High Resolution VDB renders blocky artifacts in Cycles #81590
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Reference: blender/blender#81590
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System Information
Operating system: Windows-10-10.0.18362-SP0 64 Bits
Graphics card: GeForce GTX 1080/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 452.06
Blender Version
Broken: version: 2.90.1, branch: master, commit date: 2020-09-23 06:43, hash:
3e85bb34d0
Worked: 2.83.5
Rendering a high-res Open VDB file in Cycles creates blocky artifacts
Rendering an Open VDB cloud using both a low-resolution version and a high-resolution version, the low res version renders fine, however the high resolution version renders with blocky artifacts in Cycles. EEVEE is fine. Back in Cycles, changing the Step Size from its default of 0 to a value of 0.0001 does not improve the quality.
Cycles Render:
Look at the left side of the cloud and you'll clearly see the blocky artifacts.
Product Render showing how it should look (low and high res):
Here's an EEVEE render, same high res model but different scene lighting.
Here's the same scene with the cycles render. Again, you can clearly see the blocky artifacts.
Here's the viewport display using Cycles. You don't see any artifacts in the viewport display render.
Exact steps for others to reproduce the error
Open the attached blend file.
Make sure to link the high res VDB to the object in the scene
Render and look at the blocky artifacts
Now swap out the VDB for the low res object.
Render again.
Notice that there are no artifacts.
VDB.7z
Added subscriber: @stevewarner
#86770 was marked as duplicate of this issue
This seems to be an issue with GPU rendering. I rendered with Cycles using CPU instead of GPU and got no blocky artifacts.
For comparison, here's the CPU Render:
And here's the GPU render:
Added subscriber: @iss
Changed status from 'Needs Triage' to: 'Needs User Info'
I can reproduce the same artifacts with CPU in latest 2.91.
I had to set clipping to 0 otherwise I got this:
With my GPU I will probably render for a week so I won't test that.
Please re-check CPU and GPU result with alpha build from https://builder.blender.org/download/
I tested today with the October 12th build of 2.91 and can confirm that I'm still getting artifacts with both GPU and CPU.
The scene in the attached file has the VDB object's step size set to 0.001. For these tests, I set that back to 0. I also set the clip value to 0.
Here's the CPU render:
Here's the GPU render:
And just for kicks, I went to the rendering settings (the globals) and set the Max Step size to 2048 (double the default) and the Step Rate to 0.5 (half the default). Both should increase detail in the final render. Here's what I got.
Not what I was expecting. I figured by increasing the step size and rate I'd simply get more detail. But here, the entire shading changed. The volume blows out on the right an now has dark splotches along with artifacts on the left.
Also, for what it's worth, I went back to 2.90 and tried rendering with CPU and GPU. Both now have artifacts. Even if I disable GPU rendering, I still get artifacts. So I'm not sure why I got a clean render using CPU in my previous post. But it's not working again regardless what I set.
Out of curiosity, I opened the scene in 2.83.5. Rendered there with GPU and CPU. Absolutely no artifacts.
GPU:
CPU:
Clearly something changed in the way volumes are handled in 2.9x that is causing rendering problems. It may be worth noting that the 2.83 GPU render took 1 minute whereas the 2.90 render takes 47 seconds.
Also worth noting, the 2.83 renders are less noisy - not just blocky artifacts, but less noise - than the 2.83 renders. Compare the dark parts of the cloud in 2.9x renders to that in the 2.83.5 renders. Overall, the image is much cleaner in the 2.83 render.
Thanks for update. if you get issues on CPU as well I can at least confirm this, even though my result looks a bit different.
Changed status from 'Needs User Info' to: 'Confirmed'
Added subscriber: @Daniel-Gascoyne
Added subscribers: @andywalshart, @mano-wii
Added subscriber: @GaryRitchie
Added subscriber: @brecht
Changed status from 'Confirmed' to: 'Resolved'
I can confirm the issue in 2.90, but seems to be solved in 2.93 and 3.0.
Added subscriber: @Iago-Diogo-de-Vasconcelos-Mota
Hello, I think this bug is still present in Blender 3.1.2 and Blender 3.1. Keep in mind that this is a very thin sheet of VDB data, so the issue could also be related to that.
This is what the render looks like in the cycles rendered viewport mode (these artifacts are the same when rendered through f12 as well). Keep in mind that this issue exists in CPU and GPU renders, and the Clipping in the VDB settings is set to 0. It's also unaffected by the step rate and number.
And this is what it looks like in the solid shading mode.
Just for reference, this is what it looks like in EEVEE. There aren't any artifacts here either. However, because of how difficult it is to render high-quality volumes in EEVEE, I can't rely on this, as I will be increasing the smoke resolution here in the future. So, I'm just hoping that this gets fixed in Cycles.
Here is the project file. I'm sending the first four frames of the simulation as well (the rest is about 30 Gb of data, so I can't send the whole thing). You may be able to observe that, on frame 2, there's plenty of simulation data already visible in the solid shading mode. However, once rendered (either through f12 or in the viewport), the sheet of smoke is not even visible at all. Only starting from frame 3 does it show. I think this might be due to the same issue, as, between frames 2 and 3, the smoke expands to upper voxels slightly and gains some density. So, as it spreads out, it becomes less thin, and easier for Cycles to render, if I'm assuming the cause of this problem correctly.
CyclesBlockyVolumeBug.zip
@Iago-Diogo-de-Vasconcelos-Mota, please make a new bug report.