A window is an area of the screen that can be used to display a buffer (Buffers). Windows are grouped into frames (Frames). Each frame contains at least one window; the user can subdivide a frame 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 term "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 graphical X window owned by the Emacs process corresponds to one Emacs frame. When Emacs is run on a text terminal, each Emacs frame fills the entire terminal screen. In either case, the frame may contain one or more Emacs windows. For disambiguation, we use the term window-system window when we mean the window-system window corresponding to an Emacs frame. Unlike X windows, Emacs windows are tiled; they never overlap within the area of their frame. When a window is created, resized, or deleted, the change in window space is taken from or given to other windows on the same frame, so that the total area of the frame is unchanged. In Emacs Lisp, windows are represented by a special Lisp object type (Window Type).

windowp

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.

window-live-p

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. 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 A valid window can be deleted, i.e., removed from its frame (Deleting Windows); then it is no longer valid, but the Lisp object representing it might be still referenced from other Lisp objects.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 (Window Configurations). You can distinguish valid windows from deleted windows with window-valid-p.

window-valid-p

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.

The following schematic shows the structure of a live window:

____________________________________________
       |________________ Tab Line _______________|RD| ^
       |______________ Header Line ______________|  | |
     ^ |LS|LM|LF|                       |RF|RM|RS|  | |
     | |  |  |  |                       |  |  |  |  | |
Window |  |  |  |                       |  |  |  |  | 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 that window is the body, where the buffer text is displayed. The body can be surrounded by a series of optional areas which we will call window decorations. On the left and right, from innermost to outermost, these are the left and right fringes, denoted by LF and RF (Fringes); the left and right margins, denoted by LM and RM in the schematic (Display Margins); the left or right vertical scroll bar, only one of which is present at any time, denoted by LS and RS (Scroll Bars); and the right divider, denoted by RD (Window Dividers). Together these are the window's left and right decorations. At the top of the window are the tab line and the header line (Header Lines). The text area of the window includes the header line and the tab line, if they are present in the window. At the bottom of the window are the horizontal scroll bar (Scroll Bars); the mode line (Mode Line Format); and the bottom divider (Window Dividers). Together these form the window's top and bottom decorations. There are two special areas omitted in the schematic:

• When any of the fringes is missing, the display engine may use one character cell in its place for showing a continuation or truncation glyph provided a text line doesn't fit in a window.
• When both, the vertical scroll bar and the right divider are missing, the display engine usurps one pixel for drawing a vertical divider line between this window and the window on its right, provided such a window exists. On a text terminal, this divider always occupies an entire character cell.

In either case, the resulting artifact is considered part of the window's body although its screen space cannot be used for displaying buffer text. Note also, that line numbers (and their surrounding whitespace) as displayed by display-line-numbers-mode (Display Custom) do not count as decorations either; they are part of the window's body too. Internal windows neither show any text nor do they have decorations. Hence, the concept of "body" does not make sense for them. In fact, most functions operating on the body of a window will yield an error when applied to an internal window. By default, an Emacs frame exhibits one special live window that is used for displaying messages and accepting user input—the minibuffer window (Minibuffer Windows). Since the minibuffer window is used for displaying text, it has a body but it does not have a tab or header line or any margins. Finally, a tooltip window which is used for displaying a tooltip in a tooltip frame (Tooltips) has a body too but no decorations at all.

Each window belongs to exactly one frame (Frames). For all windows belonging to a specific frame, we sometimes also say that these windows are owned by that frame or simply that they are on that frame.

window-frame

This function returns the specified window's frame—the frame that window belongs to. If window is omitted or nil, it defaults to the selected window (Selecting Windows).

window-list

This function returns a list of all live windows owned by the specified frame. If frame is omitted or nil, it defaults to the selected frame (Input Focus). The optional argument minibuffer specifies whether to include the minibuffer window (Minibuffer Windows) in that list. If minibuffer is t, the minibuffer window is included. If 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, must 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 frame (Selecting Windows) is the first element.

Windows on 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 is either a live window or an internal window. If it is a live window, then the frame has just one window besides the minibuffer window, or the frame is a minibuffer-only frame, Frame Layout. A minibuffer window (Minibuffer Windows) that is not alone on its frame does not have a parent window, so it strictly speaking is not part of its frame's window tree. Nonetheless, it is a sibling window of the frame's root window, and thus can be reached from the root window via window-next-sibling, see below. Also, the function window-tree described at the end of this section lists the minibuffer window alongside the actual window tree.

frame-root-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 live window is split (Splitting Windows), 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. The set of windows that share the same parent are called siblings.

window-parent

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).

