Compositing widgets in GTK2?

[Brett Granger <bdgranger alum mit edu>]

Suppose I want to build a UI by layering several widgets with 
translucent png images in them.  Is this possible?

For example, my main window has a background pixmap, and then I want to 
place a button over that which has a translucent background pixmap as 
well, which I would like to see composited with the window's background 
pixmap.  The pixmap engine seems to be able to do this, but is it required?

Another example: same window with background, but now I want a label 
inside an eventbox which has a translucent background pixmap.  I want 
the label anti-aliased on top of the composited pixmaps from the 
eventbox and the window.  Possible?

I tried using the pixmap engine, and buttons do indeed seem to be able 
to be translucent.  However, eventboxes don't seem to be able to (I 
always get the png composited with the default gray background).  The 
only difference between the two as far as I can tell is that buttons use 
the BOX function whereas eventboxes use the FLAT_BOX function.  However, 
I can't see in the pixbuf engine source code why the two should behave 
differently.

Do I have to use the pixmap/pixbuf engine to achieve this kind of 
functionality, or is there some other way to have "layered" widgets 
composite on top of each other?

Any suggestions or thoughts would be greatly appreciated.
--Brett Granger