true if the event was sent explicitly.
the new visibility state (gdk.types.VisibilityState.FullyObscured, gdk.types.VisibilityState.Partial or gdk.types.VisibilityState.Unobscured).
the type of the event (gdk.types.EventType.VisibilityNotify).
the window which received the event.
Deprecated: Modern composited windowing systems with pervasive transparency make it impossible to track the visibility of a window reliably, so this event can not be guaranteed to provide useful information.
Generated when the window visibility status has changed.