Arnold displacement on GPU not rendering properly

[kestas3d]

Hi ,

I recently ran into an issue where the displacement on the GPU doesn't render correctly, however if I switch to CPU rendering it works fine so it only happens on the GPU.

I'm using Maya 2022 MtoA 4.2.3 and Arnold Core 6.2.1.1

My shading network is pretty simple I'm using a Zbrush displacement and adding some random procedural noise on top which is controlled with an intensity mask. I've tried disabling the noise and feeding the ZB displacement directly but still produces the same result on the GPU.

Here are a few images for illustration:

GPU:

CPU:

[kestas3d]

I've been digging around this issue for a little longer, tried with the latest Arnold 7 and Mtoa 5.0.0 and the problem still persists.

I may have found something in the logs that says something about it:

[gpu] Disabling autobump on shape %s as the displacement shader %s (%s) is used with a raytracing shader elsewhere in the scene.

Could anyone provide a little insight of what that error means?

[thiago.ize]

You're citing a summary of all the warnings in the log file. If you scroll up in the log you should find four log messages that replace the %s string tokens with the actual object and shader names so you know what to fix.

In any case, this is happening due to a limitation in Optix 6 where if you use, in your case, a cell_noise for both displacement and as an input to a shader that traces rays, like curvature, then you'll get this warning and the autobump will be disabled. We suspect this will be fixed when we move to Optix 7, which is something we are working on, though we don't know when it will be ready.