[Bug 34266] Division by zero in shader results in NaNs

[wine-bugs at winehq.org]

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

--- Comment #6 from Henri Verbeet <hverbeet at gmail.com> 2013-08-17 05:56:42 CDT ---
(In reply to comment #4)
> Thanks for the insight.  (For reference, I'm using an NVIDIA GTX450; I'm not
> familiar with the ISA, but I assume it has a similar zeroing MUL instruction
> for use with D3D9.)
> 
Afaik at least older hardware has a context global switch for this, newer
hardware may have separate instructions.

> It looks like D3D10 and later follow the IEEE rules as well, so I'm not sure
> how much support we could get for an OpenGL extension just to support legacy
> shaders.  I wonder if we could work around the problem with the mix() function
> from GLSL 1.30?  Something like:
> 
> dest = mix(vecN(0), a * b, equal(a, vecN(0)) || equal(b, vecN(0)))
That would be really expensive, the performance impact would pretty much not
make it worth it. In terms of hacks, avoiding infinities in instructions like
rcp, rsq, etc. tends to work well enough, although the performance hit is still
noticeable, but it's not something that can go into Wine either way.

We've brought this up with driver vendors in the past, and at least NVIDIA and
Mesa seemed open to the idea. We didn't get a direct response from fglrx. At
some point we talked about an EXT_zero_mul_conventions extension with NVIDIA,
but that seems to have stalled somewhere inside NVIDIA for reasons that aren't
entirely clear to me.

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