Displacement

[John_Do]

Hi,

I'm having shading artifacts with the default displacement settings, it seems that normals smoothing isn't applied at the subdivision level :





Material is applied on a low poly sphere, without Subdivision options. Below are the settings :

[John_Do]

I've found the culprit, it is the inverted normal map.




This gives some weight to my other post : it would be really useful to have some settings in the Bump tab related to color channels since Cinema 4D doesn't give any efficient option.

[John_Do]

Hi,

I've made more tests on the final release and the bug is still here. Doesn't seems tied to normal map orientation since it works as expected in CPU, just normal map in GPU mode ( CUDA and RTX ).


CPU



GPU CUDA and RTX ( no other change than switching the render engine )

[John_Do]

Do you think you could fix this bug as soon as possible please ? It makes the Displacement unusable in GPU mode and it's not a V-ray core issue since it works as expected in other plugins.

( I've checked it in V-Ray Next for Modo )

[deyan.hadzhiev]

Hi John_Do, this seems like a bug on our side. We will investigate further and will let you know when there is more information for the fix.

[John_Do]

Thanks for the fast feedback !

[deyan.hadzhiev]

Hi John_Do, do you have enabled the cache normals in all cases when the problem is observed? It might be best if you provide a scene.

It makes the Displacement unusable in GPU mode and it's not a V-ray core issue since it works as expected in other plugins.

Cinema 4D uses left-handed coordinate system, whereas most other 3D DCCs use right-handed coordinate system (as well as the V-Ray core). This is the source of several differences, most probably including this one, which I'm still investigating.

[John_Do]

Hi deyan.hadzhiev , thank you for the explanation. I've just checked the setup.

Cache Normals disabled




Cache Normals enabled



So the Cache Normals setting seems to improve a little bit the result, but doesn't fix the first issue encountered. Since the shading error happens on every face, I guess it's related to the coordinates system issue you've explained.

[deyan.hadzhiev]

In both cases it probably is. Apart from the displacement texture, do you have anything else in the material - normal bump or anything else that might also affect the result?

[John_Do]

A normal map yes. You'll find a link to download the scene in your Messages.

[deyan.hadzhiev]

Thanks, I have found and fixed the issue with the cache normals option, and will check your scene for the other issue. I'll write here when the issue is fixed in the stable nightlies.

[deyan.hadzhiev]

After some investigation, it turned out to be a core GPU issue, that will be further investigated, but may take more time. However, it is only present when both normal displacement and normal bump map are used on the same geometry, and the quality settings of the displacement produce a subdivision.
Until we fix the issue in the GPU render, as a workaround you may change the quality settings of the displacement to prevent subdivisions (by setting the max levels parameter to 1) and subdivide the geometry using the cinema 4D subdivision.
I will write again when there is some change on this issue.