@c -*-texinfo-*- @c This is part of the GNU Emacs Lisp Reference Manual. @c Copyright (C) 1990-1995, 1998-1999, 2001-2014 Free Software @c Foundation, Inc. @c See the file elisp.texi for copying conditions. @node Windows @chapter Windows This chapter describes the functions and variables related to Emacs windows. @xref{Frames}, for how windows are assigned an area of screen available for Emacs to use. @xref{Display}, for information on how text is displayed in windows. @menu * Basic Windows:: Basic information on using windows. * Windows and Frames:: Relating windows to the frame they appear on. * Window Sizes:: Accessing a window's size. * Resizing Windows:: Changing the sizes of windows. * Splitting Windows:: Creating a new window. * Deleting Windows:: Removing a window from its frame. * Recombining Windows:: Preserving the frame layout when splitting and deleting 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. * Switching Buffers:: Higher-level functions for switching to a buffer. * Choosing Window:: How to choose a window for displaying a buffer. * Display Action Functions:: Subroutines for @code{display-buffer}. * Choosing Window Options:: Extra options affecting how buffers are displayed. * Window History:: Each window remembers the buffers displayed in it. * Dedicated Windows:: How to avoid displaying another buffer in a specific window. * Quitting Windows:: How to restore the state prior to displaying a buffer. * Window Point:: Each window has its own location of point. * Window Start and End:: Buffer positions indicating which text is on-screen in a 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. * Coordinates and Windows:: Converting coordinates to windows. * Window Configurations:: Saving and restoring the state of the screen. * Window Parameters:: Associating additional information with windows. * 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 A @dfn{window} is an area of the screen that is used to display a buffer (@pxref{Buffers}). In Emacs Lisp, windows are represented by a special Lisp object type. @cindex multiple windows Windows are grouped into frames (@pxref{Frames}). Each frame contains at least one window; the user can subdivide it into multiple, non-overlapping windows to view several buffers at once. Lisp programs can use multiple windows for a variety of purposes. In Rmail, for example, you can view a summary of message titles in one window, and the contents of the selected message in another window. @cindex terminal screen @cindex screen of terminal Emacs uses the word ``window'' with a different meaning than in graphical desktop environments and window systems, such as the X Window System. When Emacs is run on X, each of its graphical X windows is an Emacs frame (containing one or more Emacs windows). When Emacs is run on a text terminal, the frame fills the entire terminal screen. @cindex tiled windows Unlike X windows, Emacs windows are @dfn{tiled}; they never overlap within the area of the frame. When a window is created, resized, or deleted, the change in window space is taken from or given to the adjacent windows, so that the total area of the frame is unchanged. @defun windowp object This function returns @code{t} if @var{object} is a window (whether or not it displays a buffer). Otherwise, it returns @code{nil}. @end defun @cindex live windows A @dfn{live window} is one that is actually displaying a buffer in a frame. @defun window-live-p object This function returns @code{t} if @var{object} is a live window and @code{nil} otherwise. A live window is one that displays a buffer. @end defun @cindex internal windows The windows in each frame are organized into a @dfn{window tree}. @xref{Windows and Frames}. The leaf nodes of each window tree are live windows---the ones actually displaying buffers. The internal nodes of the window tree are @dfn{internal windows}, which are not live. @cindex valid windows A @dfn{valid window} is one that is either live or internal. A valid window can be @dfn{deleted}, i.e., removed from its frame (@pxref{Deleting Windows}); then it is no longer valid, but the Lisp object representing it might be still referenced from other Lisp objects. A deleted window may be made valid again by restoring a saved window configuration (@pxref{Window Configurations}). You can distinguish valid windows from deleted windows with @code{window-valid-p}. @defun window-valid-p object This function returns @code{t} if @var{object} is a live window, or an internal window in a window tree. Otherwise, it returns @code{nil}, including for the case where @var{object} is a deleted window. @end defun @cindex selected window @cindex window selected within a frame In each frame, at any time, exactly one Emacs window is designated as @dfn{selected within the frame}. For the selected frame, that window is called the @dfn{selected window}---the one in which most editing takes place, and in which the cursor for selected windows appears (@pxref{Cursor Parameters}). The selected window's buffer is usually also the current buffer, except when @code{set-buffer} has been used (@pxref{Current Buffer}). As for non-selected frames, the window selected within the frame becomes the selected window if the frame is ever selected. @xref{Selecting Windows}. @defun selected-window This function returns the selected window (which is always a live window). @end defun @node Windows and Frames @section Windows and Frames Each window belongs to exactly one frame (@pxref{Frames}). @defun window-frame &optional window This function returns the frame that the window @var{window} belongs to. If @var{window} is @code{nil}, it defaults to the selected window. @end defun @defun window-list &optional frame minibuffer window This function returns a list of live windows belonging to the frame @var{frame}. If @var{frame} is omitted or @code{nil}, it defaults to the selected frame. The optional argument @var{minibuffer} specifies whether to include the minibuffer window in the returned list. If @var{minibuffer} is @code{t}, the minibuffer window is included. If @var{minibuffer} is @code{nil} or omitted, the minibuffer window is included only if it is active. If @var{minibuffer} is neither @code{nil} nor @code{t}, the minibuffer window is never included. The optional argument @var{window}, if non-@code{nil}, should be a live window on the specified frame; then @var{window} will be the first element in the returned list. If @var{window} is omitted or @code{nil}, the window selected within the frame is the first element. @end defun @cindex window tree @cindex root window Windows in the same frame are organized into a @dfn{window tree}, whose leaf nodes are the live windows. The internal nodes of a window tree are not live; they exist for the purpose of organizing the relationships between live windows. The root node of a window tree is called the @dfn{root window}. It can be either a live window (if the frame has just one window), or an internal window. A minibuffer window (@pxref{Minibuffer Windows}) is not part of its frame's window tree unless the frame is a minibuffer-only frame. Nonetheless, most of the functions in this section accept the minibuffer window as an argument. Also, the function @code{window-tree} described at the end of this section lists the minibuffer window alongside the actual window tree. @defun frame-root-window &optional frame-or-window This function returns the root window for @var{frame-or-window}. The argument @var{frame-or-window} should be either a window or a frame; if omitted or @code{nil}, it defaults to the selected frame. If @var{frame-or-window} is a window, the return value is the root window of that window's frame. @end defun @cindex parent window @cindex child window @cindex sibling window When a window is split, there are two live windows where previously there was one. One of these is represented by the same Lisp window object as the original window, and the other is represented by a newly-created Lisp window object. Both of these live windows become leaf nodes of the window tree, as @dfn{child windows} of a single internal window. If necessary, Emacs automatically creates this internal window, which is also called the @dfn{parent window}, and assigns it to the appropriate position in the window tree. A set of windows that share the same parent are called @dfn{siblings}. @cindex parent window @defun window-parent &optional window This function returns the parent window of @var{window}. If @var{window} is omitted or @code{nil}, it defaults to the selected window. The return value is @code{nil} if @var{window} has no parent (i.e., it is a minibuffer window or the root window of its frame). @end defun Each internal window always has at least two child windows. If this number falls to one as a result of window deletion, Emacs automatically deletes the internal window, and its sole remaining child window takes its place in the window tree. Each child window can be either a live window, or an internal window (which in turn would have its own child windows). Therefore, each internal window can be thought of as occupying a certain rectangular @dfn{screen area}---the union of the areas occupied by the live windows that are ultimately descended from it. @cindex window combination @cindex vertical combination @cindex horizontal combination For each internal window, the screen areas of the immediate children are arranged either vertically or horizontally (never both). If the child windows are arranged one above the other, they are said to form a @dfn{vertical combination}; if they are arranged side by side, they are said to form a @dfn{horizontal combination}. Consider the following example: @smallexample @group ______________________________________ | ______ ____________________________ | || || __________________________ || || ||| ||| || ||| ||| || ||| ||| || |||____________W4____________||| || || __________________________ || || ||| ||| || ||| ||| || |||____________W5____________||| ||__W2__||_____________W3_____________ | |__________________W1__________________| @end group @end smallexample @noindent The root window of this frame is an internal window, @var{W1}. Its child windows form a horizontal combination, consisting of the live window @var{W2} and the internal window @var{W3}. The child windows of @var{W3} form a vertical combination, consisting of the live windows @var{W4} and @var{W5}. Hence, the live windows in this window tree are @var{W2}, @var{W4}, and @var{W5}. The following functions can be used to retrieve a child window of an internal window, and the siblings of a child window. @defun window-top-child &optional window This function returns the topmost child window of @var{window}, if @var{window} is an internal window whose children form a vertical combination. For any other type of window, the return value is @code{nil}. @end defun @defun window-left-child &optional window This function returns the leftmost child window of @var{window}, if @var{window} is an internal window whose children form a horizontal combination. For any other type of window, the return value is @code{nil}. @end defun @defun window-child window This function returns the first child window of the internal window @var{window}---the topmost child window for a vertical combination, or the leftmost child window for a horizontal combination. If @var{window} is a live window, the return value is @code{nil}. @end defun @defun window-combined-p &optional window horizontal This function returns a non-@code{nil} value if and only if @var{window} is part of a vertical combination. If @var{window} is omitted or @code{nil}, it defaults to the selected one. If the optional argument @var{horizontal} is non-@code{nil}, this means to return non-@code{nil} if and only if @var{window} is part of a horizontal combination. @end defun @defun window-next-sibling &optional window This function returns the next sibling of the window @var{window}. If omitted or @code{nil}, @var{window} defaults to the selected window. The return value is @code{nil} if @var{window} is the last child of its parent. @end defun @defun window-prev-sibling &optional window This function returns the previous sibling of the window @var{window}. If omitted or @code{nil}, @var{window} defaults to the selected window. The return value is @code{nil} if @var{window} is the first child of its parent. @end defun The functions @code{window-next-sibling} and @code{window-prev-sibling} should not be confused with the functions @code{next-window} and @code{previous-window}, which return the next and previous window, respectively, in the cyclic ordering of windows (@pxref{Cyclic Window Ordering}). You can use the following functions to find the first live window on a frame and the window nearest to a given window. @defun frame-first-window &optional frame-or-window This function returns the live window at the upper left corner of the frame specified by @var{frame-or-window}. The argument @var{frame-or-window} must denote a window or a live frame and defaults to the selected frame. If @var{frame-or-window} specifies a window, this function returns the first window on that window's frame. Under the assumption that the frame from our canonical example is selected @code{(frame-first-window)} returns @var{W2}. @end defun @cindex window in direction @defun window-in-direction direction &optional window ignore sign wrap mini This function returns the nearest live window in direction @var{direction} as seen from the position of @code{window-point} in window @var{window}. The argument @var{direction} must be one of @code{above}, @code{below}, @code{left} or @code{right}. The optional argument @var{window} must denote a live window and defaults to the selected one. This function does not return a window whose @code{no-other-window} parameter is non-@code{nil} (@pxref{Window Parameters}). If the nearest window's @code{no-other-window} parameter is non-@code{nil}, this function tries to find another window in the indicated direction whose @code{no-other-window} parameter is @code{nil}. If the optional argument @var{ignore} is non-@code{nil}, a window may be returned even if its @code{no-other-window} parameter is non-@code{nil}. If the optional argument @var{sign} is a negative number, it means to use the right or bottom edge of @var{window} as reference position instead of @code{window-point}. If @var{sign} is a positive number, it means to use the left or top edge of @var{window} as reference position. If the optional argument @var{wrap} is non-@code{nil}, this means to wrap @var{direction} around frame borders. For example, if @var{window} is at the top of the frame and @var{direction} is @code{above}, then return the minibuffer window provided the frame has one, and a window at the bottom of the frame otherwise. If the optional argument @var{mini} is @code{nil}, this means to return the minibuffer window if and only if it is currently active. If @var{mini} is non-@code{nil}, it returns the minibuffer window even when it's not active. However, if @var{wrap} non-@code{nil}, it always acts as if @var{mini} were @code{nil}. If it doesn't find a suitable window, this function returns @code{nil}. @end defun The following function allows to retrieve the entire window tree of a frame: @defun window-tree &optional frame This function returns a list representing the window tree for frame @var{frame}. If @var{frame} is omitted or @code{nil}, it defaults to the selected frame. The return value is a list of the form @code{(@var{root} @var{mini})}, where @var{root} represents the window tree of the frame's root window, and @var{mini} is the frame's minibuffer window. If the root window is live, @var{root} is that window itself. Otherwise, @var{root} is a list @code{(@var{dir} @var{edges} @var{w1} @var{w2} ...)