[Xr] Clipping to rectangles

[Owen Taylor]

Some thoughts about this discussion:

Typical an entire drawing operation in GTK+ is clipped
to the expose area that is being redrawn, an arbitrary rectangle list.

 - The efficiency question, as has been discussed here.

 - The Xr clip operator, at least as Carl described
   it initially, differs significantly from the
   Postscript clip operator in that it replaces
   the clip path, instead of intersecting with the
   clip path.

   So, I can't use the Xr clip for this purpose, since
   it would prevent users from doing their own clipping.

As things stand right now, I'd probably just do
operations on a target surface the size of the bounding
box, and do the clip when copying from the backing store (*)
but being able to tell Xr about the real clip region
would be nice from a performance point of view.

Regards,
                                  Owen

(*) This brings back up the question of the problem
    of "clipped" not meaning "untouched" with the 
    current semantics.