enabling Composite

[Adam Jackson]

On Sun, 2008-07-27 at 19:49 -0400, Adam K Kirchhoff wrote:
> On Mon, 28 Jul 2008 01:11:09 +0200
> "Edwin Smulders" <edwin.smulders at gmail.com> wrote:
> > Yes I am. I was adviced to use this by a wine developer, at first I
> > was using Twinview but this did not report my resolutions correctly. I
> > will look in to changing back Twinview tomorrow.
> > 
> > I'm curious though, how could you see that I'm using it?
> > Also, did you mean this as something which might fix my problem, or
> > just general advice?
> > 
> 
> This will definitely fix your problem.  Xinerama + Composite do not
> work together with the nvidia drivers.  nvidia says this is a
> limitation in the xserver.  I'm not sure what, if anything, the Xorg
> developers say.

They are correct.  The Composite extension (and the Damage and Fixes
extensions underneath it) are fundamentally unaware of Xinerama at a
protocol dispatch level.  Extending Damage and Fixes to be
Xinerama-aware is fairly straightforward, last I looked at it, although
there's some potential for optimisation around Damage.

The obvious way of extending Composite is kind of nasty.  Most of the
reason Xinerama performs at all reasonably (which is not saying a lot)
is because even though all drawables are instantiated on all screens,
window drawing is still clipped.  With Composite, you'd suddenly turn
all windows into pixmaps, and pixmap rendering is unclipped, so now
you're drawing the full contents of every window on every GPU.  Ouch.

- ajax
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