public void set_clip (Allocation clip)
Sets the widget’s clip.
This must not be used directly, but from within a widget’s size_allocate method. It must be called after set_allocation (or after chaining up to the parent class), because that function resets the clip.
The clip set should be the area that this draws on. If this is a Container, the area must contain all children's clips.
If this function is not called by this during a size_allocate handler, the clip will be set to this's allocation.
a pointer to a Allocation to copy from