Bug with Phoenix FD in GPU RTX renders

[Svetlin.Nikolov]

Hey, can you send any scenes that show the issue but don't have Phoenix? nVidia responded and gave us directions, but seems like the fix might be a bit tedious so we gotta test it on as many scenes as possible.

Cheers!

[Paul Oblomov]

In my case any sim mesh from h with moblur. As I remember alembics.

[GregCooper]

If I get time to prepare a scene I will but it takes time and I'm pretty busy at the moment. What I can tell you is its happening on a mesh thats being deformed with a Maya sin wave deformer, it also has vray subdiv to smooth it and rendering with motion blur, and as I mentioned before it happens on random frames with no obvious pattern I can see

[Svetlin.Nikolov]

Hmmm, so it might not be limited only to simulation meshes (which have changing topology e.g. vertex and poly count on each frame). But it seems to always involve motion blur and meshes with deforming vertices...

[Paul Oblomov]

May that be tensor cores, which are optimizes moblur and dof? The only difference, between 2080 and 3090.

[Svetlin.Nikolov]

Hey guys, our GPU guys have narrowed down the problem and there is a quick and dirty fix that seems to work after little testing. We need to do much more testing though.

They also spoke to nVidia and we'll see if we need to wait for driver update or if it can go in the nightlies sooner.

Will ping you when there are more news, cheers!

[Paul Oblomov]

So it is not about how new rt blocks accelerates moblur calculations? I wonder if vray uses it by default or not. Quite interesting

[peter_hoehsl]

Got the same issue in Houdini using RTX with an RTX3090 and RTX3080ti, and sorry but I can't share any project files due to an NDA. What happens is that with motion blur on and the camera (Physical Camera) in motion random individual polygons are 'deleted' and show either the background or a self illuminated object behind it. It's truly random in that in every frame a different set of faces disappears. With a static camera I did not see the effect. In two cases where this happens the geometry is deforming with a constant point count and read from a file cache. One is an RBD simulation and the other just geometry deformed in VEX similar to a soft transform. Both have a velocity attribute and "Geometry Velocity Blur" was set to "Velocity Blur". I'd also like to point out that this seems to only happen when rendering a sequence to disk. I did not notice this happening when rendering a still to the frame buffer. I just did a test with CUDA and luckily this seems to be fine.

[GregCooper]

Yeah RTX seems like it should be the default renderer if you have RTX cards, but it’s basically unusable for me at the moment

[peter_hoehsl]

I have come across other issues that seem to be UV related. The presence of a UV Explicit node will lead to a crash. Having nodes in the material builder that are not connected to an output and are even disabled (which can happen during lookdev) can corrupt UV mapping in the render. When the renderer is set to GPU I can't change the UV name in either the Image File or UV Channel Name nodes. That option is disabled and I have to switch to CPU to change the name and then switch back to GPU. I'll make a separate post for these with a project file once I have some time.

[GregCooper]

I have come across other issues that seem to be UV related. The presence of a UV Explicit node will lead to a crash. Having nodes in the material builder that are not connected to an output and are even disabled (which can happen during lookdev) can corrupt UV mapping in the render. When the renderer is set to GPU I can't change the UV name in either the Image File or UV Channel Name nodes. That option is disabled and I have to switch to CPU to change the name and then switch back to GPU. I'll make a separate post for these with a project file once I have some time.

Right yeah, sounds maybe similar to another issue I've been getting in Maya when using motion blur and vray subdiv nodes. Sometimes just disables all nodes connected to my material so it renders as a plain vray material. I don't know, maybe the non 3dsmax versions aren't getting the same love from Chaos or something. Honestly I can't keep up with the bugs at this rate, or have the time to keep logging support requests.

[georgi.zhekov]

Hey guys,

Just wanted to let you know that ultimately the issue turned out to be a problem in the GPU drivers. NVIDIA already have a fix that should be coming really soon with one of the new driver updates.
Will update the thread once they are live and can be downloaded.

Thanks a lot for the scenes and all the help!

[Paul Oblomov]

I hope this won't be tied to windows 11

[peter_hoehsl]

Motion blur is messed up on both CUDA and RTX when used in conjunction with opacity or refraction as soon as the camera is moving.

[georgi.zhekov]

Motion blur is messed up on both CUDA and RTX when used in conjunction with opacity or refraction as soon as the camera is moving.

Is this Phoenix related? Can you send us a scene representing the issue?

Thanks!