Gradients are broken with glamor when RepeatReflect is set

[Adam Jackson]

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

- ajax