LightmapGI: Custom Sky environment does not contribute to ambient light

[michaelharmonart]

Tested versions

Reproducible in the Godot v4.4.dev (7f5c469) build (built from the AUR and currently only a few commits behind)

System information

Godot v4.4.dev (7f5c469) - Manjaro Linux #1 SMP PREEMPT_DYNAMIC Mon, 09 Dec 2024 11:58:37 +0000 on Wayland - X11 display driver, Multi-window, 1 monitor - Vulkan (Forward+) - dedicated NVIDIA GeForce RTX 3060 (nvidia; 565.77) - AMD Ryzen 9 9900X 12-Core Processor (24 threads)

Issue description

Currently setting the environment mode of the lightmapGI node to custom sky results in completely black bakes (assuming there are no other lights contributing bounces)

This doesn't happen when using the scene sky.

Here's a scene with the lightmapGI node set to use the scene sky:

And here is the same scene when setting the lightmapGI node to use a custom sky (which is identical to the scene sky here so it's even more clear)

Steps to reproduce

Create an object with UV2, and LightmapGI node.
Set the environment mode to "Custom Sky" (it doesn't matter what kind of sky material you use here, they're all broken)
Bake lighting
Notice the object is dark and not illuminated by the sky at all. (Which is clear if you change the sky energy to a stupidly high number and the object still doesn't change in brightness.)

Minimal reproduction project (MRP)

ambient-light-baking-issue.zip

This is the same scene as above but with the custom sky already set.

[AThousandShips]

Please upload an MRP to help in testing and fixing this, to ensure everything is exactly as you are using it

Preparing an MRP is important and helpful as multiple people will almost certainly be going through and testing this bug and any potential fix, and it helps to have one single reference point to work from

[michaelharmonart]

@AThousandShips I've added an MRP

[Calinou]

• Related to LightmapGI ignores ambient light when using the Scene environment mode #83485.