Blocky artifacts in various render passes when rendering Mantaflow volumes in Cycles #101484
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Reference: blender/blender#101484
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Simplified Report
blockyVolumeShadowPass.blend
fluid_noise_0060.vdb
Original Report
System Information
system-info.txt
Blender Version
Broken: 3.1, 3.4.0 Alpha, branch: master, commit date: 2022-09-27 23:42, hash:
5beaecb33eWorked: most likely never
Short description of error
Rendering imported vdb generated with Mantaflow in Cycles gives blocky artifacts in various passes.
Most visible artifacts are in shadow pass and denoising albedo. Less visible can be seen in volume direct and indirect.
This bug is particularly nasty as the artifacts are mostly invisible in beauty pass.
However when volume have high density and is illuminated with intense light the artifacts starts to appear in combine pass.
Artifacts in denoising albedo pass can ruin seemingly good volume render.
I wasn't able to replicate the artifacts in EEVEE.
Here is how the bug looks with Quick smoke on default cube (scene in attached blend file):
shadow pass
denoise albedo pass
And here is an example how this bug might affect production scene:
shadow pass
denoise albedo pass
volume direct
volume indirect
beauty (cropped)
Exact steps for others to reproduce the error
Reproduce render artifacts:
F12Render Layeroutput inCompositorif neededRecreate vdb (optional):
Properties->Physics Properties->Fluid->Cacheset path for cacheBake Alland wait until bake is completednoisefolder, pick one file (better to pick one from the end where the smoke have more complicated shape)volume_bug_render.blend
volume_bug_sim.blend
Added subscriber: @silex
Added subscriber: @mod_moder
Changed status from 'Needs Triage' to: 'Needs User Info'
Can you change the example files or attach your volumetrics. These files are located separately on the disk and you did not send them. Without this, these files do not reproduce the problem.
Changed status from 'Needs User Info' to: 'Confirmed'
Added subscriber: @SteffenD
Hello just an update here, I've looked into some production scenes where this is a problem with VDB overlaps once they get to a certain complexity eg. the main wdas cloud but not wdas_sixteeth if you want to know what level of complexity this is seen in. Overlaps onto both regular surface meshes and other vdbs.
I've narrowed it down to the mesh that gets generated around the volume. Using a simple bounding box mesh approach, the artifacts disappear.
I've only got this working with Cycles Standalone currently, but it shouldn't take too much effort to land it into Blender with a UI toggle:
https://projects.blender.org/boberfly/cycles/src/branch/volume_boundbox_mesh
I suppose there is a speed loss due to empty space now getting calculated, but in-practice I believe the mesh generation could be seen as a speed loss for time to first pixel or excess memory used for the mesh once the VDB hits a certain complexity. Maybe we can figure out a way to generate this mesh at a lower depth complexity? I'm not that savvy with OpenVDB's, that's something which could be looked into also...
Hey @boberfly , it's best to create a PR so that potential reviewers can see it.
@mod_moder I'd like to test with more VDBs first before I make one
@boberfly please create a PR. can't believe this issue is still there even in 4.0. it has been around in one form or another at least since 2018 reported here multiple times.
is there a way for a workaround currently?
hope to see it fixed for good soon!
Same issue. Just finished my render. Years? Well, time to move to UE.
Blender 4.0 with VDB files. As you can see, it has some blocky shapes around the cloud, almost
Like large pixels. Turning up the volume rate made no difference.