XSetRegion(display, gc, r) 
      Display *display;
 
      GC gc;
 
      Region r;
 
XDestroyRegion(r) 
      Region r;
 
The XSetRegion function sets the clip-mask in the GC to the specified region. The region is specified relative to the drawable's origin. The resulting GC clip origin is implementation-dependent. Once it is set in the GC, the region can be destroyed.
The XDestroyRegion function deallocates the storage associated with a specified region.