void propagate_expose(GtkWidget child
When a container receives an expose event, it must send synthetic
expose events to all children that don't have their own
GdkWindows. This function provides a convenient
way of doing this. A container, when it receives an expose event, calls
propagate_expose once for each child, passing in the
event the container received.
propagate_expose() takes care of deciding whether an expose event needs
to be sent to the child, intersecting the event's area with the child
area, and sending the event.
In most cases, a container can simply either simply inherit the
expose implementation from GtkContainer, or,
do some drawing and then chain to the expose implementation from