[Bug 7284] Max Payne 2 light reflections on people are too bright and blocky

[wine-bugs at winehq.org]

http://bugs.winehq.org/show_bug.cgi?id=7284

Alexander Dorofeyev <alexd4 at inbox.lv> changed:

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--- Comment #77 from Alexander Dorofeyev <alexd4 at inbox.lv> 2013-10-21 11:50:45 CDT ---
Created attachment 46375
  --> http://bugs.winehq.org/attachment.cgi?id=46375
updated testcase rcp(0)*0

attaching updated patch with testcase, that can apply to current git
it reproduces the problem (rcp(0)*0). Result on geforce 8800:

visual.c:4238: Test failed: Color is 00ffffff, expected 000000

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Here is a more recent app affected by the same problem:

http://bugs.winehq.org/show_bug.cgi?id=34266

Quite possibly there are more. At the moment, it seems to only affect Nvidia,
but not because of a driver bug - rather, it seems that a behavior undefined in
GLSL is triggered:

on native, DirectX <= 9: rcp(0)*0 == Inf*0 == 0 (DirectX >= 10 has different
rules)

in GLSL: Inf*0 == undefined; in practice, appears to be NaN on nvidia vs 0 on
ATI (Intel graphics probably same a ATI) at the moment, that's why people can't
see this on Intel or ATI; can easily change in the future though.

With GLSL specs as they currently are, and without some kind of extension to
deal with this problem, the "technically valid" solution might be something
like what is suggested in bug #34266:

"dest = mix(vecN(0), a * b, equal(a, vecN(0)) || equal(b, vecN(0)))"

But Henri Verbeet said there that this is probably too costly performance-wise.

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