A parent window always has at least two child windows. If this number were to fall to one as a result of window deletion (Deleting Windows), Emacs automatically deletes the parent window too, and its sole remaining child window takes its place in the window tree. A 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. Their window argument always defaults to the selected window (Selecting Windows).

window-top-child

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.

window-left-child

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.

window-child

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.

window-combined-p

This function returns a non-nil value if and only if window is part of a vertical combination. 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.

window-next-sibling

This function returns the next sibling of the specified window. The return value is nil if window is the last child of its parent.

window-prev-sibling

This function returns the previous sibling of the specified 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 in the cyclic ordering of windows (Cyclic Window Ordering). The following functions can be useful to locate a window within its frame.

frame-first-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.

window-at-side-p

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 (Minibuffer Windows). Hence, with side equal to bottom it may return t also when the minibuffer window appears right below window.

window-in-direction

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 (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 minibuf is t, this function may return the minibuffer window even when it's not active. If the optional argument minibuf is nil, this means to return the minibuffer window if and only if it is currently active. If minibuf is neither nil nor t, this function never returns the minibuffer window. However, if wrap is non-nil, it always acts as if minibuf 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 retrieves the entire window tree of a frame:

window-tree

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 (Coordinates and Windows).

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 (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 (Current Buffer). As for non-selected frames, the window selected within the frame becomes the selected window if the frame is ever selected.

selected-window

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

The following function explicitly selects a window and its frame.

select-window

This function makes window the selected window and the window selected within its frame, and selects that frame. It also makes window's buffer (Buffers and Windows) current and sets that buffer's value of point to the value of window-point (Window 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 (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's display 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. 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 (Buffer List). Consequently, that hook provides one 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. Emacs also runs the hook window-selection-change-functions whenever the redisplay routine detects that another window has been selected since last redisplay. Window Hooks, for a detailed explanation. window-state-change-functions (described in the same section) is another abnormal hook run after a different window has been selected but is triggered by other window changes as well. The sequence of calls to select-window with a non-nil norecord argument determines an ordering of windows by their selection or use time, see below. The function get-lru-window, for example, can then be used to retrieve the least recently selected window (Cyclic Window Ordering).

frame-selected-window

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.

set-frame-selected-window

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 ordering of the most recently selected windows, nor the buffer list.

The following macros are useful to temporarily select a window without affecting the ordering of recently selected windows or the buffer list.

save-selected-window

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.

with-selected-window

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.

with-selected-frame

This macro executes forms with frame as the selected frame. The value returned is the value of the last form in forms. This macro saves and restores the selected frame, and changes the order of neither the recently selected windows nor the buffers in the buffer list.

window-use-time

This function 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 (Cyclic Window Ordering).

window-bump-use-time

This function marks window as being the most recently used one. This can be useful when writing certain pop-to-buffer scenarios (Switching Buffers). window must be a live window and defaults to the selected one.

Sometimes several windows collectively and cooperatively display a buffer, for example, under the management of Follow Mode (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 (Window Start and End) allow you to do this by supplying, as an argument, one of the windows as a stand-in for the whole group.

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).

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 (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 its body and its top and bottom decorations (Basic Windows).

window-total-height

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 (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 columns comprising its body and its left and right decorations (Basic Windows).

window-total-width

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 columns 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 (Coordinates and Windows). The optional argument round behaves as it does for window-total-height.

window-total-size

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.

window-pixel-height

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 the heights of window's top and bottom decorations. If window is an internal window, its pixel height is the pixel height of the screen areas spanned by its children.

window-pixel-width

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 widths of window's left and right decorations. If window is an internal window, its pixel width is the width of the screen areas spanned by its children.

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

window-full-height-p

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.

window-full-width-p

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 body, which does not include any of its top or bottom decorations (Basic Windows).

window-body-height

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 body and of the text area, which does not include any of its left or right decorations (Basic Windows). 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.)

window-body-width

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.

window-body-size

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.

The pixel heights of a window's mode, tab 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.

window-mode-line-height

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.

window-tab-line-height

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

window-header-line-height

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 (Window Dividers), fringes (Fringes), scroll bars (Scroll Bars), and display margins (Display Margins) are described in the corresponding sections. If your Lisp program needs to make layout decisions, you will find the following function useful:

window-max-chars-per-line

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 (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 (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 (Resizing Windows), or split them (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 (Preserving Window Sizes).

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 and any top or bottom decorations.

window-min-width

This option specifies the minimum total width, in columns, of any window. Its value has to accommodate at least two text columns and any left or right decorations.

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 (Preserving Window Sizes).

window-min-size

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 any top or bottom decorations. With horizontal non-nil it includes any left or right decorations of window. 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.

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 at least one other window. If there is just one window on a frame, its size cannot be changed except by resizing the frame (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.

window-resizable

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 (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 of a window as the sum of its top and bottom decorations plus the text of one line; and its minimum width as the sum of its left and right decorations plus text that takes two columns. If the optional argument pixelwise is non-nil, delta is interpreted as pixels.

window-resize

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. Recombining Windows. To resize by moving only the bottom or right edge of a window, use the function adjust-window-trailing-edge.

adjust-window-trailing-edge

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.

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 (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

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 any top or bottom decorations of window. 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 any left or right decorations of window. The optional argument preserve-size, if non-nil, will install a parameter to preserve the size of window during future resize operations (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).

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.

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

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.

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.

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

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

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 (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

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

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.

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 (Splitting Windows, Deleting Windows) or when resizing the window's frame (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.

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. 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:

window-preserve-size

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 (Resizing Windows) is non-nil, the size established by that function is preserved.

display-buffer

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

window-preserve-size installs a window parameter (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:

window-preserved-size

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.

