[Bug 33172] [r600g] ingame rendering broken (black screen) in ut2003

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=33172

--- Comment #2 from Tobias Jakobi <liquid.acid at gmx.net> 2011-01-19 14:35:02 PST ---
We (Jan and me) did some tests today and found out that the issue is probably
related to the use of VBOs (or more specifically: not using them).

In ut2004 there is a option called 'UseVBO' for the OpenGL renderer. I guess
enabling this one lets the engine use the 'ARB_vertex_buffer_object' extension.
It turned out that in my ut2004 config it was enabled, but Jan had it disabled.
So after enabling it for Jan the rendering suddenly worked. And when I disabled
UseVBO on my system it suddenly failed and produced the black screen, plus the
relocation parser errors in the kernel log.

I can only guess here, but maybe the problem is with Gallium's immediate mode
implementation -- if that's how the engine submits vertices when ARB_vbo is not
used.

The next thing we found out is even more interesting: In ut2003 there is no
such option, so he had to stick to the 'immediate mode' rendering path. All the
tests were done on Jan's system. We noticed that is was possible to get ingame
when being logged in as root. This only worked for a short time, maybe like 10
seconds, before the game segfaulted. After it segfaulted, it wasn't possible
any more to get ingame. The game just instantly segfaulted. Restarting X didn't
help, only a full reboot did the trick.

Another thing that worked: Reboot, start ut03 as root, watch some game scenary
for like 3 seconds, quickly exit the game, start ut03 as root, repear
procedure...

The maximum amount of time we managed to get into game was three. After that it
didn't work any more.

It was like we hit some memory leak, maybe in VRAM?

Then we switched over to ut2004 and disabled UseVBO there. We got the black
screen (with the kernel messages) when we got ingame and then we waited a bit.
But just like ut03 the game segfaulted after some seconds and we even managed
it at one time to trigger the kernel OOM killer.

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