39.15 Window Dividers

Window dividers are bars drawn between a frame’s windows. A right divider is drawn between a window and any adjacent windows on the right. Its width (thickness) is specified by the frame parameter right-divider-width. A bottom divider is drawn between a window and adjacent windows on the bottom or the echo area. Its width is specified by the frame parameter bottom-divider-width. In either case, specifying a width of zero means to not draw such dividers. See Layout Parameters.

Technically, a right divider belongs to the window on its left, which means that its width contributes to the total width of that window. A bottom divider belongs to the window above it, which means that its width contributes to the total height of that window. See Window Sizes. When a window has both, a right and a bottom divider, the bottom divider prevails. This means that a bottom divider is drawn over the full total width of its window while the right divider ends above the bottom divider.

Dividers can be dragged with the mouse and are therefore useful for adjusting the sizes of adjacent windows with the mouse. They also serve to visually set apart adjacent windows when no scroll bars or mode lines are present. The following three faces allow the customization of the appearance of dividers:

window-divider

When a divider is less than three pixels wide, it is drawn solidly with the foreground of this face. For larger dividers this face is used for the inner part only, excluding the first and last pixel.

window-divider-first-pixel

This is the face used for drawing the first pixel of a divider that is at least three pixels wide. To obtain a solid appearance, set this to the same value used for the window-divider face.

window-divider-last-pixel

This is the face used for drawing the last pixel of a divider that is at least three pixels wide. To obtain a solid appearance, set this to the same value used for the window-divider face.

You can get the sizes of the dividers of a specific window with the following two functions.

function window-right-divider-width \&optional window

Return the width (thickness) in pixels of window’s right divider. window must be a live window and defaults to the selected one. The return value is always zero for a rightmost window.

function window-bottom-divider-width \&optional window

Return the width (thickness) in pixels of window’s bottom divider. window must be a live window and defaults to the selected one. The return value is zero for the minibuffer window or a bottommost window on a minibuffer-less frame.