[VrayVolumeGrid] MotionBlur bug when more than 10 VrayVolumeGrids in scene

[tdugard]

Hello,

We are façing a really annoying but since many months now, we are rendering the motion blur in vray and we are facing a weird issue when we have multiples VrayVolumeGrid in scene precisely more than 10. The volume grids are simulated at the center of the world and then linked to objects in scene and offseted in time (like assets moving along with some meshes).
When we have less than 10 volume grid the motion blur is correct, and then when we add one more volumegrid the motionblur on the volume is not rendered
I've made a simple test scene with a vdb sphere with no velocity channel linked to a animated cylinder :



You can see that the motion blur is bugged, i've just unhide one more VolumeGrid.
Is there some option to disable to have to correct behavior ? Is it some bug ?

We are working on VrayNext update 3.1 and 3dsmax 2019

Here is the test scene if you want to reproduce the bug : https://we.tl/t-e1JhneKMHl

Thanks

[hermit.crab]

Thanks for the provided scene. It seems to happen in V-Ray 5 as well, I'll notify the developers and write back. I've noticed that the issue does not occur when the VolumeGrid's rendering mode is set to "Volumetric Geometry". Could you try it out?

[tdugard]

Thanks for the quick answer.

"Volumetric Geometry" is the first thing i've tried but the render times goes crazy with this mode. So it's not a solution. In the past we have rendered 10 by 10 grids with our renderpass manager but it's a long process.

[hermit.crab]

I've logged the issue (internal bug-tracker id: PHI-6273) for developer investigation. The issue seems to affect only the 3ds Max integrated Phoenix version; rendering with Standalone may be used as a workaround.

[tdugard]

Thanks for th bug report, unfortunately we don't have much time to dive into .vrscene converting, we will separate volumegrid rendering 10 by 10, hope this issue will get fixed soon.