Vulkan Mobile backend: Radiance prefiltering worsens rough reflection quality

[Calinou]

Godot version

4.0.alpha (0393057)

System information

Fedora 34, GeForce GTX 1080 (NVIDIA 495.46)

Issue description

Radiance prefiltering looks good on the Vulkan Clustered backend, but it doesn't see the same improvements in the mobile backend (running with desktop default settings). Reverting #58177 restores filtering quality to what it was before in the Vulkan Mobile backend (although the Real-Time filter mode still exhibits the issue).

Vulkan Clustered

High Quality	Real-Time

Vulkan Mobile

High Quality	Real-Time

Closeups

High Quality

Real-Time

Vulkan Mobile (with #58177 reverted)

High Quality	Real-Time

Closeups

High Quality

Real-Time

Steps to reproduce

• Use an HDRI panorama sky from a website such as Poly Haven.
• Add meshes with rough materials to the scene.
• Switch to the Vulkan Mobile backend in the project settings (search for back end).
• Restart the editor.

Minimal reproduction project

tests/3d/test_pbr_radiance_high_quality.tscn and tests/3d/test_pbr_radiance_real_time.tscn in https://github.com/Calinou/godot-rendering-tests

[clayjohn]

This may be related to mobile not using the full HDR range. I wonder if your clamping PR (#58164) would fix this

[Calinou]

This may be related to mobile not using the full HDR range. I wonder if your clamping PR (#58164) would fix this

I tried and the clamping doesn't resolve the issue. This is made more evident by #67172, which only uses a SDR sky (ProceduralSkyMaterial does not use overbright colors in its default settings).

[Calinou]

I checked the minimal reproduction project and can confirm this was fixed by #68511.

Screenshots from 4004f3f:

Forward Clustered

High Quality	Real-Time

Forward Mobile

High Quality	Real-Time