[PHI-5329] Multiple volumes LC calc stuck

[psanitra]

I`m having issues with rendering multiple volumes at the same time when they are overlapping and their OBJs have same(zero) world transforms. Volumes are just density and their shading is GI(multiscatter).
Each volume renders fine on it`s own, LC will run sub 5 second. But when i turn on both volumes at the same time LC will be stuck on start(progress bar not moving) .
Overlap seems to be the culprit here. If i move one of volumes for example 0.01m up, LC will work again...

latest nightly on 18.0.391

[Gosho.Genchev]

Hey, Peter,

we managed to reproduce the problem here. I'll inform you once it's been resolved.

Thank you!

[psanitra]

Gosho.Genchev Any progress on the issue, it`s becoming a real problem for me on current project.....

I figured out that for some reason turning on probabilistic volumetric in the ROP settings, will solve this and LC will go trought.., without probabilistic ON it will get stuck....., hope that helps you locate the issue.

[Gosho.Genchev]

Hey, Peter,

reducing the Opacity of the smoke, or the Light Cache Depth also resolves this - would either of those workarounds do the job for you for the time being ? I've pinged the dev team but I can't say for certain when this will be resolved.

I hope you don't mind me asking - what is your scene setup that requires volumes perfectly overlapping each-other ? I'm counting on us being able to optimize things if we knew what the use-case is.

Thank you!

[psanitra]

For my situation - my volumes are not perfectly overlaping, Far from it! they are maybe overlaping 5%, it`s nothing crazy Just density vdbs on the ground with bit of overlap.Reducing opacity will not work, i`m rendering those volumes almost as solid volume, very dense. Light cache depth also not, i`m actually using GI multiscatter on shader and need depth, i cannot use approximation for this case, too complicated..
One workeround i use is merging all vdbs into new GEO node and rendering as single HUGE volume. Painful but at least it works.