gdk:window-update-area (window)

window -- a gdk:window object

The cairo:region-t update area for window.

Transfers ownership of the update area from window to the caller of the function. That is, after calling this function, window will no longer have an invalid/dirty region; the update area is removed from window and handed to you. If a window has no update area, the gdk:window-update-area function returns nil. You are responsible for calling the cairo:region-destroy function on the returned region if it is non-nil.