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authorRoland Scheidegger <[email protected]>2013-11-11 14:29:25 +0000
committerRoland Scheidegger <[email protected]>2013-11-14 12:24:55 +0000
commit754319490f6946a9ad5ee619822d5fe4254e6759 (patch)
treeaa89800a7fcd530661b8018feaeadba480182f44 /docs/developers.html
parenta15a19f0d1b024f5f18f1dfe878ae8d399e38469 (diff)
gallivm,llvmpipe: fix float->srgb conversion to handle NaNs
d3d10 requires us to convert NaNs to zero for any float->int conversion. We don't really do that but mostly seems to work. In particular I suspect the very common float->unorm8 path only really passes because it relies on sse2 pack intrinsics which just happen to work by luck for NaNs (float->int conversion in hw gives integer indeterminate value, which just happens to be -0x80000000 hence gets converted to zero in the end after pack intrinsics). However, float->srgb didn't get so lucky, because we need to clamp before blending and clamping resulted in NaN behavior being undefined (and actually got converted to 1.0 by clamping with sse2). Fix this by using a zero/one clamp with defined nan behavior as we can handle the NaN for free this way. I suspect there's more bugs lurking in this area (e.g. converting floats to snorm) as we don't really use defined NaN behavior everywhere but this seems to be good enough. While here respecify nan behavior modes a bit, in particular the return_second mode didn't really do what we wanted. From the caller's perspective, we really wanted to say we need the non-nan result, but we already know the second arg isn't a NaN. So we use this now instead, which means that cpu architectures which actually implement min/max by always returning non-nan (that is adhering to ieee754-2008 rules) don't need to bend over backwards for nothing. Reviewed-by: Jose Fonseca <[email protected]>
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