Difference in VrayRT CPU vs CUDA

V-Ray V-Ray for 3ds Max Issues
1

Hi,
I’ve checked the supported features list for VrayRT and did setup a simple scene with one VRmat and one FastSSS (raytraced solid) and a glass material as well as a carpaint shader.
I’ve rendered one time with VRayRT on CPU vs CUDA enabled.
The results are quite different.
What did I do wrong?
Thanks,
Akira

VrayRT-CPU_test.jpg
VrayRT-CPU_test.jpg640×480 72.6 KB

VrayRT-CUDA_test.jpg
VrayRT-CUDA_test.jpg640×480 62.2 KB

2

Can you post the scene here?

3

Here you go.
VrayRT_Test.zip (2.78 MB)

4

This look like a issue for our developers :slight_smile:
I just reproduce the difference and for example the teapot, which uses VRayVRmatMtl renders very differently between RT/CPU and RT/GPU with different materials. I will make some more tests and will let you
know if this will be added to our bug tracking system or if it is fixed in the latest nightly builds.

5

Just make a note in our bug tracking system, so will keep you informed for any fixes regarding this issue.

6

I don’t know, if it’s important but the VRMat Library was created in Maya.
Only the teappt has the VRayVRMat applied.

7

Hello,

1. For the glass - increase the Trace Depth / GI Depth from the V-Ray RT tab in the settings. Keep in mind that you have to restart V-Ray in order these changes to have affect.
2. For the SSS - Single Scatter can be “None” or “Simple” on the GPU and “scatter gi” is always on. This is written in the log as warning, too.

8

You have to? I thought it works interactively, at least it does for me. If it doesn’t you should make a bug report about it.

Best regards,
Vlado

9

To be more correct this is only for the nightly builds and it is reported already. For official builds there is no such problem with interactivity.

Also using higher values for reflection in the material will produce very close results when you compare CPU and GPU final renders.