+ /* an eWidgetDesktopCompBuffer is a composition buffer. in
+ immediate composition mode, we only have one composition
+ buffer - the screen.
+ in buffered mode, we have one buffer for each widget, plus
+ the screen.
+
+ even in buffered mode, we have a background region, because
+ a window can be arbitrary shaped. the screen size acts as a bounding
+ box in these cases. */
+
+struct eWidgetDesktopCompBuffer