Banding-like effect in Cycles using OpenVDB volumes #100714
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Reference: blender/blender#100714
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System Information
Operating system: Linux-5.15.0-46-generic-x86_64-with-glibc2.35 64 Bits
Graphics card: Quadro RTX 6000/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 510.85.02
Blender Version
Broken: version: 3.4.0 Alpha, branch: master, commit date: 2022-08-29 23:11, hash:
5ae3fa50e2
Worked: unkown
Short description of error
I have some weird looking artifacts going on when importing custom OpenVDB files.
Let's take a look at these screenshots:
b814f64f4a
):5ae3fa50e2
):I am not talking about this giant black thing (but I wanted to show it too because this is also weird).
The point here is about this banding effect:
blender_weird_issue_1.webm
Hypotheses:
Exact steps for others to reproduce the error
#100714.blend
vdb_sample.zip
Added subscriber: @Felix-Olart
I think I have the same sort of issue using another file.
Here is what it looks like:
blender_weird_issue_2.webm
Exact steps for others to reproduce the error
vdb_sample_2.zip
Added subscriber: @iss
Looking at provided VDB, I see there is volume filling the space, which seems to be the black thing you saw in previous versions. Here it is rendered as blackbody
I am not very knowleddgable in this area and not sure how shader is supposed to blend blackbody. I would guess it should be pure emissive color if it has no density, which it does not have, but not sure really, will have to read up on this.
First, thank you very much for your answer.
Ok, so if I understand correctly, this area corresponds to volume, but does not have enough density to be rendered? Or something like that?
I tried to replicate what you have done with the second example I provided, here is the result:
Here is the result when I boost the density (multiplied by 1e9):
So I am not sure to be right seeing this, I thought I would see the whole volume turn red as the density would be > 1 for each voxel.
I tried to set the clipping value of the volume down to 0 instead of 1e-4.
Here is the result:
Thus, it seems to be solving my issue:Screencast from 31-08-2022 08:59:23.webm
I don't really understand why.
Added subscriber: @OmarEmaraDev
Changed status from 'Needs Triage' to: 'Needs Developer To Reproduce'
If I understand correctly, lowering the clipping to zero fixes the issue. Is that correct?
This seems similar to #53472. Voxels in the volume whose value is less that the clipping value are "turned off" and are not rendered resulting in those empty spaces.
So the workaround for now is to never turn off any voxels by lowering the clipping to zero.
I am not sure why that depends on the viewing angle as you have showed though. So I will tag the module for more information.
Banding-like effect in Cycles using OpenVDB volumesto Banding-like effect in Cycles using OpenVDB volumes when clipping is not zeroHum. I tested it on the first sample I provided and it does not give the same result.
Screencast from 31-08-2022 10:27:20.webm
I think with this video we can clearly see the "black bars" which are not visible using the first shader and then revealed using the second shader.
Thus, we can sort of deduce how this banding-like effect is affected by the viewing angle.
So to answer your question, I am not convinced that lowering the clipping value to zero fixes the issue.
About #53472, if I understand correctly, that issue is more related to camera clipping values.
Whereas I was mentioning the clipping settings in the volume properties. I don't know if it is related but I don't think so.
Changed status from 'Needs Developer To Reproduce' to: 'Needs Triage'
Does the scale of the volume object have any effect on the banding effect?
No, it does not seem to have any effect.
Screencast from 31-08-2022 10:46:26.webm
Just a note, looking at the attached files, it seems they include negative values, contrary to a number of OpenVDB file samples I looked at, and those negatives values seems to take the shape of those bands, so I suspect this might have something to do with the issue you are experiencing.
Yes, I think you are pointing out an interesting element. I also checked the values and some of them are negative. I did not managed to see how these data are arranged but that could be something causing my issue.
Maybe this could explain why setting the clipping value to 0 was not giving any result in this video.
Indeed, if the negative values are causing these artifacts, then setting the clipping value to 0 or not won't probably change anything.
That said, is it still normal that the volume is rendered like that for negative values? Because it seems to act like a powerful filter.
I will try to ask the developers about this and get back to you.
Changed status from 'Needs Triage' to: 'Needs Developer To Reproduce'
Added subscriber: @Raimund58
Changed status from 'Needs Developer To Reproduce' to: 'Confirmed'
Banding-like effect in Cycles using OpenVDB volumes when clipping is not zeroto Banding-like effect in Cycles using OpenVDB volumesThis issue was referenced by
b5ff47667d
This issue was referenced by
e665f0f497
This issue was referenced by None@63016
Changed status from 'Confirmed' to: 'Resolved'