First of all happy new year everyone!I recently noticed that ramps like the Karma Ramp Constant and the Karma Ramp Parameter seem to be completely broken in Karma XPU rendering. It's very easy to reproduce; Take any roughness texture map, feed it into a ramp to remap values and then into a mtlX standard surface or openPBR standard shader. While the look changes initially compared to not having the ramp plugged in, any further tweaking of values is not reflected visually. Switch over to CPU however and everything is working as expected. So basically right now there is now way of using ramps in shaders if you wanna render with XPU which is a major problem imho. I can't rule out that it also might be an Nvidia driver issue. I've updated to the latest studio drivers two or three days ago, so maybe that might also be the issue? Maybe someone who hasn't updated yet can cofirm the issue? I also always precompile shaders after updating my driver(new feature in H21), maybe something could've gone wrong there?
The only way around that I found so far is importing the texture maps into COPS, do the remap there and then pull the result back into the VOP network with the 'op:' syntax. While this works generally there's one major problem; op: doesn't work for UDIM textures (would be really nice if it did btw) so the only real option right now is baking out remapped texture maps from COPS and read them in with mtlx image nodes in the shader which is painstakingly slow and horrible for iteration.
Looking forward to hearing back from you and if I'm alone with this problem or if it's actually a bug.
I tested this on 21.0.585, .588, .590 daily builds and also on .559 production.
System is Windows 11 25H2, Nvidia RTX 4090 Studio driver v591.74, 128GB DDR5 RAM
