Enhancements for Render composite request

[Chris Wilson]

Excerpts from Keith Packard's message of Tue Aug 25 18:34:21 +0100 2009:
>  1) Only one rectangle per request. Apps generate a lot of protocol,
>     the server spends a lot of time decoding requests and the driver
>     has to merge requests back together to hand more than one polygon
>     to the hardware. It's interesting that exa (and hence uxa by
>     derivation) have a poly-rectangle composite operation in their
>     driver interface.

In cairo, a composite region operation (i.e. multiple composite
rectangles with identical op, source and destination) is performed using
a single RenderComposite with a clipping region. So out of curiosity are
you looking at cairo apps, and if so, have you found a bug in cairo or
merely bad usage?

The interface looks more efficient that setting a temporary clip region
on the Picture and would indeed mean that we could eliminate all use of
clipping on Pictures.
-ickle