Flickering in graphics-heavy applications

Duncan 1i5t5.duncan at cox.net
Wed Mar 31 14:23:37 BST 2010

Dotan Cohen posted on Wed, 31 Mar 2010 14:46:40 +0300 as excerpted:

> In KDE 4.4 with Composting enabled I get flickering in graphics-heavy
> applications such as Stellarium and Google Earth. I have an ATI video
> card and use the FOSS drivers as provided by my distro (Kubuntu). Is
> this a Kwin bug, or Stellarium/Google Earth bug? Video plays fine.

Which ATI card?

The Radeon r600/r700 series cards (most of the hdXXXX) are only now 
getting proper OpenGL support in the stack, requiring pre-release mesa and 
xf86-video-ati drivers, and strongly preferring a 2.6.33 kernel, so you'd 
need to be running kubuntu 10.4-betas in ordered to get proper support 
there and even they'd be pre-release upstream drivers.  Evergreen (r800, 
hd5xxx) will take a bit longer, at least another six months beyond that, 
probably a year, as it just got 2D support merged, 3D/OpenGL isn't working 
at all.  It's very possible they'll go straight Gallium drivers for it.

The older r300-r500 drivers (generally the xXXXX series cards, with a few 
exceptions at either end) are somewhat better, but of course, the hardware 
is generally weaker, too.  That'd probably depend on the resolution you're 
running stuff.  The ancient r100/r200 drivers have been well supported for 
years, but the hardware is just not upto modern graphics demands, and 
OpenGL breaks with resolutions above 2048 either direction.

And if you mean XRender instead of OpenGL based compositing, it works, but 
is generally slower than OpenGL, so yeah, you're going to have artifacts.

Basically at this stage, you're best toggling off compositing when you're 
doing heavy graphics.  I /think/ it's supposed to turn it off when you run 
a full-screen app on top of the stack anyway, but I never see it as I run 
dual monitors and basically don't full-screen to both, only one, which 
apparently doesn't turn off the compositing automatically, so if I want it 
off I have to toggle it off.

The good news is that for r600/r700 series, what's currently upstream 
(both kernel and x/mesa drivers) works quite well, so when it hits stable 
release and the distribs pick it up for the fall release, things should 
finally look quite good for semi-modern Radeon card users, tho not 

Duncan - List replies preferred.   No HTML msgs.
"Every nonfree program has a lord, a master --
and if you use the program, he is your master."  Richard Stallman

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