} where @var{dir} is @code{nil} for a horizontal combination and @code{t} for a vertical combination, @var{edges} gives the size and position of the combination, and the remaining elements are the child windows. Each child window may again be a window object (for a live window) or a list with the same format as above (for an internal window). The @var{edges} element is a list @code{(@var{left} @var{top} @var{right} @var{bottom})}, similar to the value returned by @code{window-edges} (@pxref{Coordinates and Windows}). @end defun @node Window Sizes @section Window Sizes @cindex window size @cindex size of window The following schematic shows the structure of a live window: @smallexample @group ____________________________________________ |______________ Header Line ______________|RD| ^ ^ |LS|LF|LM| |RM|RF|RS| | | | | | | | | | | | | | Window | | | | Text Area | | | | | Window Body | | | | | (Window Body) | | | | | Total Height | | | | | | | | | Height | | | | |<- Window Body Width ->| | | | | | v |__|__|__|_______________________|__|__|__| | | |_______________ Mode Line _______________|__| | |_____________ Bottom Divider _______________| v <---------- Window Total Width ------------> @end group @end smallexample @cindex window body @cindex text area of a window @cindex body of a window At the center of the window is the @dfn{text area}, or @dfn{body}, where the buffer text is displayed. The text area can be surrounded by a series of optional areas. On the left and right, from innermost to outermost, these are the left and right margins, denoted by LM and RM in the schematic (@pxref{Display Margins}); the left and right fringes, denoted by LF and RF (@pxref{Fringes}); the left or right scroll bar, only one of which is present at any time, denoted by LS and RS (@pxref{Scroll Bars}); and the right divider, denoted by RD (@pxref{Window Dividers}). At the top of the window is the header line (@pxref{Header Lines}); at the bottom of the window is the mode line (@pxref{Mode Line Format}) followed by the bottom divider (@pxref{Window Dividers}). Emacs provides miscellaneous functions for finding the height and width of a window. The return value of many of these functions can be specified either in units of pixels or in units of lines and columns. On a graphical display, the latter actually correspond to the height and width of a ``default'' character specified by the frame's default font as returned by @code{frame-char-height} and @code{frame-char-width} (@pxref{Size and Position}). Thus, if a window is displaying text with a different font or size, the reported line height and column width for that window may differ from the actual number of text lines or columns displayed within it. @cindex window height @cindex height of a window @cindex total height of a window The @dfn{total height} of a window is the number of lines comprising the window's body, the header line, the mode line and the bottom divider (if any). Note that the height of a frame is not the same as the height of its root window (@pxref{Windows and Frames}), since a frame may also contain an echo area, a menu bar, and a tool bar (@pxref{Size and Position}). @defun window-total-height &optional window round This function returns the total height, in lines, of the window @var{window}. If @var{window} is omitted or @code{nil}, it defaults to the selected window. If @var{window} is an internal window, the return value is the total height occupied by its descendant windows. If a window's pixel height is not an integral multiple of its frame's default character height, the number of lines occupied by the window is rounded internally. This is done in a way such that, if the window is a parent window, the sum of the total heights of all its child windows internally equals the total height of their parent. This means that although two windows have the same pixel height, their internal total heights may differ by one line. This means also, that if this window is vertically combined and has a right sibling, the topmost row of that sibling can be calculated as the sum of this window's topmost row and total height (@pxref{Coordinates and Windows}) If the optional argument @var{round} is @code{ceiling}, this function returns the smallest integer larger than @var{window}'s pixel height divided by the character height of its frame; if it is @code{floor}, it returns the largest integer smaller than said value; with any other @var{round} it returns the internal value of @var{windows}'s total height. @end defun @cindex window width @cindex width of a window @cindex total width of a window The @dfn{total width} of a window is the number of lines comprising the window's body, its margins, fringes, scroll bars and a right divider (if any). @defun window-total-width &optional window round This function returns the total width, in columns, of the window @var{window}. If @var{window} is omitted or @code{nil}, it defaults to the selected window. If @var{window} is internal, the return value is the total width occupied by its descendant windows. If a window's pixel width is not an integral multiple of its frame's character width, the number of lines occupied by the window is rounded internally. This is done in a way such that, if the window is a parent window, the sum of the total widths of all its children internally equals the total width of their parent. This means that although two windows have the same pixel width, their internal total widths may differ by one column. This means also, that if this window is horizontally combined and has a right sibling, the leftmost column of that sibling can be calculated as the sum of this window's leftmost column and total width (@pxref{Coordinates and Windows}). The optional argument @var{round} behaves as it does for @code{window-total-height}. @end defun @defun window-total-size &optional window horizontal round This function returns either the total height in lines or the total width in columns of the window @var{window}. If @var{horizontal} is omitted or @code{nil}, this is equivalent to calling @code{window-total-height} for @var{window}; otherwise it is equivalent to calling @code{window-total-width} for @var{window}. The optional argument @var{round} behaves as it does for @code{window-total-height}. @end defun The following two functions can be used to return the total size of a window in units of pixels. @cindex window pixel height @cindex pixel height of a window @cindex total pixel height of a window @defun window-pixel-height &optional window This function returns the total height of window @var{window} in pixels. @var{window} must be a valid window and defaults to the selected one. The return value includes mode and header line and a bottom divider, if any. If @var{window} is an internal window, its pixel height is the pixel height of the screen areas spanned by its children. @end defun @cindex window pixel height @cindex pixel height of a window @cindex total pixel height of a window @defun window-pixel-width &optional Lisp_Object &optional window This function returns the width of window @var{window} in pixels. @var{window} must be a valid window and defaults to the selected one. The return value includes the fringes and margins of @var{window} as well as any vertical dividers or scroll bars belonging to @var{window}. If @var{window} is an internal window, its pixel width is the width of the screen areas spanned by its children. @end defun @cindex full-width window @cindex full-height window The following functions can be used to determine whether a given window has any adjacent windows. @defun window-full-height-p &optional window This function returns non-@code{nil} if @var{window} has no other window above or below it in its frame, i.e., its total height equals the total height of the root window on that frame. If @var{window} is omitted or @code{nil}, it defaults to the selected window. @end defun @defun window-full-width-p &optional window This function returns non-@code{nil} if @var{window} has no other window to the left or right in its frame, i.e., its total width equals that of the root window on that frame. If @var{window} is omitted or @code{nil}, it defaults to the selected window. @end defun @cindex window body height @cindex body height of a window @cindex window body width The @dfn{body height} of a window is the height of its text area, which does not include a mode or header line or a bottom divider. @defun window-body-height &optional window pixelwise This function returns the height, in lines, of the body of window @var{window}. If @var{window} is omitted or @code{nil}, it defaults to the selected window; otherwise it must be a live window. If the optional argument @var{pixelwise} is non-@code{nil}, this function returns the body height of @var{window} counted in pixels. If @var{pixelwise} is @code{nil}, the return value is rounded down to the nearest integer, if necessary. This means that if a line at the bottom of the text area is only partially visible, that line is not counted. It also means that the height of a window's body can never exceed its total height as returned by @code{window-total-height}. @end defun @cindex body width of a window @cindex body size of a window @cindex window body size The @dfn{body width} of a window is the width of its text area, which does not include the scroll bar, fringes, margins or a right divider. @defun window-body-width &optional window pixelwise This function returns the width, in columns, of the body of window @var{window}. If @var{window} is omitted or @code{nil}, it defaults to the selected window; otherwise it must be a live window. If the optional argument @var{pixelwise} is non-@code{nil}, this function returns the body width of @var{window} in units of pixels. If @var{pixelwise} is @code{nil}, the return value is rounded down to the nearest integer, if necessary. This means that if a column on the right of the text area is only partially visible, that column is not counted. It also means that the width of a window's body can never exceed its total width as returned by @code{window-total-width}. @end defun @defun window-body-size &optional window horizontal pixelwise This function returns the body height or body width of @var{window}. If @var{horizontal} is omitted or @code{nil}, it is equivalent to calling @code{window-body-height} for @var{window}; otherwise it is equivalent to calling @code{window-body-width}. In either case, the optional argument @var{pixelwise} is passed to the function called. @end defun For compatibility with previous versions of Emacs, @code{window-height} is an alias for @code{window-total-height}, and @code{window-width} is an alias for @code{window-body-width}. These aliases are considered obsolete and will be removed in the future. The pixel heights of a window's mode and header line can be retrieved with the functions given below. Their return value is usually accurate unless the window has not been displayed before: In that case, the return value is based on an estimate of the font used for the window's frame. @defun window-mode-line-height &optional window This function returns the height in pixels of @var{window}'s mode line. @var{window} must be a live window and defaults to the selected one. If @var{window} has no mode line, the return value is zero. @end defun @defun window-header-line-height &optional window This function returns the height in pixels of @var{window}'s header line. @var{window} must be a live window and defaults to the selected one. If @var{window} has no header line, the return value is zero. @end defun Functions for retrieving the height and/or width of window dividers (@pxref{Window Dividers}), fringes (@pxref{Fringes}), scroll bars (@pxref{Scroll Bars}), and display margins (@pxref{Display Margins}) are described in the corresponding sections. @cindex fixed-size window @vindex window-min-height @vindex window-min-width Commands that change the size of windows (@pxref{Resizing Windows}), or split them (@pxref{Splitting Windows}), obey the variables @code{window-min-height} and @code{window-min-width}, which specify the smallest allowable window height and width. They also obey the variable @code{window-size-fixed}, with which a window can be @dfn{fixed} in size: @defopt window-min-height This option specifies the minimum total height, in lines, of any window. Its value has to accommodate at least one text line as well as a mode and header line and a bottom divider, if present. @end defopt @defopt window-min-width This option specifies the minimum total width, in columns, of any window. Its value has to accommodate two text columns as well as margins, fringes, a scroll bar and a right divider, if present. @end defopt @defvar window-size-fixed If this buffer-local variable is non-@code{nil}, the size of any window displaying the buffer cannot normally be changed. Deleting a window or changing the frame's size may still change its size, if there is no choice. 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 non-@code{nil} value fixes both the width and the height. If this variable is @code{nil}, this does not necessarily mean that any window showing the buffer can be resized in the desired direction. To determine that, use the function @code{window-resizable}. @xref{Resizing Windows}. @end defvar The following function tells how small a specific window can get taking into account the sizes of its areas and the values of @code{window-min-height}, @code{window-min-width} and @code{window-size-fixed}. @defun window-min-size &optional window horizontal ignore pixelwise This function returns the minimum size of @var{window}. @var{window} must be a valid window and defaults to the selected one. The optional argument @var{horizontal} non-@code{nil} means to return the minimum number of columns of @var{window}; otherwise return the minimum number of @var{window}'s lines. The return value makes sure that all components of @var{window} remain fully visible if @var{window}'s size were actually set to it. With @var{horizontal} @code{nil} it includes the mode and header line and the bottom divider. With @var{horizontal} non-@code{nil} it includes the fringes, a scroll bar, and a right divider, if present. It does not, however, include the space reserved for the margins. The optional argument @var{ignore}, if non-@code{nil}, means ignore restrictions imposed by fixed size windows, @code{window-min-height} or @code{window-min-width} settings. If @var{ignore} equals @code{safe}, live windows may get as small as @code{window-safe-min-height} lines and @code{window-safe-min-width} columns. If @var{ignore} is a window, ignore restrictions for that window only. Any other non-@code{nil} value means ignore all of the above restrictions for all windows. The optional argument @var{pixelwise} non-@code{nil} means to return the minimum size of @var{window} counted in pixels. @end defun @node Resizing Windows @section Resizing Windows @cindex window resizing @cindex resize window @cindex changing window size @cindex window size, changing This section describes functions for resizing a window without changing the size of its frame. Because live windows do not overlap, these functions are meaningful only on frames that contain two or more windows: resizing a window also changes the size of a neighboring window. If there is just one window on a frame, its size cannot be changed except by resizing the frame (@pxref{Size and Position}). Except where noted, these functions also accept internal windows as arguments. Resizing an internal window causes its child windows to be resized to fit the same space. @defun window-resizable window delta &optional horizontal ignore pixelwise This function returns @var{delta} if the size of @var{window} can be changed vertically by @var{delta} lines. If the optional argument @var{horizontal} is non-@code{nil}, it instead returns @var{delta} if @var{window} can be resized horizontally by @var{delta} columns. It does not actually change the window size. If @var{window} is @code{nil}, it defaults to the selected window. A positive value of @var{delta} means to check whether the window can be enlarged by that number of lines or columns; a negative value of @var{delta} means to check whether the window can be shrunk by that many lines or columns. If @var{delta} is non-zero, a return value of 0 means that the window cannot be resized. Normally, the variables @code{window-min-height} and @code{window-min-width} specify the smallest allowable window size (@pxref{Window Sizes}). However, if the optional argument @var{ignore} is non-@code{nil}, this function ignores @code{window-min-height} and @code{window-min-width}, as well as @code{window-size-fixed}. Instead, it considers the minimum-height window to be one consisting of a header, a mode line and a bottom divider (if any), plus a text area one line tall; and a minimum-width window as one consisting of fringes, margins, a scroll bar and a right divider (if any), plus a text area two columns wide. If the optional argument @var{pixelwise} is non-@code{nil}, @var{delta} is interpreted as pixels. @end defun @defun window-resize window delta &optional horizontal ignore pixelwise This function resizes @var{window} by @var{delta} increments. If @var{horizontal} is @code{nil}, it changes the height by @var{delta} lines; otherwise, it changes the width by @var{delta} columns. A positive @var{delta} means to enlarge the window, and a negative @var{delta} means to shrink it. If @var{window} is @code{nil}, it defaults to the selected window. If the window cannot be resized as demanded, an error is signaled. The optional argument @var{ignore} has the same meaning as for the function @code{window-resizable} above. If the optional argument @var{pixelwise} is non-@code{nil}, @var{delta} will be interpreted as pixels. The choice of which window edges this function alters depends on the values of the option @code{window-combination-resize} and the combination limits of the involved windows; in some cases, it may alter both edges. @xref{Recombining Windows}. To resize by moving only the bottom or right edge of a window, use the function @code{adjust-window-trailing-edge}. @end defun @c The commands enlarge-window, enlarge-window-horizontally, @c shrink-window, and shrink-window-horizontally are documented in the @c Emacs manual. They are not preferred for calling from Lisp. @defun adjust-window-trailing-edge window delta &optional horizontal pixelwise This function moves @var{window}'s bottom edge by @var{delta} lines. If optional argument @var{horizontal} is non-@code{nil}, it instead moves the right edge by @var{delta} columns. If @var{window} is @code{nil}, it defaults to the selected window. If the optional argument @var{pixelwise} is non-@code{nil}, @var{delta} is interpreted as pixels. A positive @var{delta} moves the edge downwards or to the right; a negative @var{delta} moves it upwards or to the left. If the edge cannot be moved as far as specified by @var{delta}, this function moves it as far as possible but does not signal a error. This function tries to resize windows adjacent to the edge that is moved. If this is not possible for some reason (e.g., if that adjacent window is fixed-size), it may resize other windows. @end defun @cindex pixelwise, resizing windows @defopt window-resize-pixelwise If the value of this option is non-@code{nil}, Emacs resizes windows in units of pixels. This currently affects functions like @code{split-window} (@pxref{Splitting Windows}), @code{maximize-window}, @code{minimize-window}, @code{fit-window-to-buffer}, @code{shrink-window-if-larger-than-buffer} (all listed below) and @code{fit-frame-to-buffer} (@pxref{Size and Position}). Note that when a frame's pixel size is not a multiple of its character size, at least one window may get resized pixelwise even if this option is @code{nil}. The default value is @code{nil}. @end defopt The following commands resize windows in more specific ways. When called interactively, they act on the selected window. @deffn Command fit-window-to-buffer &optional window max-height min-height max-width min-width This command adjusts the height or width of @var{window} to fit the text in it. It returns non-@code{nil} if it was able to resize @var{window}, and @code{nil} otherwise. If @var{window} is omitted or @code{nil}, it defaults to the selected window. Otherwise, it should be a live window. If @var{window} is part of a vertical combination, this function adjusts @var{window}'s height. The new height is calculated