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Votes
0
Found in
2020.3.46f1
2021.3.21f1
2022.2.11f1
2023.1.0b8
2023.2.0a6
Issue ID
UUM-30771
Regression
No
[URP] ClearCoat material causes metallic discolouration when Coat Mask is set to 1
Reproduction steps:
1. Open user attached "URP Beta.zip" project
2. Select Assets > Materials > “Clearcoat1” material
3. Set “Coat Mask” to 1
4. Select Assets > Materials > “Clearcoat2” material
5. Set “Coat Mask” to 1
Expected result: A clearcoat is added to the materials
Actual result: Metallic colours below a certain threshold turn completely black
Reproduced with: 2020.3.46f1, 2021.3.21f1, 2022.2.11f1, 2023.1.0b8, 2023.2.0a6
Reproducible on: macOS 13.2.1 (Intel), Windows 11 (by user)
Notes:
* Can’t test Player, blue screen when built
* Not reproducible in HDRP, no ClearCoat material
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Resolution Note:
The base material is 100% metallic, which means there is no diffuse component (black) and the specular highlight (reflection) is colored.
The coat has a white specular, but also no diffuse (pass through).
Both are 100% smooth so both have about the same size specular highlight.
The light here reflects off the coat, masking the metallic base layer specular. In non-specular highlight areas the base layer black diffuse is shown through the coat layer.
The coat adjusts base roughness and darkens the base layer. This can be seen in the bug repro case if you look closely. The spheres and material are not fully black in the highlight area.
In this example there is only a single point light that lights the spheres and produces a specular reflection. Only that area is colored for a metallic material, rest of the sphere is black.
In a more realistic scene there is also indirect light from the environment. This can be achieved with a skybox.
Open Window->Rendering->Lighting->Environment.
Set a sky box texture.
At the bottom, click Generate Lighting->Bake Reflection Probes.
This will give a more realistic look which I suspect matches closer to the expectations.
In general the PBR material model used in URP does not cover all real world materials. And some parameterizations of the model can produce materials that have no practical real world counterpart.