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1 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.


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1.1 Basic Concepts of Emacs Windows

A 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.

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.

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.

Unlike X windows, Emacs windows are 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.

Function: windowp object

This function returns t if object is a window (whether or not it displays a buffer). Otherwise, it returns nil.

A live window is one that is actually displaying a buffer in a frame.

Function: window-live-p object

This function returns t if object is a live window and nil otherwise. A live window is one that displays a buffer.

The windows in each frame are organized into a window tree. See section 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 internal windows, which are not live.

A valid window is one that is either live or internal. A valid window can be deleted, i.e., removed from its frame (see section Deleting Windows); then it is no longer valid, but the Lisp object representing it might be still referenced from other Lisp objects.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 (see section Window Configurations).

You can distinguish valid windows from deleted windows with window-valid-p.

Function: window-valid-p object

This function returns t if object is a live window, or an internal window in a window tree. Otherwise, it returns nil, including for the case where object is a deleted window.

In each frame, at any time, exactly one Emacs window is designated as selected within the frame. For the selected frame, that window is called the selected window—the one in which most editing takes place, and in which the cursor for selected windows appears (@pxref{Cursor Parameters}). Keyboard input that inserts or deletes text is also normally directed to this window. The selected window’s buffer is usually also the current buffer, except when 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. See section Selecting Windows.

Function: selected-window

This function returns the selected window (which is always a live window).

Sometimes several windows collectively and cooperatively display a buffer, for example, under the management of Follow Mode (see (emacs)Follow Mode), where the windows together display a bigger portion of the buffer than one window could alone. It is often useful to consider such a window group as a single entity. Several functions such as window-group-start (see section The Window Start and End Positions) allow you to do this by supplying, as an argument, one of the windows as a stand in for the whole group.

Function: selected-window-group

When the selected window is a member of a group of windows, this function returns a list of the windows in the group, ordered such that the first window in the list is displaying the earliest part of the buffer, and so on. Otherwise the function returns a list containing just the selected window.

The selected window is considered part of a group when the buffer local variable selected-window-group-function is set to a function. In this case, selected-window-group calls it with no arguments and returns its result (which should be the list of windows in the group).


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1.2 Windows and Frames

Each window belongs to exactly one frame (@pxref{Frames}).

Function: window-frame &optional window

This function returns the frame that the window window belongs to. If window is nil, it defaults to the selected window.

Function: window-list &optional frame minibuffer window

This function returns a list of live windows belonging to the frame frame. If frame is omitted or nil, it defaults to the selected frame.

The optional argument minibuffer specifies whether to include the minibuffer window in the returned list. If minibuffer is t, the minibuffer window is included. If minibuffer is nil or omitted, the minibuffer window is included only if it is active. If minibuffer is neither nil nor t, the minibuffer window is never included.

The optional argument window, if non-nil, should be a live window on the specified frame; then window will be the first element in the returned list. If window is omitted or nil, the window selected within the frame is the first element.

Windows in the same frame are organized into a 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 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 window-tree described at the end of this section lists the minibuffer window alongside the actual window tree.

Function: frame-root-window &optional frame-or-window

This function returns the root window for frame-or-window. The argument frame-or-window should be either a window or a frame; if omitted or nil, it defaults to the selected frame. If frame-or-window is a window, the return value is the root window of that window’s frame.

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 child windows of a single internal window. If necessary, Emacs automatically creates this internal window, which is also called the parent window, and assigns it to the appropriate position in the window tree. A set of windows that share the same parent are called siblings.

Function: window-parent &optional window

This function returns the parent window of window. If window is omitted or nil, it defaults to the selected window. The return value is nil if window has no parent (i.e., it is a minibuffer window or the root window of its frame).

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 screen area—the union of the areas occupied by the live windows that are ultimately descended from it.

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 vertical combination; if they are arranged side by side, they are said to form a horizontal combination. Consider the following example:

     ______________________________________
    | ______  ____________________________ |
    ||      || __________________________ ||
    ||      |||                          |||
    ||      |||                          |||
    ||      |||                          |||
    ||      |||____________W4____________|||
    ||      || __________________________ ||
    ||      |||                          |||
    ||      |||                          |||
    ||      |||____________W5____________|||
    ||__W2__||_____________W3_____________ |
    |__________________W1__________________|

The root window of this frame is an internal window, W1. Its child windows form a horizontal combination, consisting of the live window W2 and the internal window W3. The child windows of W3 form a vertical combination, consisting of the live windows W4 and W5. Hence, the live windows in this window tree are W2, W4, and W5.

The following functions can be used to retrieve a child window of an internal window, and the siblings of a child window.

Function: window-top-child &optional window

This function returns the topmost child window of window, if window is an internal window whose children form a vertical combination. For any other type of window, the return value is nil.

Function: window-left-child &optional window

This function returns the leftmost child window of window, if window is an internal window whose children form a horizontal combination. For any other type of window, the return value is nil.

Function: window-child window

This function returns the first child window of the internal window window—the topmost child window for a vertical combination, or the leftmost child window for a horizontal combination. If window is a live window, the return value is nil.

Function: window-combined-p &optional window horizontal

This function returns a non-nil value if and only if window is part of a vertical combination. If window is omitted or nil, it defaults to the selected one.

If the optional argument horizontal is non-nil, this means to return non-nil if and only if window is part of a horizontal combination.

Function: window-next-sibling &optional window

This function returns the next sibling of the window window. If omitted or nil, window defaults to the selected window. The return value is nil if window is the last child of its parent.

Function: window-prev-sibling &optional window

This function returns the previous sibling of the window window. If omitted or nil, window defaults to the selected window. The return value is nil if window is the first child of its parent.

The functions window-next-sibling and window-prev-sibling should not be confused with the functions next-window and previous-window, which return the next and previous window, respectively, in the cyclic ordering of windows (see section Cyclic Ordering of Windows).

The following functions can be useful to locate a window within its frame.

Function: frame-first-window &optional frame-or-window

This function returns the live window at the upper left corner of the frame specified by frame-or-window. The argument frame-or-window must denote a window or a live frame and defaults to the selected frame. If 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 (frame-first-window) returns W2.

Function: window-at-side-p &optional window side

This function returns t if window is located at side of its containing frame. The argument window must be a valid window and defaults to the selected one. The argument side can be any of the symbols left, top, right or bottom. The default value nil is handled like bottom.

Note that this function disregards the minibuffer window (@pxref{Minibuffer Windows}). Hence, with side equal to bottom it may return t also when the minibuffer window appears right below window.

Function: window-in-direction direction &optional window ignore sign wrap mini

This function returns the nearest live window in direction direction as seen from the position of window-point in window window. The argument direction must be one of above, below, left or right. The optional argument window must denote a live window and defaults to the selected one.

This function does not return a window whose no-other-window parameter is non-nil (see section Window Parameters). If the nearest window’s no-other-window parameter is non-nil, this function tries to find another window in the indicated direction whose no-other-window parameter is nil. If the optional argument ignore is non-nil, a window may be returned even if its no-other-window parameter is non-nil.

If the optional argument sign is a negative number, it means to use the right or bottom edge of window as reference position instead of window-point. If sign is a positive number, it means to use the left or top edge of window as reference position.

If the optional argument wrap is non-nil, this means to wrap direction around frame borders. For example, if window is at the top of the frame and direction is above, then this function usually returns the frame’s minibuffer window if it’s active and a window at the bottom of the frame otherwise.

If the optional argument mini is nil, this means to return the minibuffer window if and only if it is currently active. If mini is non-nil, this function may return the minibuffer window even when it’s not active. However, if wrap is non-nil, it always acts as if mini were nil.

If it doesn’t find a suitable window, this function returns nil.

Don’t use this function to check whether there is no window in direction. Calling window-at-side-p described above is a much more efficient way to do that.

The following function allows the entire window tree of a frame to be retrieved:

Function: window-tree &optional frame

This function returns a list representing the window tree for frame frame. If frame is omitted or nil, it defaults to the selected frame.

The return value is a list of the form (root mini), where root represents the window tree of the frame’s root window, and mini is the frame’s minibuffer window.

If the root window is live, root is that window itself. Otherwise, root is a list (dir edges w1 w2 ...) where dir is nil for a horizontal combination and t for a vertical combination, 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 edges element is a list (left top right bottom), similar to the value returned by window-edges (see section Coordinates and Windows).


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1.3 Window Sizes

The following schematic shows the structure of a live window:

        ____________________________________________
       |______________ Header Line ______________|RD| ^
     ^ |LS|LM|LF|                       |RF|RM|RS|  | |
     | |  |  |  |                       |  |  |  |  | |
Window |  |  |  |       Text Area       |  |  |  |  | Window
Body | |  |  |  |     (Window Body)     |  |  |  |  | Total
Height |  |  |  |                       |  |  |  |  | Height
     | |  |  |  |<- Window Body Width ->|  |  |  |  | |
     v |__|__|__|_______________________|__|__|__|  | |
       |_________ Horizontal Scroll Bar _________|  | |
       |_______________ Mode Line _______________|__| |
       |_____________ Bottom Divider _______________| v
        <---------- Window Total Width ------------>

At the center of the window is the text area, or 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 fringes, denoted by LF and RF (@pxref{Fringes}); the left and right margins, denoted by LM and RM in the schematic (@pxref{Display Margins}); the left or right vertical 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 are the horizontal scroll bar (@pxref{Scroll Bars}); the mode line (@pxref{Mode Line Format}); and 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 frame-char-height and frame-char-width (@pxref{Frame Font}). 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.

The total height of a window is the number of lines comprising the window’s body, the header line, the horizontal scroll bar, the mode line and the bottom divider (if any).

Function: window-total-height &optional window round

This function returns the total height, in lines, of the window window. If window is omitted or nil, it defaults to the selected window. If 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 window is vertically combined and has a next sibling, the topmost row of that sibling can be calculated as the sum of this window’s topmost row and total height (see section Coordinates and Windows)

If the optional argument round is ceiling, this function returns the smallest integer larger than window’s pixel height divided by the character height of its frame; if it is floor, it returns the largest integer smaller than said value; with any other round it returns the internal value of windows’s total height.

The 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).

Function: window-total-width &optional window round

This function returns the total width, in columns, of the window window. If window is omitted or nil, it defaults to the selected window. If 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 next sibling, the leftmost column of that sibling can be calculated as the sum of this window’s leftmost column and total width (see section Coordinates and Windows). The optional argument round behaves as it does for window-total-height.

Function: 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 window. If horizontal is omitted or nil, this is equivalent to calling window-total-height for window; otherwise it is equivalent to calling window-total-width for window. The optional argument round behaves as it does for window-total-height.

The following two functions can be used to return the total size of a window in units of pixels.

Function: window-pixel-height &optional window

This function returns the total height of window window in pixels. window must be a valid window and defaults to the selected one.

The return value includes mode and header line, a horizontal scroll bar and a bottom divider, if any. If window is an internal window, its pixel height is the pixel height of the screen areas spanned by its children.

Function: window-pixel-height-before-size-change &optional Lisp_Object &optional window

This function returns the height of window window in pixels at the time window-size-change-functions was run for the last time on window’s frame (see section Hooks for Window Scrolling and Changes).

Function: window-pixel-width &optional window

This function returns the width of window window in pixels. window must be a valid window and defaults to the selected one.

The return value includes the fringes and margins of window as well as any vertical dividers or scroll bars belonging to window. If window is an internal window, its pixel width is the width of the screen areas spanned by its children.

Function: window-pixel-width-before-size-change &optional Lisp_Object &optional window

This function returns the width of window window in pixels at the time window-size-change-functions was run for the last time on window’s frame (see section Hooks for Window Scrolling and Changes).

The following functions can be used to determine whether a given window has any adjacent windows.

Function: window-full-height-p &optional window

This function returns non-nil if window has no other window above or below it in its frame. More precisely, this means that the total height of window equals the total height of the root window on that frame. The minibuffer window does not count in this regard. If window is omitted or nil, it defaults to the selected window.

Function: window-full-width-p &optional window

This function returns non-nil if 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 window is omitted or nil, it defaults to the selected window.

The body height of a window is the height of its text area, which does not include a mode or header line, a horizontal scroll bar, or a bottom divider.

Function: window-body-height &optional window pixelwise

This function returns the height, in lines, of the body of window window. If window is omitted or nil, it defaults to the selected window; otherwise it must be a live window.

If the optional argument pixelwise is non-nil, this function returns the body height of window counted in pixels.

If pixelwise is 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 window-total-height.

The 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. Note that when one or both fringes are removed (by setting their width to zero), the display engine reserves two character cells, one on each side of the window, for displaying the continuation and truncation glyphs, which leaves 2 columns less for text display. (The function window-max-chars-per-line, described below, takes this peculiarity into account.)

Function: window-body-width &optional window pixelwise

This function returns the width, in columns, of the body of window window. If window is omitted or nil, it defaults to the selected window; otherwise it must be a live window.

If the optional argument pixelwise is non-nil, this function returns the body width of window in units of pixels.

If pixelwise is 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 window-total-width.

Function: window-body-size &optional window horizontal pixelwise

This function returns the body height or body width of window. If horizontal is omitted or nil, it is equivalent to calling window-body-height for window; otherwise it is equivalent to calling window-body-width. In either case, the optional argument pixelwise is passed to the function called.

For compatibility with previous versions of Emacs, window-height is an alias for window-total-height, and window-width is an alias for 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.

Function: window-mode-line-height &optional window

This function returns the height in pixels of window’s mode line. window must be a live window and defaults to the selected one. If window has no mode line, the return value is zero.

Function: window-header-line-height &optional window

This function returns the height in pixels of window’s header line. window must be a live window and defaults to the selected one. If window has no header line, the return value is zero.

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.

If your Lisp program needs to make layout decisions, you will find the following function useful:

Function: window-max-chars-per-line &optional window face

This function returns the number of characters displayed in the specified face face in the specified window window (which must be a live window). If face was remapped (@pxref{Face Remapping}), the information is returned for the remapped face. If omitted or nil, face defaults to the default face, and window defaults to the selected window.

