Blocky artifacts when rendering sims in Volume Grid, lit from the inside.

[egz]

I'm working on a shot with thunderclouds that need to be lit from the inside. However, I'm getting these weird rectangular blocky artifacts.
The volumes are VDB files, lit from within with very strong V-Ray lights. I'm just getting started with the shot and will start troubleshooting this, but just thought I'd ask here if anyone has come across this before.

[Svetlin.Nikolov]

Hey, are you using V-Ray 5 update 1 by any chance? It has a known issue that looks like this.

[egz]

Yes, I'm using V-Ray 5 update 1. Do you know if a fix is far away? I can work around this for a little while.

[Svetlin.Nikolov]

Yess, try the latest stable nightly here: https://nightlies.chaosgroup.com/mai...e_5.1/20210317

Please ping me if the issue still persists - it looks very much like the one which is fixed in the stable nightlies, but if this nightly does not help, we have to investigate...

Cheers!

[egz]

Thanks, I'll give it a try and let you know.

[egz]

Unfortunately, I still get the artifacts with build 30661. I can send a simplified file if you need it.

[Svetlin.Nikolov]

Ahh, yes, please! A volume grid, the lights and one cache should do it...

[egz]

Here's a download link. Max 2021 file with just the camera, lights, and grid+cache. See result of frame 32 attached.
https://we.tl/t-ThuTJbFaso

[Svetlin.Nikolov]

Hey, thanks, we got the scene! Will ping you when we know more...

[georgi.zhekov]

Thanks a lot for the scene - we have reproduced in our side as well.

There are a few workarounds you can use until we fix the problem.

1.Change the adaptive lights option in the V-Ray Global switches Advanced tab - if you set it to Full lights it should work correctly
2. Use Brute Force GI instead of Light Cache
3. You can change the scattering option in the Smoke color rollout of the Volumetric Options to Raytraced instead of Approximate (note that this will change the look of the volume a bit)

Using either one should get rid of the artifacts.

Cheers!

[egz]

Great! And thanks for the workarounds!