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28.24 Coordinates and Windows

This section describes functions that report positions of and within a window. Most of these functions report positions relative to an origin at the native position of the window’s frame (see 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 (see Frame Font).

function window-edges \&optional window body absolute pixelwise​

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

The return value has the form (left top right bottom). These list elements are, respectively, the X coordinate of the leftmost column occupied by the window, the Y coordinate of the topmost row, the X coordinate one column to the right of the rightmost column, and the Y coordinate one row down from the bottommost row.

Note that these are the actual outer edges of the window, including any header line, mode line, scroll bar, fringes, window divider and display margins. On a text terminal, if the window has a neighbor on its right, its right edge includes the separator line between the window and its neighbor.

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

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

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

function window-body-edges \&optional window​

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

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

function window-at x y \&optional frame​

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

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

function coordinates-in-window-p coordinates window​

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

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

function window-pixel-edges \&optional window​

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

function window-body-pixel-edges \&optional window​

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

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

function window-absolute-pixel-edges \&optional window​

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

function window-absolute-body-pixel-edges \&optional window​

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

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

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

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

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

function window-absolute-pixel-position \&optional position window​

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

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

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

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

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

function window-largest-empty-rectangle \&optional window count min-width min-height positions left​

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

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

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

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

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

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

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