Vulkan Mobile backend: Fog is only rendered on the background sky, not 3D objects

[Calinou]

Godot version

4.0.dev (2a9dd65)

System information

Fedora 34, GeForce GTX 1080 (NVIDIA 470.74)

Issue description

Fog (the non-volumetric kind) is not applied to 3D objects when using the Vulkan Mobile backend. It works when using the Vulkan Clustered backend.

Vulkan Clustered backend

Vulkan Mobile backend

Steps to reproduce

• Add a MeshInstance3D node with any PrimitiveMesh resource inside.
• Add a WorldEnvironment node. Enable Fog (not Volumetric Fog) in the Environment resource. Increase the density to something easily visible such as 0.05.
• Move the camera away from the object. Notice fog becoming stronger over distance.
• 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 fog only affects the background sky, not the object.

Minimal reproduction project

test_vulkan_clustered_vs_mobile_fog.zip

[clayjohn]

This has been fixed at some point. Testing in RC3 and fog looks the same in Mobile and Forward+