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:
