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Baked Ambient Occlusion strength does not change when the alpha value is changed in the custom MetaPass file
Steps to reproduce:
1. Open the attached project “AlphaIssue“
2. Open the “Assets/Scenes/SampleScene.unity“ Scene
3. Open Window > Rendering > Lighting > Generate Lighting
4. Observe the transparency of the “Transparent Color alpha“ GameObjects in the Scene view
5. Open the “Assets/CustomSetup/LitMetaPass.hlsl“ file
6. Change the alpha value from 0.0 to 0.5 (“col.a = 0.0” to “col.a = 0.5“)
7. Repeat the 3-4 steps
Expected result: Ambient Occlusion strength changes thus making the GameObjects more or less transparent
Actual result: Ambient Occlusion strength stays the same
Reproducible with: 2020.3.43f1, 2021.3.17f1, 2022.2.5f1, 2023.1.0b1
Reproducible on: Windows 10
Note: In the URP/Lit Shader decreasing the alpha channel in the base map color decreases the Ambient Occlusion power when Baked
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The alpha used in the lightmapper never comes from the MetaPass but is taken out of the alpha channel of Material.MainTexture.
That said there is a way to customize the transparency just for the lightmapper by adding property named TransparencyLM to a material's shader.