Hello everyone, I’m a casual blender user, my main software is Houdini since 2 years now…But when I saw what blender 2.83 have now a vdb import support…I have to try to render one of my R&D vdb simulation.
First, render volume in cycle with cuda CPU+GPU is a way faster than Arnold on Houdini…that just blow my mind…but sadly when I rendered and played the animation I get some shadows flickering.
Before posting anything, I wanted to better understand cycle and blender and for that I made a smaller simulation (in scale and voxel count) to work with.
First thing I noticed, the shadows flickering are less present on this small sim. I’m not sure that I have cover all the volume rendering with cycle, but whatever I do I kept some shadow flickering. I have Increased the light sampling, the global sampling, change the volume interpolation in cubic, lower the step rate, put more max step, but nothing solve this shadow issue. As I don’t know so much cycle and blender, perhaps I miss some technical tips…or I did something in a bad way.
Check the shadow flickering at the bottom of the render here :
And all the flickering on the big one here :
I share my blender files and the VDB of the small sim. You get also the 50 last VDB of the big one, where the flickering are the most significant. Warning It’s more or less 60Go to download…
I did a quick test with one sun light at 0°angle on Arnold and Cycle.
Cycle seem to “see” and trace opaque spots witch appear only in the shadows.
Perhaps that could be the origin of the shadow flickering.
CPU + GPU is not the best combination for volumes in cycles. CPU has certain optimizations that GPU doesn’t have, and those might be the cause of your flicker. Try only CPU or GPU and see if it’s better then.
Those black spots compared to Arnold stem from the ray bounces being set too low. increasing transparent bounces, if I remember correctly, should take care of it.
Yeahh, that’s seem to work…I sent a render for testing the overall animation. But it’s a bit weird…unexpected for me. As you mention the transparency bounce I did again a test but this time with a very high value. In Arnold 10-12 bounces was enough for all most the case I had until now. For example on the image above it’s the default value 10 bounces). But with cycle I had to push up to 20 transparency bounces to remove all the black spots. During my first tests I pushed the transparency bounce 8 to 12…and expected that work a bit like Arnold. But as I didn’t get any difference between 8 and 12 I’ve moved on. Thanks a lot for your help
Hey Damien!
Thanks for sharing!!
I will also step into VDB in Blender from Houdini. Due to missing motion blur, it´s quite impossible to do some renders for FX stuff in Blender. Also comparing stuff to Arnold, Mantra or Vray and so on make it difficult. I checked also the latest 2.91 alpha, but it seems not to render motion blur either.