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 (Side Windows) and atomic windows (Atomic Windows).

split-window

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 (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 that is 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 of their decorations like a mode line or a scroll bar. The function window-min-size (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. 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:

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    ||_________________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:

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    | ______  ____________________________ |
    ||      || __________________________ ||
    ||      |||                          |||
    ||      |||                          |||
    ||      |||                          |||
    ||      |||____________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

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

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.

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.

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 (Window Configurations).

Command delete-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 (Side Windows), an error is signaled. If window is part of an atomic window (Atomic Windows), this function tries to delete the root of that atomic window instead. 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. 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. Window Parameters.

When delete-window deletes the selected window of its frame, it has to make another window the new selected window of that frame. The following option allows configuring which window is chosen.

delete-window-choose-selected

This option allows specifying which window should become a frame's selected window after delete-window has deleted the previously selected one. Possible choices are

?

mru (the default) choose the most recently used window on that frame.

?

pos choose the window comprising the frame coordinates of point of the previously selected window on that frame.

?

nil choose the first window (the window returned by frame-first-window) on that frame.

A window with a non-nil no-other-window parameter is chosen only if all other windows on that frame have that parameter set to a non-nil value too.

Command delete-other-windows

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 (Side Windows). If window is part of an atomic window (Atomic Windows), this function tries to make the root of that atomic window fill its frame. 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. 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

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:

?

nil means operate on all frames.

?

t means operate on the selected frame.

?

visible means operate on all visible frames.

?

0 means operate on all visible or iconified frames.

?

A frame means operate on that frame.

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

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 (Windows and Frames). In some occasions, deleting a live window may even entail the deletion of two internal windows.

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    | ______  ____________________________ |
    ||      || __________________________ ||
    ||      ||| ___________  ___________ |||
    ||      ||||           ||           ||||
    ||      ||||____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.

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

Split W2 to make a new window W4 as follows.

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    ||_________________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.

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

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

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

This can be counterintuitive, in particular if W4 were used for displaying a buffer only temporarily (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.

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 (Buffer Display Action Functions). 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 (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 (Temporary Displays). Otherwise, window splitting behaves as for nil.

display-buffer

This means that when display-buffer (Choosing Window) 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:

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    || __________________________________ ||
    |||                                  |||
    |||________________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.

set-window-combination-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.

window-combination-limit

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.

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.

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    ||_________________W2_________________||
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    ||_________________W3_________________||
    |__________________W1__________________|

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

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

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

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    | ____________________________________ |
    ||                                    ||
    ||                                    ||
    ||_________________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.

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 (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.

next-window

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 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:

?

nil means to consider windows on window's frame. If the minibuffer window is considered (as specified by the minibuf argument), then frames that share the minibuffer window are considered too.

?

t means to consider windows on all existing frames.

?

visible means to consider windows on all visible frames.

?

0 means to consider windows on all visible or iconified frames.

?

A frame means to consider windows on that specific frame.

?

Anything else means to consider windows on window's frame, and no others.

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 (Finding All Frames).

previous-window

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

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 (Window Parameters), provided that ignore-window-parameters is nil. If the other-window parameter of the selected window is a function, and ignore-window-parameters is nil, that function will be called with the arguments count and all-frames instead of the normal operation of this function.

walk-windows

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.

one-window-p

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:

get-lru-window

This function returns a live window which is heuristically the least recently used one. The least recently used window is the least recently selected one—the window whose use time is less than the use time of all other live windows (Selecting Windows). 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 (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. The optional argument no-other, if non-nil, means to never return a window whose no-other-window parameter is non-nil.

get-mru-window

This function is like get-lru-window, but it returns the most recently used window instead. The most recently used window is the most recently selected one—the window whose use time exceeds the use time of all other live windows (Selecting Windows). The meaning of the arguments is the same as for get-lru-window. Since in practice the most recently used window is always the selected one, it usually makes sense to call this function with a non-nil not-selected argument only.

get-largest-window

This function returns the window with the largest area (height times width). If there are two candidate windows of the same size, it prefers the one that comes first in the cyclic ordering of windows, starting from the selected window. The meaning of the arguments is the same as for get-lru-window.

get-window-with-predicate

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.

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

window-buffer

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.

set-window-buffer

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 (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. 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 display-buffer (Choosing Window) or the higher-level functions described in Switching Buffers, instead of calling set-window-buffer directly. This runs window-scroll-functions, followed by window-configuration-change-hook. Window Hooks.

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.

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 (Time of Day).

get-buffer-window

This function returns the first window displaying buffer-or-name in the cyclic ordering of windows, starting from the selected window (Cyclic Window Ordering). 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:

?

t means consider windows on all existing frames.

?

visible means consider windows on all visible frames.

?

0 means consider windows on all visible or iconified frames.

?

A frame means consider windows on that frame only.

?

Any other value means consider windows on the selected frame.

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

get-buffer-window-list

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 (Cyclic Window Ordering). Note that the all-frames argument does not behave exactly like in get-buffer-window.

Command replace-buffer-in-windows

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 (Window History). With the exception of side windows (Side Windows), any dedicated window displaying buffer-or-name is deleted if possible (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.

