check_window_event(+Window, +EventMask, -Type, ?XEvent)
window_event/4, but fails if there is no matching
event in the queue, and does not block waiting for one. The output
buffer is flushed only on failure.
The user can pass an existing XEvent X11 structure, which is
then destructively filled with the received event's contents, or an
unbound variable. In the latter case,
unify XEvent with a private, local structure, which the user can
not hang on to, but is guaranteed not to change its value until the
next call to an event getting routine.
EventMask is an integer bitmask, that specifies the selected
events. The predicate
event_list_mask/2 is useful to
translate between X11 event mask names and bitmasks.