VoxelGI has a visible effect on the scene when energy = 0

[JustASquid]

Tested versions

4.4-stable

System information

Godot v4.4.stable.mono - Windows 10 (build 19045) - Multi-window, 2 monitors - Vulkan (Forward+) - dedicated NVIDIA GeForce RTX 4090 (NVIDIA; 32.0.15.6094) - AMD Ryzen 9 7950X 16-Core Processor (32 threads)

Issue description

VoxelGI has a visual impact on the scene when energy=0.

This is an issue as I want to fade out my voxelGI lighting under certain circumstances. When the voxelGI is fully faded out, setting it to invisible is important to reduce performance impact on the scene. But right now this causes a visual hitch as it's not possible to smoothly transition between voxelGI visible -> voxelGI invisible.

Steps to reproduce

Whjen a voxelGI node in a scene has energy=0, the scene still looks different depending on if the voxelGI node is visible or invisible.

Enabled:

Disabled:

Minimal reproduction project (MRP)

voxelgi_energy_issue_mrp.zip

[Calinou]

This is done by design. Reducing VoxelGI energy reduces the brightness of its global illumination, but it does not blend between the fallback environment lighting and VoxelGI. Otherwise, you wouldn't be able to reduce the VoxelGI energy without introducing additional light leaking (since environment sky lighting is global).

Blending VoxelGI with other GI sources requires a dedicated implementation, ideally one that is localized similar to ReflectionProbe blend distance.

This is an issue as I want to fade out my voxelGI lighting under certain circumstances.

Out of curiosity, what circumstances are you looking to disable VoxelGI under?

[JustASquid]

@Calinou Basically I have an outdoor scene with 2 lighting situations, "daytime" and "nighttime". During the day I don't need voxelGI as the sunlight is sufficient. During the night, things like lights etc. become much more relevant and so GI reflections etc. are important.

I suppose I could just have voxelGI on all the time, but I was hoping to optimize slightly by disabling it during the day. Anyway your explanation is sufficient that this is not a bug, so feel free to close the issue.

[Calinou]

Closing per the above comment. Feel free to open a proposal if needed.