Transfers ownership of the update area from this to the caller of the function.
That is, after calling this function, this will no longer have an invalid/dirty region; the update
area is removed from this and handed to you. If a window has no update area,
get_update_area returns null. You are responsible for calling cairo_region_destroy
on the returned region if it’s non-null.
| this |
a Window |
|
the update area for this |