Unlike window-body-width, this function accounts for the actual size of face’s font, instead of working in units of the canonical character width of window’s frame (@pxref{Frame Font}). It also accounts for space used by the continuation glyph, if window lacks one or both of its fringes.

Commands that change the size of windows (see section Resizing Windows), or split them (see section Splitting Windows), obey the variables window-min-height and window-min-width, which specify the smallest allowable window height and width. They also obey the variable window-size-fixed, with which a window can be fixed in size (see section Preserving Window Sizes).

User Option: 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, a horizontal scroll bar and a bottom divider, if present.

User Option: 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.

The following function tells how small a specific window can get taking into account the sizes of its areas and the values of window-min-height, window-min-width and window-size-fixed (see section Preserving Window Sizes).

Function: window-min-size &optional window horizontal ignore pixelwise

This function returns the minimum size of window. window must be a valid window and defaults to the selected one. The optional argument horizontal non-nil means to return the minimum number of columns of window; otherwise return the minimum number of window’s lines.

The return value makes sure that all components of window remain fully visible if window’s size were actually set to it. With horizontal nil it includes the mode and header line, the horizontal scroll bar and the bottom divider, if present. With horizontal non-nil it includes the margins and fringes, the vertical scroll bar and the right divider, if present.

The optional argument ignore, if non-nil, means ignore restrictions imposed by fixed size windows, window-min-height or window-min-width settings. If ignore equals safe, live windows may get as small as window-safe-min-height lines and window-safe-min-width columns. If ignore is a window, ignore restrictions for that window only. Any other non-nil value means ignore all of the above restrictions for all windows.

The optional argument pixelwise non-nil means to return the minimum size of window counted in pixels.


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1.4 Resizing Windows

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{Frame Size}).

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.

Function: window-resizable window delta &optional horizontal ignore pixelwise

This function returns delta if the size of window can be changed vertically by delta lines. If the optional argument horizontal is non-nil, it instead returns delta if window can be resized horizontally by delta columns. It does not actually change the window size.

If window is nil, it defaults to the selected window.

A positive value of delta means to check whether the window can be enlarged by that number of lines or columns; a negative value of delta means to check whether the window can be shrunk by that many lines or columns. If delta is non-zero, a return value of 0 means that the window cannot be resized.

Normally, the variables window-min-height and window-min-width specify the smallest allowable window size (see section Window Sizes). However, if the optional argument ignore is non-nil, this function ignores window-min-height and window-min-width, as well as window-size-fixed. Instead, it considers the minimum-height window to be one consisting of a header and a mode line, a horizontal scrollbar 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 pixelwise is non-nil, delta is interpreted as pixels.

Function: window-resize window delta &optional horizontal ignore pixelwise

This function resizes window by delta increments. If horizontal is nil, it changes the height by delta lines; otherwise, it changes the width by delta columns. A positive delta means to enlarge the window, and a negative delta means to shrink it.

If window is nil, it defaults to the selected window. If the window cannot be resized as demanded, an error is signaled.

The optional argument ignore has the same meaning as for the function window-resizable above.

If the optional argument pixelwise is non-nil, delta will be interpreted as pixels.

The choice of which window edges this function alters depends on the values of the option window-combination-resize and the combination limits of the involved windows; in some cases, it may alter both edges. See section Recombining Windows. To resize by moving only the bottom or right edge of a window, use the function adjust-window-trailing-edge.

Function: adjust-window-trailing-edge window delta &optional horizontal pixelwise

This function moves window’s bottom edge by delta lines. If optional argument horizontal is non-nil, it instead moves the right edge by delta columns. If window is nil, it defaults to the selected window.

If the optional argument pixelwise is non-nil, delta is interpreted as pixels.

A positive delta moves the edge downwards or to the right; a negative delta moves it upwards or to the left. If the edge cannot be moved as far as specified by delta, this function moves it as far as possible but does not signal an 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.

User Option: window-resize-pixelwise

If the value of this option is non-nil, Emacs resizes windows in units of pixels. This currently affects functions like split-window (see section Splitting Windows), maximize-window, minimize-window, fit-window-to-buffer, fit-frame-to-buffer and shrink-window-if-larger-than-buffer (all listed below).

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 nil. The default value is nil.

The following commands resize windows in more specific ways. When called interactively, they act on the selected window.

Command: fit-window-to-buffer &optional window max-height min-height max-width min-width preserve-size

This command adjusts the height or width of window to fit the text in it. It returns non-nil if it was able to resize window, and nil otherwise. If window is omitted or nil, it defaults to the selected window. Otherwise, it should be a live window.

If window is part of a vertical combination, this function adjusts window’s height. The new height is calculated from the actual height of the accessible portion of its buffer. The optional argument max-height, if non-nil, specifies the maximum total height that this function can give window. The optional argument min-height, if non-nil, specifies the minimum total height that it can give, which overrides the variable window-min-height. Both max-height and min-height are specified in lines and include mode and header line and a bottom divider, if any.

If window is part of a horizontal combination and the value of the option fit-window-to-buffer-horizontally (see below) is non-nil, this function adjusts window’s width. The new width of window is calculated from the maximum length of its buffer’s lines that follow the current start position of window. The optional argument max-width specifies a maximum width and defaults to the width of window’s frame. The optional argument min-width specifies a minimum width and defaults to window-min-width. Both max-width and min-width are specified in columns and include fringes, margins and scrollbars, if any.

The optional argument preserve-size, if non-nil, will install a parameter to preserve the size of window during future resize operations (see section Preserving Window Sizes).

If the option fit-frame-to-buffer (see below) is non-nil, this function will try to resize the frame of window to fit its contents by calling fit-frame-to-buffer (see below).

User Option: fit-window-to-buffer-horizontally

If this is non-nil, fit-window-to-buffer can resize windows horizontally. If this is nil (the default) fit-window-to-buffer never resizes windows horizontally. If this is only, it can resize windows horizontally only. Any other value means fit-window-to-buffer can resize windows in both dimensions.

User Option: fit-frame-to-buffer

If this option is non-nil, 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-nil. If this is horizontally, frames are fit horizontally only. If this is vertically, frames are fit vertically only. Any other non-nil value means frames can be resized in both dimensions.

If you have a frame that displays only one window, you can fit that frame to its buffer using the command fit-frame-to-buffer.

Command: fit-frame-to-buffer &optional frame max-height min-height max-width min-width only

This command adjusts the size of frame to display the contents of its buffer exactly. frame can be any live frame and defaults to the selected one. Fitting is done only if frame’s root window is live. The arguments max-height, min-height, max-width and min-width specify bounds on the new total size of frame’s root window. min-height and min-width default to the values of window-min-height and window-min-width respectively.

If the optional argument only is vertically, this function may resize the frame vertically only. If only is horizontally, it may resize the frame horizontally only.

The behavior of fit-frame-to-buffer can be controlled with the help of the two options listed next.

User Option: fit-frame-to-buffer-margins

This option can be used to specify margins around frames to be fit by fit-frame-to-buffer. Such margins can be useful to avoid, for example, that the resized frame overlaps the taskbar or parts of its parent frame.

It specifies the numbers of pixels to be left free on the left, above, the right, and below a frame that shall be fit. The default specifies nil for each which means to use no margins. The value specified here can be overridden for a specific frame by that frame’s fit-frame-to-buffer-margins parameter, if present.

User Option: fit-frame-to-buffer-sizes

This option specifies size boundaries for fit-frame-to-buffer. It specifies the total maximum and minimum lines and maximum and minimum columns of the root window of any frame that shall be fit to its buffer. If any of these values is non-nil, it overrides the corresponding argument of fit-frame-to-buffer.

Command: shrink-window-if-larger-than-buffer &optional window

This command attempts to reduce window’s height as much as possible while still showing its full buffer, but no less than window-min-height lines. The return value is non-nil if the window was resized, and nil otherwise. If window is omitted or 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 fit-window-to-buffer (see above) to do its work.

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 window-or-frame specifies a frame, it balances all windows on that frame. If window-or-frame specifies a window, it balances only that window and its siblings (see section Windows and Frames).

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.

Command: maximize-window &optional window

This function attempts to make window as large as possible, in both dimensions, without resizing its frame or deleting other windows. If window is omitted or nil, it defaults to the selected window.

Command: minimize-window &optional window

This function attempts to make window as small as possible, in both dimensions, without deleting it or resizing its frame. If window is omitted or nil, it defaults to the selected window.


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1.5 Preserving Window Sizes

A window can get resized explicitly by using one of the functions from the preceding section or implicitly, for example, when resizing an adjacent window, when splitting or deleting a window (see section Splitting Windows, see section Deleting Windows) or when resizing the window’s frame (@pxref{Frame Size}).

It is possible to avoid implicit resizing of a specific window when there are one or more other resizable windows on the same frame. For this purpose, Emacs must be advised to preserve the size of that window. There are two basic ways to do that.

Variable: window-size-fixed

If this buffer-local variable is non-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 the window’s size, if there is no choice.

If the value is height, then only the window’s height is fixed; if the value is width, then only the window’s width is fixed. Any other non-nil value fixes both the width and the height.

If this variable is 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 window-resizable. See section Resizing Windows.

Often window-size-fixed is overly aggressive because it inhibits any attempt to explicitly resize or split an affected window as well. This may even happen after the window has been resized implicitly, for example, when deleting an adjacent window or resizing the window’s frame. The following function tries hard to never disallow resizing such a window explicitly:

Function: window-preserve-size &optional window horizontal preserve

This function (un-)marks the height of window window as preserved for future resize operations. window must be a live window and defaults to the selected one. If the optional argument horizontal is non-nil, it (un-)marks the width of window as preserved.

If the optional argument preserve is t, this means to preserve the current height/width of window’s body. The height/width of window will change only if Emacs has no better choice. Resizing a window whose height/width is preserved by this function never throws an error.

If preserve is nil, this means to stop preserving the height/width of window, lifting any respective restraint induced by a previous call of this function for window. Calling enlarge-window, shrink-window or fit-window-to-buffer with window as argument may also remove the respective restraint.

window-preserve-size is currently invoked by the following functions:

fit-window-to-buffer

If the optional argument preserve-size of that function (see section Resizing Windows) is non-nil, the size established by that function is preserved.

display-buffer

If the alist argument of that function (see section Choosing a Window for Display) contains a preserve-size entry, the size of the window produced by that function is preserved.

window-preserve-size installs a window parameter (see section Window Parameters) called window-preserved-size which is consulted by the window resizing functions. This parameter will not prevent resizing the window when the window shows another buffer than the one when window-preserve-size was invoked or if its size has changed since then.

The following function can be used to check whether the height of a particular window is preserved:

Function: window-preserved-size &optional window horizontal

This function returns the preserved height of window window in pixels. window must be a live window and defaults to the selected one. If the optional argument horizontal is non-nil, it returns the preserved width of window. It returns nil if the size of window is not preserved.


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1.6 Splitting Windows

This section describes functions for creating a new window by splitting an existing one. Note that some windows are special in the sense that these functions may fail to split them as described here. Examples of such windows are side windows (see section Side Windows) and atomic windows (see section Atomic Windows).

Function: split-window &optional window size side pixelwise

This function creates a new live window next to the window window. If window is omitted or 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 size determines the sizes of window and/or the new window. If it is omitted or nil, both windows are given equal sizes; if there is an odd line, it is allocated to the new window. If size is a positive number, window is given size lines (or columns, depending on the value of side). If size is a negative number, the new window is given -size lines (or columns).

If size is nil, this function obeys the variables window-min-height and window-min-width (see section Window Sizes). Thus, it signals an error if splitting would result in making a window smaller than those variables specify. However, a non-nil value for 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 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 window-min-size (see section Window Sizes) can be used to determine the minimum requirements of window in this regard. Since the new window usually inherits areas like the mode line or the scroll bar from 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 side determines the position of the new window relative to window. If it is nil or below, the new window is placed below window. If it is above, the new window is placed above window. In both these cases, size specifies a total window height, in lines.

If side is t or right, the new window is placed on the right of window. If side is left, the new window is placed on the left of window. In both these cases, size specifies a total window width, in columns.

The optional fourth argument pixelwise, if non-nil, means to interpret size in units of pixels, instead of lines and columns.

If window is a live window, the new window inherits various properties from it, including margins and scroll bars. If window is an internal window, the new window inherits the properties of the window selected within window’s frame.

The behavior of this function may be altered by the window parameters of window, so long as the variable ignore-window-parameters is nil. If the value of the split-window window parameter is t, this function ignores all other window parameters. Otherwise, if the value of the split-window window parameter is a function, that function is called with the arguments window, size, and side, in lieu of the usual action of split-window. Otherwise, this function obeys the window-atom or window-side window parameter, if any. See section Window Parameters.

As an example, here is a sequence of split-window calls that yields the window configuration discussed in 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 W4. Calling (split-window W4) yields this window configuration:

     ______________________________________
    | ____________________________________ |
    ||                                    ||
    ||                                    ||
    ||                                    ||
    ||_________________W4_________________||
    | ____________________________________ |
    ||                                    ||
    ||                                    ||
    ||                                    ||
    ||_________________W5_________________||
    |__________________W3__________________|

The split-window call has created a new live window, denoted by W5. It has also created a new internal window, denoted by W3, which becomes the root window and the parent of both W4 and W5.

Next, we call (split-window W3 nil 'left), passing the internal window W3 as the argument. The result:

     ______________________________________
    | ______  ____________________________ |
    ||      || __________________________ ||
    ||      |||                          |||
    ||      |||                          |||
    ||      |||                          |||
    ||      |||____________W4____________|||
    ||      || __________________________ ||
    ||      |||                          |||
    ||      |||                          |||
    ||      |||____________W5____________|||
    ||__W2__||_____________W3_____________ |
    |__________________W1__________________|

A new live window W2 is created, to the left of the internal window W3. A new internal window W1 is created, becoming the new root window.

For interactive use, Emacs provides two commands which always split the selected window. These call split-window internally.

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 size is positive, the left window gets size columns; if size is negative, the right window gets -size columns.

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 size is positive, the upper window gets size lines; if size is negative, the lower window gets -size lines.

User Option: split-window-keep-point

If the value of this variable is non-nil (the default), split-window-below behaves as described above.

If it is nil, 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 split-window-below, not the lower-level split-window function.


