Overlapping GtkWidgets - any advice?

["Jeff Smith" <jeff smithicus com>]

I've looked all over the place, but I can't find a concise answer to this question.

I have a custom widget, call it Foo, that draws a circle. I want to be
able to overlap two Foo widgets in a GtkFixed window, and have them
draw two, overlapping circles. (I've implemented Foo's expose-event
handler with Cairo.)

My current implementation works fine, except that the entire window of
each Foo gets cleared with the background color before my expose
handler gets called, and this clear obliterates part of the underlying
circle from the first Foo. Is there a simple way to suppress this
background clearing behavior? Will that do what I want, or do I have to
start looking at more complex solutions like RGBA window compositing?

Any pointers to help me over this confusion will be greatly appreciated.

Jefficus