[Xorg-driver-geode] Rendering in geode

[Jonathan Morton]

> > An unfortunate fact of EXA is that you need to throughly understand
> > XRender's requirements when implementing the Composite function.
> > This is fairly poorly documented.
> 
> What's missing exactly?

I think all of the necessary bits can be found in various places.  The
problem is that you have to know they're necessary and then go looking
for them.  The result is buggy drivers because of incomplete design,
entirely due to misunderstanding the specification requirements.

Normally one would like to read a reference implementation, but Pixman's
source code is extremely opaque and so it's very easy to miss things.

Also, the expected behaviour of the ModifyPixmapHeader hook is decidedly
unclear, particularly in the various corner cases that crop up in
practice.

-- 
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From: Jonathan Morton
      jonathan.morton at movial.com