Vulkan: LightmapGI environment lighting samples the sky upside-down

[Calinou]

Godot version

4.0.dev (8485d0c)

System information

Fedora 34, GeForce GTX 1080 (NVIDIA 470.74)

Issue description

When using LightmapGI, Environment lighting is sampled upside down, regardless of the mesh's rotation. In most scenes, this causes environment lighting to be darker than expected when viewed from above, and brighter than expected when viewed from below.

Left: Real-time ambient light, right: baked ambient light

Steps to reproduce

• Add a WorldEnvironment node with a PanoramaSkyMaterial.
• Add a DirectionalLight and set its Energy to 0, so that the preview light is disabled and it does not intefere with baking.
• Add a LightmapGI node. Set the environment mode to Scene.
• Instance two identical 3D scenes imported with the Static Lightmaps option. Right-click one of them in the Scene tree dock then enable Editable Children. Select its child mesh and set Global Illumination > Mode to Disabled, so that it is not included in baking. This step is not required, but it's useful to compare real-time ambient lighting with baked ambient lighting.
• Select the LightmapGI node and click Bake at the top of the 3D editor viewport.

Minimal reproduction project

test_lightmap_environment_upside_down.zip

[williamd67]

It looks like that the panorama texture is upside down (see picture). I do not know if that is as expected, if so the code need to correct for that, else we have to verify why this texture is like this.