[Bug 162541] Re: Google-earth display problems with Compiz

[Mirco Müller]

Every OpenGL-based application running under compiz (and being driven by
OpenSource Xorg-drivers or ATI's flgrx) will yield rendering glitches as
described, because the drivers in question are all still based on DRI
and not DRI2. What DRI lacks and DRI2 introduces - among other things -
is hw-accelerated indirect rendering. This affects composited window-
managers (like compiz) mostly. Currently with DRI the DRM does not care
if the desktop is composited or not and just hands any OpenGL-app, that
asks for a rendering-context to draw to, a pointer to the front-buffer.
Thus the OpenGL-app happy starts drawing to the front-buffer, ignoring
the fact that there might be a compositing manager running and it should
rather render to an off-screen area and let the compositing-manager do
the work of blitting the OpenGL-apps window-contents to the front-
buffer. DRI2 is more intelligent in that regard in fixes this.

All that is overly simplified of course, but should give an idea about
what is going on "under the hood".

On nvidia (using the proprietary driver) one does not run into this
issue because nvidia does not use any form of DRI but their own
infrastructure, which happens to have hw-accelerated indirect rendering
for some time now. If one would be so bold to use the OpenSource
nouveau-driver, they'd see the same rendering glitches. But nouveau will
of course also switch to DRI2.

Over time all OpenSource Xorg-video-driver will switch to DRI2 of
course. It will take time. The first driver that is pretty far in
development to adapt to DRI2, is the intel-video driver (for i915, i945
and i965 that should work already). Second in line will probalby be the
OpenSource radeon-driver (the one without HD in the name).

-- 
Google-earth display problems with Compiz
https://bugs.launchpad.net/bugs/162541
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