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1.7 Deleting Windows

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 (see section Window Configurations).

Command: delete-window &optional window

This function removes window from display and returns nil. If window is omitted or 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) or all remaining windows on window’s frame are side windows (see section Side Windows), an error is signaled.

By default, the space taken up by window is given to one of its adjacent sibling windows, if any. However, if the variable window-combination-resize is non-nil, the space is proportionally distributed among any remaining windows in the same window combination. See section Recombining Windows.

The behavior of this function may be altered by the window parameters of window, so long as the variable ignore-window-parameters is nil. If the value of the delete-window window parameter is t, this function ignores all other window parameters. Otherwise, if the value of the delete-window window parameter is a function, that function is called with the argument window, in lieu of the usual action of delete-window. See section Window Parameters.

Command: delete-other-windows &optional window

This function makes window fill its frame, deleting other windows as necessary. If window is omitted or nil, it defaults to the selected window. An error is signaled if window is a side window (see section Side Windows). The return value is nil.

The behavior of this function may be altered by the window parameters of window, so long as the variable ignore-window-parameters is nil. If the value of the delete-other-windows window parameter is t, this function ignores all other window parameters. Otherwise, if the value of the delete-other-windows window parameter is a function, that function is called with the argument window, in lieu of the usual action of delete-other-windows. See section Window Parameters.

Also, if ignore-window-parameters is nil, this function does not delete any window whose no-delete-other-windows parameter is non-nil.

Command: delete-windows-on &optional buffer-or-name frame

This function deletes all windows showing buffer-or-name, by calling delete-window on those windows. buffer-or-name should be a buffer, or the name of a buffer; if omitted or 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 frame specifies which frames to operate on:

Note that this argument does not have the same meaning as in other functions which scan all live windows (see section Cyclic Ordering of Windows). Specifically, the meanings of t and nil here are the opposite of what they are in those other functions.


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1.8 Recombining Windows

When deleting the last sibling of a window W, its parent window is deleted too, with W replacing it in the window tree. This means that W must be recombined with its parent’s siblings to form a new window combination (see section Windows and Frames). In some occasions, deleting a live window may even entail the deletion of two internal windows.

     ______________________________________
    | ______  ____________________________ |
    ||      || __________________________ ||
    ||      ||| ___________  ___________ |||
    ||      ||||           ||           ||||
    ||      ||||____W6_____||_____W7____||||
    ||      |||____________W4____________|||
    ||      || __________________________ ||
    ||      |||                          |||
    ||      |||                          |||
    ||      |||____________W5____________|||
    ||__W2__||_____________W3_____________ |
    |__________________W1__________________|

Deleting W5 in this configuration normally causes the deletion of W3 and W4. The remaining live windows W2, W6 and W7 are recombined to form a new horizontal combination with parent W1.

Sometimes, however, it makes sense to not delete a parent window like 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 W2 and W3 and their parent W1.

     ______________________________________
    | ____________________________________ |
    ||                                    ||
    ||                                    ||
    ||                                    ||
    ||                                    ||
    ||                                    ||
    ||                                    ||
    ||_________________W2_________________||
    | ____________________________________ |
    ||                                    ||
    ||                                    ||
    ||_________________W3_________________||
    |__________________W1__________________|

Split W2 to make a new window W4 as follows.

     ______________________________________
    | ____________________________________ |
    ||                                    ||
    ||                                    ||
    ||_________________W2_________________||
    | ____________________________________ |
    ||                                    ||
    ||                                    ||
    ||_________________W4_________________||
    | ____________________________________ |
    ||                                    ||
    ||                                    ||
    ||_________________W3_________________||
    |__________________W1__________________|

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 W4 will steal space from W3.

     ______________________________________
    | ____________________________________ |
    ||                                    ||
    ||                                    ||
    ||_________________W2_________________||
    | ____________________________________ |
    ||                                    ||
    ||                                    ||
    ||                                    ||
    ||                                    ||
    ||_________________W4_________________||
    | ____________________________________ |
    ||_________________W3_________________||
    |__________________W1__________________|

Deleting W4 will now give its entire space to W2, including the space earlier stolen from W3.

     ______________________________________
    | ____________________________________ |
    ||                                    ||
    ||                                    ||
    ||                                    ||
    ||                                    ||
    ||                                    ||
    ||                                    ||
    ||                                    ||
    ||                                    ||
    ||_________________W2_________________||
    | ____________________________________ |
    ||_________________W3_________________||
    |__________________W1__________________|

This can be counterintuitive, in particular if 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 W2. The variable described next allows that to be done.

User Option: window-combination-limit

This variable controls whether splitting a window shall make a new parent window. The following values are recognized:

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).

window-size

This means that display-buffer makes a new parent window when it splits a window and is passed a window-height or window-width entry in the alist argument (see section Action Functions for display-buffer). Otherwise, window splitting behaves as for a value of nil.

temp-buffer-resize

In this case with-temp-buffer-window makes a new parent window when it splits a window and temp-buffer-resize-mode is enabled (@pxref{Temporary Displays}). Otherwise, window splitting behaves as for nil.

temp-buffer

In this case with-temp-buffer-window always makes a new parent window when it splits an existing window (@pxref{Temporary Displays}). Otherwise, window splitting behaves as for nil.

display-buffer

This means that when display-buffer (see section Choosing a Window for Display) splits a window it always makes a new parent window. Otherwise, window splitting behaves as for nil.

t

This means that splitting a window always creates a new parent window. Thus, if the value of this variable is at all times 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).

The default is window-size. Other values are reserved for future use.

If, as a consequence of this variable’s setting, split-window makes a new parent window, it also calls 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).

If window-combination-limit is t, splitting W2 in the initial configuration of our scenario would have produced this:

     ______________________________________
    | ____________________________________ |
    || __________________________________ ||
    |||                                  |||
    |||________________W2________________|||
    || __________________________________ ||
    |||                                  |||
    |||________________W4________________|||
    ||_________________W5_________________||
    | ____________________________________ |
    ||                                    ||
    ||                                    ||
    ||_________________W3_________________||
    |__________________W1__________________|

A new internal window W5 has been created; its children are W2 and the new live window W4. Now, W2 is the only sibling of W4, so enlarging W4 will try to shrink W2, leaving W3 unaffected. Observe that W5 represents a vertical combination of two windows embedded in the vertical combination W1.

Function: set-window-combination-limit window limit

This function sets the combination limit of the window window to limit. This value can be retrieved via the function window-combination-limit. See below for its effects; note that it is only meaningful for internal windows. The split-window function automatically calls this function, passing it t as limit, provided the value of the variable window-combination-limit is t when it is called.

Function: window-combination-limit window

This function returns the combination limit for window.

The combination limit is meaningful only for an internal window. If it is nil, then Emacs is allowed to automatically delete window, in response to a window deletion, in order to group the child windows of window with its sibling windows to form a new window combination. If the combination limit is t, the child windows of window are never automatically recombined with its siblings.

If, in the configuration shown at the beginning of this section, the combination limit of W4 (the parent window of W6 and W7) is t, deleting W5 will not implicitly delete W4 too.

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 splitting windows that would be otherwise too small for such an operation.

User Option: window-combination-resize

If this variable is nil, split-window can only split a window (denoted by window) if window’s screen area is large enough to accommodate both itself and the new window.

If this variable is t, split-window tries to resize all windows that are part of the same combination as window, in order to accommodate the new window. In particular, this may allow split-window to succeed even if window is a fixed-size window or too small to ordinarily split. Furthermore, subsequently resizing or deleting window may resize all other windows in its combination.

The default is nil. Other values are reserved for future use. A specific split operation may ignore the value of this variable if it is affected by a non-nil value of window-combination-limit.

To illustrate the effect of window-combination-resize, consider the following frame layout.

     ______________________________________
    | ____________________________________ |
    ||                                    ||
    ||                                    ||
    ||                                    ||
    ||                                    ||
    ||_________________W2_________________||
    | ____________________________________ |
    ||                                    ||
    ||                                    ||
    ||                                    ||
    ||                                    ||
    ||_________________W3_________________||
    |__________________W1__________________|

If window-combination-resize is nil, splitting window W3 leaves the size of W2 unchanged:

     ______________________________________
    | ____________________________________ |
    ||                                    ||
    ||                                    ||
    ||                                    ||
    ||                                    ||
    ||_________________W2_________________||
    | ____________________________________ |
    ||                                    ||
    ||_________________W3_________________||
    | ____________________________________ |
    ||                                    ||
    ||_________________W4_________________||
    |__________________W1__________________|

If window-combination-resize is t, splitting W3 instead leaves all three live windows with approximately the same height:

     ______________________________________
    | ____________________________________ |
    ||                                    ||
    ||                                    ||
    ||_________________W2_________________||
    | ____________________________________ |
    ||                                    ||
    ||                                    ||
    ||_________________W3_________________||
    | ____________________________________ |
    ||                                    ||
    ||                                    ||
    ||_________________W4_________________||
    |__________________W1__________________|

Deleting any of the live windows W2, W3 or W4 will distribute its space proportionally among the two remaining live windows.


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1.9 Selecting Windows

Function: select-window window &optional norecord

This function makes window the selected window and the window selected within its frame (see section Basic Concepts of Emacs Windows), and selects that frame. It also makes window’s buffer (see section Buffers and Windows) current and sets that buffer’s value of point to the value of window-point (see section Windows and Point) in window. window must be a live window. The return value is window.

By default, this function also moves window’s buffer to the front of the buffer list (@pxref{Buffer List}) and makes window the most recently selected window. If the optional argument norecord is non-nil, these additional actions are omitted.

In addition, this function by default also tells the display engine to update the display of window when its frame gets redisplayed the next time. If norecord is non-nil, such updates are usually not performed. If, however, norecord equals the special symbol mark-for-redisplay, the additional actions mentioned above are omitted but window will be nevertheless updated.

Note that sometimes selecting a window is not enough to show it, or make its frame the top-most frame on display: you may also need to raise the frame or make sure input focus is directed to that frame. @xref{Input Focus}.

For historical reasons, Emacs does not run a separate hook whenever a window gets selected. Applications and internal routines often temporarily select a window to perform a few actions on it. They do that either to simplify coding—because many functions by default operate on the selected window when no window argument is specified—or because some functions did not (and still do not) take a window as argument and always operate(d) on the selected window instead. Running a hook every time a window gets selected for a short time and once more when the previously selected window gets restored is not useful.

However, when its norecord argument is nil, select-window updates the buffer list and thus indirectly runs the normal hook buffer-list-update-hook (@pxref{Buffer List}). Consequently, that hook provides a reasonable way to run a function whenever a window gets selected more “permanently”.

Since buffer-list-update-hook is also run by functions that are not related to window management, it will usually make sense to save the value of the selected window somewhere and compare it with the value of selected-window while running that hook. Also, to avoid false positives when using buffer-list-update-hook, it is good practice that every select-window call supposed to select a window only temporarily passes a non-nil norecord argument. If possible, the macro with-selected-window (see below) should be used in such cases.

The sequence of calls to select-window with a non-nil norecord argument determines an ordering of windows by their selection time. The function get-lru-window can be used to retrieve the least recently selected live window (see section Cyclic Ordering of Windows).

Macro: save-selected-window forms…

This macro records the selected frame, as well as the selected window of each frame, executes 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 forms.

This macro does not save or restore anything about the sizes, arrangement or contents of windows; therefore, if forms change them, the change persists. If the previously selected window of some frame is no longer live at the time of exit from 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 forms remains selected. The current buffer is restored if and only if it is still live when exiting forms.

This macro changes neither the ordering of recently selected windows nor the buffer list.

Macro: with-selected-window window forms…

This macro selects window, executes 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 forms; for example, by calling select-window with argument norecord nil. Hence, this macro is the preferred way to temporarily work with window as the selected window without needlessly running buffer-list-update-hook.

Function: frame-selected-window &optional frame

This function returns the window on frame that is selected within that frame. frame should be a live frame; if omitted or nil, it defaults to the selected frame.

Function: set-frame-selected-window frame window &optional norecord

This function makes window the window selected within the frame frame. frame should be a live frame; if nil, it defaults to the selected frame. window should be a live window; if nil, it defaults to the selected window.

If frame is the selected frame, this makes window the selected window.

If the optional argument norecord is non-nil, this function does not alter the list of most recently selected windows, nor the buffer list.

Function: window-use-time &optional window

This functions returns the use time of window window. window must be a live window and defaults to the selected one.

The use time of a window is not really a time value, but an integer that does increase monotonically with each call of select-window with a nil norecord argument. The window with the lowest use time is usually called the least recently used window while the window with the highest use time is called the most recently used one (see section Cyclic Ordering of Windows).


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1.10 Cyclic Ordering of Windows

When you use the command C-x o (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 cyclic ordering of windows.

The ordering is determined by a depth-first traversal of each frame’s window tree, retrieving the live windows which are the leaf nodes of the tree (see section 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.

Function: next-window &optional window minibuf all-frames

This function returns a live window, the one following window in the cyclic ordering of windows. window should be a live window; if omitted or nil, it defaults to the selected window.

The optional argument minibuf specifies whether minibuffer windows should be included in the cyclic ordering. Normally, when minibuf is nil, a minibuffer window is included only if it is currently active; this matches the behavior of C-x o. (Note that a minibuffer window is active as long as its minibuffer is in use; see @ref{Minibuffers}).

If minibuf is t, the cyclic ordering includes all minibuffer windows. If minibuf is neither t nor nil, minibuffer windows are not included even if they are active.

The optional argument all-frames specifies which frames to consider:

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}).

Function: previous-window &optional window minibuf all-frames

This function returns a live window, the one preceding window in the cyclic ordering of windows. The other arguments are handled like in next-window.

Command: other-window count &optional all-frames

This function selects a live window, one count places from the selected window in the cyclic ordering of windows. If count is a positive number, it skips count windows forwards; if count is negative, it skips -count windows backwards; if count is zero, that simply re-selects the selected window. When called interactively, count is the numeric prefix argument.

The optional argument all-frames has the same meaning as in next-window, like a nil minibuf argument to next-window.

This function does not select a window that has a non-nil no-other-window window parameter (see section Window Parameters).

