[Bug 10477] Weird graphics with vertex shaders in Soul Reaver 2 Demo

[wine-bugs at winehq.org]

http://bugs.winehq.org/show_bug.cgi?id=10477

Matteo Bruni <matteo.mystral at gmail.com> changed:

           What    |Removed                     |Added
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                 CC|                            |matteo.mystral at gmail.com

--- Comment #25 from Matteo Bruni <matteo.mystral at gmail.com> 2012-02-06 13:39:56 CST ---
I've spent quite some time on this bug and I guess I found something
interesting...

The 1.00 demo which was last linked here, with current video drivers, is broken
on Windows too (both on Nvidia and AMD). The 1.02 demo version (which can be
downloaded e.g. from
http://games.softpedia.com/get/Games-Demo/Legacy-of-Kain-Soul-Reaver-2.shtml,
beware it's about 650MB big) works fine on Windows AND on Wine instead.
The patch notes cite "Fix for ATI Radeon 8500. Almost the entire screen used to
be a single color" among the issues fixed by the update
(http://www.fileplanet.com/81971/80000/fileinfo/Soul-Reaver-2-Patch-v1.02). My
current hypothesis is that Nvidia, at some point, changed the fog behavior in
their drivers to match ATI/AMD, specifically about what happens when the fog
factor is outside of the 0.0-1.0 range, thus becoming affected by the same
issue as the Radeon 8500.

So, I'd say this is not really a Wine bug and Wine behaves as it should. The
only thing which needs to be fixed, in accordance with some tests I've done, is
that the fog coordinate set from a vertex shader needs to be clamped. "Fixing"
that makes the 1.00 demo constantly fogged: so it clearly doesn't help the
demo, but it makes Wine accurately match fogging as for current Nvidia/AMD
Windows drivers.

BTW, the fog in Prince of Persia: the Sands of Time is broken with current
Nvidia drivers (Windows and Wine), but faking an AMD GPU on Wine makes the game
use a different fog setup which works correctly. I guess that may be the same
basic issue.

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