Vray GPU Jittering Geometry with Motion Blur

[sam_wickert]

Experiencing a very frustrating issue with Vray GPU rendering and motion blur. The render causes positional jitter in geometry from frame to frame in the render. This is non-existent in the Vray CPU renderings.

Here is a project file with the issue as well as a test render: https://www.dropbox.com/t/1SRyKsqVd0Pbwobc

[hermit.crab]

The culprit seems to be the value "4" motion blur samples in the jittering objects. A value of 5 seems to resolve the issue. I've seen this issue before, but I need to find the reason for this behavior. I'll write back soon.

[sam_wickert]

Ah, the issue does still seem to exist even with the value set to 5. Hoping you might find a better fix here? Thanks!

Update: tried again, it appears it's necessary to do the specific set of commands in a specific order for it to properly work. Switching up the order of "turning motion blur on" before raising the value to 5, then turning Depth of Field on seemed to fix the issue. Still needed to be set to a value of 5.

Hope that helps in your search.

[hermit.crab]

The reason for the issue is the following:
Since time in 3ds Max is in integer ticks, transform samples for motion blur do not always align with it. This is solved for rendering in 3ds Max by using non-uniform motion time slices, however, the solution is not implemented for the .vrscene exporter (hence why the issue happens in GPU).

[hermit.crab]

FYI, I've logged the issue (internal bug-tracker id: VGPU-6005) for dev analysis.