Function: walk-windows fun &optional minibuf all-frames

This function calls the function fun once for each live window, with the window as the argument.

It follows the cyclic ordering of windows. The optional arguments minibuf and all-frames specify the set of windows included; these have the same arguments as in next-window. If all-frames specifies a frame, the first window walked is the first window on that frame (the one returned by frame-first-window), not necessarily the selected window.

If 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 fun for the first time.

Function: one-window-p &optional no-mini all-frames

This function returns t if the selected window is the only live window, and nil otherwise.

If the minibuffer window is active, it is normally considered (so that this function returns nil). However, if the optional argument no-mini is non-nil, the minibuffer window is ignored even if active. The optional argument all-frames has the same meaning as for next-window.

The following functions return a window which satisfies some criterion, without selecting it:

Function: get-lru-window &optional all-frames dedicated not-selected

This function returns a live window which is heuristically the least recently used. The optional argument all-frames has the same meaning as in next-window.

If any full-width windows are present, only those windows are considered. A minibuffer window is never a candidate. A dedicated window (see section Dedicated Windows) is never a candidate unless the optional argument dedicated is non-nil. The selected window is never returned, unless it is the only candidate. However, if the optional argument not-selected is non-nil, this function returns nil in that case.

Function: get-mru-window &optional all-frames dedicated not-selected

This function is like get-lru-window, but it returns the most recently used window instead. The meaning of the arguments is the same as described for get-lru-window.

Function: get-largest-window &optional all-frames dedicated not-selected

This function returns the window with the largest area (height times width). The optional argument all-frames specifies the windows to search, and has the same meaning as in next-window.

A minibuffer window is never a candidate. A dedicated window (see section Dedicated Windows) is never a candidate unless the optional argument dedicated is non-nil. The selected window is not a candidate if the optional argument not-selected is non-nil. If the optional argument not-selected is non-nil and the selected window is the only candidate, this function returns 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.

Function: get-window-with-predicate predicate &optional minibuf all-frames default

This function calls the function 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-nil for any window, this function stops and returns that window. If no such window is found, the return value is default (which defaults to nil).

The optional arguments minibuf and all-frames specify the windows to search, and have the same meanings as in next-window.


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1.11 Buffers and Windows

This section describes low-level functions for examining and setting the contents of windows. See section Switching to a Buffer in a Window, for higher-level functions for displaying a specific buffer in a window.

Function: window-buffer &optional window

This function returns the buffer that window is displaying. If window is omitted or nil it defaults to the selected window. If window is an internal window, this function returns nil.

Function: set-window-buffer window buffer-or-name &optional keep-margins

This function makes window display buffer-or-name. window should be a live window; if nil, it defaults to the selected window. 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 nil.

If window is strongly dedicated to a buffer and buffer-or-name does not specify that buffer, this function signals an error. See section Dedicated Windows.

By default, this function resets 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 keep-margins is non-nil, it leaves window’s display margins, fringes and scroll bar settings alone.

When writing an application, you should normally use the higher-level functions described in Switching to a Buffer in a Window, instead of calling set-window-buffer directly.

This runs window-scroll-functions, followed by window-configuration-change-hook. See section Hooks for Window Scrolling and Changes.

Variable: 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 set-window-buffer is called for the buffer.

Variable: buffer-display-time

This buffer-local variable records the time at which a buffer was last displayed in a window. The value is nil if the buffer has never been displayed. It is updated each time set-window-buffer is called for the buffer, with the value returned by current-time (@pxref{Time of Day}).

Function: get-buffer-window &optional buffer-or-name all-frames

This function returns the first window displaying buffer-or-name in the cyclic ordering of windows, starting from the selected window (see section Cyclic Ordering of Windows). If no such window exists, the return value is nil.

buffer-or-name should be a buffer or the name of a buffer; if omitted or nil, it defaults to the current buffer. The optional argument all-frames specifies which windows to consider:

Note that these meanings differ slightly from those of the all-frames argument to next-window (see section Cyclic Ordering of Windows). This function may be changed in a future version of Emacs to eliminate this discrepancy.

Function: get-buffer-window-list &optional buffer-or-name minibuf all-frames

This function returns a list of all windows currently displaying buffer-or-name. buffer-or-name should be a buffer or the name of an existing buffer. If omitted or nil, it defaults to the current buffer. If the currently selected window displays buffer-or-name, it will be the first in the list returned by this function.

The arguments minibuf and all-frames have the same meanings as in the function next-window (see section Cyclic Ordering of Windows). Note that the all-frames argument does not behave exactly like in get-buffer-window.

Command: replace-buffer-in-windows &optional buffer-or-name

This command replaces buffer-or-name with some other buffer, in all windows displaying it. buffer-or-name should be a buffer, or the name of an existing buffer; if omitted or nil, it defaults to the current buffer.

The replacement buffer in each window is chosen via switch-to-prev-buffer (see section Window History). Any dedicated window displaying buffer-or-name is deleted if possible (see section 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.


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1.12 Switching to a Buffer in a Window

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 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 (see section 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 with-current-buffer, save-current-buffer, or set-buffer. @xref{Current Buffer}.

Command: switch-to-buffer buffer-or-name &optional norecord force-same-window

This command attempts to display buffer-or-name in the selected window and make it the current buffer. It is often used interactively (as the binding of C-x b), as well as in Lisp programs. The return value is the buffer switched to.

If buffer-or-name is nil, it defaults to the buffer returned by other-buffer (@pxref{Buffer List}). If 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 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 norecord is non-nil.

Sometimes, the selected window may not be suitable for displaying the buffer. This happens if the selected window is a minibuffer window, or if the selected window is strongly dedicated to its buffer (see section Dedicated Windows). In such cases, the command normally tries to display the buffer in some other window, by invoking pop-to-buffer (see below).

If the optional argument force-same-window is non-nil and the selected window is not suitable for displaying the buffer, this function always signals an error when called non-interactively. In interactive use, if the selected window is a minibuffer window, this function will try to use some other window instead. If the selected window is strongly dedicated to its buffer, the option switch-to-buffer-in-dedicated-window described next can be used to proceed.

User Option: switch-to-buffer-in-dedicated-window

This option, if non-nil, allows switch-to-buffer to proceed when called interactively and the selected window is strongly dedicated to its buffer.

The following values are respected:

nil

Disallows switching and signals an error as in non-interactive use.

prompt

Prompts the user whether to allow switching.

pop

Invokes pop-to-buffer to proceed.

t

Marks the selected window as non-dedicated and proceeds.

This option does not affect non-interactive calls of switch-to-buffer.

By default, switch-to-buffer tries to preserve window-point. This behavior can be tuned using the following option.

User Option: switch-to-buffer-preserve-window-point

If this variable is nil, switch-to-buffer displays the buffer specified by buffer-or-name at the position of that buffer’s point. If this variable is 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 t, 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 switch-to-buffer calls pop-to-buffer to display the buffer.

The next two commands are similar to switch-to-buffer, except for the described features.

Command: switch-to-buffer-other-window buffer-or-name &optional norecord

This function displays the buffer specified by buffer-or-name in some window other than the selected window. It uses the function 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 buffer-or-name and norecord arguments have the same meanings as in switch-to-buffer.

Command: switch-to-buffer-other-frame buffer-or-name &optional norecord

This function displays the buffer specified by buffer-or-name in a new frame. It uses the function 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 buffer-or-name and norecord arguments have the same meanings as in switch-to-buffer.

The above commands use the function pop-to-buffer, which flexibly displays a buffer in some window and selects that window for editing. In turn, pop-to-buffer uses display-buffer for displaying the buffer. Hence, all the variables affecting display-buffer will affect it as well. See section Choosing a Window for Display, for the documentation of display-buffer.

Command: pop-to-buffer buffer-or-name &optional action norecord

This function makes buffer-or-name the current buffer and displays it in some window, preferably not the window currently 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}).

If buffer-or-name is nil, it defaults to the buffer returned by other-buffer (@pxref{Buffer List}). If 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 major-mode (@pxref{Major Modes}). In any case, that buffer is made current and returned, even when no suitable window was found to display it.

If action is non-nil, it should be a display action to pass to display-buffer (see section Choosing a Window for Display). Alternatively, a non-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 switch-to-buffer, this function updates the buffer list unless norecord is non-nil.


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1.13 Choosing a Window for Display

The command 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 C-x 4 C-o. It is also used as a subroutine by many functions and commands, including switch-to-buffer and pop-to-buffer (see section Switching to a Buffer in a Window).

This command performs several complex steps to find a window to display in. These steps are described by means of display actions, which have the form (function . alist). Here, function is either a function or a list of functions, which we refer to as action functions; alist is an association list, which we refer to as an action alist.

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 nil. See section Action Functions for display-buffer, for a list of predefined action functions.

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-nil value.

Command: display-buffer buffer-or-name &optional action frame

This command makes buffer-or-name appear in some window, without selecting the window or making the buffer current. The argument 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 action, if non-nil, should normally be a display action (described above). display-buffer builds a list of action functions and an action alist, by consolidating display actions from the following sources (in order):

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-nil. The caller can pass (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 action can also have a non-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, action is t.

The optional argument frame, if non-nil, specifies which frames to check when deciding whether the buffer is already displayed. It is equivalent to adding an element (reusable-frames . frame) to the action alist of action. See section Action Functions for display-buffer.

Variable: display-buffer-overriding-action

The value of this variable should be a display action, which is treated with the highest priority by display-buffer. The default value is empty, i.e., (nil . nil).

User Option: 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 action argument passed to display-buffer. If the name of the buffer passed to display-buffer either matches a regular expression in this alist or the function specified by a condition returns non-nil, then display-buffer uses the corresponding display action to display the buffer.

User Option: 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 display-buffer.

Constant: display-buffer-fallback-action

This display action specifies the fallback behavior for display-buffer if no other display actions are given.


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1.14 Action Functions for display-buffer

The following basic action functions are defined in Emacs. Each of these functions takes two arguments: buffer, the buffer to display, and alist, an action alist. Each action function returns the window if it succeeds, and nil if it fails.

Function: display-buffer-same-window buffer alist

This function tries to display buffer in the selected window. It fails if the selected window is a minibuffer window or is dedicated to another buffer (see section Dedicated Windows). It also fails if alist has a non-nil inhibit-same-window entry.

Function: display-buffer-reuse-window buffer alist

This function tries to display buffer by finding a window that is already displaying it.

If alist has a non-nil inhibit-same-window entry, the selected window is not eligible for reuse. If alist contains a reusable-frames entry, its value determines which frames to search for a reusable window:

Note that these meanings differ slightly from those of the all-frames argument to next-window (see section Cyclic Ordering of Windows).

If alist contains no reusable-frames entry, this function normally searches just the selected frame; however, if the variable pop-up-frames is non-nil, it searches all frames on the current terminal. See section Additional Options for Displaying Buffers.

If this function chooses a window on another frame, it makes that frame visible and, unless alist contains an inhibit-switch-frame entry (see section Additional Options for Displaying Buffers), raises that frame if necessary.

Function: display-buffer-reuse-mode-window buffer alist

This function tries to display buffer by finding a window that is displaying a buffer in a given mode.

If alist contains a mode entry, its value is a major mode (a symbol) or a list of major modes. If alist contains no mode entry, the current major mode of buffer is used. A window is a candidate if it displays a buffer that derives from one of the given modes.

The behavior is also controlled by entries for inhibit-same-window, reusable-frames and inhibit-switch-frame as is done in the function display-buffer-reuse-window.

Function: 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 pop-up-frame-function (see section Additional Options for Displaying Buffers). If alist contains a pop-up-frame-parameters entry, the associated value is added to the newly created frame’s parameters.

Function: display-buffer-in-child-frame buffer alist

This function tries to display buffer in a child frame (@pxref{Child Frames}) of the selected frame, either reusing an existing child frame or by making a new one. If alist has a non-nil child-frame-parameters entry, the corresponding value is an alist of frame parameters to give the new frame. A parent-frame parameter specifying the selected frame is provided by default. If the child frame should be or become the child of another frame, a corresponding entry must be added to alist.

The appearance of child frames is largely dependent on the parameters provided via alist. It is advisable to use at least ratios to specify the size (@pxref{Size Parameters}) and the position (@pxref{Position Parameters}) of the child frame and to add the keep-ratio in order to make sure that the child frame remains visible. For other parameters that should be considered see @ref{Child Frames}.

Function: display-buffer-use-some-frame buffer alist

This function tries to display buffer by trying to find a frame that meets a predicate (by default any frame other than the current frame).

If this function chooses a window on another frame, it makes that frame visible and, unless alist contains an inhibit-switch-frame entry (see section Additional Options for Displaying Buffers), raises that frame if necessary.

If alist has a non-nil frame-predicate entry, its value is a function taking one argument (a frame), returning non-nil if the frame is a candidate; this function replaces the default predicate.

If alist has a non-nil inhibit-same-window entry, the selected window is used; thus if the selected frame has a single window, it is not used.

Function: display-buffer-pop-up-window buffer alist

This function tries to display 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 split-window-preferred-function (see section Additional Options for Displaying Buffers).

The size of the new window can be adjusted by supplying window-height and window-width entries in alist. To adjust the window’s height, use an entry whose CAR is window-height and whose CDR is one of:

To adjust the window’s width, use an entry whose CAR is window-width and whose CDR is one of:

If alist contains a preserve-size entry, Emacs will try to preserve the size of the new window during future resize operations (see section Preserving Window Sizes). The CDR of that entry must be a cons cell whose CAR, if non-nil, means to preserve the width of the window and whose CDR, if non-nil, means to preserve the height of the window.

This function can fail if no window splitting can be performed for some reason (e.g., if the selected frame has an unsplittable frame parameter; @pxref{Buffer Parameters}).

Function: display-buffer-below-selected buffer alist

This function tries to display buffer in a window below the selected window. If there is a window below the selected one and that window already displays buffer, it reuses that window.

If there is no such window, this function tries to create a new window by splitting the selected one and display buffer there. It will also adjust that window’s size provided alist contains a suitable window-height or window-width entry, see above.

If splitting the selected window fails and there is a non-dedicated window below the selected one showing some other buffer, it uses that window for showing buffer.

