CPU lightmapper ray generation is not deterministic, making comparisons more difficult

[Calinou]

Godot version

3.4.stable, 3.5.beta (71d8ccb)

This does not occur on the master branch (tested on 2a9dd65). Noise appears always in the same location across bakes there.

System information

Fedora 34, GeForce GTX 1080 (NVIDIA 470.74)

Issue description

CPU lightmapper ray generation is not deterministic, making quality comparisons more difficult. This means that even if you don't change any geometry or lightmap baking settings, the noise will appear with a different pattern every time you bake lightmaps. This is more noticeable when not using denoising, but it still has an impact when denoising is enabled.

Denoising disabled

Bake 1

Bake 2

Denoising enabled

Bake 1

Bake 2

Steps to reproduce

• Create a mesh in Blender and export it as glTF (required for UV mapping).
• Configure the bake mode in the glTF's import options to Gen Lightmaps and click Reimport.
• Add a BakedLightmap node. Uncheck Use Denoiser to make the issue more appearant.
• Add an OmniLight with bake mode set to All (Direct + Indirect). This makes the issue more visible than the default Indirect bake mode.
• Click Bake a first time. Take a screenshot of the editor (Ctrl + F12). Don't move the camera.
• Click Bake a second time. Take a screenshot of the editor (Ctrl + F12).
• Compare the two screenshots together.

Minimal reproduction project

test_lightmap_noise_pattern.zip