[Mesa-dev] [Mesa-stable] [PATCH 2/2] radeonsi: hard-code pixel center for interpolateAtSample without multisample buffers

Nicolai Hähnle nicolai.haehnle at amd.com
Thu Oct 12 18:13:21 UTC 2017

On 12.10.2017 18:55, Emil Velikov wrote:
> Hi Nicolai,
> On 11 September 2017 at 16:11, Nicolai Hähnle <nhaehnle at gmail.com> wrote:
>> From: Nicolai Hähnle <nicolai.haehnle at amd.com>
>> The GLSL rules for interpolateAtSample are unfortunate:
>>     "Returns the value of the input interpolant variable at
>>      the location of sample number sample. If
>>      multisample buffers are not available, the input
>>      variable will be evaluated at the center of the pixel.
>>      If sample sample does not exist, the position used to
>>      interpolate the input variable is undefined."
>> This fix will fallback to monolithic shader compilation when
>> interpolateAtSample is used without multisampling.
>> One alternative would be to always upload 16 sample positions,
>> filling the buffer up with repetition when the actual number of
>> samples is less, and then ANDing the sample ID with 0xf. However,
>> that punishes all well-behaving users of interpolateAtSample,
>> when in reality, only conformance tests should be affected by
>> the issue.
>> Fixes
>> dEQP-GLES31.functional.shaders.multisample_interpolation.interpolate_at_sample.non_multisample_buffer.*
>> ---
> Going through the lists, shows that this has landed without the stable tag.
> Normally that's considered as self-rejecting the patch.
> Is that really the case here or we want to pick it up?

Hmm, this may have happened because only one patch in the series had the 

To be honest, this isn't a high impact change so we can just drop it to 
be on the safe side.


> Thanks
> Emil

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