Function: display-buffer-in-previous-window buffer alist

This function tries to display buffer in a window previously showing it. If alist has a non-nil inhibit-same-window entry, the selected window is not eligible for reuse. If alist contains a reusable-frames entry, its value determines which frames to search for a suitable window as with display-buffer-reuse-window.

If alist has a 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 buffer before.

Function: display-buffer-at-bottom buffer alist

This function tries to display 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.

Function: display-buffer-use-some-window buffer alist

This function tries to display buffer by choosing an existing window and displaying the buffer in that window. It can fail if all windows are dedicated to another buffer (see section Dedicated Windows).

Function: display-buffer-no-window buffer alist

If alist has a non-nil allow-no-window entry, then this function does not display buffer. This allows you to override the default action and avoid displaying the buffer. It is assumed that when the caller specifies a non-nil allow-no-window value it can handle a nil value returned from display-buffer in this case.

If the alist argument of any of these functions contains a window-parameters entry, display-buffer assigns the elements of the associated value as window parameters of the chosen window.

To illustrate the use of action functions, consider the following example.

(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)))

Evaluating the form above will cause 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 display-buffer-base-action and display-buffer-fallback-action prescribe.

Furthermore, display-buffer will try to adjust a reused window (provided *foo* was put by 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 fit-window-to-buffer, 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 split-window-preferred-function, split-height-threshold and split-width-threshold (see section Additional Options for Displaying Buffers).

Now suppose we combine this call with a preexisting setup for display-buffer-alist as follows.

(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))))

This form will have 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, 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 action argument of display-buffer.


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1.15 Additional Options for Displaying Buffers

The behavior of the standard display actions of display-buffer (see section Choosing a Window for Display) can be modified by a variety of user options.

User Option: pop-up-windows

If the value of this variable is non-nil, 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 display-buffer via a special mechanism in display-buffer-fallback-action, which only calls the action function display-buffer-pop-up-window (see section Action Functions for display-buffer) when the value is nil. It is not consulted by display-buffer-pop-up-window itself, which the user may specify directly in display-buffer-alist etc.

User Option: 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 display-buffer-pop-up-window action function to actually split the window (see section Action Functions for display-buffer).

The default value is 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 nil (which means the splitting failed).

Function: split-window-sensibly &optional window

This function tries to split window, and return the newly created window. If window cannot be split, it returns nil. If window is omitted or nil, it defaults to the selected window.

This function obeys the usual rules that determine when a window may be split (see section Splitting Windows). It first tries to split by placing the new window below, subject to the restriction imposed by 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 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 split-height-threshold. If this fails as well, this function gives up and returns nil.

User Option: split-height-threshold

This variable, used by 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 nil, that means not to split this way.

User Option: split-width-threshold

This variable, used by 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 nil, that means not to split this way.

User Option: even-window-sizes

This variable, if non-nil, causes display-buffer to even window sizes whenever it reuses an existing window and that window is adjacent to the selected one.

If its value is width-only, sizes are evened only if the reused window is on the left or right of the selected one and the selected window is wider than the reused one. If its value is height-only sizes are evened only if the reused window is above or beneath the selected window and the selected window is higher than the reused one. Any other non-nil value means to even sizes in any of these cases provided the selected window is larger than the reused one in the sense of their combination.

User Option: pop-up-frames

If the value of this variable is non-nil, that means display-buffer may display buffers by making new frames. The default is nil.

A non-nil value also means that when display-buffer is looking for a window already displaying 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 display-buffer via a special mechanism in display-buffer-fallback-action, which calls the action function display-buffer-pop-up-frame (see section Action Functions for display-buffer) if the value is non-nil. (This is done before attempting to split a window.) This variable is not consulted by display-buffer-pop-up-frame itself, which the user may specify directly in display-buffer-alist etc.

User Option: 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 display-buffer-pop-up-frame action function (see section Action Functions for display-buffer).

The value should be a function that takes no arguments and returns a frame, or nil if no frame could be created. The default value is a function that creates a frame using the parameters specified by pop-up-frame-alist (see below).

User Option: pop-up-frame-alist

This variable holds an alist of frame parameters (@pxref{Frame Parameters}), which is used by the default function in pop-up-frame-function to make a new frame. The default is nil.

User Option: 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, display-buffer handles the buffer by showing it in the selected window.

User Option: 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, display-buffer handles the buffer by showing it in the selected window.

Function: same-window-p buffer-name

This function returns t if displaying a buffer named buffer-name with display-buffer would put it in the selected window.


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1.16 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 replace-buffer-in-windows (see section Buffers and Windows), and when quitting windows (see section Quitting Windows). The list is automatically maintained by Emacs, but you can use the following functions to explicitly inspect or alter it:

Function: window-prev-buffers &optional window

This function returns a list specifying the previous contents of window. The optional argument window should be a live window and defaults to the selected one.

Each list element has the form (buffer window-start window-pos), where buffer is a buffer previously shown in the window, window-start is the window start position (see section The Window Start and End Positions) when that buffer was last shown, and window-pos is the point position (see section Windows and Point) when that buffer was last shown in 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.

Function: set-window-prev-buffers window prev-buffers

This function sets window’s previous buffers to the value of prev-buffers. The argument window must be a live window and defaults to the selected one. The argument prev-buffers should be a list of the same form as that returned by window-prev-buffers.

In addition, each buffer maintains a list of next buffers, which is a list of buffers re-shown by switch-to-prev-buffer (see below). This list is mainly used by switch-to-prev-buffer and switch-to-next-buffer for choosing buffers to switch to.

Function: window-next-buffers &optional window

This function returns the list of buffers recently re-shown in window via switch-to-prev-buffer. The window argument must denote a live window or nil (meaning the selected window).

Function: set-window-next-buffers window next-buffers

This function sets the next buffer list of window to next-buffers. The window argument should be a live window or nil (meaning the selected window). The argument next-buffers should be a list of buffers.

The following commands can be used to cycle through the global buffer list, much like bury-buffer and 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 switch-to-prev-buffer command, in particular, is used by replace-buffer-in-windows, bury-buffer and quit-window to find a replacement buffer for a window.

Command: switch-to-prev-buffer &optional window bury-or-kill

This command displays the previous buffer in window. The argument window should be a live window or nil (meaning the selected window). If the optional argument bury-or-kill is non-nil, this means that the buffer currently shown in 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 window. However, a buffer that has been buried or killed, or has been already shown by a recent invocation of switch-to-prev-buffer, does not qualify as previous buffer.

If repeated invocations of this command have already shown all buffers previously shown in window, further invocations will show buffers from the buffer list of the frame window appears on (@pxref{Buffer List}), trying to skip buffers that are already shown in another window on that frame.

Command: switch-to-next-buffer &optional window

This command switches to the next buffer in window, thus undoing the effect of the last switch-to-prev-buffer command in window. The argument window must be a live window and defaults to the selected one.

If there is no recent invocation of switch-to-prev-buffer that can be undone, this function tries to show a buffer from the buffer list of the frame window appears on (@pxref{Buffer List}).

By default switch-to-prev-buffer and 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.

User Option: switch-to-visible-buffer

If this variable is non-nil, switch-to-prev-buffer and 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 nil, switch-to-prev-buffer and 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 t.


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1.17 Dedicated Windows

Functions for displaying a buffer can be told to not use specific windows by marking these windows as dedicated to their buffers. display-buffer (see section Choosing a Window for Display) never uses a dedicated window for displaying another buffer in it. get-lru-window and get-largest-window (see section Cyclic Ordering of Windows) do not consider dedicated windows as candidates when their dedicated argument is non-nil. The behavior of set-window-buffer (see section 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, delete-windows-on (see section 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 replace-buffer-in-windows (see section Buffers and Windows) which is called when a buffer gets killed, deletes the window in case (1) and behaves like delete-windows-on otherwise.

When bury-buffer (@pxref{Buffer List}) operates on the selected window (which shows the buffer that shall be buried), it handles case (2) by calling frame-auto-hide-function (see section Quitting Windows) to deal with the selected frame. The other two cases are handled as with replace-buffer-in-windows.

Function: window-dedicated-p &optional window

This function returns non-nil if window is dedicated to its buffer and nil otherwise. More precisely, the return value is the value assigned by the last call of set-window-dedicated-p for window, or nil if that function was never called with window as its argument. The default for window is the selected window.

Function: set-window-dedicated-p window flag

This function marks window as dedicated to its buffer if flag is non-nil, and non-dedicated otherwise.

As a special case, if flag is t, window becomes strongly dedicated to its buffer. 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 t differently from any non-nil value.


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1.18 Quitting Windows

When you want to get rid of a window used for displaying a buffer, you can call delete-window or delete-windows-on (see section Deleting Windows) to remove that window from its frame. If the buffer is shown on a separate frame, you might want to call 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 switch-to-prev-buffer (see section 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.

Command: quit-window &optional kill window

This command quits window and buries its buffer. The argument window must be a live window and defaults to the selected one. With prefix argument kill non-nil, it kills the buffer instead of burying it. It calls the function quit-restore-window described next to deal with the window and its buffer.

Function: quit-restore-window &optional window bury-or-kill

This function handles window and its buffer after quitting. The optional argument window must be a live window and defaults to the selected one. The function’s behavior is determined by the four elements of the quit-restore window parameter (see section Window Parameters), which is set to nil afterwards.

The window is deleted entirely if: 1) the first element of the quit-restore parameter is one of ’window or ’frame, 2) the window has no history of previously-displayed buffers, and 3) the displayed buffer matches the one in the fourth element of the quit-restore parameter. If window is the only window on its frame and there are other frames on the frame’s terminal, the value of the optional argument bury-or-kill determines how to proceed with the window. If bury-or-kill equals kill, the frame is deleted unconditionally. Otherwise, the fate of the frame is determined by calling frame-auto-hide-function (see below) with that frame as sole argument.

If the third element of the quit-restore parameter is a list of buffer, window start (see section The Window Start and End Positions), and point (see section Windows and Point), and that buffer is still live, the buffer will be displayed, and start and point set accordingly. If, in addition, window’s buffer was temporarily resized, this function will also try to restore the original height of window.

Otherwise, if window was previously used for displaying other buffers (see section Window History), the most recent buffer in that history will be displayed.

The optional argument bury-or-kill specifies how to deal with window’s buffer. The following values are handled:

nil

This means to not deal with the buffer in any particular way. As a consequence, if window is not deleted, invoking switch-to-prev-buffer will usually show the buffer again.

append

This means that if window is not deleted, its buffer is moved to the end of window’s list of previous buffers, so it’s less likely that a future invocation of switch-to-prev-buffer will switch to it. Also, it moves the buffer to the end of the frame’s buffer list.

bury

This means that if window is not deleted, its buffer is removed from 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 switch-to-prev-buffer switch to this buffer again without killing the buffer.

kill

This means to kill window’s buffer.

Typically, the display routines run by display-buffer will set the quit-restore window parameter correctly. It’s also possible to set it manually, using the following code for displaying buffer in window:

(display-buffer-record-window type window buffer)

(set-window-buffer window buffer)

(set-window-prev-buffers window nil)

Setting the window history to nil ensures that a future call to quit-window can delete the window altogether.

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.

User Option: 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 bury-buffer (@pxref{Buffer List}) when the selected window is dedicated and shows the buffer to bury. It is also called by 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 iconify-frame (@pxref{Visibility of Frames}). Alternatively, you may specify either delete-frame (@pxref{Deleting Frames}) to remove the frame from its display, make-frame-invisible to make the frame invisible, 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.

For a particular frame, the value specified here may be overridden by that frame’s auto-hide-function frame parameter (@pxref{Frame Interaction Parameters}).


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1.19 Side Windows

Side windows are special windows positioned at any of the four sides of a frame’s root window (see section Windows and Frames). In practice, this means that the area of the frame’s root window is subdivided into a main window and a number of side windows surrounding that main window. The main window is either a “normal” live window or specifies the area containing all the normal windows.

In their most simple form of use, side windows allow to display specific buffers always in the same area of a frame. Hence they can be regarded as a generalization of the concept provided by display-buffer-at-bottom (see section Action Functions for display-buffer) to the remaining sides of a frame. With suitable customizations, however, side windows can be also used to provide frame layouts similar to those found in so-called integrated development environments (IDEs).


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1.19.1 Displaying Buffers in Side Windows

The following action function for display-buffer (see section Action Functions for display-buffer) creates or reuses a side window for displaying the specified buffer.

Function: display-buffer-in-side-window buffer alist

This function displays buffer in a side window of the selected frame. It returns the window used for displaying buffer, nil if no such window can be found or created.

alist is an association list of symbols and values as for display-buffer. The following symbols in alist are special for this function:

side

Denotes the side of the frame where the window shall be located. Valid values are left, top, right and bottom. If unspecified, the window is located at the bottom of the frame.

slot

Denotes a slot at the specified side where to locate the window. A value of zero means to preferably position the window in the middle of the specified side. A negative value means to use a slot preceding (that is, above or on the left of) the middle slot. A positive value means to use a slot following (that is, below or on the right of) the middle slot. Hence, all windows on a specific side are ordered by their slot value. If unspecified, the window is located in the middle of the specified side.

If you specify the same slot on the same side for two or more different buffers, the buffer displayed last is shown in the corresponding window. Hence, slots can be used for sharing the same side window between buffers.

This function installs the window-side and window-slot parameters (see section Window Parameters) and makes them persistent. It does not install any other window parameters unless they have been explicitly provided via a window-parameters entry in alist.

By default, side windows cannot be split via split-window (see section Splitting Windows). Also, a side window is not reused or split by any buffer display action (see section Action Functions for display-buffer) unless it is explicitly specified as target of that action. Note also that delete-other-windows cannot make a side window the only window on its frame (see section Deleting Windows).

Once set up, side windows also change the behavior of the commands switch-to-prev-buffer and switch-to-next-buffer (see section Window History). In particular, these commands will refrain from showing, in a side window, buffers that have not been displayed in that window before. They will also refrain from having a normal, non-side window show a buffer that has been already displayed in a side window. A notable exception to the latter rule occurs when an application, after displaying a buffer, resets that buffer’s local variables.


