2017-01-11 19:09 GMT+01:00 Jason Ekstrand <ja...@jlekstrand.net>: > Another reason why I'm not a huge fan is that there is some momentum in the > industry to make GLSL better defined with respect to NaN. I don't know that > anything will ever come of it (because it may break apps) but if something > does, we may find ourselves having to make SQRT and RSQ NaN-correct in the > future and, hey look, it'll break apps.
Hijacking the thread to focus on this. What's the interest about specifically (assuming that's something that can be talked about publicly?) I'm asking because in Wine we have been bitten many times by the GLSL behavior WRT NaN and at the moment we really can't do anything sensible about it in the general case. Many d3d9 applications depend on not generating NaN in cases where e.g. IEEE 754 would expect to. The RSQ (i.e. inversesqrt()) from the original thread is one of those, but that's not really a problem for sane applications since it's "defined" in d3d8/d3d9 as taking the absolute value of the operand and indeed we translate RSQ to inversesqrt(abs(x)). The real issue is with cases like 0*inf, which AFAIK on d3d9 are supposed to give 0 as result. Of course, that changes with d3d10+, which generally requires to generate and preserve NaN, as Roland already mentioned. So, what would be really nice to have is a GLSL extension for some kind of switch to select the requested behavior WRT NaN. For example a three-way option with "don't generate NaN in arithmetic operations", "do generate NaN" and "don't care". It could also be a GL state if that's easier to implement with the existing hardware, since an individual application isn't supposed to require different behavior from one shader to the next. Is anyone interested in / favorable to something like this? It would solve the issue with defining NaN behavior in GLSL while making things a bit more compatible with "other API a lot of games are ported from which happens to be supported by all the desktop GPUs". Cheers, Matteo Bruni. _______________________________________________ mesa-dev mailing list mesa-dev@lists.freedesktop.org https://lists.freedesktop.org/mailman/listinfo/mesa-dev