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 (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. Current Buffer.

Command switch-to-buffer

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 (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 (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 (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 (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.

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.

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.

switch-to-buffer-obey-display-actions

If this variable is non-nil, switch-to-buffer respects display actions specified by display-buffer-overriding-action, display-buffer-alist and other display related variables.

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

Command switch-to-buffer-other-window

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

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. Choosing Window, for the documentation of display-buffer.

Command pop-to-buffer

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 (Input Focus). If buffer-or-name is nil, it defaults to the buffer returned by other-buffer (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 (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 (Choosing Window). 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.

This section describes lower-level functions Emacs uses to find or create a window for displaying a specified buffer. The common workhorse of these functions is display-buffer which eventually handles all incoming requests for buffer display (Choosing Window). display-buffer delegates the task of finding a suitable window to so-called action functions (Buffer Display Action Functions). First, display-buffer compiles a so-called action alist—a special association list that action functions can use to fine-tune their behavior. Then it passes that alist on to each action function it calls (Buffer Display Action Alists). The behavior of display-buffer is highly customizable. To understand how customizations are used in practice, you may wish to study examples illustrating the order of precedence which display-buffer uses to call action functions (Precedence of Action Functions). To avoid conflicts between Lisp programs calling display-buffer and user customizations of its behavior, it may make sense to follow a number of guidelines which are sketched in the final part of this section (The Zen of Buffer Display).

(display-buffer (get-buffer-create "*foo*"))

(customize-set-variable
 'display-buffer-base-action
 '((display-buffer-reuse-window display-buffer-pop-up-frame)
   (reusable-frames . 0)))

(let ((pop-up-frame-function 'ignore))
  (display-buffer (get-buffer-create "*foo*")))

(customize-set-variable
 'display-buffer-base-action
 '(display-buffer-pop-up-frame (reusable-frames . 0)))

(display-buffer
 (get-buffer-create "*foo*")
 '((display-buffer-below-selected display-buffer-at-bottom)))

(customize-set-variable
 'display-buffer-alist
 '(("\\*foo\\*"
    (display-buffer-reuse-window display-buffer-pop-up-frame))))

(customize-set-variable
 'display-buffer-alist
 '(("\\*foo\\*"
    (display-buffer-reuse-window display-buffer-pop-up-frame)
    (reusable-frames . visible))))

(display-buffer (get-buffer-create "*bar*"))

(let ((display-buffer-overriding-action
       '((display-buffer-same-window))))
  (display-buffer
   (get-buffer-create "*foo*")
   '((display-buffer-below-selected display-buffer-at-bottom))))

(display-buffer-same-window  ;; `display-buffer-overriding-action'
 display-buffer-reuse-window ;; `display-buffer-alist'
 display-buffer-pop-up-frame
 display-buffer-below-selected ;; ACTION argument
 display-buffer-at-bottom
 display-buffer-reuse-window ;; `display-buffer-base-action'
 display-buffer-pop-up-frame
 display-buffer--maybe-same-window ;; `display-buffer-fallback-action'
 display-buffer-reuse-window
 display-buffer--maybe-pop-up-frame-or-window
 display-buffer-in-previous-window
 display-buffer-use-some-window
 display-buffer-pop-up-frame)

((reusable-frames . visible)
 (reusable-frames . 0))

(customize-set-variable
 'display-buffer-alist
 '(("\\*foo\\*"
    (display-buffer-reuse-window display-buffer-pop-up-frame)
    (inhibit-same-window . t)
    (reusable-frames . visible))))

(let ((display-buffer-overriding-action
       '(display-buffer-same-window (inhibit-same-window . nil))))
  (display-buffer (get-buffer-create "*foo*")))

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

window-prev-buffers

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 (Window Start and End) when that buffer was last shown, and window-pos is the point position (Window 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.

set-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 window 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.

window-next-buffers

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).

set-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

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 (Buffer List). The option switch-to-prev-buffer-skip described below can be used to inhibit switching to certain buffers, for example, to those already shown in another window. Also, if window's frame has a buffer-predicate parameter (Buffer Parameters), that predicate may inhibit switching to certain buffers.

Command switch-to-next-buffer

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 (Buffer List). The option switch-to-prev-buffer-skip and the buffer-predicate (Buffer Parameters) of window's frame affect this command as they do for switch-to-prev-buffer.

By default switch-to-prev-buffer and switch-to-next-buffer can switch to a buffer that is already shown in another window. The following option can be used to override this behavior.

switch-to-prev-buffer-skip

If this variable is nil, switch-to-prev-buffer may switch to any buffer, including those already shown in other windows. If this variable is non-nil, switch-to-prev-buffer will refrain from switching to certain buffers. The following values can be used:

?

this means do not switch to a buffer shown on the frame that hosts the window switch-to-prev-buffer is acting upon.

?

visible means do not switch to a buffer shown on any visible frame.

?

0 (the number zero) means do not switch to a buffer shown on any visible or iconified frame.

?

t means do not switch to a buffer shown on any live frame.

?