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1.19.2 Side Window Options and Functions

The following options provide additional control over the placement of side windows.

User Option: window-sides-vertical

If non-nil, the side windows on the left and right of a frame occupy the frame’s full height. Otherwise, the side windows on the top and bottom of the frame occupy the frame’s full width.

User Option: window-sides-slots

This option specifies the maximum number of side windows on each side of a frame. The value is a list of four elements specifying the number of side window slots on (in this order) the left, top, right and bottom of each frame. If an element is a number, it means to display at most that many windows on the corresponding side. If an element is nil, it means there’s no bound on the number of slots on that side.

If any of the specified values is zero, no window can be created on the corresponding side. display-buffer-in-side-window will not signal an error in that case, but will return nil. If a specified value just forbids the creation of an additional side window, the most suitable window on that side is reused and may have its window-slot parameter changed accordingly.

User Option: window-sides-reversed

This option specifies whether top/bottom side windows should appear in reverse order. When this is nil, side windows on the top and bottom of a frame are always drawn from left to right with increasing slot values. When this is t, the drawing order is reversed and side windows on the top and bottom of a frame are drawn from right to left with increasing slot values.

When this is bidi, the drawing order is reversed if and only if the value of bidi-paragraph-direction (@pxref{Bidirectional Display}) is right-to-left in the buffer displayed in the window most recently selected within the main window area of this frame. Sometimes that window may be hard to find, so heuristics are used to avoid that the drawing order changes inadvertently when another window gets selected.

The layout of side windows on the left or right of a frame is not affected by the value of this variable.

When a frame has side windows, the following function returns the main window of that frame.

Function: window-main-window &optional frame

This function returns the main window of the specified frame. The optional argument frame must be a live frame and defaults to the selected one.

If frame has no side windows, it returns frame’s root window. Otherwise, it returns either an internal non-side window such that all other non-side windows on frame descend from it, or the single live non-side window of frame. Note that the main window of a frame cannot be deleted via delete-window.

The following command is handy to toggle the appearance of all side windows on a specified frame.

Command: window-toggle-side-windows &optional frame

This command toggles side windows on the specified frame. The optional argument frame must be a live frame and defaults to the selected one.

If frame has at least one side window, this command saves the state of frame’s root window in the frame’s window-state frame parameter and deletes all side windows on frame afterwards.

If frame has no side windows, but does have a window-state parameter, this command uses that parameter’s value to restore the side windows on frame leaving frame’s main window alone.

An error is signaled if frame has no side windows and no saved state is found for it.


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1.19.3 Frame Layouts with Side Windows

Side windows can be used to create more complex frame layouts like those provided by integrated development environments (IDEs). In such layouts, the area of the main window is where the normal editing activities take place. Side windows are not conceived for editing in the usual sense. Rather, they are supposed to display information complementary to the current editing activity, like lists of files, tags or buffers, help information, search or grep results or shell output.

The layout of such a frame might appear as follows:

     ___________________________________
    |          *Buffer List*            |
    |___________________________________|
    |     |                       |     |
    |  *  |                       |  *  |
    |  d  |                       |  T  |
    |  i  |                       |  a  |
    |  r  |   Main Window Area    |  g  |
    |  e  |                       |  s  |
    |  d  |                       |  *  |
    |  *  |                       |     |
    |_____|_______________________|_____|
    | *help*/*grep*/  |  *shell*/       |
    | *Completions*   |  *compilation*  |
    |_________________|_________________|
    |             Echo Area             |
    |___________________________________|


The following example illustrates how window parameters (see section Window Parameters) can be used with display-buffer-in-side-window (see section Displaying Buffers in Side Windows) to set up code for producing the frame layout sketched above.

(defvar parameters
  '(window-parameters . ((no-other-window . t)
                         (no-delete-other-windows . t))))

(setq fit-window-to-buffer-horizontally t)
(setq window-resize-pixelwise t)

(setq
 display-buffer-alist
 `(("\\*Buffer List\\*" display-buffer-in-side-window
    (side . top) (slot . 0) (window-height . fit-window-to-buffer)
    (preserve-size . (nil . t)) ,parameters)
   ("\\*Tags List\\*" display-buffer-in-side-window
    (side . right) (slot . 0) (window-width . fit-window-to-buffer)
    (preserve-size . (t . nil)) ,parameters)
   ("\\*\\(?:help\\|grep\\|Completions\\)\\*"
    display-buffer-in-side-window
    (side . bottom) (slot . -1) (preserve-size . (nil . t))
    ,parameters)
   ("\\*\\(?:shell\\|compilation\\)\\*" display-buffer-in-side-window
    (side . bottom) (slot . 1) (preserve-size . (nil . t))
    ,parameters)))

This specifies display-buffer-alist entries (see section Choosing a Window for Display) for buffers with fixed names. In particular, it asks for showing ‘*Buffer List*’ with adjustable height at the top of the frame and ‘*Tags List*’ with adjustable width on the frame’s right. It also asks for having the ‘*help*’, ‘*grep*’ and ‘*Completions*’ buffers share a window on the bottom left side of the frame and the ‘*shell*’ and ‘*compilation*’ buffers appear in a window on the bottom right side of the frame.

Note that the option fit-window-to-buffer-horizontally must have a non-nil value in order to allow horizontal adjustment of windows. Entries are also added that ask for preserving the height of side windows at the top and bottom of the frame and the width of side windows at the left or right of the frame. To assure that side windows retain their respective sizes when maximizing the frame, the variable window-resize-pixelwise is set to a non-nil value. See section Resizing Windows.

The last form also makes sure that none of the created side windows are accessible via C-x o by installing the no-other-window parameter for each of these windows. In addition, it makes sure that side windows are not deleted via C-x 1 by installing the no-delete-other-windows parameter for each of these windows.

Since dired buffers have no fixed names, we use a special function dired-default-directory-on-left in order to display a lean directory buffer on the left side of the frame.

(defun dired-default-directory-on-left ()
  "Display `default-directory' in side window on left, hiding details."
  (interactive)
  (let ((buffer (dired-noselect default-directory)))
    (with-current-buffer buffer (dired-hide-details-mode t))
    (display-buffer-in-side-window
     buffer `((side . left) (slot . 0)
              (window-width . fit-window-to-buffer)
              (preserve-size . (t . nil)) ,parameters))))

Evaluating the preceding forms and typing, in any order, M-x list-buffers, C-h f, M-x shell, M-x list-tags, and M-x dired-default-directory-on-left should now reproduce the frame layout sketched above.


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1.20 Atomic Windows

Atomic windows are rectangular compositions of at least two live windows. They have the following distinctive characteristics:

This means that the basic groups of functions that alter the window structure treat an atomic window like a live one, thus preserving the internal structure of the atomic window.

Atomic windows are useful to construct and preserve window layouts that are meaningful only when all involved buffers are shown simultaneously in a specific manner, such as when showing differences between file revisions, or the same text in different languages or markups. They can also be used to permanently display information pertinent to a specific window in bars on that window’s sides.

Atomic windows are implemented with the help of the reserved window-atom window parameter (see section Window Parameters) and an internal window (see section Basic Concepts of Emacs Windows) called the root window of the atomic window. All windows that are part of the same atomic window have this root window as their common ancestor and are assigned a non-nil window-atom parameter.

The following function returns the root of the atomic window a specified window is part of:

Function: window-atom-root &optional window

This functions returns the root of the atomic window window is a part of. The specified window must be a valid window and defaults to the selected one. It returns nil if window is not part of an atomic window.

The most simple approach to make a new atomic window is to take an existing internal window and apply the following function:

Function: window-make-atom window

This function converts window into an atomic window. The specified window must be an internal window. All this function does is to set the window-atom parameter of each descendant of window to t.

To create a new atomic window from an existing live window or to add a new window to an existing atomic window, the following buffer display action function (see section Action Functions for display-buffer) can be used:

Function: display-buffer-in-atom-window buffer alist

This function tries to display buffer in a new window that will be combined with an existing window to form an atomic window. If the existing window is already part of an atomic window, it adds the new window to that atomic window.

The specified alist is an association list of symbols and values. The following symbols have a special meaning:

window

The value of such an element specifies an existing window the new window shall be combined with. If it specifies an internal window, all children of that window become part of the atomic window too. If no window is specified, the new window becomes a sibling of the selected window. The window-atom parameter of the existing window is set to main provided that window is live and its window-atom parameter was not already set.

side

The value of such an element denotes the side of the existing window where the new window shall be located. Valid values are below, right, above and left. The default is below. The window-atom parameter of the new window is set to this value.

The return value is the new window, nil when creating that window failed.

Note that the value of the window-atom parameter does not really matter as long as it is non-nil. The values assigned by display-buffer-in-atom-window just allow for easy retrieval of the original and the new window after that function has been applied. Note also that the window-atom parameter is the only window parameter assigned by display-buffer-in-atom-window. Further parameters have to be set by the application explicitly via a window-parameters entry in alist.

The following code snippet, when applied to a single-window frame, first splits the selected window and makes the selected and the new window constituents of an atomic window with their parent as root. It then displays the buffer ‘*Messages*’ in a new window at the frame’s bottom and makes that new window part of the atomic window just created.

(let ((window (split-window-right)))
  (window-make-atom (window-parent window))
  (display-buffer-in-atom-window
   (get-buffer-create "*Messages*")
   `((window . ,(window-parent window)) (window-height . 5))))

At this moment typing C-x 2 in any window of that frame produces a new window at the bottom of the frame. Typing C-x 3 instead will put the new window at the frame’s right. In either case, typing now C-x 1 in any window of the atomic window will remove the new window only. Typing C-x 0 in any window of the atomic window will make that new window fill the frame.


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1.21 Windows and Point

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.

Emacs displays the cursor, by default as a rectangular block, in each window at the position of that window’s point. When the user switches to another buffer in a window, Emacs moves that window’s cursor to where point is in that buffer. If the exact position of point is hidden behind some display element, such as a display string or an image, Emacs displays the cursor immediately before or after that display element.

Function: window-point &optional window

This function returns the current position of point in 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 window is the selected window.

When 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 save-excursion forms. But that value is hard to find.

Function: set-window-point window position

This function positions point in window at position position in window’s buffer. It returns position.

If window is selected, this simply does goto-char in window’s buffer.

Variable: window-point-insertion-type

This variable specifies the marker insertion type (@pxref{Marker Insertion Types}) of window-point. The default is nil, so window-point will stay behind text inserted there.


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1.22 The Window Start and End Positions

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 display-start position of the window (or just the 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.

Function: window-start &optional window

This function returns the display-start position of window window. If window is 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 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.

Function: window-group-start &optional window

This function is like window-start, except that when window is a part of a group of windows (see Window Group), window-group-start returns the start position of the entire group. This condition holds when the buffer local variable window-group-start-function is set to a function. In this case, window-group-start calls the function with the single argument window, then returns its result.

Function: window-end &optional window update

This function returns the position where display of its buffer ends in window. The default for window is the selected window.

Simply changing the buffer text or moving point does not update the value that window-end returns. The value is updated only when Emacs redisplays and redisplay completes without being preempted.

If the last redisplay of 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 nil.

If update is non-nil, window-end always returns an up-to-date value for where display ends, based on the current window-start value. If a previously saved value of that position is still valid, window-end returns that value; otherwise it computes the correct value by scanning the buffer text.

Even if update is non-nil, 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 window-start value. In effect, it reports where the displayed text will end if scrolling is not required.

Function: window-group-end &optional window update

This function is like window-end, except that when window is a part of a group of windows (see Window Group), window-group-end returns the end position of the entire group. This condition holds when the buffer local variable window-group-end-function is set to a function. In this case, window-group-end calls the function with the two arguments window and update, then returns its result. The argument update has the same meaning as in window-end.

Function: set-window-start window position &optional noforce

This function sets the display-start position of window to position in window’s buffer. It returns 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 nil for noforce, it means you want display to start at 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 is 1 and you set the start of the window 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:

;; Here is what ‘foo’ looks like before executing
;;   the set-window-start expression.
---------- Buffer: foo ----------
∗This is the contents of buffer foo.
2
3
4
5
6
---------- Buffer: foo ----------
(set-window-start
 (selected-window)
 (save-excursion
   (goto-char 1)
   (forward-line 1)
   (point)))
⇒ 37
;; Here is what ‘foo’ looks like after executing
;;   the set-window-start expression.
---------- Buffer: foo ----------
2
3
∗4
5
6
---------- Buffer: foo ----------

If noforce is non-nil, and 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 position is not used.

Function: set-window-group-start window position &optional noforce

This function is like set-window-start, except that when window is a part of a group of windows (see Window Group), set-window-group-start sets the start position of the entire group. This condition holds when the buffer local variable set-window-group-start-function is set to a function. In this case, set-window-group-start calls the function with the three arguments window, position, and noforce, then returns its result. The arguments position and noforce in this function have the same meaning as in set-window-start.

Function: pos-visible-in-window-p &optional position window partially

This function returns non-nil if position is within the range of text currently visible on the screen in window. It returns nil if position is scrolled vertically out of view. Locations that are partially obscured are not considered visible unless partially is non-nil. The argument position defaults to the current position of point in window; window defaults to the selected window. If position is t, that means to check either the first visible position of the last screen line in window, or the end-of-buffer position, whichever comes first.

This function considers only vertical scrolling. If position is out of view only because window has been scrolled horizontally, pos-visible-in-window-p returns non-nil anyway. See section Horizontal Scrolling.

If position is visible, pos-visible-in-window-p returns t if partially is nil; if partially is non-nil, and the character following position is fully visible, it returns a list of the form (x y), where x and y are the pixel coordinates relative to the top left corner of the window; otherwise it returns an extended list of the form (x y rtop rbot rowh vpos), where rtop and rbot specify the number of off-window pixels at the top and bottom of the row at position, rowh specifies the visible height of that row, and vpos specifies the vertical position (zero-based row number) of that row.

