Vulkan Mobile backend: LightmapGI is not sampled during rendering if a DirectionalLight3D with shadows enabled is visible

[Calinou]

Godot version

4.0.dev (2a9dd65)

System information

Fedora 34, GeForce GTX 1080 (NVIDIA 470.74)

Issue description

If a DirectionalLight3D with shadows enabled is visible, LightmapGI won't be sampled during rendering. This means the scene will not receive lighting from the lightmap (but it will still ignore environment lighting).

Vulkan Clustered backend

Vulkan Mobile backend

Edit: I've found that this is linked to directional light shadows.

DirectionalLight3D hidden

DirectionalLight3D without shadows visible

DirectionalLight3D with shadows visible

Steps to reproduce

• Import a glTF scene. Set the light bake mode to Static Lightmaps in the Import dock and click Reimport.
• Add a LightmapGI node.
• Bake lightmaps.
• Switch to Vulkan Mobile backend in the project settings (search for back end).
  • Note: The MRP linked below already uses the Vulkan Mobile backend by default.
• Restart the editor. Notice lightmaps no longer contribute to the static objects' lighting.

Minimal reproduction project

test_vulkan_clustered_vs_mobile_lightmap_sampling.zip

With .godot/ included to workaround importing issue: https://0x0.st/orQD.zip _{(link expires in September 2022)}

[luketrueaxis]

Workaround: Create a duplicate mesh with shadow casting only, make invisible. Bake light mapping. Turn shadow casting off on the original mesh. Make duplicate mesh visible. Works for me. (Revert the visibility and shadow settings to bake again)

We wasted a bunch of time on this before realizing it seems to be a bug. Surprised it still seems broken all this time later. Got the idea for the work around later after it was discovered disabling shadow casting on the static object enables light maps, while still letting it receive light map shadows from other objects.

[Lasuch69]

I will take a look into it.

Edit: It is reproducible when selecting any mesh instance in the editor, however I can't find where the issue is. The fact that there are no errors in the editor and in the validation layers isn't helping either. Now that I think about it I should've used --verbose flag.