A function that takes three arguments—the window argument of switch-to-prev-buffer, a buffer switch-to-prev-buffer intends to switch to and the bury-or-kill argument of switch-to-prev-buffer. If that function returns non-nil, switch-to-prev-buffer will refrain from switching to the buffer specified by the second argument.

The command switch-to-next-buffer obeys this option in a similar way. If this option specifies a function, switch-to-next-buffer will call that function with the third argument always nil. Note that since switch-to-prev-buffer is called by bury-buffer, replace-buffer-in-windows and quit-restore-window as well, customizing this option may also affect the behavior of Emacs when a window is quit or a buffer gets buried or killed. Note also that under certain circumstances switch-to-prev-buffer and switch-to-next-buffer may ignore this option, for example, when there is only one buffer left these functions can switch to.

Functions for displaying a buffer can be told to not use specific windows by marking these windows as dedicated to their buffers. display-buffer (Choosing Window) never uses a dedicated window for displaying another buffer in it. get-lru-window and get-largest-window (Cyclic Window Ordering) do not consider dedicated windows as candidates when their dedicated argument is non-nil. The behavior of set-window-buffer (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 four 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, (3) the window is the only window on the only frame on the same terminal, and (4) the dedication's value is side (Displaying Buffers in Side Windows). In particular, delete-windows-on (Deleting Windows) handles case (2) by deleting the associated frame and cases (3) and (4) by showing another buffer in that frame's only window. The function replace-buffer-in-windows (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 (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 (Quitting Windows) to deal with the selected frame. The other two cases are handled as with replace-buffer-in-windows.

window-dedicated-p

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.

set-window-dedicated-p

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.

You can also tell display-buffer to mark a window it creates as dedicated to its buffer by providing a suitable dedicated action alist entry (Buffer Display Action Alists).

After a command uses display-buffer to put a buffer on the screen, the user may decide to hide it and return to the previous configuration of the Emacs display. We call that quitting the window. The way to do this is to call quit-window while the window used by display-buffer is the selected window. The right way to restore the previous configuration of the display depends on what was done to the window where the buffer now appears. It might be right to delete that window, or delete its frame, or just display another buffer in that window. One complication is that the user may have changed the window configuration since the act of displaying that buffer, and it would be undesirable to undo the user's explicitly requested changes. To enable quit-window to do the right thing, display-buffer saves information about what it did in the window's quit-restore parameter (Window Parameters).

Command quit-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. The function quit-window first runs quit-window-hook. Then it calls the function quit-restore-window, described next, which does the hard work.

You can get more control by calling quit-restore-window instead.

quit-restore-window

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 takes account of the window's quit-restore parameter. The optional argument bury-or-kill specifies how to deal with window's buffer. The following values are meaningful:

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 (Window History), so it's less likely that future invocations of switch-to-prev-buffer will switch to it. Also, it moves the buffer to the end of the frame's buffer list (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 is the most reliable way to prevent switch-to-prev-buffer from switching to this buffer again, short of killing the buffer.

kill

This means to kill window's buffer.

The argument bury-or-kill also specifies what to do with window's frame when window should be deleted, if it is the only window on its frame, and there are other frames on that frame's terminal. If bury-or-kill equals kill, it means to delete the frame. Otherwise, the fate of the frame is determined by calling frame-auto-hide-function (see below) with that frame as sole argument. This function always sets window's quit-restore parameter to nil unless it deletes the window. The window window's quit-restore parameter (Window Parameters) should be nil or a list of four elements:

(METHOD OBUFFER OWINDOW THIS-BUFFER)

The first element, method, is one of the four symbols window, frame, same and other. frame and window control how to delete window, while same and other control displaying some other buffer in it. Specifically, window means that the window has been specially created by display-buffer; frame means that a separate frame has been created; same, that the window has only ever displayed this buffer; other, that the window showed another buffer before. The second element, obuffer, is either one of the symbols window or frame, or a list of the form

(PREV-BUFFER PREV-WINDOW-START PREV-WINDOW-POINT HEIGHT)

which says which buffer was shown in window before, that buffer's window start (Window Start and End) and window point (Window Point) positions at that time, and window's height at that time. If prev-buffer is still live when quitting window, quitting the window may reuse window to display prev-buffer. The third element, owindow, is the window that was selected just before the displaying was done. If quitting deletes window, it tries to select owindow. The fourth element, this-buffer, is the buffer whose displaying set the quit-restore parameter. Quitting window may delete that window only if it still shows that buffer. Quitting window tries to delete it if and only if (1) method is either window or frame, (2) the window has no history of previously-displayed buffers and (3) this-buffer equals the buffer currently displayed in window. If window is part of an atomic window (Atomic Windows), quitting will try to delete the root of that atomic window instead. In either case, it tries to avoid signaling an error when window cannot be deleted. If obuffer is a list, and prev-buffer is still live, quitting displays prev-buffer in window according to the rest of the elements of obuffer. This includes resizing the window to height if it was temporarily resized to display this-buffer. Otherwise, if window was previously used for displaying other buffers (Window History), the most recent buffer in that history will be displayed. The following option specifies a function to do the right thing with a frame containing one window when quitting that window.