from the actual height of the accessible portion of its buffer. The optional argument @var{max-height}, if non-@code{nil}, specifies the maximum total height that this function can give @var{window}. The optional argument @var{min-height}, if non-@code{nil}, specifies the minimum total height that it can give, which overrides the variable @code{window-min-height}. Both @var{max-height} and @var{min-height} are specified in lines and include mode and header line and a bottom divider, if any. If @var{window} is part of a horizontal combination and the value of the option @code{fit-window-to-buffer-horizontally} (see below) is non-@code{nil}, this function adjusts @var{window}'s height. The new width of @var{window} is calculated from the maximum length of its buffer's lines that follow the current start position of @var{window}. The optional argument @var{max-width} specifies a maximum width and defaults to the width of @var{window}'s frame. The optional argument @var{min-width} specifies a minimum width and defaults to @code{window-min-width}. Both @var{max-width} and @var{min-width} are specified in columns and include fringes, margins and scrollbars, if any. If the option @code{fit-frame-to-buffer} (see below) is non-@code{nil}, this function will try to resize the frame of @var{window} to fit its contents by calling @code{fit-frame-to-buffer} (@pxref{Size and Position}). @end deffn @defopt fit-window-to-buffer-horizontally If this is non-@code{nil}, @code{fit-window-to-buffer} can resize windows horizontally. If this is @code{nil} (the default) @code{fit-window-to-buffer} never resizes windows horizontally. If this is @code{only}, it can resize windows horizontally only. Any other value means @code{fit-window-to-buffer} can resize windows in both dimensions. @end defopt @defopt fit-frame-to-buffer If this option is non-@code{nil}, @code{fit-window-to-buffer} can fit a frame to its buffer. A frame is fit if and only if its root window is a live window and this option is non-@code{nil}. If this is @code{horizontally}, frames are fit horizontally only. If this is @code{vertically}, frames are fit vertically only. Any other non-@code{nil} value means frames can be resized in both dimensions. @end defopt @deffn Command shrink-window-if-larger-than-buffer &optional window This command attempts to reduce @var{window}'s height as much as possible while still showing its full buffer, but no less than @code{window-min-height} lines. The return value is non-@code{nil} if the window was resized, and @code{nil} otherwise. If @var{window} is omitted or @code{nil}, it defaults to the selected window. Otherwise, it should be a live window. This command does nothing if the window is already too short to display all of its buffer, or if any of the buffer is scrolled off-screen, or if the window is the only live window in its frame. This command calls @code{fit-window-to-buffer} (see above) to do its work. @end deffn @cindex balancing window sizes @deffn Command balance-windows &optional window-or-frame This function balances windows in a way that gives more space to full-width and/or full-height windows. If @var{window-or-frame} specifies a frame, it balances all windows on that frame. If @var{window-or-frame} specifies a window, it balances only that window and its siblings (@pxref{Windows and Frames}). @end deffn @deffn Command balance-windows-area This function attempts to give all windows on the selected frame approximately the same share of the screen area. Full-width or full-height windows are not given more space than other windows. @end deffn @cindex maximizing windows @deffn Command maximize-window &optional window This function attempts to make @var{window} as large as possible, in both dimensions, without resizing its frame or deleting other windows. If @var{window} is omitted or @code{nil}, it defaults to the selected window. @end deffn @cindex minimizing windows @deffn Command minimize-window &optional window This function attempts to make @var{window} as small as possible, in both dimensions, without deleting it or resizing its frame. If @var{window} is omitted or @code{nil}, it defaults to the selected window. @end deffn @node Splitting Windows @section Splitting Windows @cindex splitting windows @cindex window splitting This section describes functions for creating a new window by @dfn{splitting} an existing one. @defun split-window &optional window size side pixelwise This function creates a new live window next to the window @var{window}. If @var{window} is omitted or @code{nil}, it defaults to the selected window. That window is ``split'', and reduced in size. The space is taken up by the new window, which is returned. The optional second argument @var{size} determines the sizes of @var{window} and/or the new window. If it is omitted or @code{nil}, both windows are given equal sizes; if there is an odd line, it is allocated to the new window. If @var{size} is a positive number, @var{window} is given @var{size} lines (or columns, depending on the value of @var{side}). If @var{size} is a negative number, the new window is given @minus{}@var{size} lines (or columns). If @var{size} is @code{nil}, this function obeys the variables @code{window-min-height} and @code{window-min-width} (@pxref{Window Sizes}). Thus, it signals an error if splitting would result in making a window smaller than those variables specify. However, a non-@code{nil} value for @var{size} causes those variables to be ignored; in that case, the smallest allowable window is considered to be one that has space for a text area one line tall and/or two columns wide. Hence, if @var{size} is specified, it's the caller's responsibility to check whether the emanating windows are large enough to encompass all areas like a mode line or a scroll bar. The function @code{window-min-size} (@pxref{Window Sizes}) can be used to determine the minimum requirements of @var{window} in this regard. Since the new window usually ``inherits'' areas like the mode line or the scroll bar from @var{window}, that function is also a good guess for the minimum size of the new window. The caller should specify a smaller size only if it correspondingly removes an inherited area before the next redisplay. The optional third argument @var{side} determines the position of the new window relative to @var{window}. If it is @code{nil} or @code{below}, the new window is placed below @var{window}. If it is @code{above}, the new window is placed above @var{window}. In both these cases, @var{size} specifies a total window height, in lines. If @var{side} is @code{t} or @code{right}, the new window is placed on the right of @var{window}. If @var{side} is @code{left}, the new window is placed on the left of @var{window}. In both these cases, @var{size} specifies a total window width, in columns. The optional fourth argument @var{pixelwise}, if non-@code{nil}, means to interpret @var{size} in units of pixels, instead of lines and columns. If @var{window} is a live window, the new window inherits various properties from it, including margins and scroll bars. If @var{window} is an internal window, the new window inherits the properties of the window selected within @var{window}'s frame. The behavior of this function may be altered by the window parameters of @var{window}, so long as the variable @code{ignore-window-parameters} is @code{nil}. If the value of the @code{split-window} window parameter is @code{t}, this function ignores all other window parameters. Otherwise, if the value of the @code{split-window} window parameter is a function, that function is called with the arguments @var{window}, @var{size}, and @var{side}, in lieu of the usual action of @code{split-window}. Otherwise, this function obeys the @code{window-atom} or @code{window-side} window parameter, if any. @xref{Window Parameters}. @end defun As an example, here is a sequence of @code{split-window} calls that yields the window configuration discussed in @ref{Windows and Frames}. This example demonstrates splitting a live window as well as splitting an internal window. We begin with a frame containing a single window (a live root window), which we denote by @var{W4}. Calling @code{(split-window W4)} yields this window configuration: @smallexample @group ______________________________________ | ____________________________________ | || || || || || || ||_________________W4_________________|| | ____________________________________ | || || || || || || ||_________________W5_________________|| |__________________W3__________________| @end group @end smallexample @noindent The @code{split-window} call has created a new live window, denoted by @var{W5}. It has also created a new internal window, denoted by @var{W3}, which becomes the root window and the parent of both @var{W4} and @var{W5}. Next, we call @code{(split-window W3 nil 'left)}, passing the internal window @var{W3} as the argument. The result: @smallexample @group ______________________________________ | ______ ____________________________ | || || __________________________ || || ||| ||| || ||| ||| || ||| ||| || |||____________W4____________||| || || __________________________ || || ||| ||| || ||| ||| || |||____________W5____________||| ||__W2__||_____________W3_____________ | |__________________W1__________________| @end group @end smallexample @noindent A new live window @var{W2} is created, to the left of the internal window @var{W3}. A new internal window @var{W1} is created, becoming the new root window. For interactive use, Emacs provides two commands which always split the selected window. These call @code{split-window} internally. @deffn Command split-window-right &optional size This function splits the selected window into two side-by-side windows, putting the selected window on the left. If @var{size} is positive, the left window gets @var{size} columns; if @var{size} is negative, the right window gets @minus{}@var{size} columns. @end deffn @deffn Command split-window-below &optional size This function splits the selected window into two windows, one above the other, leaving the upper window selected. If @var{size} is positive, the upper window gets @var{size} lines; if @var{size} is negative, the lower window gets @minus{}@var{size} lines. @end deffn @defopt split-window-keep-point If the value of this variable is non-@code{nil} (the default), @code{split-window-below} behaves as described above. If it is @code{nil}, @code{split-window-below} adjusts point in each of the two windows to minimize redisplay. (This is useful on slow terminals.) It selects whichever window contains the screen line that point was previously on. Note that this only affects @code{split-window-below}, not the lower-level @code{split-window} function. @end defopt @node Deleting Windows @section Deleting Windows @cindex deleting windows @dfn{Deleting} a window removes it from the frame's window tree. If the window is a live window, it disappears from the screen. If the window is an internal window, its child windows are deleted too. Even after a window is deleted, it continues to exist as a Lisp object, until there are no more references to it. Window deletion can be reversed, by restoring a saved window configuration (@pxref{Window Configurations}). @deffn Command delete-window &optional window This function removes @var{window} from display and returns @code{nil}. If @var{window} is omitted or @code{nil}, it defaults to the selected window. If deleting the window would leave no more windows in the window tree (e.g., if it is the only live window in the frame), an error is signaled. By default, the space taken up by @var{window} is given to one of its adjacent sibling windows, if any. However, if the variable @code{window-combination-resize} is non-@code{nil}, the space is proportionally distributed among any remaining windows in the window combination. @xref{Recombining Windows}. The behavior of this function may be altered by the window parameters of @var{window}, so long as the variable @code{ignore-window-parameters} is @code{nil}. If the value of the @code{delete-window} window parameter is @code{t}, this function ignores all other window parameters. Otherwise, if the value of the @code{delete-window} window parameter is a function, that function is called with the argument @var{window}, in lieu of the usual action of @code{delete-window}. Otherwise, this function obeys the @code{window-atom} or @code{window-side} window parameter, if any. @xref{Window Parameters}. @end deffn @deffn Command delete-other-windows &optional window This function makes @var{window} fill its frame, by deleting other windows as necessary. If @var{window} is omitted or @code{nil}, it defaults to the selected window. The return value is @code{nil}. The behavior of this function may be altered by the window parameters of @var{window}, so long as the variable @code{ignore-window-parameters} is @code{nil}. If the value of the @code{delete-other-windows} window parameter is @code{t}, this function ignores all other window parameters. Otherwise, if the value of the @code{delete-other-windows} window parameter is a function, that function is called with the argument @var{window}, in lieu of the usual action of @code{delete-other-windows}. Otherwise, this function obeys the @code{window-atom} or @code{window-side} window parameter, if any. @xref{Window Parameters}. @end deffn @deffn Command delete-windows-on &optional buffer-or-name frame This function deletes all windows showing @var{buffer-or-name}, by calling @code{delete-window} on those windows. @var{buffer-or-name} should be a buffer, or the name of a buffer; if omitted or @code{nil}, it defaults to the current buffer. If there are no windows showing the specified buffer, this function does nothing. If the specified buffer is a minibuffer, an error is signaled. If there is a dedicated window showing the buffer, and that window is the only one on its frame, this function also deletes that frame if it is not the only frame on the terminal. The optional argument @var{frame} specifies which frames to operate on: @itemize @bullet @item @code{nil} means operate on all frames. @item @code{t} means operate on the selected frame. @item @code{visible} means operate on all visible frames. @item @code{0} means operate on all visible or iconified frames. @item A frame means operate on that frame. @end itemize Note that this argument does not have the same meaning as in other functions which scan all live windows (@pxref{Cyclic Window Ordering}). Specifically, the meanings of @code{t} and @code{nil} here are the opposite of what they are in those other functions. @end deffn @node Recombining Windows @section Recombining Windows When deleting the last sibling of a window @var{W}, its parent window is deleted too, with @var{W} replacing it in the window tree. This means that @var{W} must be recombined with its parent's siblings to form a new window combination (@pxref{Windows and Frames}). In some occasions, deleting a live window may even entail the deletion of two internal windows. @smallexample @group ______________________________________ | ______ ____________________________ | || || __________________________ || || ||| ___________ ___________ ||| || |||| || |||| || ||||____W6_____||_____W7____|||| || |||____________W4____________||| || || __________________________ || || ||| ||| || ||| ||| || |||____________W5____________||| ||__W2__||_____________W3_____________ | |__________________W1__________________| @end group @end smallexample @noindent Deleting @var{W5} in this configuration normally causes the deletion of @var{W3} and @var{W4}. The remaining live windows @var{W2}, @var{W6} and @var{W7} are recombined to form a new horizontal combination with parent @var{W1}. Sometimes, however, it makes sense to not delete a parent window like @var{W4}. In particular, a parent window should not be removed when it was used to preserve a combination embedded in a combination of the same type. Such embeddings make sense to assure that when you split a window and subsequently delete the new window, Emacs reestablishes the layout of the associated frame as it existed before the splitting. Consider a scenario starting with two live windows @var{W2} and @var{W3} and their parent @var{W1}. @smallexample @group ______________________________________ | ____________________________________ | || || || || || || || || || || || || ||_________________W2_________________|| | ____________________________________ | || || || || ||_________________W3_________________|| |__________________W1__________________| @end group @end smallexample @noindent Split @var{W2} to make a new window @var{W4} as follows. @smallexample @group ______________________________________ | ____________________________________ | || || || || ||_________________W2_________________|| | ____________________________________ | || || || || ||_________________W4_________________|| | ____________________________________ | || || || || ||_________________W3_________________|| |__________________W1__________________| @end group @end smallexample @noindent Now, when enlarging a window vertically, Emacs tries to obtain the corresponding space from its lower sibling, provided such a window exists. In our scenario, enlarging @var{W4} will steal space from @var{W3}. @smallexample @group ______________________________________ | ____________________________________ | || || || || ||_________________W2_________________|| | ____________________________________ | || || || || || || || || ||_________________W4_________________|| | ____________________________________ | ||_________________W3_________________|| |__________________W1__________________| @end group @end smallexample @noindent Deleting @var{W4} will now give its entire space to @var{W2}, including the space earlier stolen from @var{W3}. @smallexample @group ______________________________________ | ____________________________________ | || || || || || || || || || || || || || || || || ||_________________W2_________________|| | ____________________________________ | ||_________________W3_________________|| |__________________W1__________________| @end group @end smallexample @noindent This can be counterintuitive, in particular if @var{W4} were used for displaying a buffer only temporarily (@pxref{Temporary Displays}), and you want to continue working with the initial layout. The behavior can be fixed by making a new parent window when splitting @var{W2}. The variable described next allows to do that. @defopt window-combination-limit This variable controls whether splitting a window shall make a new parent window. The following values are recognized: @table @code @item nil This means that the new live window is allowed to share the existing parent window, if one exists, provided the split occurs in the same direction as the existing window combination (otherwise, a new internal window is created anyway). @item window-size In this case @code{display-buffer} makes a new parent window if it is passed a @code{window-height} or @code{window-width} entry in the @var{alist} argument (@pxref{Display Action Functions}). @item temp-buffer This value causes the creation of a new parent window when a window is split for showing a temporary buffer (@pxref{Temporary Displays}) only. @item display-buffer This means that when @code{display-buffer} (@pxref{Choosing Window}) splits a window it always makes a new parent window. @item t In this case a new parent window is always created when splitting a window. Thus, if the value of this variable is at all times @code{t}, then at all times every window tree is a binary tree (a tree where each window except the root window has exactly one sibling). @end table The default is @code{nil}. Other values are reserved for future use. If, as a consequence of this variable's setting, @code{split-window} makes a new parent window, it also calls @code{set-window-combination-limit} (see below) on the newly-created internal window. This affects how the window tree is rearranged when the child windows are deleted (see below). @end defopt If @code{window-combination-limit} is @code{t}, splitting @var{W2} in the initial configuration of our scenario would have produced this: @smallexample @group ______________________________________ | ____________________________________ | || __________________________________ || ||| ||| |||________________W2________________||| || __________________________________ || ||| ||| |||________________W4________________||| ||_________________W5_________________|| | ____________________________________ | || || || || ||_________________W3_________________|| |__________________W1__________________| @end group @end smallexample @noindent A new internal window @var{W5} has been created; its children are @var{W2} and the new live window @var{W4}. Now, @var{W2} is the only sibling of @var{W4}, so enlarging @var{W4} will try to shrink @var{W2}, leaving @var{W3} unaffected. Observe that @var{W5} represents a vertical combination of two windows embedded in the vertical combination @var{W1}. @cindex window combination limit @defun set-window-combination-limit window limit This function sets the @dfn{combination limit} of the window @var{window} to @var{limit}. This value can be retrieved via the function @code{window-combination-limit}. See below for its effects; note that it is only meaningful for internal windows. The @code{split-window} function automatically calls this function, passing it @code{t} as @var{limit}, provided the value of the variable @code{window-combination-limit} is @code{t} when it is called. @end defun @defun window-combination-limit window This function returns the combination limit for @var{window}. The combination limit is meaningful only for an internal window. If it is @code{nil}, then Emacs is allowed to automatically delete @var{window}, in response to a window deletion, in order to group the child windows of @var{window} with its sibling windows to form a new window combination. If the combination limit is @code{t}, the child windows of @var{window} are never automatically recombined with its siblings. If, in the configuration shown at the beginning of this section, the combination limit of @var{W4} (the parent window of @var{W6} and @var{W7}) is @code{t}, deleting @var{W5} will not implicitly delete @var{W4} too. @end defun Alternatively, the problems sketched above can be avoided by always resizing all windows in the same combination whenever one of its windows is split or deleted. This also permits to split windows that would be otherwise too small for such an operation. @defopt window-combination-resize If this variable is @code{nil}, @code{split-window} can only split a window (denoted by @var{window}) if @var{window}'s screen area is large enough to accommodate both itself and the new window. If this variable is @code{t}, @code{split-window} tries to resize all windows that are part of the same combination as @var{window}, in order to accommodate the new window. In particular, this may allow @code{split-window} to succeed even if @var{window} is a fixed-size window or too small to ordinarily split. Furthermore, subsequently resizing or deleting @var{window} may resize all other windows in its combination. The default is @code{nil}. Other values are reserved for future use. The value of this variable is ignored when @code{window-combination-limit} is non-@code{nil}. @end defopt To illustrate the effect of @code{window-combination-resize}, consider the following frame layout. @smallexample @group ______________________________________ | ____________________________________ | || || || || || || || || ||_________________W2_________________|| | ____________________________________ | || || || || || || || || ||_________________W3_________________|| |__________________W1__________________| @end group @end smallexample @noindent If @code{window-combination-resize} is @code{nil}, splitting window @var{W3} leaves the size of @var{W2} unchanged: @smallexample @group ______________________________________ | ____________________________________ | || || || || || || || || ||_________________W2_________________|| | ____________________________________ | || || ||_________________W3_________________|| | ____________________________________ | || || ||_________________W4_________________|| |__________________W1__________________| @end group @end smallexample @noindent If @code{window-combination-resize} is @code{t}, splitting @var{W3} instead leaves all three live windows with approximately the same height: @smallexample @group ______________________________________ | ____________________________________ | || || || || ||_________________W2_________________|| | ____________________________________ | || || || || ||_________________W3_________________|| | ____________________________________ | || || || || ||_________________W4_________________|| |__________________W1__________________| @end group @end smallexample @noindent Deleting any of the live windows @var{W2}, @var{W3} or @var{W4} will distribute its space proportionally among the two remaining live windows. @node Selecting Windows @section Selecting Windows @cindex selecting a window @defun select-window window &optional norecord This function makes @var{window} the selected window and the window selected within its frame (@pxref{Basic Windows}) and selects that frame. It also makes @var{window}'s buffer (@pxref{Buffers and Windows}) current and sets that buffer's value of @code{point} to the value of @code{window-point} (@pxref{Window Point}) in @var{window}. @var{window} must be a live window. The return value is @var{window}. By default, this function also moves @var{window}'s buffer to the front of the buffer list (@pxref{Buffer List}), and makes @var{window} the most recently selected window. However, if the optional argument @var{norecord} is non-@code{nil}, these additional actions are omitted. This function runs @code{buffer-list-update-hook} (@pxref{Buffer List}) unless @var{norecord} is non-@code{nil}. Note that applications and internal routines often temporarily select a window in order to simplify coding. As a rule, such selections (including those made by the macros @code{save-selected-window} and @code{with-selected-window} below) are not recorded thus avoiding to pollute @code{buffer-list-update-hook}. Selections that ``really count'' are those causing a visible change in the next redisplay of @var{window}'s frame and should be always recorded. This also means that to run a function each time a window gets selected, putting it on @code{buffer-list-update-hook} should be the right choice. @end defun @cindex most recently selected windows The sequence of calls to @code{select-window} with a non-@code{nil} @var{norecord} argument determines an ordering of windows by their selection time. The function @code{get-lru-window} can be used to retrieve the least recently selected live window (@pxref{Cyclic Window Ordering}). @defmac save-selected-window forms@dots{} This macro records the selected frame, as well as the selected window of each frame, executes @var{forms} in sequence, then restores the earlier selected frame and windows. It also saves and restores the current buffer. 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 @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. The current buffer is restored if and only if it is still live when exiting @var{forms}. This macro changes neither the ordering of recently selected windows nor the buffer list. @end defmac @defmac with-selected-window window forms@dots{} This macro selects @var{window}, executes @var{forms} in sequence, then restores the previously selected window and current buffer. The ordering of recently selected windows and the buffer list remain unchanged unless you deliberately change them within @var{forms}; for example, by calling @code{select-window} with argument @var{norecord} @code{nil}. This macro does not change the order of recently selected windows or the buffer list. @end defmac @defun frame-selected-window &optional frame This function returns the window on @var{frame} that is selected within that frame. @var{frame} should be a live frame; if omitted or @code{nil}, it defaults to the selected frame. @end defun @defun set-frame-selected-window frame window &optional norecord This function makes @var{window} the window selected within the frame @var{frame}. @var{frame} should be a live frame; if @code{nil}, it defaults to the selected frame. @var{window} should be a live window; if @code{nil}, it defaults to the selected window. If @var{frame} is the selected frame, this makes @var{window} the selected window. If the optional argument @var{norecord} is non-@code{nil}, this function does not alter the list of most recently selected windows, nor the buffer list. @end defun @node Cyclic Window Ordering @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 some other window, it moves through live windows in a specific order. For any given configuration of windows, this order never varies. It is called the @dfn{cyclic ordering of windows}. The ordering is determined by a depth-first traversal of the frame's window tree, retrieving the live windows which are the leaf nodes of the tree (@pxref{Windows and Frames}). If the minibuffer is active, the minibuffer window is included too. The ordering is cyclic, so the last window in the sequence is followed by the first one. @defun next-window &optional window minibuf all-frames @cindex minibuffer window, and @code{next-window} This function returns a live window, the one following @var{window} in the cyclic ordering of windows. @var{window} should be a live window; if omitted or @code{nil}, it defaults to the selected window. The optional argument @var{minibuf} specifies whether minibuffer windows should be included in the cyclic ordering. Normally, when @var{minibuf} is @code{nil}, a minibuffer window is included only if it is currently ``active''; this matches the behavior of @kbd{C-x o}. (Note that a minibuffer window is active as long as its minibuffer is in use; see @ref{Minibuffers}). If @var{minibuf} is @code{t}, the cyclic ordering includes all minibuffer windows. If @var{minibuf} is neither @code{t} nor @code{nil}, minibuffer windows are not included even if they are active. The optional argument @var{all-frames} specifies which frames to consider: @itemize @bullet @item @code{nil} means to consider windows on @var{window}'s frame. If the minibuffer window is considered (as specified by the @var{minibuf} argument), then frames that share the minibuffer window are considered too. @item @code{t} means to consider windows on all existing frames. @item @code{visible} means to consider windows on all visible frames. @item 0 means to consider windows on all visible or iconified frames. @item A frame means to consider windows on that specific frame. @item Anything else means to consider windows on @var{window}'s frame, and no others. @end itemize If more than one frame is considered, the cyclic ordering is obtained by appending the orderings for those frames, in the same order as the list of all live frames (@pxref{Finding All Frames}). @end defun @defun previous-window &optional window minibuf all-frames This function returns a live window, the one preceding @var{window} in the cyclic ordering of windows. The other arguments are handled like in @code{next-window}. @end defun @deffn Command other-window count &optional all-frames This function selects a live window, one @var{count} places from the selected window in the cyclic ordering of windows. If @var{count} is a positive number, it skips @var{count} windows forwards; if @var{count} is negative, it skips @minus{}@var{count} windows backwards; if @var{count} is zero, that simply re-selects the selected window. When called interactively, @var{count} is the numeric prefix argument. The optional argument @var{all-frames} has the same meaning as in @code{next-window}, like a @code{nil} @var{minibuf} argument to @code{next-window}. This function does not select a window that has a non-@code{nil} @code{no-other-window} window parameter (@pxref{Window Parameters}). @end deffn @defun walk-windows fun &optional minibuf all-frames This function calls the function @var{fun} once for each live window, with the window as the argument. It follows the cyclic ordering of windows. The optional arguments @var{minibuf} and @var{all-frames} specify the set of windows included; these have the same arguments as in @code{next-window}. If @var{all-frames} specifies a frame, the first window walked is the first window on that frame (the one returned by @code{frame-first-window}), not necessarily the selected window. If @var{fun} changes the window configuration by splitting or deleting windows, that does not alter the set of windows walked, which is determined prior to calling @var{fun} for the first time. @end defun @defun one-window-p &optional no-mini all-frames This function returns @code{t} if the selected window is the only live window, and @code{nil} otherwise. If the minibuffer window is active, it is normally considered (so that this function returns @code{nil}). However, if the optional argument @var{no-mini} is non-@code{nil}, the minibuffer window is ignored even if active. The optional argument @var{all-frames} has the same meaning as for @code{next-window}. @end defun @cindex finding windows The following functions return a window which satisfies some criterion, without selecting it: @cindex least recently used window @defun get-lru-window &optional all-frames dedicated not-selected This function returns a live window which is heuristically the ``least recently used'' window. The optional argument @var{all-frames} has the same meaning as in @code{next-window}. If any full-width windows are present, only those windows are considered. A minibuffer window is never a candidate. A dedicated window (@pxref{Dedicated Windows}) is never a candidate unless the optional argument @var{dedicated} is non-@code{nil}. The selected window is never returned, unless it is the only candidate. However, if the optional argument @var{not-selected} is non-@code{nil}, this function returns @code{nil} in that case. @end defun @cindex largest window @defun get-largest-window &optional all-frames dedicated not-selected This function returns the window with the largest area (height times width). The optional argument @var{all-frames} specifies the windows to search, and has the same meaning as in @code{next-window}. A minibuffer window is never a candidate. A dedicated window (@pxref{Dedicated Windows}) is never a candidate unless the optional argument @var{dedicated} is non-@code{nil}. The selected window is not a candidate if the optional argument @var{not-selected} is non-@code{nil}. If the optional argument @var{not-selected} is non-@code{nil} and the selected window is the only candidate, this function returns @code{nil}. If there are two candidate windows of the same size, this function prefers the one that comes first in the cyclic ordering of windows, starting from the selected window. @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 calls the function @var{predicate} for each of the windows in the cyclic order of windows in turn, passing it the window as an argument. If the predicate returns non-@code{nil} for any window, this function stops and returns that window. If no such window is found, the return value is @var{default} (which defaults to @code{nil}). The optional arguments @var{minibuf} and @var{all-frames} specify the windows to search, and have the same meanings as in @code{next-window}. @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 for examining and setting the contents of windows. @xref{Switching Buffers}, for higher-level functions for displaying a specific buffer in a window. @defun window-buffer &optional window This function returns the buffer that @var{window} is displaying. If @var{window} is omitted or @code{nil} it defaults to the selected window. If @var{window} is an internal window, this function returns @code{nil}. @end defun @defun set-window-buffer window buffer-or-name &optional keep-margins This function makes @var{window} display @var{buffer-or-name}. @var{window} should be a live window; if @code{nil}, it defaults to the selected window. @var{buffer-or-name} should