Here is an example:

;; If point is off the screen now, recenter it now.
(or (pos-visible-in-window-p
     (point) (selected-window))
    (recenter 0))
Function: pos-visible-in-window-group-p &optional position window partially

This function is like pos-visible-in-window-p, except that when window is a part of a group of windows (see Window Group), pos-visible-in-window-group-p tests the visibility of pos in the entire group, not just in the single window. This condition holds when the buffer local variable pos-visible-in-window-group-p-function is set to a function. In this case pos-visible-in-window-group-p calls the function with the three arguments position, window, and partially, then returns its result. The arguments position and partially have the same meaning as in pos-visible-in-window-p.

Function: window-line-height &optional line window

This function returns the height of text line line in window. If line is one of header-line or mode-line, window-line-height returns information about the corresponding line of the window. Otherwise, line is a text line number starting from 0. A negative number counts from the end of the window. The default for line is the current line in window; the default for window is the selected window.

If the display is not up to date, window-line-height returns nil. In that case, pos-visible-in-window-p may be used to obtain related information.

If there is no line corresponding to the specified line, window-line-height returns nil. Otherwise, it returns a list (height vpos ypos offbot), where height is the height in pixels of the visible part of the line, vpos and ypos are the vertical position in lines and pixels of the line relative to the top of the first text line, and 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, ypos is negative.


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1.23 Textual Scrolling

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 window-point to keep point on the screen (see section Windows and Point).

The basic textual scrolling functions are scroll-up (which scrolls forward) and 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 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 <PageDown> on modern keyboards.

Textual scrolling functions (aside from 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 auto-window-vscroll to nil (see section Vertical Fractional Scrolling).

Command: scroll-up &optional count

This function scrolls forward by count lines in the selected window.

If count is negative, it scrolls backward instead. If count is nil (or omitted), the distance scrolled is 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 nil.

Command: scroll-down &optional count

This function scrolls backward by count lines in the selected window.

If count is negative, it scrolls forward instead. In other respects, it behaves the same way as scroll-up does.

Command: scroll-up-command &optional count

This behaves like scroll-up, except that if the selected window cannot be scrolled any further and the value of the variable scroll-error-top-bottom is t, it tries to move to the end of the buffer instead. If point is already there, it signals an error.

Command: scroll-down-command &optional count

This behaves like scroll-down, except that if the selected window cannot be scrolled any further and the value of the variable scroll-error-top-bottom is t, it tries to move to the beginning of the buffer instead. If point is already there, it signals an error.

Command: scroll-other-window &optional count

This function scrolls the text in another window upward count lines. Negative values of count, or nil, are handled as in scroll-up.

You can specify which buffer to scroll by setting the variable other-window-scroll-buffer to a buffer. If that buffer isn’t already displayed, 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 minibuffer-scroll-window. This variable has no effect when any other window is selected. When it is non-nil and the minibuffer is selected, it takes precedence over 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, 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 ‘End of buffer’.

Variable: other-window-scroll-buffer

If this variable is non-nil, it tells scroll-other-window which buffer’s window to scroll.

User Option: 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.

User Option: maximum-scroll-margin

This variable limits the effective value of scroll-margin to a fraction of the current window line height. For example, if the current window has 20 lines and maximum-scroll-margin is 0.1, then the scroll margins will never be larger than 2 lines, no matter how big scroll-margin is.

maximum-scroll-margin itself has a maximum value of 0.5, which allows setting margins large to keep the cursor at the middle line of the window (or two middle lines if the window has an even number of lines). If it’s set to a larger value (or any value other than a float between 0.0 and 0.5) then the default value of 0.25 will be used instead.

User Option: 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 n, then redisplay scrolls the text up to n lines in either direction, if that will bring point back into proper view. This behavior is called conservative scrolling. Otherwise, scrolling happens in the usual way, under the control of other variables such as scroll-up-aggressively and scroll-down-aggressively.

The default value is zero, which means that conservative scrolling never happens.

User Option: scroll-down-aggressively

The value of this variable should be either nil or a fraction 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 f part of the window height from the top. The larger f, the more aggressive the scrolling.

A value of nil is equivalent to .5, since its effect is to center point. This variable automatically becomes buffer-local when set in any fashion.

User Option: scroll-up-aggressively

Likewise, for scrolling up. The value, f, specifies how far point should be placed from the bottom of the window; thus, as with scroll-up-aggressively, a larger value scrolls more aggressively.

User Option: scroll-step

This variable is an older variant of scroll-conservatively. The difference is that if its value is n, that permits scrolling only by precisely n lines, not a smaller number. This feature does not work with scroll-margin. The default value is zero.

User Option: scroll-preserve-screen-position

If this option is 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-nil and not 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-nil scroll-command symbol property.

User Option: 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, scroll-up with an argument of nil scrolls so that this many lines at the bottom of the window appear instead at the top. The default value is 2.

User Option: scroll-error-top-bottom

If this option is nil (the default), scroll-up-command and scroll-down-command simply signal an error when no more scrolling is possible.

If the value is 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.

Command: recenter &optional count

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 count is a non-negative number, that puts the line containing point count lines down from the top of the window. If count is a negative number, then it counts upward from the bottom of the window, so that -1 stands for the last usable line in the window.

If count is nil (or a non-nil list), recenter puts the line containing point in the middle of the window. If count is nil, this function may redraw the frame, according to the value of recenter-redisplay.

When recenter is called interactively, count is the raw prefix argument. Thus, typing C-u as the prefix sets the count to a non-nil list, while typing C-u 4 sets count to 4, which positions the current line four lines from the top.

With an argument of zero, recenter positions the current line at the top of the window. The command recenter-top-bottom offers a more convenient way to achieve this.

Function: recenter-window-group &optional count

This function is like recenter, except that when the selected window is part of a group of windows (see Window Group), recenter-window-group scrolls the entire group. This condition holds when the buffer local variable recenter-window-group-function is set to a function. In this case, recenter-window-group calls the function with the argument count, then returns its result. The argument count has the same meaning as in recenter, but with respect to the entire window group.

User Option: recenter-redisplay

If this variable is non-nil, calling recenter with a nil argument redraws the frame. The default value is tty, which means only redraw the frame if it is a tty frame.

Command: recenter-top-bottom &optional count

This command, which is the default binding for C-l, acts like recenter, except if called with no argument. In that case, successive calls place point according to the cycling order defined by the variable recenter-positions.

User Option: recenter-positions

This variable controls how recenter-top-bottom behaves when called with no argument. The default value is (middle top bottom), which means that successive calls of recenter-top-bottom with no argument cycle between placing point at the middle, top, and bottom of the window.


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1.24 Vertical Fractional Scrolling

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 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.

Function: window-vscroll &optional window pixels-p

This function returns the current vertical scroll position of window. The default for window is the selected window. If pixels-p is non-nil, the return value is measured in pixels, rather than in units of the normal line height.

(window-vscroll)
     ⇒ 0
Function: set-window-vscroll window lines &optional pixels-p

This function sets window’s vertical scroll position to lines. If window is nil, the selected window is used. The argument 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.

(set-window-vscroll (selected-window) 1.2)
     ⇒ 1.13

If pixels-p is non-nil, lines specifies a number of pixels. In this case, the return value is lines.

Variable: auto-window-vscroll

If this variable is non-nil, the line-move, scroll-up, and 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.


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1.25 Horizontal Scrolling

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 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 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.

If 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.

The default value of auto-hscroll-mode is t; setting it to current-line activates a variant of automatic horizontal scrolling whereby only the line showing the cursor is horizontally scrolled to make point visible, the rest of the window is left either unscrolled, or at the minimum scroll amount set by scroll-left and scroll-right, see below.

Command: scroll-left &optional count set-minimum

This function scrolls the selected window count columns to the left (or to the right if count is negative). The default for 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 window-hscroll (below).

Note that text in paragraphs whose base direction is right-to-left (@pxref{Bidirectional Display}) moves in the opposite direction: e.g., it moves to the right when scroll-left is invoked with a positive value of count.

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 set-minimum is non-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-nil for set-minimum.

Command: scroll-right &optional count set-minimum

This function scrolls the selected window count columns to the right (or to the left if count is negative). The default for count is the window width, minus 2. Aside from the direction of scrolling, this works just like scroll-left.

Function: window-hscroll &optional window

This function returns the total leftward horizontal scrolling of window—the number of columns by which the text in window is scrolled left past the left margin. (In right-to-left paragraphs, the value is the total amount of the rightward scrolling instead.) The default for window is the selected window.

The return value is never negative. It is zero when no horizontal scrolling has been done in window (which is usually the case).

(window-hscroll)
     ⇒ 0
(scroll-left 5)
     ⇒ 5
(window-hscroll)
     ⇒ 5
Function: set-window-hscroll window columns

This function sets horizontal scrolling of window. The value of columns specifies the amount of scrolling, in terms of columns from the left margin (right margin in right-to-left paragraphs). The argument columns should be zero or positive; if not, it is taken as zero. Fractional values of columns are not supported at present.

Note that set-window-hscroll may appear not to work if you test it by evaluating a call with 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 columns.

(set-window-hscroll (selected-window) 10)
     ⇒ 10

Here is how you can determine whether a given position position is off the screen due to horizontal scrolling:

(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)))))

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1.26 Coordinates and Windows

This section describes functions that report positions of and within a window. Most of these functions report positions relative to an origin at the native position of the window’s frame (@pxref{Frame Geometry}). Some functions report positions relative to the origin of the display of the window’s frame. In any case, the origin has the coordinates (0, 0) and X and Y coordinates increase rightward and downward respectively.

For the following functions, 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 the default character specified by the frame’s default font (@pxref{Frame Font}).

Function: window-edges &optional window body absolute pixelwise

This function returns a list of the edge coordinates of window. If window is omitted or nil, it defaults to the selected window.

The return value has the form (left top right 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.

If the optional argument body is nil, this means to return the edges corresponding to the total size of window. body non-nil means to return the edges of window’s body (aka text area). If body is non-nil, window must specify a live window.

If the optional argument absolute is nil, this means to return edges relative to the native position of window’s frame. absolute non-nil means to return coordinates relative to the origin (0, 0) of window’s display. On non-graphical systems this argument has no effect.

If the optional argument pixelwise is nil, this means to return the coordinates in terms of the default character width and height of window’s frame (@pxref{Frame Font}), rounded if necessary. pixelwise non-nil means to return the coordinates in pixels. Note that the pixel specified by right and bottom is immediately outside of these edges. If absolute is non-nil, pixelwise is implicitly non-nil too.

Function: window-body-edges &optional window

This function returns the edges of window’s body (see section Window Sizes). Calling (window-body-edges window) is equivalent to calling (window-edges window t), see above.

The following functions can be used to relate a set of frame-relative coordinates to a window:

Function: window-at x y &optional frame

This function returns the live window at the coordinates x and y given in default character sizes (@pxref{Frame Font}) relative to the native position of frame (@pxref{Frame Geometry}).

If there is no window at that position, the return value is nil. If frame is omitted or nil, it defaults to the selected frame.

Function: coordinates-in-window-p coordinates window

This function checks whether a window window occupies the frame relative coordinates coordinates, and if so, which part of the window that is. window should be a live window.

coordinates should be a cons cell of the form (x . y), where x and y are given in default character sizes (@pxref{Frame Font}) relative to the native position of window’s frame (@pxref{Frame Geometry}).

If there is no window at the specified position, the return value is nil . Otherwise, the return value is one of the following:

(relx . rely)

The coordinates are inside window. The numbers relx and rely are the equivalent window-relative coordinates for the specified position, counting from 0 at the top left corner of the window.

mode-line

The coordinates are in the mode line of window.

header-line

The coordinates are in the header line of window.

right-divider

The coordinates are in the divider separating window from a window on the right.

bottom-divider

The coordinates are in the divider separating window from a window beneath.

vertical-line

The coordinates are in the vertical line between 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.

left-fringe
right-fringe

The coordinates are in the left or right fringe of the window.

left-margin
right-margin

The coordinates are in the left or right margin of the window.

nil

The coordinates are not in any part of window.

The function coordinates-in-window-p does not require a frame as argument because it always uses the frame that window is on.

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.

Function: window-pixel-edges &optional window

This function returns a list of pixel coordinates for the edges of window. Calling (window-pixel-edges window) is equivalent to calling (window-edges window nil nil t), see above.

Function: window-body-pixel-edges &optional window

This function returns the pixel edges of window’s body. Calling (window-body-pixel-edges window) is equivalent to calling (window-edges window t nil t), see above.

The following functions return window positions in pixels, relative to the origin of the display screen rather than that of the frame:

Function: window-absolute-pixel-edges &optional window

This function returns the pixel coordinates of window relative to an origin at (0, 0) of the display of window’s frame. Calling (window-absolute-pixel-edges) is equivalent to calling (window-edges window nil t t), see above.

Function: window-absolute-body-pixel-edges &optional window

This function returns the pixel coordinates of window’s body relative to an origin at (0, 0) of the display of window’s frame. Calling (window-absolute-body-pixel-edges window) is equivalent to calling (window-edges window t t t), see above.

Combined with set-mouse-absolute-pixel-position, this function can be used to move the mouse pointer to an arbitrary buffer position visible in some window:

(let ((edges (window-absolute-body-pixel-edges))
      (position (pos-visible-in-window-p nil nil t)))
  (set-mouse-absolute-pixel-position
   (+ (nth 0 edges) (nth 0 position))
   (+ (nth 1 edges) (nth 1 position))))

On a graphical terminal this form “warps” the mouse cursor to the upper left corner of the glyph at the selected window’s point. A position calculated this way can be also used to show a tooltip window there.

The following function returns the screen coordinates of a buffer position visible in a window:

Function: window-absolute-pixel-position &optional position window

If the buffer position position is visible in window window, this function returns the display coordinates of the upper/left corner of the glyph at position. The return value is a cons of the X- and Y-coordinates of that corner, relative to an origin at (0, 0) of window’s display. It returns nil if position is not visible in window.

window must be a live window and defaults to the selected window. position defaults to the value of window-point of window.

This means that in order to move the mouse pointer to the position of point in the selected window, it’s sufficient to write:

(let ((position (window-absolute-pixel-position)))
  (set-mouse-absolute-pixel-position
   (car position) (cdr position)))

The following function returns the largest rectangle that can be inscribed in a window without covering text displayed in that window.

