EXA and migration [was: shrink xrender featureset]

[Clemens Eisserer]

> That's not 'strong vocabulary' but simply baseless flamebait.

Would it make sence to implement some fallback-optimizations like:
- Copy pictures without drawables (gradients) to a temporary surface,
if the driver supports composition?
- Support solid write-only operations (X11 core drawing) for which EXA
does not provide hooks (e.g. diagonal lines) through a temporal mask,
if the driver supports composition?

For both cases I saw ping-pong migration killing performance, and I
had to implement work-arrounds in my application myself which are
built on assumptions about the accaleration architecture's behaviour
and sometimes cause degraded performance.

By the way thanks a lot for the EXA improvements in 1.5/1.6 :)

- Clemens