[ubuntu-x] DRi2 intel drivers in Jaunty?

Peter Clifton pcjc2 at cam.ac.uk
Fri Jan 23 14:20:44 GMT 2009

Hi guys..

I was just about to write an email asking if there were any plans to get
the 2.6.x intel driver into Jaunty, with / without DRI2 support, and it
turns out the packages hit the repositories about 3 hours ago ;).

What this does mean.. is that you might start to see some reports of
corrupt alpha rendering with compiz. (I've been testing locally with the
new intel drivers for a while now.. and have been debugging that issue).

The DRI2 texture from pixmap implementation isn't taking care to
override the texture format in the 3D driver, so when compiz redirects a
24bit depth window, the texture it gets has an undefined alpha channel.
(The old DRI implementation kludged the overrode the texture depth /
zero'd the image, depending on whether a zero copy tfp was in use).

I've brought this up on the mesa3d-dev list, and had a brief chat to krh
about it. I'm not convinced he thinks this is a bug, suggesting that it
would be up to compiz to check the visuals on the images it is

I do have the start of a workaround in compiz, fixing the common case of
a 24 bit depth window (e.g. menu popup) which compiz wants to fade onto
the screen. It requires an ABI bump though, since to hack around the
problem, I added a field to CompTexture, tracking if the texture's alpha
channel should be used.

The remaining (as yet incomplete) fix, is to adjust the blending
operations used during painting to take into account this fact. I've
only got a fix so far for the code-path taken when a window's
brightness / opacity is modified. (It doesn't work if the saturation is
changed as well).

I've not tried to implement fixes for the fragment shaders method of
blending the window texture, since that isn't a code path which seems to
be getting hit on my GM45 laptop.

I'll keep prodding to see if the DRI2 tfp implementation can be fixed,
but if not.. give me a shout, and I'm sure we'll be able to come up with
some patches for the Ubuntu compiz packages which will hide the problem
from users in 99.9% of the cases with intel + DRI2.

Best wishes,

Peter Clifton

Electrical Engineering Division,
Engineering Department,
University of Cambridge,
9, JJ Thomson Avenue,

Tel: +44 (0)7729 980173 - (No signal in the lab!)

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