Function: window-largest-empty-rectangle &optional window count min-width min-height positions left

This function calculates the dimensions of the largest empty rectangle that can be inscribed in the specified window’s text area. window must be a live window and defaults to the selected one.

The return value is a triple of the width and the start and end y-coordinates of the largest rectangle that can be inscribed into the empty space (space not displaying any text) of the text area of window. No x-coordinates are returned by this function—any such rectangle is assumed to end at the right edge of window’s text area. If no empty space can be found, the return value is nil.

The optional argument count, if non-nil, specifies a maximum number of rectangles to return. This means that the return value is a list of triples specifying rectangles with the largest rectangle first. count can be also a cons cell whose car specifies the number of rectangles to return and whose CDR, if non-nil, states that all rectangles returned must be disjoint.

The optional arguments min-width and min-height, if non-nil, specify the minimum width and height of any rectangle returned.

The optional argument positions, if non-nil, is a cons cell whose CAR specifies the uppermost and whose CDR specifies the lowermost pixel position that must be covered by any rectangle returned. These positions measure from the start of the text area of window.

The optional argument left, if non-nil, means to return values suitable for buffers displaying right to left text. In that case, any rectangle returned is assumed to start at the left edge of window’s text area.

Note that this function has to retrieve the dimensions of each line of window’s glyph matrix via window-lines-pixel-dimensions (@pxref{Size of Displayed Text}). Hence, this function may also return nil when the current glyph matrix of window is not up-to-date.


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1.27 Mouse Window Auto-selection

The following option allows to automatically select the window under the mouse pointer. This accomplishes a policy similar to that of window managers that give focus to a frame (and thus trigger its subsequent selection) whenever the mouse pointer enters its window-system window (@pxref{Input Focus}).

User Option: mouse-autoselect-window

If this variable is non-nil, Emacs will try to automatically select the window under the mouse pointer. The following values are meaningful:

A positive number

This specifies a delay in seconds after which auto-selection triggers. The window under the mouse pointer is selected after the mouse has remained in it for the entire duration of the delay.

A negative number

A negative number has a similar effect as a positive number, but selects the window under the mouse pointer only after the mouse pointer has remained in it for the entire duration of the absolute value of that number and in addition has stopped moving.

Other value

Any other non-nil value means to select a window instantaneously as soon as the mouse pointer enters it.

In either case, the mouse pointer must enter the text area of a window in order to trigger its selection. Dragging the scroll bar slider or the mode line of a window conceptually should not cause its auto-selection.

Mouse auto-selection selects the minibuffer window only if it is active, and never deselects the active minibuffer window.

Mouse auto-selection can be used to emulate a focus follows mouse policy for child frames (@pxref{Child Frames}) which usually are not tracked by the window manager. This requires to set the value of focus-follows-mouse (@pxref{Input Focus}) to a non-nil value. If the value of focus-follows-mouse is auto-raise, entering a child frame with the mouse will raise it automatically above all other child frames of that frame’s parent frame.


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1.28 Window Configurations

A window configuration records the entire layout of one frame—all windows, their sizes, which buffers they contain, how those buffers are scrolled, and their value of point; also their fringes, margins, and scroll bar settings. It also includes the value of 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}.

Function: current-window-configuration &optional frame

This function returns a new object representing frame’s current window configuration. The default for frame is the selected frame. The variable window-persistent-parameters specifies which window parameters (if any) are saved by this function. See section Window Parameters.

Function: set-window-configuration configuration

This function restores the configuration of windows and buffers as specified by configuration, for the frame that configuration was created for.

The argument configuration must be a value that was previously returned by current-window-configuration. The configuration is restored in the frame from which configuration was made, whether that frame is selected or not. In some rare cases this may trigger execution of the window-size-change-functions (see section Hooks for Window Scrolling and Changes) even if the size of windows did not change at all. The window-configuration-change-hook functions will be called if and only if at least one window was added to or deleted from the frame.

If the frame from which configuration was saved is dead, all this function does is restore the three variables window-min-height, window-min-width and minibuffer-scroll-window. In this case, the function returns nil. Otherwise, it returns t.

Here is a way of using this function to get the same effect as save-window-excursion:

(let ((config (current-window-configuration)))
  (unwind-protect
      (progn (split-window-below nil)
             …)
    (set-window-configuration config)))
Macro: save-window-excursion forms…

This macro records the window configuration of the selected frame, executes forms in sequence, then restores the earlier window configuration. The return value is the value of the final form in forms.

Most Lisp code should not use this macro; save-selected-window is typically sufficient. In particular, this macro cannot reliably prevent the code in forms from opening new windows, because new windows might be opened in other frames (see section Choosing a Window for Display), and save-window-excursion only saves and restores the window configuration on the current frame.

Do not use this macro in window-size-change-functions; exiting the macro triggers execution of window-size-change-functions, leading to an endless loop.

Function: window-configuration-p object

This function returns t if object is a window configuration.

Function: compare-window-configurations config1 config2

This function compares two window configurations as regards the structure of windows, but ignores the values of point and the saved scrolling positions—it can return t even if those aspects differ.

The function equal can also compare two window configurations; it regards configurations as unequal if they differ in any respect, even a saved point.

Function: window-configuration-frame config

This function returns the frame for which the window configuration config was made.

Other primitives to look inside of window configurations would make sense, but are not implemented because we did not need them. See the file ‘winner.el’ for some more operations on windows configurations.

The objects returned by 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 (set-window-configuration effectively clones the windows of a frame into the root window of that very frame only).

Function: window-state-get &optional window writable

This function returns the state of window as a Lisp object. The argument window must be a valid window and defaults to the root window of the selected frame.

If the optional argument writable is non-nil, this means to not use markers for sampling positions like window-point or window-start. This argument should be non-nil when the state will be written to disk and read back in another session.

Together, the argument writable and the variable window-persistent-parameters specify which window parameters are saved by this function. See section Window Parameters.

The value returned by 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.

Function: window-state-put state &optional window ignore

This function puts the window state state into window. The argument state should be the state of a window returned by an earlier invocation of window-state-get, see above. The optional argument window can be either a live window or an internal window (see section Windows and Frames) and defaults to the selected one. If window is not live, it is replaced by a live window before putting state into it.

If the optional argument ignore is non-nil, it means to ignore minimum window sizes and fixed-size restrictions. If ignore is safe, this means windows can get as small as one line and/or two columns.

The functions window-state-get and window-state-put also allow to exchange the contents of two live windows. The following function does precisely that:

Command: window-swap-states &optional window-1 window-2 size

This command swaps the states of the two live windows window-1 and window-2. window-1 must specify a live window and defaults to the selected one. window-2 must specify a live window and defaults to the window following window-1 in the cyclic ordering of windows, excluding minibuffer windows and including live windows on all visible frames.

Optional argument size non-nil means to try swapping the sizes of window-1 and window-2 as well. A value of height means to swap heights only, a value of width means to swap widths only, while t means to swap both widths and heights, if possible. Frames are not resized by this function.


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1.29 Window Parameters

This section describes how window parameters can be used to associate additional information with windows.

Function: window-parameter window parameter

This function returns window’s value for parameter. The default for window is the selected window. If window has no setting for parameter, this function returns nil.

Function: window-parameters &optional window

This function returns all parameters of window and their values. The default for window is the selected window. The return value is either nil, or an association list whose elements have the form (parameter . value).

Function: set-window-parameter window parameter value

This function sets window’s value of parameter to value and returns value. The default for window is the selected window.

By default, the functions that save and restore window configurations or the states of windows (see section Window Configurations) do not care about window parameters. This means that when you change the value of a parameter within the body of a save-window-excursion, the previous value is not restored when that macro exits. It also means that when you restore via window-state-put a window state saved earlier by window-state-get, all cloned windows have their parameters reset to nil. The following variable allows you to override the standard behavior:

Variable: window-persistent-parameters

This variable is an alist specifying which parameters get saved by current-window-configuration and window-state-get, and subsequently restored by set-window-configuration and window-state-put. See section Window Configurations.

The CAR of each entry of this alist is a symbol specifying the parameter. The CDR should be one of the following:

nil

This value means the parameter is saved neither by window-state-get nor by current-window-configuration.

t

This value specifies that the parameter is saved by current-window-configuration and (provided its writable argument is nil) by window-state-get.

writable

This means that the parameter is saved unconditionally by both current-window-configuration and window-state-get. This value should not be used for parameters whose values do not have a read syntax. Otherwise, invoking window-state-put in another session may fail with an invalid-read-syntax error.

Some functions (notably delete-window, delete-other-windows and split-window), may behave specially when the window specified by their window argument has a parameter whose name is equal to the function’s name. You can override such special behavior by binding the following variable to a non-nil value:

Variable: ignore-window-parameters

If this variable is non-nil, some standard functions do not process window parameters. The functions currently affected by this are split-window, delete-window, delete-other-windows, and other-window.

An application can bind this variable to a non-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.

The following parameters are currently used by the window management code:

delete-window

This parameter affects the execution of delete-window (see section Deleting Windows).

delete-other-windows

This parameter affects the execution of delete-other-windows (see section Deleting Windows).

no-delete-other-windows

This parameter marks the window as not deletable by delete-other-windows (see section Deleting Windows).

split-window

This parameter affects the execution of split-window (see section Splitting Windows).

other-window

This parameter affects the execution of other-window (see section Cyclic Ordering of Windows).

no-other-window

This parameter marks the window as not selectable by other-window (see section Cyclic Ordering of Windows).

clone-of

This parameter specifies the window that this one has been cloned from. It is installed by window-state-get (see section Window Configurations).

window-preserved-size

This parameter specifies a buffer, a direction where nil means vertical and t horizontal, and a size in pixels. If this window displays the specified buffer and its size in the indicated direction equals the size specified by this parameter, then Emacs will try to preserve the size of this window in the indicated direction. This parameter is installed and updated by the function window-preserve-size (see section Preserving Window Sizes).

quit-restore

This parameter is installed by the buffer display functions (see section Choosing a Window for Display) and consulted by quit-restore-window (see section Quitting Windows). It contains four elements:

The first element is one of the symbols window, meaning that the window has been specially created by display-buffer; frame, a separate frame has been created; same, the window has only ever displayed this buffer; or other, the window showed another buffer before. frame and window affect how the window is quit, while same and other affect the redisplay of buffers previously shown in this window.

The second element is either one of the symbols window or 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. If that buffer is still live when the window is quit, then the function quit-restore-window reuses the window to display the buffer.

The third element is the window selected at the time the parameter was created. If quit-restore-window deletes the window passed to it as argument, it then tries to reselect this window.

The fourth element is the buffer whose display caused the creation of this parameter. quit-restore-window deletes the specified window only if it still shows that buffer.

See the description of quit-restore-window in Quitting Windows for details.

window-side window-slot

These parameters are used for implementing side windows (see section Side Windows).

window-atom

This parameter is used for implementing atomic windows, see Atomic Windows.

mode-line-format

This parameter replaces the value of the buffer-local variable mode-line-format (@pxref{Mode Line Basics}) of this window’s buffer whenever this window is displayed. The symbol none means to suppress display of a mode line for this window. Display and contents of the mode line on other windows showing this buffer are not affected.

header-line-format

This parameter replaces the value of the buffer-local variable header-line-format (@pxref{Mode Line Basics}) of this window’s buffer whenever this window is displayed. The symbol none means to suppress display of a header line for this window. Display and contents of the header line on other windows showing this buffer are not affected.

min-margins

The value of this parameter is a cons cell whose CAR and CDR, if non-nil, specify the minimum values (in columns) for the left and right margin of this window. When present, Emacs will use these values instead of the actual margin widths for determining whether a window can be split or shrunk horizontally.

Emacs never auto-adjusts the margins of any window after splitting or resizing it. It is the sole responsibility of any application setting this parameter to adjust the margins of this window as well as those of any new window that inherits this window’s margins due to a split. Both window-configuration-change-hook and window-size-change-functions (see section Hooks for Window Scrolling and Changes) should be employed for this purpose.

This parameter was introduced in Emacs version 25.1 to support applications that use large margins to center buffer text within a window and should be used, with due care, exclusively by those applications. It might be replaced by an improved solution in future versions of Emacs.


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1.30 Hooks for Window Scrolling and Changes

This section describes how a Lisp program can take action whenever a window displays a different part of its buffer or a different buffer. There are three actions that can change this: scrolling the window, switching buffers in the window, and changing the size of the window. The first two actions run window-scroll-functions; the last runs window-size-change-functions.

Variable: 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. At the time of the call, the display-start position of the window argument is already set to its new value, and the buffer to be displayed in the window is already set as the current buffer.

These functions must take care when using window-end (see section The Window Start and End Positions); if you need an up-to-date value, you must use the update argument to ensure you get it.

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.

Function: run-window-scroll-functions &optional window

This function calls window-scroll-functions for the specified window, which defaults to the selected window.

Variable: 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 once per redisplay, and once for each frame on which size changes have occurred.

Each function receives the frame as its sole argument. To find out whether a specific window has changed size, compare the return values of window-pixel-width-before-size-change and window-pixel-width respectively window-pixel-height-before-size-change and window-pixel-height for that window (see section Window Sizes).

These function are usually only called when at least one window was added or has changed size since the last time this hook was run for the associated frame. In some rare cases this hook also runs when a window that was added intermittently has been deleted afterwards. In these cases none of the windows on the frame will appear to have changed its size.

You may use save-selected-window in these functions (see section Selecting Windows). However, do not use save-window-excursion (see section Window Configurations); exiting that macro counts as a size change, which would cause these functions to be called again.

Variable: window-configuration-change-hook

A normal hook that is run every time the window configuration of a frame changes. Window configuration changes include splitting and deleting windows, and the display of a different buffer in a window. Resizing the frame or individual windows do not count as configuration changes. Use window-size-change-functions, see above, when you want to track size changes that are not caused by the deletion or creation of windows.

The buffer-local value of this hook is run once for each window on the affected frame, with the relevant window selected and its buffer current. The global value of this hook is run once for the modified frame, with that frame selected.

Function: run-window-configuration-change-hook &optional frame

This function runs window-configuration-change-hook for the specified frame, which defaults to the selected frame.

In addition, you can use 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}.


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