Add an editor setting to limit the maximum GPU usage ratio for lightmap baking

[Calinou]

Related to #3335, which was about the CPU lightmapper and is now implemented.

Describe the project you are working on

The Godot editor 🙂

Describe the problem or limitation you are having in your project

The GPU lightmapper uses 100% GPU while baking lightmaps. Since modern desktop environments and applications often rely on GPU acceleration, this makes the desktop unresponsive while lightmaps are baking.

Describe the feature / enhancement and how it helps to overcome the problem or limitation

Add an editor setting to limit the maximum GPU usage ratio for lightmap baking. This is a floating-point value that should be set between 0.1 (10% GPU usage) and 1.0 (100% GPU usage).

Values between 0.6 and 0.8 should make it possible to keep a responsive desktop without slowing down bakes too much.

Additionally, this setting can be used to limit heat/noise emissions when baking lightmaps.

Describe how your proposal will work, with code, pseudo-code, mock-ups, and/or diagrams

This probably involves sleeping between iterations of the GPU lightmapper to ensure the GPU isn't always busy.

If this enhancement will not be used often, can it be worked around with a few lines of script?

No, as the lightmapper is part of the engine and its behavior can't be overridden from a script.

Is there a reason why this should be core and not an add-on in the asset library?

See above.

[atirut-w]

Maybe this deserves more attention after all. Baking lightmap for a moderately-large scene on Fedora KDE Spin with RX 6700 XT absolutely cripples the desktop experience. Everything including the cursor lagged down to the single digits, to the point of being unusable. This is a huge problem considering you currently cannot cancel bakes.

Any chance someone will pick this up?

[Calinou]

Baking lightmap for a moderately-large scene on Fedora KDE Spin with RX 6700 XT absolutely cripples the desktop experience

Are you on X11 or Wayland? If on X11, try disabling compositing by pressing Alt + Shift + F12.

[atirut-w]

I'm on Wayland