be a buffer, or the name of an existing buffer. This function does not change which window is selected, nor does it directly change which buffer is current (@pxref{Current Buffer}). Its return value is @code{nil}. If @var{window} is @dfn{strongly dedicated} to a buffer and @var{buffer-or-name} does not specify that buffer, this function signals an error. @xref{Dedicated Windows}. By default, this function resets @var{window}'s position, display margins, fringe widths, and scroll bar settings, based on the local variables in the specified buffer. However, if the optional argument @var{keep-margins} is non-@code{nil}, it leaves the display margins and fringe widths unchanged. When writing an application, you should normally use the higher-level functions described in @ref{Switching Buffers}, instead of calling @code{set-window-buffer} directly. This runs @code{window-scroll-functions}, followed by @code{window-configuration-change-hook}. @xref{Window Hooks}. @end defun @defvar buffer-display-count This buffer-local variable records the number of times a buffer has been displayed in a window. It is incremented each time @code{set-window-buffer} is called for the buffer. @end defvar @defvar buffer-display-time This buffer-local variable records the time at which a buffer was last displayed in a window. The value is @code{nil} if the buffer has never been displayed. It is updated each time @code{set-window-buffer} is called for the buffer, with the value returned by @code{current-time} (@pxref{Time of Day}). @end defvar @defun get-buffer-window &optional buffer-or-name all-frames This function returns the first window displaying @var{buffer-or-name} in the cyclic ordering of windows, starting from the selected window (@pxref{Cyclic Window Ordering}). If no such window exists, the return value is @code{nil}. @var{buffer-or-name} should be a buffer or the name of a buffer; if omitted or @code{nil}, it defaults to the current buffer. The optional argument @var{all-frames} specifies which windows to consider: @itemize @bullet @item @code{t} means consider windows on all existing frames. @item @code{visible} means consider windows on all visible frames. @item 0 means consider windows on all visible or iconified frames. @item A frame means consider windows on that frame only. @item Any other value means consider windows on the selected frame. @end itemize Note that these meanings differ slightly from those of the @var{all-frames} argument to @code{next-window} (@pxref{Cyclic Window Ordering}). This function may be changed in a future version of Emacs to eliminate this discrepancy. @end defun @defun get-buffer-window-list &optional buffer-or-name minibuf all-frames This function returns a list of all windows currently displaying @var{buffer-or-name}. @var{buffer-or-name} should be a buffer or the name of an existing buffer. If omitted or @code{nil}, it defaults to the current buffer. The arguments @var{minibuf} and @var{all-frames} have the same meanings as in the function @code{next-window} (@pxref{Cyclic Window Ordering}). Note that the @var{all-frames} argument does @emph{not} behave exactly like in @code{get-buffer-window}. @end defun @deffn Command replace-buffer-in-windows &optional buffer-or-name This command replaces @var{buffer-or-name} with some other buffer, in all windows displaying it. @var{buffer-or-name} should be a buffer, or the name of an existing buffer; if omitted or @code{nil}, it defaults to the current buffer. The replacement buffer in each window is chosen via @code{switch-to-prev-buffer} (@pxref{Window History}). Any dedicated window displaying @var{buffer-or-name} is deleted if possible (@pxref{Dedicated Windows}). If such a window is the only window on its frame and there are other frames on the same terminal, the frame is deleted as well. If the dedicated window is the only window on the only frame on its terminal, the buffer is replaced anyway. @end deffn @node Switching Buffers @section Switching to a Buffer in a Window @cindex switching to a buffer @cindex displaying a buffer This section describes high-level functions for switching to a specified buffer in some window. In general, ``switching to a buffer'' means to (1) show the buffer in some window, (2) make that window the selected window (and its frame the selected frame), and (3) make the buffer the current buffer. Do @emph{not} use these functions to make a buffer temporarily current just so a Lisp program can access or modify it. They have side-effects, such as changing window histories (@pxref{Window History}), which will surprise the user if used that way. If you want to make a buffer current to modify it in Lisp, use @code{with-current-buffer}, @code{save-current-buffer}, or @code{set-buffer}. @xref{Current Buffer}. @deffn Command switch-to-buffer buffer-or-name &optional norecord force-same-window This command attempts to display @var{buffer-or-name} in the selected window and make it the current buffer. It is often used interactively (as the binding of @kbd{C-x b}), as well as in Lisp programs. The return value is the buffer switched to. If @var{buffer-or-name} is @code{nil}, it defaults to the buffer returned by @code{other-buffer} (@pxref{Buffer List}). If @var{buffer-or-name} is a string that is not the name of any existing buffer, this function creates a new buffer with that name; the new buffer's major mode is determined by the variable @code{major-mode} (@pxref{Major Modes}). Normally, the specified buffer is put at the front of the buffer list---both the global buffer list and the selected frame's buffer list (@pxref{Buffer List}). However, this is not done if the optional argument @var{norecord} is non-@code{nil}. Sometimes, @code{switch-to-buffer} may be unable to display the buffer in the selected window. This happens if the selected window is a minibuffer window, or if the selected window is strongly dedicated to its buffer (@pxref{Dedicated Windows}). In that case, the command normally tries to display the buffer in some other window, by invoking @code{pop-to-buffer} (see below). However, if the optional argument @var{force-same-window} is non-@code{nil}, it signals an error instead. @end deffn By default, @code{switch-to-buffer} shows the buffer at its position of @code{point}. This behavior can be tuned using the following option. @defopt switch-to-buffer-preserve-window-point If this variable is @code{nil}, @code{switch-to-buffer} displays the buffer specified by @var{buffer-or-name} at the position of that buffer's @code{point}. If this variable is @code{already-displayed}, it tries to display the buffer at its previous position in the selected window, provided the buffer is currently displayed in some other window on any visible or iconified frame. If this variable is @code{t}, @code{switch-to-buffer} unconditionally tries to display the buffer at its previous position in the selected window. This variable is ignored if the buffer is already displayed in the selected window or never appeared in it before, or if @code{switch-to-buffer} calls @code{pop-to-buffer} to display the buffer. @end defopt The next two commands 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 displays the buffer specified by @var{buffer-or-name} in some window other than the selected window. It uses the function @code{pop-to-buffer} internally (see below). If the selected window already displays the specified buffer, it continues to do so, but another window is nonetheless found to display it as well. The @var{buffer-or-name} and @var{norecord} arguments have the same meanings as in @code{switch-to-buffer}. @end deffn @deffn Command switch-to-buffer-other-frame buffer-or-name &optional norecord This function displays the buffer specified by @var{buffer-or-name} in a new frame. It uses the function @code{pop-to-buffer} internally (see below). If the specified buffer is already displayed in another window, in any frame on the current terminal, this switches to that window instead of creating a new frame. However, the selected window is never used for this. The @var{buffer-or-name} and @var{norecord} arguments have the same meanings as in @code{switch-to-buffer}. @end deffn The above commands use the function @code{pop-to-buffer}, which flexibly displays a buffer in some window and selects that window for editing. In turn, @code{pop-to-buffer} uses @code{display-buffer} for displaying the buffer. Hence, all the variables affecting @code{display-buffer} will affect it as well. @xref{Choosing Window}, for the documentation of @code{display-buffer}. @deffn Command pop-to-buffer buffer-or-name &optional action norecord This function makes @var{buffer-or-name} the current buffer and displays it in some window, preferably not the window previously selected. It then selects the displaying window. If that window is on a different graphical frame, that frame is given input focus if possible (@pxref{Input Focus}). The return value is the buffer that was switched to. If @var{buffer-or-name} is @code{nil}, it defaults to the buffer returned by @code{other-buffer} (@pxref{Buffer List}). If @var{buffer-or-name} is a string that is not the name of any existing buffer, this function creates a new buffer with that name; the new buffer's major mode is determined by the variable @code{major-mode} (@pxref{Major Modes}). If @var{action} is non-@code{nil}, it should be a display action to pass to @code{display-buffer} (@pxref{Choosing Window}). Alternatively, a non-@code{nil}, non-list value means to pop to a window other than the selected one---even if the buffer is already displayed in the selected window. Like @code{switch-to-buffer}, this function updates the buffer list unless @var{norecord} is non-@code{nil}. @end deffn @node Choosing Window @section Choosing a Window for Display The command @code{display-buffer} flexibly chooses a window for display, and displays a specified buffer in that window. It can be called interactively, via the key binding @kbd{C-x 4 C-o}. It is also used as a subroutine by many functions and commands, including @code{switch-to-buffer} and @code{pop-to-buffer} (@pxref{Switching Buffers}). @cindex display action @cindex action function, for @code{display-buffer} @cindex action alist, for @code{display-buffer} This command performs several complex steps to find a window to display in. These steps are described by means of @dfn{display actions}, which have the form @code{(@var{function} . @var{alist})}. Here, @var{function} is either a function or a list of functions, which we refer to as @dfn{action functions}; @var{alist} is an association list, which we refer to as @dfn{action alists}. An action function accepts two arguments: the buffer to display and an action alist. It attempts to display the buffer in some window, picking or creating a window according to its own criteria. If successful, it returns the window; otherwise, it returns @code{nil}. @xref{Display Action Functions}, for a list of predefined action functions. @code{display-buffer} works by combining display actions from several sources, and calling the action functions in turn, until one of them manages to display the buffer and returns a non-@code{nil} value. @deffn Command display-buffer buffer-or-name &optional action frame This command makes @var{buffer-or-name} appear in some window, without selecting the window or making the buffer current. The argument @var{buffer-or-name} must be a buffer or the name of an existing buffer. The return value is the window chosen to display the buffer. The optional argument @var{action}, if non-@code{nil}, should normally be a display action (described above). @code{display-buffer} builds a list of action functions and an action alist, by consolidating display actions from the following sources (in order): @itemize @item The variable @code{display-buffer-overriding-action}. @item The user option @code{display-buffer-alist}. @item The @var{action} argument. @item The user option @code{display-buffer-base-action}. @item The constant @code{display-buffer-fallback-action}. @end itemize @noindent Each action function is called in turn, passing the buffer as the first argument and the combined action alist as the second argument, until one of the functions returns non-@code{nil}. The caller can pass @code{(allow-no-window . t)} as an element of the action alist to indicate its readiness to handle the case of not displaying the buffer in a window. The argument @var{action} can also have a non-@code{nil}, non-list value. This has the special meaning that the buffer should be displayed in a window other than the selected one, even if the selected window is already displaying it. If called interactively with a prefix argument, @var{action} is @code{t}. The optional argument @var{frame}, if non-@code{nil}, specifies which frames to check when deciding whether the buffer is already displayed. It is equivalent to adding an element @code{(reusable-frames . @var{frame})} to the action alist of @var{action}. @xref{Display Action Functions}. @end deffn @defvar display-buffer-overriding-action The value of this variable should be a display action, which is treated with the highest priority by @code{display-buffer}. The default value is empty, i.e., @code{(nil . nil)}. @end defvar @defopt display-buffer-alist The value of this option is an alist mapping conditions to display actions. Each condition may be either a regular expression matching a buffer name or a function that takes two arguments: a buffer name and the @var{action} argument passed to @code{display-buffer}. If the name of the buffer passed to @code{display-buffer} either matches a regular expression in this alist or the function specified by a condition returns non-@code{nil}, then @code{display-buffer} uses the corresponding display action to display the buffer. @end defopt @defopt display-buffer-base-action The value of this option should be a display action. This option can be used to define a ``standard'' display action for calls to @code{display-buffer}. @end defopt @defvr Constant display-buffer-fallback-action This display action specifies the fallback behavior for @code{display-buffer} if no other display actions are given. @end defvr @node Display Action Functions @section Action Functions for @code{display-buffer} The following basic action functions are defined in Emacs. Each of these functions takes two arguments: @var{buffer}, the buffer to display, and @var{alist}, an action alist. Each action function returns the window if it succeeds, and @code{nil} if it fails. @defun display-buffer-same-window buffer alist This function tries to display @var{buffer} in the selected window. It fails if the selected window is a minibuffer window or is dedicated to another buffer (@pxref{Dedicated Windows}). It also fails if @var{alist} has a non-@code{nil} @code{inhibit-same-window} entry. @end defun @defun display-buffer-reuse-window buffer alist This function tries to ``display'' @var{buffer} by finding a window that is already displaying it. If @var{alist} has a non-@code{nil} @code{inhibit-same-window} entry, the selected window is not eligible for reuse. If @var{alist} contains a @code{reusable-frames} entry, its value determines which frames to search for a reusable window: @itemize @bullet @item @code{nil} means consider windows on the selected frame. (Actually, the last non-minibuffer frame.) @item @code{t} means consider windows on all frames. @item @code{visible} means consider windows on all visible frames. @item 0 means consider windows on all visible or iconified frames. @item A frame means consider windows on that frame only. @end itemize Note that these meanings differ slightly from those of the @var{all-frames} argument to @code{next-window} (@pxref{Cyclic Window Ordering}). If @var{alist} contains no @code{reusable-frames} entry, this function normally searches just the selected frame; however, if the variable @code{pop-up-frames} is non-@code{nil}, it searches all frames on the current terminal. @xref{Choosing Window Options}. If this function chooses a window on another frame, it makes that frame visible and, unless @var{alist} contains an @code{inhibit-switch-frame} entry (@pxref{Choosing Window Options}), raises that frame if necessary. @end defun @defun display-buffer-pop-up-frame buffer alist This function creates a new frame, and displays the buffer in that frame's window. It actually performs the frame creation by calling the function specified in @code{pop-up-frame-function} (@pxref{Choosing Window Options}). If @var{alist} contains a @code{pop-up-frame-parameters} entry, the associated value is added to the newly created frame's parameters. @end defun @defun display-buffer-pop-up-window buffer alist This function tries to display @var{buffer} by splitting the largest or least recently-used window (typically one on the selected frame). It actually performs the split by calling the function specified in @code{split-window-preferred-function} (@pxref{Choosing Window Options}). The size of the new window can be adjusted by supplying @code{window-height} and @code{window-width} entries in @var{alist}. To adjust the window's height, use an entry whose @sc{car} is @code{window-height} and whose @sc{cdr} is one of: @itemize @bullet @item @code{nil} means to leave the height of the new window alone. @item A number specifies the desired height of the new window. An integer specifies the number of lines of the window. A floating-point number gives the fraction of the window's height with respect to the height of the frame's root window. @item If the @sc{cdr} specifies a function, that function is called with one argument: the new window. The function is supposed to adjust the height of the window; its return value is ignored. Suitable functions are @code{shrink-window-if-larger-than-buffer} and @code{fit-window-to-buffer}, see @ref{Resizing Windows}. @end itemize To adjust the window's width, use an entry whose @sc{car} is @code{window-width} and whose @sc{cdr} is one of: @itemize @bullet @item @code{nil} means to leave the width of the new window alone. @item A number specifies the desired width of the new window. An integer specifies the