window-configuration-frame config
+ This function returns the frame for which the window configuration
+ @var{config} was made.
+ @end defun
+
+ Other primitives to look inside of window configurations would make
+ sense, but are not implemented because we did not need them. See the
+ file @file{winner.el} for some more operations on windows
+ configurations.
+
+ @node Window Hooks
+ @section Hooks for Window Scrolling and Changes
+
+ This section describes how a Lisp program can take action whenever a
+ window displays a different part of its buffer or a different buffer.
+ There are three actions that can change this: scrolling the window,
+ switching buffers in the window, and changing the size of the window.
+ The first two actions run @code{window-scroll-functions}; the last runs
+ @code{window-size-change-functions}. The paradigmatic use of these
+ hooks is in the implementation of Lazy Lock mode; see @file{lazy-lock.el}.
+
+ @defvar window-scroll-functions
+ This variable holds a list of functions that Emacs should call before
+ redisplaying a window with scrolling. It is not a normal hook, because
+ each function is called with two arguments: the window, and its new
+ display-start position.
+
+ Displaying a different buffer in the window also runs these functions.
+
+ These functions must be careful in using @code{window-end}
+ (@pxref{Window Start}); if you need an up-to-date value, you must use
+ the @var{update} argument to ensure you get it.
+ @end defvar
+
+ @defvar window-size-change-functions
+ This variable holds a list of functions to be called if the size of any
+ window changes for any reason. The functions are called just once per
+ redisplay, and just once for each frame on which size changes have
+ occurred.
+
+ Each function receives the frame as its sole argument. There is no
+ direct way to find out which windows on that frame have changed size, or
+ precisely how. However, if a size-change function records, at each
+ call, the existing windows and their sizes, it can also compare the
+ present sizes and the previous sizes.
+
+ Creating or deleting windows counts as a size change, and therefore
+ causes these functions to be called. Changing the frame size also
+ counts, because it changes the sizes of the existing windows.
+
+ It is not a good idea to use @code{save-window-excursion} (@pxref{Window
+ Configurations}) in these functions, because that always counts as a
+ size change, and it would cause these functions to be called over and
+ over. In most cases, @code{save-selected-window} (@pxref{Selecting
+ Windows}) is what you need here.
+ @end defvar
+
+ @defvar redisplay-end-trigger-functions
+ This abnormal hook is run whenever redisplay in a window uses text that
+ extends past a specified end trigger position. You set the end trigger
+ position with the function @code{set-window-redisplay-end-trigger}. The
+ functions are called with two arguments: the window, and the end trigger
+ position. Storing @code{nil} for the end trigger position turns off the
+ feature, and the trigger value is automatically reset to @code{nil} just
+ after the hook is run.
+ @end defvar
+
+ @defun set-window-redisplay-end-trigger window position
+ This function sets @var{window}'s end trigger position at
+ @var{position}.
+ @end defun
+
+ @defun window-redisplay-end-trigger &optional window
+ This function returns @var{window}'s current end trigger position.
+ If @var{window} is @code{nil} or omitted, it uses the selected window.
+ @end defun
+
+ @defvar window-configuration-change-hook
+ A normal hook that is run every time you change the window configuration
+ of an existing frame. This includes splitting or deleting windows,
+ changing the sizes of windows, or displaying a different buffer in a
+ window. The frame whose window configuration has changed is the
+ selected frame when this hook runs.
+ @end defvar
+
+ @ignore
+ arch-tag: 3f6c36e8-df49-4986-b757-417feed88be3
+ @end ignore
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