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 (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 (Visibility of Frames). Alternatively, you may specify either delete-frame (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 (Frame Interaction Parameters).

Side windows are special windows positioned at any of the four sides of a frame's root window (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 (Buffer Display Action Functions) 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).

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

(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)))

(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))))

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

• The function split-window (Splitting Windows), when applied to a constituent of an atomic window, will try to create the new window outside of the atomic window.
• The function delete-window (Deleting Windows), when applied to a constituent of an atomic window, will try to delete the entire atomic window instead.
• The function delete-other-windows (Deleting Windows), when applied to a constituent of an atomic window, will try to make the atomic window fill its frame or main window (Side Windows).

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 (Window Parameters) and an internal window (Basic 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:

window-atom-root

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:

window-make-atom

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 (Buffer Display Action Functions) can be used:

display-buffer-in-atom-window

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. Atomic windows automatically cease to exist when one of their constituents gets deleted. To dissolve an atomic window manually, reset the window-atom parameter of its constituents—the root of the atomic window and all its descendants. 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.

Each window has its own value of point (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.

• The window point is established when a window is first created; it is initialized from the buffer's point, or from the window point of another window opened on the buffer if such a window exists.
• Selecting a window sets the value of point in its buffer from the window's value of point. Conversely, deselecting a window sets the window's value of point from that of the buffer. Thus, when you switch between windows that display a given buffer, the point value for the selected window is in effect in the buffer, while the point values for the other windows are stored in those windows.
• As long as the selected window displays the current buffer, the window's point and the buffer's point always move together; they remain equal.

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.

window-point

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.

set-window-point

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.

window-point-insertion-type

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

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.

window-start

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.

window-group-start

This function is like window-start, except that when window is a part of a group of windows (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.

window-end

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. Note that the position it returns might be only partially visible.

window-group-end

This function is like window-end, except that when window is a part of a group of windows (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.

set-window-start

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 select the display-start position according to their internal logic (and scroll the window if 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 attempt to 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 the attempt to make point visible (i.e., in a fully-visible screen line) fails, the display routines will disregard the requested window-start position and compute a new one anyway. Thus, for reliable results Lisp programs that call this function should always move point to be inside the window whose display starts at position. 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.

set-window-group-start

This function is like set-window-start, except that when window is a part of a group of windows (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.

pos-visible-in-window-p

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. 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
(or (pos-visible-in-window-p
     (point) (selected-window))
    (recenter 0))

pos-visible-in-window-group-p

This function is like pos-visible-in-window-p, except that when window is a part of a group of windows (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.

window-line-height

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.

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 (Window 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. 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 (Vertical Scrolling).

Command scroll-up

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 body. If the selected window cannot be scrolled any further, this function signals an error. Otherwise, it returns nil.

Command scroll-down

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

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

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

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. Definition of minibuffer-scroll-window.

Command scroll-other-window-down

This function scrolls the text in another window downward count lines. Negative values of count, or nil, are handled as in scroll-down. In other respects, it behaves the same way as scroll-other-window does.

other-window-scroll-buffer

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

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.

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.

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.

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.

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-down-aggressively, a larger value scrolls more aggressively.

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.

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.

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.

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

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 and redisplay is non-nil, this function may redraw the frame, according to the value of recenter-redisplay. Thus, omitting the second argument can be used to countermand the effect of recenter-redisplay being non-nil. Interactive calls pass non-‘nil’ for 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.

recenter-window-group

This function is like recenter, except that when the selected window is part of a group of windows (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.

recenter-redisplay

If this variable is non-nil, calling recenter with a nil count argument and non-nil redisplay 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

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.

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.

Vertical fractional scrolling means shifting text in a window up or down by a specified multiple or fraction of a line. Emacs uses it, for example, on images and screen lines which are taller than the window. 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 when displaying them. 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 will be 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.

window-vscroll

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

set-window-vscroll

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.

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.

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

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 (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

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.

window-hscroll

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

set-window-hscroll

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)))))

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 (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 (Frame Font).

window-edges

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 of its decorations. 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. 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 (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.

window-body-edges

This function returns the edges of window's body (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:

window-at

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

coordinates-in-window-p

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 (Frame Font) relative to the native position of window's frame (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.

tab-line

The coordinates are in the tab 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.

window-pixel-edges

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.

window-body-pixel-edges

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:

window-absolute-pixel-edges

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.

window-absolute-body-pixel-edges

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:

window-absolute-pixel-position

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.

window-largest-empty-rectangle

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 (Size of Displayed Text). Hence, this function may also return nil when the current glyph matrix of window is not up-to-date.

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 (Input Focus).

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 (Child Frames) which usually are not tracked by the window manager. This requires to set the value of focus-follows-mouse (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.