number of columns of the window. A floating-point number gives the fraction of the window's width with respect to the width of the frame's root window. @item If the @sc{cdr} specifies a function, that function is called with one argument: the new window. The function is supposed to adjust the width of the window; its return value is ignored. @end itemize This function can fail if no window splitting can be performed for some reason (e.g., if the selected frame has an @code{unsplittable} frame parameter; @pxref{Buffer Parameters}). @end defun @defun display-buffer-below-selected buffer alist This function tries to display @var{buffer} in a window below the selected window. This means to either split the selected window or use the window below the selected one. If it does create a new window, it will also adjust its size provided @var{alist} contains a suitable @code{window-height} or @code{window-width} entry, see above. @end defun @defun display-buffer-in-previous-window buffer alist This function tries to display @var{buffer} in a window previously showing it. If @var{alist} has a non-@code{nil} @code{inhibit-same-window} entry, the selected window is not eligible for reuse. If @var{alist} contains a @code{reusable-frames} entry, its value determines which frames to search for a suitable window as with @code{display-buffer-reuse-window}. If @var{alist} has a @code{previous-window} entry, the window specified by that entry will override any other window found by the methods above, even if that window never showed @var{buffer} before. @end defun @defun display-buffer-at-bottom buffer alist This function tries to display @var{buffer} in a window at the bottom of the selected frame. This either splits the window at the bottom of the frame or the frame's root window, or reuses an existing window at the bottom of the selected frame. @end defun @defun display-buffer-use-some-window buffer alist This function tries to display @var{buffer} by choosing an existing window and displaying the buffer in that window. It can fail if all windows are dedicated to another buffer (@pxref{Dedicated Windows}). @end defun @defun display-buffer-no-window buffer alist If @var{alist} has a non-@code{nil} @code{allow-no-window} entry, then this function does not display @code{buffer}. This allows to override the default action and avoid displaying the buffer. It is assumed that when the caller specifies a non-@code{nil} @code{allow-no-window} value it can handle a @code{nil} value returned from @code{display-buffer} in this case. @end defun To illustrate the use of action functions, consider the following example. @example @group (display-buffer (get-buffer-create "*foo*") '((display-buffer-reuse-window display-buffer-pop-up-window display-buffer-pop-up-frame) (reusable-frames . 0) (window-height . 10) (window-width . 40))) @end group @end example @noindent Evaluating the form above will cause @code{display-buffer} to proceed as follows: If a buffer called *foo* already appears on a visible or iconified frame, it will reuse its window. Otherwise, it will try to pop up a new window or, if that is impossible, a new frame and show the buffer there. If all these steps fail, it will proceed using whatever @code{display-buffer-base-action} and @code{display-buffer-fallback-action} prescribe. Furthermore, @code{display-buffer} will try to adjust a reused window (provided *foo* was put by @code{display-buffer} there before) or a popped-up window as follows: If the window is part of a vertical combination, it will set its height to ten lines. Note that if, instead of the number ``10'', we specified the function @code{fit-window-to-buffer}, @code{display-buffer} would come up with a one-line window to fit the empty buffer. If the window is part of a horizontal combination, it sets its width to 40 columns. Whether a new window is vertically or horizontally combined depends on the shape of the window split and the values of @code{split-window-preferred-function}, @code{split-height-threshold} and @code{split-width-threshold} (@pxref{Choosing Window Options}). Now suppose we combine this call with a preexisting setup for `display-buffer-alist' as follows. @example @group (let ((display-buffer-alist (cons '("\\*foo\\*" (display-buffer-reuse-window display-buffer-below-selected) (reusable-frames) (window-height . 5)) display-buffer-alist))) (display-buffer (get-buffer-create "*foo*") '((display-buffer-reuse-window display-buffer-pop-up-window display-buffer-pop-up-frame) (reusable-frames . 0) (window-height . 10) (window-width . 40)))) @end group @end example @noindent This form will have @code{display-buffer} first try reusing a window that shows *foo* on the selected frame. If there's no such window, it will try to split the selected window or, if that is impossible, use the window below the selected window. If there's no window below the selected one, or the window below the selected one is dedicated to its buffer, @code{display-buffer} will proceed as described in the previous example. Note, however, that when it tries to adjust the height of any reused or popped-up window, it will in any case try to set its number of lines to ``5'' since that value overrides the corresponding specification in the @var{action} argument of @code{display-buffer}. @node Choosing Window Options @section Additional Options for Displaying Buffers The behavior of the standard display actions of @code{display-buffer} (@pxref{Choosing Window}) can be modified by a variety of user options. @defopt pop-up-windows If the value of this variable is non-@code{nil}, @code{display-buffer} is allowed to split an existing window to make a new window for displaying in. This is the default. This variable is provided mainly for backward compatibility. It is obeyed by @code{display-buffer} via a special mechanism in @code{display-buffer-fallback-action}, which only calls the action function @code{display-buffer-pop-up-window} (@pxref{Display Action Functions}) when the value is @code{nil}. It is not consulted by @code{display-buffer-pop-up-window} itself, which the user may specify directly in @code{display-buffer-alist} etc. @end defopt @defopt split-window-preferred-function This variable specifies a function for splitting a window, in order to make a new window for displaying a buffer. It is used by the @code{display-buffer-pop-up-window} action function to actually split the window (@pxref{Display Action Functions}). The default value is @code{split-window-sensibly}, which is documented below. The value must be a function that takes one argument, a window, and return either a new window (which will be used to display the desired buffer) or @code{nil} (which means the splitting failed). @end defopt @defun split-window-sensibly window This function tries to split @var{window}, and return the newly created window. If @var{window} cannot be split, it returns @code{nil}. This function obeys the usual rules that determine when a window may be split (@pxref{Splitting Windows}). It first tries to split by placing the new window below, subject to the restriction imposed by @code{split-height-threshold} (see below), in addition to any other restrictions. If that fails, it tries to split by placing the new window to the right, subject to @code{split-width-threshold} (see below). If that fails, and the window is the only window on its frame, this function again tries to split and place the new window below, disregarding @code{split-height-threshold}. If this fails as well, this function gives up and returns @code{nil}. @end defun @defopt split-height-threshold This variable, used by @code{split-window-sensibly}, specifies whether to split the window placing the new window below. If it is an integer, that means to split only if the original window has at least that many lines. If it is @code{nil}, that means not to split this way. @end defopt @defopt split-width-threshold This variable, used by @code{split-window-sensibly}, specifies whether to split the window placing the new window to the right. If the value is an integer, that means to split only if the original window has at least that many columns. If the value is @code{nil}, that means not to split this way. @end defopt @defopt pop-up-frames If the value of this variable is non-@code{nil}, that means @code{display-buffer} may display buffers by making new frames. The default is @code{nil}. A non-@code{nil} value also means that when @code{display-buffer} is looking for a window already displaying @var{buffer-or-name}, it can search any visible or iconified frame, not just the selected frame. This variable is provided mainly for backward compatibility. It is obeyed by @code{display-buffer} via a special mechanism in @code{display-buffer-fallback-action}, which calls the action function @code{display-buffer-pop-up-frame} (@pxref{Display Action Functions}) if the value is non-@code{nil}. (This is done before attempting to split a window.) This variable is not consulted by @code{display-buffer-pop-up-frame} itself, which the user may specify directly in @code{display-buffer-alist} etc. @end defopt @defopt pop-up-frame-function This variable specifies a function for creating a new frame, in order to make a new window for displaying a buffer. It is used by the @code{display-buffer-pop-up-frame} action function (@pxref{Display Action Functions}). The value should be a function that takes no arguments and returns a frame, or @code{nil} if no frame could be created. The default value is a function that creates a frame using the parameters specified by @code{pop-up-frame-alist} (see below). @end defopt @defopt pop-up-frame-alist This variable holds an alist of frame parameters (@pxref{Frame Parameters}), which is used by the default function in @code{pop-up-frame-function} to make a new frame. The default is @code{nil}. @end defopt @defopt same-window-buffer-names A list of buffer names for buffers that should be displayed in the selected window. If a buffer's name is in this list, @code{display-buffer} handles the buffer by showing 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 showing 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 @node Window History @section Window History @cindex window history Each window remembers in a list the buffers it has previously displayed, and the order in which these buffers were removed from it. This history is used, for example, by @code{replace-buffer-in-windows} (@pxref{Buffers and Windows}). The list is automatically maintained by Emacs, but you can use the following functions to explicitly inspect or alter it: @defun window-prev-buffers &optional window This function returns a list specifying the previous contents of @var{window}. The optional argument @var{window} should be a live window and defaults to the selected one. Each list element has the form @code{(@var{buffer} @var{window-start} @var{window-pos})}, where @var{buffer} is a buffer previously shown in the window, @var{window-start} is the window start position (@pxref{Window Start and End}) when that buffer was last shown, and @var{window-pos} is the point position (@pxref{Window Point}) when that buffer was last shown in @var{window}. The list is ordered so that earlier elements correspond to more recently-shown buffers, and the first element usually corresponds to the buffer most recently removed from the window. @end defun @defun set-window-prev-buffers window prev-buffers This function sets @var{window}'s previous buffers to the value of @var{prev-buffers}. The argument @var{window} must be a live window and defaults to the selected one. The argument @var{prev-buffers} should be a list of the same form as that returned by @code{window-prev-buffers}. @end defun In addition, each buffer maintains a list of @dfn{next buffers}, which is a list of buffers re-shown by @code{switch-to-prev-buffer} (see below). This list is mainly used by @code{switch-to-prev-buffer} and @code{switch-to-next-buffer} for choosing buffers to switch to. @defun window-next-buffers &optional window This function returns the list of buffers recently re-shown in @var{window} via @code{switch-to-prev-buffer}. The @var{window} argument must denote a live window or @code{nil} (meaning the selected window). @end defun @defun set-window-next-buffers window next-buffers This function sets the next buffer list of @var{window} to @var{next-buffers}. The @var{window} argument should be a live window or @code{nil} (meaning the selected window). The argument @var{next-buffers} should be a list of buffers. @end defun The following commands can be used to cycle through the global buffer list, much like @code{bury-buffer} and @code{unbury-buffer}. However, they cycle according to the specified window's history list, rather than the global buffer list. In addition, they restore window-specific window start and point positions, and may show a buffer even if it is already shown in another window. The @code{switch-to-prev-buffer} command, in particular, is used by @code{replace-buffer-in-windows}, @code{bury-buffer} and @code{quit-window} to find a replacement buffer for a window. @deffn Command switch-to-prev-buffer &optional window bury-or-kill This command displays the previous buffer in @var{window}. The argument @var{window} should be a live window or @code{nil} (meaning the selected window). If the optional argument @var{bury-or-kill} is non-@code{nil}, this means that the buffer currently shown in @var{window} is about to be buried or killed and consequently should not be switched to in future invocations of this command. The previous buffer is usually the buffer shown before the buffer currently shown in @var{window}. However, a buffer that has been buried or killed, or has been already shown by a recent invocation of @code{switch-to-prev-buffer}, does not qualify as previous buffer. If repeated invocations of this command have already shown all buffers previously shown in @var{window}, further invocations will show buffers from the buffer list of the frame @var{window} appears on (@pxref{Buffer List}), trying to skip buffers that are already shown in another window on that frame. @end deffn @deffn Command switch-to-next-buffer &optional window This command switches to the next buffer in @var{window}, thus undoing the effect of the last @code{switch-to-prev-buffer} command in @var{window}. The argument @var{window} must be a live window and defaults to the selected one. If there is no recent invocation of @code{switch-to-prev-buffer} that can be undone, this function tries to show a buffer from the buffer list of the frame @var{window} appears on (@pxref{Buffer List}). @end deffn By default @code{switch-to-prev-buffer} and @code{switch-to-next-buffer} can switch to a buffer that is already shown in another window on the same frame. The following option can be used to override this behavior. @defopt switch-to-visible-buffer If this variable is non-@code{nil}, @code{switch-to-prev-buffer} and @code{switch-to-next-buffer} may switch to a buffer that is already visible on the same frame, provided the buffer was shown in the relevant window before. If it is @code{nil}, @code{switch-to-prev-buffer} and @code{switch-to-next-buffer} always try to avoid switching to a buffer that is already visible in another window on the same frame. The default is @code{t}. @end defopt @node Dedicated Windows @section Dedicated Windows @cindex dedicated window Functions for displaying a buffer can be told to not use specific windows by marking these windows as @dfn{dedicated} to their buffers. @code{display-buffer} (@pxref{Choosing Window}) never uses a dedicated window for displaying another buffer in it. @code{get-lru-window} and @code{get-largest-window} (@pxref{Cyclic Window Ordering}) do not consider dedicated windows as candidates when their @var{dedicated} argument is non-@code{nil}. The behavior of @code{set-window-buffer} (@pxref{Buffers and Windows}) with respect to dedicated windows is slightly different, see below. Functions supposed to remove a buffer from a window or a window from a frame can behave specially when a window they operate on is dedicated. We will distinguish three basic cases, namely where (1) the window is not the only window on its frame, (2) the window is the only window on its frame but there are other frames on the same terminal left, and (3) the window is the only window on the only frame on the same terminal. In particular, @code{delete-windows-on} (@pxref{Deleting Windows}) handles case (2) by deleting the associated frame and case (3) by showing another buffer in that frame's only window. The function @code{replace-buffer-in-windows} (@pxref{Buffers and Windows}) which is called when a buffer gets killed, deletes the window in case (1) and behaves like @code{delete-windows-on} otherwise. @c FIXME: Does replace-buffer-in-windows _delete_ a window in case (1)? When @code{bury-buffer} (@pxref{Buffer List}) operates on the selected window (which shows the buffer that shall be buried), it handles case (2) by calling @code{frame-auto-hide-function} (@pxref{Quitting Windows}) to deal with the selected frame. The other two cases are handled as with @code{replace-buffer-in-windows}. @defun window-dedicated-p &optional window This function returns non-@code{nil} if @var{window} is dedicated to its buffer and @code{nil} otherwise. More precisely, the return value is the value assigned by the last call of @code{set-window-dedicated-p} for @var{window}, or @code{nil} if that function was never called with @var{window} as its argument. The default for @var{window} is the selected window. @end defun @defun set-window-dedicated-p window flag This function marks @var{window} as dedicated to its buffer if @var{flag} is non-@code{nil}, and non-dedicated otherwise. As a special case, if @var{flag} is @code{t}, @var{window} becomes @dfn{strongly} dedicated to its buffer. @code{set-window-buffer} signals an error when the window it acts upon is strongly dedicated to its buffer and does not already display the buffer it is asked to display. Other functions do not treat @code{t} differently from any non-@code{nil} value. @end defun @node Quitting Windows @section Quitting