Hi Shawn et al.
  
I have put a patch on ftp.gimp.org/Incoming which implements
regions in GDK. It is an exact wrapper for the equivalent
X functions.
The patch includes changes to:

gdktypes.h
- added struct GdkRegion

gdkprivate.h
- added struct GdkRegionPrivate
  
gdkregion.c
- actually implements the region functions

gdk.h
- decls

the respective Makefiles

In addition, I have added the function (to gdk.h and gdkgc.c)

gdk_gc_set_clip_region( GdkGC*, GdkRegion* );

which works in the same way as

gdk_gc_set_clip_rectangle( GdkGC*, GdkRectangle* );

  Regards,
  
    Robert Roebling