cliping region

[adrian <feiguin ifir ifir edu ar>]

I'd like to know if it is possible to mask a given region of a window in
order to avoid drawing on it. It should be the oposite of 
gdk_gc_set_clip_rectangle().

The idea is that I have a widget in a scolled window (something like
gtklayout) and I want to draw on the window, and prevent drawing on the
widget (the window is its parent window).

Thank you,
<ADRIAN>