A window configuration records the entire layout of one frame—all windows, their sizes, their decorations, which buffers they contain, how those buffers are scrolled, and their value of point, 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. Frame Configurations.

current-window-configuration

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. Window Parameters.

set-window-configuration

This function restores the configuration of windows and buffers as specified by configuration, for the frame that configuration was created for, regardless of whether that frame is selected or not. The argument configuration must be a value that was previously returned by current-window-configuration for that frame. Normally the function also selects the frame which is recorded in the configuration, but if dont-set-frame is non-nil, it leaves selected the frame which was already selected at the start of the function. Normally the function restores the saved minibuffer (if any), but if dont-set-miniwindow is non-nil, the minibuffer current at the start of the function (if any) remains in the mini-window. If the frame from which configuration was saved is dead, all this function does is to restore the value of the variable minibuffer-scroll-window and to adjust the value returned by minibuffer-selected-window. In this case, the function returns nil. Otherwise, it returns t. If the buffer of a window of configuration has been killed since configuration was made, that window is, as a rule, removed from the restored configuration. However, if that window is the last window remaining in the restored configuration, another live buffer is shown in it. 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)))

save-window-excursion

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 (Choosing Window), and save-window-excursion only saves and restores the window configuration on the current frame.

window-configuration-p

This function returns t if object is a window configuration.

compare-window-configurations

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.

window-configuration-frame

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).

window-state-get

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. 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.

window-state-put

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 (Windows and Frames). If window is not a live window, it is replaced by a new live window created on the same frame before putting state into it. If window is nil, it puts the window state into a new window. 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

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.

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

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.

window-parameters

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).

set-window-parameter

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 (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:

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. 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:

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 (Deleting Windows).

delete-other-windows

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

no-delete-other-windows

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

split-window

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

other-window

This parameter affects the execution of other-window (Cyclic Window Ordering).

no-other-window

This parameter marks the window as not selectable by other-window (Cyclic Window Ordering).

clone-of

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

quit-restore

This parameter is installed by the buffer display functions (Choosing Window) and consulted by quit-restore-window (Quitting Windows). It is a list of four elements, see the description of quit-restore-window in Quitting Windows for details.

window-side, window-slot

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

window-atom

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

mode-line-format

This parameter replaces the value of the buffer-local variable mode-line-format (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 (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.

tab-line-format

This parameter replaces the value of the buffer-local variable tab-line-format (Mode Line Basics) of this window's buffer whenever this window is displayed. The symbol none means to suppress display of a tab line for this window. Display and contents of the tab 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 (Display Margins. 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 (Window Hooks) 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.

This section describes how Lisp programs can take action after a window has been scrolled or other window modifications occurred. We first consider the case where a window shows a different part of its buffer.

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 a window and making a new window also call 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 argument window is already set to its new value, and the buffer to be displayed in the window is set as the current buffer. These functions must take care when using window-end (Window Start and End); 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.

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. Other Font Lock Variables. The remainder of this section covers six hooks that are called during redisplay provided a significant, non-scrolling change of a window has been detected. For simplicity, these hooks and the functions they call will be collectively referred to as window change functions. As any hook, these hooks can be set either globally of buffer-locally via the local argument of add-hook (Setting Hooks) when the hook is installed. The first of these hooks is run after a window buffer change is detected, which means that a window was created, deleted or assigned another buffer.

window-buffer-change-functions

This variable specifies functions called during redisplay when window buffers have changed. The value should be a list of functions that take one argument. Functions specified buffer-locally are called for any window showing the corresponding buffer if that window has been created or assigned that buffer since the last time window change functions were run. In this case the window is passed as argument. Functions specified by the default value are called for a frame if at least one window on that frame has been added, deleted or assigned another buffer since the last time window change functions were run. In this case the frame is passed as argument.

The second of these hooks is run when a window size change has been detected which means that a window was created, assigned another buffer, or changed its total size or that of its text area.

window-size-change-functions

This variable specifies functions called during redisplay when a window size change occurred. The value should be a list of functions that take one argument. Functions specified buffer-locally are called for any window showing the corresponding buffer if that window has been added or assigned another buffer or changed its total or body size since the last time window change functions were run. In this case the window is passed as argument. Functions specified by the default value are called for a frame if at least one window on that frame has been added or assigned another buffer or changed its total or body size since the last time window change functions were run. In this case the frame is passed as argument.

The third of these hooks is run when a window selection change has selected another window since the last redisplay.

window-selection-change-functions

This variable specifies functions called during redisplay when the selected window or a frame's selected window has changed. The value should be a list of functions that take one argument. Functions specified buffer-locally are called for any window showing the corresponding buffer if that window has been selected or deselected (among all windows or among all windows on its frame) since the last time window change functions were run. In this case the window is passed as argument. Functions specified by the default value are called for a frame if that frame has been selected or deselected or the frame's selected window has changed since the last time window change functions were run. In this case the frame is passed as argument.

The fourth of these hooks is run when a window state change has been detected, which means that at least one of the three preceding window changes has occurred.

window-state-change-functions

This variable specifies functions called during redisplay when a window buffer or size change occurred or the selected window or a frame's selected window has changed. The value should be a list of functions that take one argument. Functions specified buffer-locally are called for any window showing the corresponding buffer if that window has been added or assigned another buffer, changed its total or body size or has been selected or deselected (among all windows or among all windows on its frame) since the last time window change functions were run. In this case the window is passed as argument. Functions specified by the default value are called for a frame if at least one window on that frame has been added, deleted or assigned another buffer, changed its total or body size or that frame has been selected or deselected or the frame's selected window has changed since the last time window change functions were run. In this case the frame is passed as argument. Functions specified by the default value are also run for a frame when that frame's window state change flag (see below) has been set since last redisplay.

