ambient_light_sky_contribution ignored

[kalbfled]

Godot version:
3.3rc8 (probably 3.2.3 too, but I didn't test)

OS/device including version:
Nvidia GTX 980, driver 450 in Ubuntu 18.04
GLES2 renderer (didn't test GLES3)

Issue description:
The ambient_light_sky_contribution of the default environment does not seem to have any effect.

I also filed #47785, which is probably related.

Steps to reproduce:

1. Open a scene, and delete or shutter all lighting except the default environment.
2. Verify that "Sky Contribution" is set to 1, which means the ambient energy should not affect the scene.
3. Set the ambient color to 0xffffff (pure white).
4. Adjust the ambient energy, and observe the effect.

UPDATE

I tried to recreate this in my test scene this morning, and now I have a different but related problem. I'm not seeing an effect from ambient energy with Sky Contribution set to 1, but now I do see an effect from background energy with Sky Contribution set to 0.

[Calinou]

4. Adjust the ambient energy, and observe the effect.

I think this is expected, since the ambient energy affects the final ambient value, regardless of the sky contribution value used. We can amend the documentation to make this clearer.

[kalbfled]

If this is the intended behavior, what is the purpose of the Sky Contribution setting? It seems like I would always need to set ambient energy to 0 if I don't want its effect, and Sky Contribution could be removed in favor of just setting the background and ambient energies independently.

[Calinou]

If this is the intended behavior, what is the purpose of the Sky Contribution setting?

The Sky Contribution setting acts as a "mix factor" between the constant ambient color you configure in Environment and the ambient light contribution brought by the sky (PanoramaSky or ProceduralSky). When set to 0, only the constant ambient color is used. When set to 1, only the sky-provided ambient light is used.

and Sky Contribution could be removed in favor of just setting the background and ambient energies independently.

This could be done, but this would mean you'd have to adjust two properties if you just want to adjust how much each ambient source should contribute to the final ambient lighting (in relation with each other).