set-window-new-pixel

set-window-new-pixel is a built-in function in `C source code'.

(set-window-new-pixel WINDOW SIZE &optional ADD)

Set new pixel size of WINDOW to SIZE.
WINDOW must be a valid window and defaults to the selected one.
Return SIZE.

Optional argument ADD non-nil means add SIZE to the new pixel size of
WINDOW and return the sum.

The new pixel size of WINDOW, if valid, will be shortly installed as
WINDOW's pixel height (see `window-pixel-height') or pixel width (see
`window-pixel-width').

Note: This function does not operate on any child windows of WINDOW.