Comment # 11 on bug 111241 from Pierre-Eric Pelloux-Prayer

(In reply to Dieter Nützel from comment #8)
> BTW
> 
> Pierre-Eric can you look into this
> 
> Shadertoy shader corruption, too?
> https://www.shadertoy.com/view/Xt3cWS
>

The "Buffer A" shader doesn't write fragColor when uv.y is < 0.1 or > 0.9.

So the content is undefined and may be black on some platform or random.

radeonsi is correct here, but we might want to replace undef values with 0x0 to
get a default value instead of random.