The fifth of these hooks is run when a window configuration change has been detected which means that either the buffer or the size of a window changed. It differs from the four preceding hooks in the way it is run.

window-configuration-change-hook

This variable specifies functions called during redisplay when either the buffer or the size of a window has changed. The value should be a list of functions that take no argument. Functions specified buffer-locally are called for any window showing the corresponding buffer if at least one window on that frame has been added, deleted or assigned another buffer or changed its total or body size since the last time window change functions were run. Each call is performed with the window showing the buffer temporarily selected and its buffer current. Functions specified by the default value are called for each frame if at least one window on that frame has been added, deleted or assigned another buffer or changed its total or body size since the last time window change functions were run. Each call is performed with the frame temporarily selected and the selected window's buffer current.

Finally, Emacs runs a normal hook that generalizes the behavior of window-state-change-functions.

window-state-change-hook

The default value of this variable specifies functions called during redisplay when a window state change has been detected or the window state change flag has been set on at least one frame. The value should be a list of functions that take no argument. Applications should put a function on this hook only if they want to react to changes that happened on (or have been signaled for) two or more frames since last redisplay. In every other case, putting the function on window-state-change-functions should be preferred.

Window change functions are called during redisplay for each frame as follows: First, any buffer-local window buffer change function, window size change function, selected window change and window state change functions are called in this order. Next, the default values for these functions are called in the same order. Then any buffer-local window configuration change functions are called followed by functions specified by the default value of those functions. Finally, functions on window-state-change-hook are run. Window change functions are run for a specific frame only if a corresponding change was registered for that frame earlier. Such changes include the creation or deletion of a window or the assignment of another buffer or size to a window. Note that even when such a change has been registered, this does not mean that any of the hooks described above is run. If, for example, a change was registered within the scope of a window excursion (Window Configurations), this will trigger a call of window change functions only if that excursion still persists at the time change functions are run. If it is exited earlier, hooks will be run only if registered by a change outside the scope of that excursion. The window state change flag of a frame, if set, will cause the default values of window-state-change-functions (for that frame) and window-state-change-hook to be run during next redisplay regardless of whether a window state change actually occurred for that frame or not. After running any functions on these hooks, the flag is reset for each frame. Applications can set that flag and inspect its value using the following functions.

set-frame-window-state-change

This function sets frame's window state change flag if arg is non-nil and resets it otherwise. frame must be a live frame and defaults to the selected one.

frame-window-state-change

This functions returns t if frame's window state change flag is set and nil otherwise. frame must be a live frame and defaults to the selected one.

While window change functions are run, the functions described next can be called to get more insight into what has changed for a specific window or frame since the last redisplay. All these functions take a live window as single, optional argument, defaulting to the selected window.

window-old-buffer

This function returns the buffer shown in window at the last time window change functions were run for window's frame. If it returns nil, window has been created after that. If it returns t, window was not shown at that time but has been restored from a previously saved window configuration afterwards. Otherwise, the return value is the buffer shown by window at that time.

window-old-pixel-width

This function returns the total pixel width of window the last time window change functions found window live on its frame. It is zero if window was created after that.

window-old-pixel-height

This function returns the total pixel height of window the last time window change functions found window live on its frame. It is zero if window was created after that.

window-old-body-pixel-width

This function returns the pixel width of window's text area the last time window change functions found window live on its frame. It is zero if window was created after that.

window-old-body-pixel-height

This function returns the pixel height of window's text area the last time window change functions found window live on its frame. It is zero if window was created after that.

In order to find out which window or frame was selected the last time window change functions were run, the following functions can be used:

frame-old-selected-window

This function returns the selected window of frame at the last time window change functions were run. If omitted or nil frame defaults to the selected frame.

old-selected-window

This function returns the selected window at the last time window change functions were run.

old-selected-frame

This function returns the selected frame at the last time window change functions were run.

Note that window change functions provide no information about which windows have been deleted since the last time they were run. If necessary, applications should remember any window showing a specific buffer in a local variable of that buffer and update it in a function run by the default values of any of the hooks that are run when a window buffer change was detected. The following caveats should be considered when adding a function to window change functions:

• Some operations will not trigger a call of window change functions. These include showing another buffer in a minibuffer window or any change of a tooltip window.
• Window change functions should not create or delete windows or change the buffer, size or selection status of any window because there is no guarantee that the information about such a change will be propagated to other window change functions. If at all, any such change should be executed only by the last function listed by the default value of window-state-change-hook.
• Macros like save-window-excursion, with-selected-window or with-current-buffer can be used when running window change functions.
• Running window change functions does not save and restore match data. Unless running window-configuration-change-hook it does not save or restore the selected window or frame or the current buffer either.
• Any redisplay triggering the run of window change functions may be aborted. If the abort occurs before window change functions have run to their completion, they will be run again with the previous values, that is, as if redisplay had not been performed. If aborted later, they will be run with the new values, that is, as if redisplay had been actually performed.