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27.3 Window Sizes

The following schematic shows the structure of a live window:

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

At the center of the window is the text area, or body, where the buffer text is displayed. The text area can be surrounded by a series of optional areas. On the left and right, from innermost to outermost, these are the left and right fringes, denoted by LF and RF (see Fringes); the left and right margins, denoted by LM and RM in the schematic (see Display Margins); the left or right vertical scroll bar, only one of which is present at any time, denoted by LS and RS (see Scroll Bars); and the right divider, denoted by RD (see Window Dividers). At the top of the window is the header line (see Header Lines). At the bottom of the window are the horizontal scroll bar (see Scroll Bars); the mode line (see Mode Line Format); and the bottom divider (see Window Dividers).

Emacs provides miscellaneous functions for finding the height and width of a window. The return value of many of these functions can be specified either in units of pixels or in units of lines and columns. On a graphical display, the latter actually correspond to the height and width of a default character specified by the frame's default font as returned by frame-char-height and frame-char-width (see Frame Font). Thus, if a window is displaying text with a different font or size, the reported line height and column width for that window may differ from the actual number of text lines or columns displayed within it.

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

— Function: window-total-height &optional window round

This function returns the total height, in lines, of the window window. If window is omitted or nil, it defaults to the selected window. If window is an internal window, the return value is the total height occupied by its descendant windows.

If a window's pixel height is not an integral multiple of its frame's default character height, the number of lines occupied by the window is rounded internally. This is done in a way such that, if the window is a parent window, the sum of the total heights of all its child windows internally equals the total height of their parent. This means that although two windows have the same pixel height, their internal total heights may differ by one line. This means also, that if window is vertically combined and has a next sibling, the topmost row of that sibling can be calculated as the sum of this window's topmost row and total height (see Coordinates and Windows)

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

The total width of a window is the number of lines comprising the window's body, its margins, fringes, scroll bars and a right divider (if any).

— Function: window-total-width &optional window round

This function returns the total width, in columns, of the window window. If window is omitted or nil, it defaults to the selected window. If window is internal, the return value is the total width occupied by its descendant windows.

If a window's pixel width is not an integral multiple of its frame's character width, the number of lines occupied by the window is rounded internally. This is done in a way such that, if the window is a parent window, the sum of the total widths of all its children internally equals the total width of their parent. This means that although two windows have the same pixel width, their internal total widths may differ by one column. This means also, that if this window is horizontally combined and has a next sibling, the leftmost column of that sibling can be calculated as the sum of this window's leftmost column and total width (see Coordinates and Windows). The optional argument round behaves as it does for window-total-height.

— Function: window-total-size &optional window horizontal round

This function returns either the total height in lines or the total width in columns of the window window. If horizontal is omitted or nil, this is equivalent to calling window-total-height for window; otherwise it is equivalent to calling window-total-width for window. The optional argument round behaves as it does for window-total-height.

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

— Function: window-pixel-height &optional window

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

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

— Function: window-pixel-width &optional window

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

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

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

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

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

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

This function returns non-nil if window has no other window to the left or right in its frame, i.e., its total width equals that of the root window on that frame. If window is omitted or nil, it defaults to the selected window.

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

— Function: window-body-height &optional window pixelwise

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

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

If pixelwise is nil, the return value is rounded down to the nearest integer, if necessary. This means that if a line at the bottom of the text area is only partially visible, that line is not counted. It also means that the height of a window's body can never exceed its total height as returned by window-total-height.

The body width of a window is the width of its text area, which does not include the scroll bar, fringes, margins or a right divider. Note that when one or both fringes are removed (by setting their width to zero), the display engine reserves two character cells, one on each side of the window, for displaying the continuation and truncation glyphs, which leaves 2 columns less for text display. (The function window-max-chars-per-line, described below, takes this peculiarity into account.)

— Function: window-body-width &optional window pixelwise

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

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

If pixelwise is nil, the return value is rounded down to the nearest integer, if necessary. This means that if a column on the right of the text area is only partially visible, that column is not counted. It also means that the width of a window's body can never exceed its total width as returned by window-total-width.

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

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

For compatibility with previous versions of Emacs, window-height is an alias for window-total-height, and window-width is an alias for window-body-width. These aliases are considered obsolete and will be removed in the future.

The pixel heights of a window's mode and header line can be retrieved with the functions given below. Their return value is usually accurate unless the window has not been displayed before: In that case, the return value is based on an estimate of the font used for the window's frame.

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

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

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

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

Functions for retrieving the height and/or width of window dividers (see Window Dividers), fringes (see Fringes), scroll bars (see Scroll Bars), and display margins (see Display Margins) are described in the corresponding sections.

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

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

This function returns the number of characters displayed in the specified face face in the specified window window (which must be a live window). If face was remapped (see 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 (see Frame Font). It also accounts for space used by the continuation glyph, if window lacks one or both of its fringes.

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

— User Option: window-min-height

This option specifies the minimum total height, in lines, of any window. Its value has to accommodate at least one text line as well as a mode and header line, a horizontal scroll bar and a bottom divider, if present.

— User Option: window-min-width

This option specifies the minimum total width, in columns, of any window. Its value has to accommodate two text columns as well as margins, fringes, a scroll bar and a right divider, if present.

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

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

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

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

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

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