Windows When you want to get rid of a window used for displaying a buffer, you can call @code{delete-window} or @code{delete-windows-on} (@pxref{Deleting Windows}) to remove that window from its frame. If the buffer is shown on a separate frame, you might want to call @code{delete-frame} (@pxref{Deleting Frames}) instead. If, on the other hand, a window has been reused for displaying the buffer, you might prefer showing the buffer previously shown in that window, by calling the function @code{switch-to-prev-buffer} (@pxref{Window History}). Finally, you might want to either bury (@pxref{Buffer List}) or kill (@pxref{Killing Buffers}) the window's buffer. The following command uses information on how the window for displaying the buffer was obtained in the first place, thus attempting to automate the above decisions for you. @deffn Command quit-window &optional kill window This command quits @var{window} and buries its buffer. The argument @var{window} must be a live window and defaults to the selected one. With prefix argument @var{kill} non-@code{nil}, it kills the buffer instead of burying it. It calls the function @code{quit-restore-window} described next to deal with the window and its buffer. @end deffn @defun quit-restore-window &optional window bury-or-kill This function tries to restore the state of @var{window} that existed before its buffer was displayed in it. The optional argument @var{window} must be a live window and defaults to the selected one. If @var{window} was created specially for displaying its buffer, this function deletes @var{window} provided its frame contains at least one other live window. If @var{window} is the only window on its frame and there are other frames on the frame's terminal, the value of the optional argument @var{bury-or-kill} determines how to proceed with the window. If @var{bury-or-kill} equals @code{kill}, the frame is deleted unconditionally. Otherwise, the fate of the frame is determined by calling @code{frame-auto-hide-function} (see below) with that frame as sole argument. Otherwise, this function tries to redisplay the buffer previously shown in @var{window}. It also tries to restore the window start (@pxref{Window Start and End}) and point (@pxref{Window Point}) positions of the previously shown buffer. If, in addition, @var{window}'s buffer was temporarily resized, this function will also try to restore the original height of @var{window}. The cases described so far require that the buffer shown in @var{window} is still the buffer displayed by the last buffer display function for this window. If another buffer has been shown in the meantime, or the buffer previously shown no longer exists, this function calls @code{switch-to-prev-buffer} (@pxref{Window History}) to show some other buffer instead. The optional argument @var{bury-or-kill} specifies how to deal with @var{window}'s buffer. The following values are handled: @table @code @item nil This means to not deal with the buffer in any particular way. As a consequence, if @var{window} is not deleted, invoking @code{switch-to-prev-buffer} will usually show the buffer again. @item append This means that if @var{window} is not deleted, its buffer is moved to the end of @var{window}'s list of previous buffers, so it's less likely that a future invocation of @code{switch-to-prev-buffer} will switch to it. Also, it moves the buffer to the end of the frame's buffer list. @item bury This means that if @var{window} is not deleted, its buffer is removed from @var{window}'s list of previous buffers. Also, it moves the buffer to the end of the frame's buffer list. This value provides the most reliable remedy to not have @code{switch-to-prev-buffer} switch to this buffer again without killing the buffer. @item kill This means to kill @var{window}'s buffer. @end table @code{quit-restore-window} bases its decisions on information stored in @var{window}'s @code{quit-restore} window parameter (@pxref{Window Parameters}), and resets that parameter to @code{nil} after it's done. @end defun The following option specifies how to deal with a frame containing just one window that should be either quit, or whose buffer should be buried. @defopt frame-auto-hide-function The function specified by this option is called to automatically hide frames. This function is called with one argument---a frame. The function specified here is called by @code{bury-buffer} (@pxref{Buffer List}) when the selected window is dedicated and shows the buffer to bury. It is also called by @code{quit-restore-window} (see above) when the frame of the window to quit has been specially created for displaying that window's buffer and the buffer is not killed. The default is to call @code{iconify-frame} (@pxref{Visibility of Frames}). Alternatively, you may specify either @code{delete-frame} (@pxref{Deleting Frames}) to remove the frame from its display, @code{ignore} to leave the frame unchanged, or any other function that can take a frame as its sole argument. Note that the function specified by this option is called only if the specified frame contains just one live window and there is at least one other frame on the same terminal. @end defopt @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 (@pxref{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. @end itemize @cindex cursor 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. The default for @var{window} is the selected window. When @var{window} is the selected window, the value returned is the value of point in that window's 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}. If @var{window} is selected, this simply does @code{goto-char} in @var{window}'s buffer. @end defun @defvar window-point-insertion-type This variable specifies the marker insertion type (@pxref{Marker Insertion Types}) of @code{window-point}. The default is @code{nil}, so @code{window-point} will stay behind text inserted there. @end defvar @node Window Start and End @section The Window Start and End Positions @cindex window start position @cindex display-start position Each window maintains 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. After switching windows or buffers, and in some other cases, if the window start is in the middle of a line, Emacs adjusts the window start to the start of a line. This prevents certain operations from leaving the window start at a meaningless point within a line. This feature may interfere with testing some Lisp code by executing it using the commands of Lisp mode, because they trigger this readjustment. To test such code, put it into a command and bind the command to a key. @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. 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 to @code{point-min} if the buffer doesn't have any. Redisplay updates the window-start position (if you have not specified it explicitly since the previous redisplay)---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. @end defun @cindex window end position @defun window-end &optional window update This function returns the position where display of its buffer ends in @var{window}. The default for @var{window} is the selected window. 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 non-@code{nil}, @code{window-end} always returns an up-to-date value for where display ends, based on the current @code{window-start} value. If a previously saved value of that position is still valid, @code{window-end} returns that value; otherwise it computes the correct value by scanning the buffer text. Even if @var{update} is non-@code{nil}, @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 37}, the start of the next line, point will 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) (save-excursion (goto-char 1) (forward-line 1) (point))) @result{} 37 @end group @group ;; @r{Here is what @samp{foo} looks like after executing} ;; @r{the @code{set-window-start} expression.} ---------- Buffer: foo ---------- 2 3 @point{}4 5 6 ---------- Buffer: foo ---------- @end group @end example If @var{noforce} is non-@code{nil}, 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 non-@code{nil} 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 non-@code{nil}. The argument @var{position} defaults to the current position of point in @var{window}; @var{window}, to the selected window. If @var{position} is @code{t}, that means to check the last visible position in @var{window}. This 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 non-@code{nil} 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 non-@code{nil}, and the character following @var{position} is fully visible, it returns a list of the form @code{(@var{x} @var{y})}, where @var{x} and @var{y} are the pixel coordinates relative to the top left corner of the window; otherwise it returns an extended list of the form @code{(@var{x} @var{y} @var{rtop} @var{rbot} @var{rowh} @var{vpos})}, where @var{rtop} and @var{rbot} specify the number of off-window pixels at the top and bottom of the row at @var{position}, @var{rowh} specifies the visible height of that row, and @var{vpos} specifies the vertical position (zero-based row number) of that row. Here is an example: @example @group ;; @r{If point is off the screen now, recenter it now.} (or (pos-visible-in-window-p (point) (selected-window)) (recenter 0)) @end group @end example @end defun @defun window-line-height &optional line window This function returns the height of text line @var{line} in @var{window}. If @var{line} is one of @code{header-line} or @code{mode-line}, @code{window-line-height} returns information about the corresponding line of the window. Otherwise, @var{line} is a text line number starting from 0. A negative number counts from the end of the window. The default for @var{line} is the current line in @var{window}; the default for @var{window} is the selected window. If the display is not up to date, @code{window-line-height} returns @code{nil}. In that case, @code{pos-visible-in-window-p} may be used to obtain related information. If there is no line corresponding to the specified @var{line}, @code{window-line-height} returns @code{nil}. Otherwise, it returns a list @code{(@var{height} @var{vpos} @var{ypos} @var{offbot})}, where @var{height} is the height in pixels of the visible part of the line, @var{vpos} and @var{ypos} are the vertical position in lines and pixels of the line relative to the top of the first text line, and @var{offbot} is the number of off-window pixels at the bottom of the text line. If there are off-window pixels at the top of the (first) text line, @var{ypos} is negative. @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 window's display-start location. It may also change the value of @code{window-point} to keep point on the screen (@pxref{Window Point}). The basic textual scrolling functions are @code{scroll-up} (which scrolls forward) and @code{scroll-down} (which scrolls backward). In these function names, ``up'' and ``down'' refer to the direction of motion of the buffer text relative to 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 the middle of a buffer and repeatedly call @code{scroll-down}, you will eventually see the beginning of the buffer. Unfortunately, this sometimes causes confusion, because some people tend to think in terms of the opposite convention: they imagine the window moving over text that remains in place, so that ``down'' commands take you to the end of the buffer. This convention is consistent with fact that such a command is bound to a key named @key{PageDown} on modern keyboards. @ignore We have not switched to this convention as that is likely to break existing Emacs Lisp code. @end ignore Textual scrolling functions (aside from @code{scroll-other-window}) have unpredictable results if the current buffer is not the one displayed in the selected window. @xref{Current Buffer}. If the window contains a row taller than the height of the window (for example in the presence of a large image), the scroll functions will adjust the window's vertical scroll position to scroll the partially visible row. Lisp callers can disable this feature by binding the variable @code{auto-window-vscroll} to @code{nil} (@pxref{Vertical Scrolling}). @deffn Command scroll-up &optional count This function scrolls forward by @var{count} lines in the selected window. If @var{count} is negative, it scrolls backward instead. If @var{count} is @code{nil} (or omitted), the distance scrolled is @code{next-screen-context-lines} lines less than the height of the window's text area. If the selected window cannot be scrolled any further, this function signals an error. Otherwise, it returns @code{nil}. @end deffn @deffn Command scroll-down &optional count This function scrolls backward by @var{count} lines in the selected window. If @var{count} is negative, it scrolls forward instead. In other respects, it behaves the same way as @code{scroll-up} does. @end deffn @deffn Command scroll-up-command &optional count This behaves like @code{scroll-up}, except that if the selected window cannot be scrolled any further and the value of the variable @code{scroll-error-top-bottom} is @code{t}, it tries to move to the end of the buffer instead. If point is already there, it signals an error. @end deffn @deffn Command scroll-down-command &optional count This behaves like @code{scroll-down}, except that if the selected window cannot be scrolled any further and the value of the variable @code{scroll-error-top-bottom} is @code{t}, it tries to move to the beginning of the buffer instead. If point is already there, it signals an error. @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 leftmost one immediately above it. 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 non-@code{nil} 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 @samp{End of buffer}. @end deffn @defvar other-window-scroll-buffer If this variable is non-@code{nil}, it tells @code{scroll-other-window} which buffer's window 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 behavior 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 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 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 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 @cindex @code{scroll-command} property @defopt scroll-preserve-screen-position If this option is @code{t}, whenever a scrolling command moves point off-window, Emacs tries to adjust point to keep the cursor at its old vertical position in the window, rather than the window edge. If the value is non-@code{nil} and not @code{t}, Emacs adjusts point to keep the cursor at the same vertical position, even if the scrolling command didn't move point off-window. This option affects all scroll commands that have a non-@code{nil} @code{scroll-command} symbol property. @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 @defopt scroll-error-top-bottom If this option is @code{nil} (the default), @code{scroll-up-command} and @code{scroll-down-command} simply signal an error when no more scrolling is possible. If the value is @code{t}, these commands instead move point to the beginning or end of the buffer (depending on scrolling direction); only if point is already on that position do they signal an error. @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 non-negative 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 @code{nil} (or a non-@code{nil} list), @code{recenter} puts the line containing point in the middle of the window. If @var{count} is @code{nil}, this function may redraw the frame, according to the value of @code{recenter-redisplay}. 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 non-@code{nil} 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. The command @code{recenter-top-bottom} offers a more convenient way to achieve this. @end deffn @defopt recenter-redisplay If this variable is non-@code{nil}, calling @code{recenter} with a @code{nil} argument redraws the frame. The default value is @code{tty}, which means only redraw the frame if it is a tty frame. @end defopt @deffn Command recenter-top-bottom &optional count This command, which is the default binding for @kbd{C-l}, acts like @code{recenter}, except if called with no argument. In that case, successive calls place point according to the cycling order defined by the variable @code{recenter-positions}. @end deffn @defopt recenter-positions This variable controls how @code{recenter-top-bottom} behaves when called with no argument. The default value is @code{(middle top bottom)}, which means that successive calls of @code{recenter-top-bottom} with no argument cycle between placing point at the middle, top, and bottom of the window. @end defopt @node Vertical Scrolling @section Vertical Fractional Scrolling @cindex vertical fractional scrolling @cindex vertical scroll position @dfn{Vertical fractional scrolling} means shifting text in a window up or down by a specified multiple or fraction of a line. 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}. The default for @var{window} is the selected window. If @var{pixels-p} is non-@code{nil}, 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}. If @var{window} is @code{nil}, the selected window is used. The argument @var{lines} should be zero or positive; if not, it is taken as zero. 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 non-@code{nil}, @var{lines} specifies a number of pixels. In this case, the return value is @var{lines}. @end defun @defvar auto-window-vscroll If this variable is non-@code{nil}, the @code{line-move}, @code{scroll-up}, and @code{scroll-down} functions will automatically modify the vertical scroll position to scroll through display rows that are taller than the height of the window, for example in the presence of large images. @end defvar @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 set-minimum 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). 