check_mask_event(+EventMask, -Type, ?XEvent) check_mask_event(+Displayable, +EventMask, -Type, ?XEvent)
mask_event/[3,4], but fail if there is no matching event
queue, and do 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,
check_mask_event/[3,4] will 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.