Gradients are broken with glamor when RepeatReflect is set

[Michel Dänzer]

On 2018-01-23 04:26 PM, Chris Wilson wrote:
> Quoting Jeffrey Smith (2018-01-23 15:15:10)
>> On Mon, Jan 22, 2018 at 3:01 PM, Chris Wilson <chris at chris-wilson.co.uk> wrote:
>>> Quoting Adam Jackson (2018-01-22 20:09:52)
>>>> On Sat, 2017-12-23 at 19:26 +0100, Clemens Eisserer wrote:
>>>>> Hi there,
>>>>>
>>>>> Glamor's gradient acceleration code is broken in case RepeatReflect is
>>>>> used, please see: https://bugs.freedesktop.org/show_bug.cgi?id=98508
>>>>> I've filed the bug report over a year ago, but except for a
>>>>> confirmation from Michel Dänzer nothing happend.
>>>>>
>>>>> Unfourntunatly I lack the expertise to fix it myself - however instead
>>>>> of leaving it broken forever, could we fall back to software for
>>>>> RepeatReflect.
>>>>> I guess slow is better than completly broken?
>>>>
>>>> Just want to note that this isn't forgotten. I got as far as testing
>>>> the reproducer with Xephyr and verifying glamor was wrong and fb was
>>>> right, but don't yet get what the RepeatReflect math is getting wrong.
>>>> I'll definitely have a fix for 1.20 one way or another, but that may
>>>> just be forcing a fallback.
>>>>
>>>> If anyone wanted to investigate this, I think this is the guilty
>>>> conditional:
>>>>
>>>> https://cgit.freedesktop.org/xorg/xserver/tree/glamor/glamor_gradient.c#n296
>>>
>>> -t = abs(fract(t * 0.5 + 0.5) * 2.0 - 1.0);
>>> +t = abs(fract(abs(t) * 0.5 + 0.5) * 2.0 - 1.0);
>>
>> Chris, where did this definition for fract come from?
> 
> Naivety.
> 
>> For negative numbers, it does not match the OpenGL definition for
>> fract, which would be
>> #define fract(t) ((t) - floor(t))
>> With fract defined thus, the original transformation of t appears to work fine.
> 
> nir also uses the same definition:
> operation("fract", 1, source_types=real_types, c_expression={'f':
> "{src0} - floorf({src0})", 'd': "{src0} - floor({src0})"}),
> 
> So maybe it's purely an amdgpu compiler issue? Michel?

It's broken with llvmpipe/softpipe as well. Does it render correctly
with glamor on i965? If so, maybe it's a Gallium non-driver issue.


-- 
Earthling Michel Dänzer               |               http://www.amd.com
Libre software enthusiast             |             Mesa and X developer