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. If @var{set-minimum} is non-@code{nil}, the new scroll amount becomes the lower bound for automatic scrolling; that is, automatic scrolling will not scroll a window to a column less than the value returned by this function. Interactive calls pass non-@code{nil} for @var{set-minimum}. @end deffn @deffn Command scroll-right &optional count set-minimum 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. Aside from the direction of scrolling, this works just like @code{scroll-left}. @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 default for @var{window} is the selected window. The return value is never negative. It is zero when no horizontal scrolling has been done in @var{window} (which is usually the case). @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: @c FIXME: Maybe hscroll-on-screen-p is a better name? @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 Coordinates and Windows @section Coordinates and Windows @cindex frame-relative coordinate @cindex coordinate, relative to frame @cindex window position This section describes functions that report the position of a window. Most of these functions report positions relative to the window's frame. In this case, the coordinate origin @samp{(0,0)} lies near the upper left corner of the frame. For technical reasons, on graphical displays the origin is not located at the exact corner of the graphical window as it appears on the screen. If Emacs is built with the GTK+ toolkit, the origin is at the upper left corner of the frame area used for displaying Emacs windows, below the title-bar, GTK+ menu bar, and tool bar (since these are drawn by the window manager and/or GTK+, not by Emacs). But if Emacs is not built with GTK+, the origin is at the upper left corner of the tool bar (since in this case Emacs itself draws the tool bar). In both cases, the X and Y coordinates increase rightward and downward respectively. Except where noted, X and Y coordinates are reported in integer character units, i.e., numbers of lines and columns respectively. On a graphical display, each ``line'' and ``column'' corresponds to the height and width of a default character specified by the frame's default font. @defun window-edges &optional window This function returns a list of the edge coordinates of @var{window}. If @var{window} is omitted or @code{nil}, it defaults to the selected window. The return value has the form @code{(@var{left} @var{top} @var{right} @var{bottom})}. These list elements are, respectively, the X coordinate of the leftmost column occupied by the window, the Y coordinate of the topmost row, the X coordinate one column to the right of the rightmost column, and the Y coordinate one row down from the bottommost row. Note that these are the actual outer edges of the window, including any header line, mode line, scroll bar, fringes, window divider and display margins. On a text terminal, if the window has a neighbor on its right, its right edge includes the separator line between the window and its neighbor. @end defun @defun window-inside-edges &optional window This function is similar to @code{window-edges}, but the returned edge values are for the text area of the window. They exclude any header line, mode line, scroll bar, fringes, window divider, display margins, and vertical separator. @end defun @defun window-top-line &optional window This function returns the Y coordinate of the topmost row of @var{window}, equivalent to the @var{top} entry in the list returned by @code{window-edges}. @end defun @defun window-left-column &optional window This function returns the X coordinate of the leftmost column of @var{window}, equivalent to the @var{left} entry in the list returned by @code{window-edges}. @end defun The following functions can be used to relate a set of frame-relative coordinates to a window: @defun window-at x y &optional frame This function returns the live window at the frame-relative coordinates @var{x} and @var{y}, on frame @var{frame}. If there is no window at that position, the return value is @code{nil}. If @var{frame} is omitted or @code{nil}, it defaults to the selected frame. @end defun @defun coordinates-in-window-p coordinates window This function checks whether a window @var{window} occupies the frame-relative coordinates @var{coordinates}, and if so, which part of the window that is. @var{window} should be a live window. @var{coordinates} should be a cons cell of the form @code{(@var{x} . @var{y})}, where @var{x} and @var{y} are frame-relative coordinates. If there is no window at the specified position, the return value is @code{nil} . Otherwise, the return value is one of the following: @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 right-divider The coordinates are in the divider separating @var{window} from a window on the right. @item right-divider The coordinates are in the divider separating @var{window} from a window beneath. @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 The following functions return window positions in pixels, rather than character units. Though mostly useful on graphical displays, they can also be called on text terminals, where the screen area of each text character is taken to be ``one pixel''. @defun window-pixel-edges &optional window This function returns a list of pixel coordinates for the edges of @var{window}. If @var{window} is omitted or @code{nil}, it defaults to the selected window. The return value has the form @code{(@var{left} @var{top} @var{right} @var{bottom})}. The list elements are, respectively, the X pixel coordinate of the left window edge, the Y pixel coordinate of the top edge, one more than the X pixel coordinate of the right edge, and one more than the Y pixel coordinate of the bottom edge. @end defun @defun window-inside-pixel-edges &optional window This function is like @code{window-pixel-edges}, except that it returns the pixel coordinates for the edges of the window's text area, rather than the pixel coordinates for the edges of the window itself. @var{window} must specify a live window. @end defun The following functions return window positions in pixels, relative to the display screen rather than the frame: @defun window-absolute-pixel-edges &optional window This function is like @code{window-pixel-edges}, except that it returns the edge pixel coordinates relative to the top left corner of the display screen. @end defun @defun window-inside-absolute-pixel-edges &optional window This function is like @code{window-inside-pixel-edges}, except that it returns the edge pixel coordinates relative to the top left corner of the display screen. @var{window} must specify a live window. @end defun @defun window-pixel-left &optional window This function returns the left pixel edge of window @var{window}. @var{window} must be a valid window and defaults to the selected one. @end defun @defun window-pixel-top &optional window This function returns the top pixel edge of window @var{window}. @var{window} must be a valid window and defaults to the selected one. @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, how those buffers are scrolled, and their values of point and the mark; also their fringes, margins, and scroll bar settings. It also includes the value of @code{minibuffer-scroll-window}. As a special exception, the window configuration does not record the value of point in the selected window for the current buffer. You can bring back an entire frame layout by restoring a previously saved window configuration. If you want to record the layout of 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. The default for @var{frame} is the selected frame. The variable @code{window-persistent-parameters} specifies which window parameters (if any) are saved by this function. @xref{Window Parameters}. @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}. The 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 from which @var{configuration} was saved 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-below nil) @dots{}) (set-window-configuration config))) @end group @end example @end defun @defmac save-window-excursion forms@dots{} This macro records the window configuration of the selected frame, executes @var{forms} in sequence, then restores the earlier window configuration. The return value is the value of the final form in @var{forms}. Most Lisp code should not use this macro; @code{save-selected-window} is typically sufficient. In particular, this macro cannot reliably prevent the code in @var{forms} from opening new windows, because new windows might be opened in other frames (@pxref{Choosing Window}), and @code{save-window-excursion} only saves and restores the window configuration on the current frame. Do not use this macro in @code{window-size-change-functions}; exiting the macro triggers execution of @code{window-size-change-functions}, leading to an endless loop. @end defmac @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. The objects returned by @code{current-window-configuration} die together with the Emacs process. In order to store a window configuration on disk and read it back in another Emacs session, you can use the functions described next. These functions are also useful to clone the state of a frame into an arbitrary live window (@code{set-window-configuration} effectively clones the windows of a frame into the root window of that very frame only). @cindex window state @defun window-state-get &optional window writable This function returns the state of @var{window} as a Lisp object. The argument @var{window} must be a valid window and defaults to the root window of the selected frame. If the optional argument @var{writable} is non-@code{nil}, this means to not use markers for sampling positions like @code{window-point} or @code{window-start}. This argument should be non-@code{nil} when the state will be written to disk and read back in another session. Together, the argument @var{writable} and the variable @code{window-persistent-parameters} specify which window parameters are saved by this function. @xref{Window Parameters}. @end defun The value returned by @code{window-state-get} can be used in the same session to make a clone of a window in another window. It can be also written to disk and read back in another session. In either case, use the following function to restore the state of the window. @defun window-state-put state &optional window ignore This function puts the window state @var{state} into @var{window}. The argument @var{state} should be the state of a window returned by an earlier invocation of @code{window-state-get}, see above. The optional argument @var{window} can be either a live window or an internal window (@pxref{Windows and Frames}) and defaults to the selected one. If @var{window} is not live, it is replaced by a live window before putting @var{state} into it. If the optional argument @var{ignore} is non-@code{nil}, it means to ignore minimum window sizes and fixed-size restrictions. If @var{ignore} is @code{safe}, this means windows can get as small as one line and/or two columns. @end defun @node Window Parameters @section Window Parameters @cindex window parameters This section describes how window parameters can be used to associate additional information with windows. @defun window-parameter window parameter This function returns @var{window}'s value for @var{parameter}. The default for @var{window} is the selected window. If @var{window} has no setting for @var{parameter}, this function returns @code{nil}. @end defun @defun window-parameters &optional window This function returns all parameters of @var{window} and their values. The default for @var{window} is the selected window. The return value is either @code{nil}, or an association list whose elements have the form @code{(@var{parameter} . @var{value})}. @end defun @defun set-window-parameter window parameter value This function sets @var{window}'s value of @var{parameter} to @var{value} and returns @var{value}. The default for @var{window} is the selected window. @end defun By default, the functions that save and restore window configurations or the states of windows (@pxref{Window Configurations}) do not care about window parameters. This means that when you change the value of a parameter within the body of a @code{save-window-excursion}, the previous value is not restored when that macro exits. It also means that when you restore via @code{window-state-put} a window state saved earlier by @code{window-state-get}, all cloned windows have their parameters reset to @code{nil}. The following variable allows you to override the standard behavior: @defvar window-persistent-parameters This variable is an alist specifying which parameters get saved by @code{current-window-configuration} and @code{window-state-get}, and subsequently restored by @code{set-window-configuration} and @code{window-state-put}. @xref{Window Configurations}. The @sc{car} of each entry of this alist is a symbol specifying the parameter. The @sc{cdr} should be one of the following: @table @asis @item @code{nil} This value means the parameter is saved neither by @code{window-state-get} nor by @code{current-window-configuration}. @item @code{t} This value specifies that the parameter is saved by @code{current-window-configuration} and (provided its @var{writable} argument is @code{nil}) by @code{window-state-get}. @item @code{writable} This means that the parameter is saved unconditionally by both @code{current-window-configuration} and @code{window-state-get}. This value should not be used for parameters whose values do not have a read syntax. Otherwise, invoking @code{window-state-put} in another session may fail with an @code{invalid-read-syntax} error. @end table @end defvar Some functions (notably @code{delete-window}, @code{delete-other-windows} and @code{split-window}), may behave specially when their @var{window} argument has a parameter set. You can override such special behavior by binding the following variable to a non-@code{nil} value: @defvar ignore-window-parameters If this variable is non-@code{nil}, some standard functions do not process window parameters. The functions currently affected by this are @code{split-window}, @code{delete-window}, @code{delete-other-windows}, and @code{other-window}. An application can bind this variable to a non-@code{nil} value around calls to these functions. If it does so, the application is fully responsible for correctly assigning the parameters of all involved windows when exiting that function. @end defvar The following parameters are currently used by the window management code: @table @asis @item @code{delete-window} This parameter affects the execution of @code{delete-window} (@pxref{Deleting Windows}). @item @code{delete-other-windows} This parameter affects the execution of @code{delete-other-windows} (@pxref{Deleting Windows}). @item @code{split-window} This parameter affects the execution of @code{split-window} (@pxref{Splitting Windows}). @item @code{other-window} This parameter affects the execution of @code{other-window} (@pxref{Cyclic Window Ordering}). @item @code{no-other-window} This parameter marks the window as not selectable by @code{other-window} (@pxref{Cyclic Window Ordering}). @item @code{clone-of} This parameter specifies the window that this one has been cloned from. It is installed by @code{window-state-get} (@pxref{Window Configurations}). @item @code{quit-restore} This parameter is installed by the buffer display functions (@pxref{Choosing Window}) and consulted by @code{quit-restore-window} (@pxref{Quitting Windows}). It contains four elements: The first element is one of the symbols @code{window}, meaning that the window has been specially created by @code{display-buffer}; @code{frame}, a separate frame has been created; @code{same}, the window has displayed the same buffer before; or @code{other}, the window showed another buffer before. The second element is either one of the symbols @code{window} or @code{frame}, or a list whose elements are the buffer shown in the window before, that buffer's window start and window point positions, and the window's height at that time. The third element is the window selected at the time the parameter was created. The function @code{quit-restore-window} tries to reselect that window when it deletes the window passed to it as argument. The fourth element is the buffer whose display caused the creation of this parameter. @code{quit-restore-window} deletes the specified window only if it still shows that buffer. @end table There are additional parameters @code{window-atom} and @code{window-side}; these are reserved and should not be used by applications. @node Window Hooks @section Hooks for Window Scrolling and Changes @cindex hooks for window operations 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}. @defvar window-scroll-functions This variable holds a list of functions that Emacs should call before redisplaying a window with scrolling. Displaying a different buffer in the window also runs these functions. This variable is not a normal hook, because each function is called with two arguments: the window, and its new display-start position. These functions must take care when using @code{window-end} (@pxref{Window Start and End}); if you need an up-to-date value, you must use the @var{update} argument to ensure you get it. @strong{Warning:} don't use this feature to alter the way the window is scrolled. It's not designed for that, and such use probably won't work. @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. You may use @code{save-selected-window} in these functions (@pxref{Selecting Windows}). However, do not use @code{save-window-excursion} (@pxref{Window Configurations}); exiting that macro counts as a size change, which would cause these functions to be called over and over. @end defvar @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 buffer-local part of this hook is run once for each window on the affected frame, with the relevant window selected and its buffer current. The global part is run once for the modified frame, with that frame selected. @end defvar In addition, you can use @code{jit-lock-register} to register a Font Lock fontification function, which will be called whenever parts of a buffer are (re)fontified because a window was scrolled or its size changed. @xref{Other Font Lock Variables}.