On 07/10/2017 11:25 PM, Kenneth Graunke wrote: > Hello, > > Mesa master has been hitting assert failures when running "XCOM: Enemy > Unknown" since commit f8d69beed49c64f883bb8ffb28d4960306baf575, where we > started asserting that the SAMPLER_STATE LOD Bias value actually fits in > the correct number of bits. > > Apparently, XCOM calls > > glTexEnv(GL_TEXTURE_FILTER_CONTROL_EXT, GL_TEXTURE_LOD_BIAS_EXT, val); > > to set the texture unit LOD bias...but according to gdb, the value is: > > -nan(0x7ffff3) > > In i965, we do CLAMP(lod bias, -16, 15)...but NaN ends up failing both > the < min and > max comparisons, so it slips through. But, that raises > the question...what value *should* we be using? 0? Min? Max? > > I couldn't find any immediately applicable GL spec text. Anyone know of > any? If not, does DirectX mandate something?
There is one place. Section 2.3.4.1 (Floating-Point Computation) of the OpenGL 4.5 core profile spec says: "The result of providing a value that is not a floating-point number to such a command is unspecified, but must not lead to GL interruption or termination. In IEEE arithmetic, for example, providing a negative zero or a denormalized number to a GL command yields predictable results, while providing a NaN or an infinity yields unspecified results." Crashing is not allowed, but nearly any other behavior is. Based on that, I like Roland's suggestion of changing the CLAMP() macro. We should also report this to the developers. I'd wager that some crazy NaN value is not what they intended. > I wrote a hack to check isnan and replace it with 0, which gets the game > working again, but...it seems like we could have this problem in a lot of > other places too...and I'm not sure what the right answer is. > > https://cgit.freedesktop.org/~kwg/mesa/commit/?h=xcom&id=6a1c0515b760c943eb547cced754b465aa3bd4ca > > Thanks for any advice :) > > --Ken
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