The create_surface signal is emitted when an offscreen window needs its surface (re)created, which happens either when the window is first drawn to, or when the window is being resized.
The first signal handler that returns a non-null surface will stop any further signal emission, and its surface will be used.
Note that it is not possible to access the window's previous surface from within any callback of this signal. Calling offscreen_window_get_surface will lead to a crash.
the width of the offscreen surface to create
the height of the offscreen surface to create
the newly created XlibSurface for the offscreen window