Partly transparent objects appear to glow in the dark when HDRI environment lighting is present (BVH2/Some GPU rendering backends) #95462
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Reference: blender/blender#95462
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System Information
Operating system: Windows 10
Graphics card: NVIDIA GeForce RTX 2080
Blender Version
Broken: 3.0.1, branch: master, date: 2022-01-25 (latest version on blender.org)
Worked: Any version before 3.0 as far as I can tell. Things are fine in 2.9x
Problem: Partly transparent object in shadow glows when HDRI based world lighting is present. With hair cards it is especially noticeable. Test file is not as stark, but issue is still present.
Exact steps for others to reproduce the error
Make a mesh that is partly transparent, where you can see through multiple layers at a time, like a plane with an array modifier so it stacks like a layer cake, enclose it in a box to block all environment light
Give it a partially transparent shader. Ideally an alpha around .1
Position camera inside the box, observing that it is dark inside the box, even if you have a world background lighting the scene
Now set the world background to have an HDRI plugged into the background node. Behold, the mesh glows, but only where you are looking through multiple layers.
It is as if an image world background is illuminating an object when it shouldn’t.
And it only seems to do this when an object has multiple layers of transparency that you are looking through. Turn the array modifier off and it goes dark.
Example image:
Example of issue in a practical setting. This character's hair does not contain any emissive shader nodes. Loading the same character file in 2.93 without making any changes does not show the "glow".
Example file:
bug test file.blend
Added subscriber: @AdrianPreston
Added subscriber: @iss
Changed status from 'Needs Triage' to: 'Needs User Info'
Can't reproduce this issue. Does this happen with any HDRI? In provided file none is packed.
Please click on Help > Save System Info and upload saved file.
Whoops, sorry. I forgot about the HDRI. Yes, it does it with any HDRI that I have tried.
bug test file.blend
I hope I packed that correctly.
Just switching to render preview in the viewport window ought to show it. Here is what it looks like for me.
Here is the system info file:
system-info.txt
One new piece of information: Switching from GPU rendering to CPU rendering makes the problem go away.
Added subscriber: @Alaska
Changed status from 'Needs User Info' to: 'Confirmed'
I can confirm the issue when rendering with CUDA with the system information below:
System Information
Operating system: Linux-5.15.0-3-amd64-x86_64-with-glibc2.33 64 Bits
Graphics card: NVIDIA GeForce RTX 3060/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 510.47.03
Blender Version: 3.2.0 Alpha, branch: master, commit date: 2022-02-02 02:53, hash:
9b779993f0
Upon further investigation the issue affects the CPU if the BVH structure is changed to BVH2. As such it will also affect HIP and Metal?
Partly transparent objects appear to glow in the dark when HDRI environment lighting is presentto Partly transparent objects appear to glow in the dark when HDRI environment lighting is present (BVH2/Some GPU rendering backends)Added subscriber: @Raimund58
@AdrianPreston when investigating a similar report, it was found that increasing the
Transparent light bounces
property in cycles gets rid of the issue when rendering with an effected rendering backend.It's not a fix, but it's a work around you, and others, can use if you face this issue with future projects.
At least in my case increasing the transparent bounces made it dimmer, not totally go away. I suppose I could turn transparent bounces up to something absurd like 100 and see how Blender deals. But this isn't a tech support forum, so I'll work on it on my own and see how good results I can get. Thanks for the workaround.
This issue was referenced by
04e89c5b06
Changed status from 'Confirmed' to: 'Resolved'