Overlapping Light2Ds on a "light only" Sprite2D blows out sprite's alpha

[romlok]

Tested versions

Reproducible in:

• v4.2.1.stable.official [b09f793]

System information

Godot v4.2.1.stable - Debian GNU/Linux trixie/sid trixie - X11 - Vulkan (Forward+) - dedicated NVIDIA GeForce GTX 1060 (nvidia) - Intel(R) Core(TM) i5-8400 CPU @ 2.80GHz (6 Threads)

Issue description

If you have a Sprite2D which uses the "Light only" light_mode on its material, multiple overlappingLight2Ds will increase the sprite's alpha beyond that of the sprite's texture, even if both lights are set to blend mode "Mix".

Maybe I'm misunderstanding something, but under these circumstances I would expect that the alpha of the light-only sprite should be capped at the original texture's alpha.

Steps to reproduce

1. Create a Sprite2D with semi-transparent areas
2. Give the sprite a CanvasItemMaterial with a "Light Only" light_mode
3. Add two solid white PointLight2Ds to the scene
4. Give both lights a blend_mode of "Mix"
5. Overlap the lights on top of a semi-transparent area of the sprite
6. 👀

Minimal reproduction project (MRP)

Single scene: lights_overlap.zip

[dalexeev]

Light only mode was not properly fixed, see #75181. Maybe the workaround mentioned in this comment will help you.

[romlok]

Light only mode was not properly fixed, see #75181. Maybe the workaround mentioned in this comment will help you.

Unfortunately, setting the sprite to "add" instead of "mix" just aggravates the blown out alpha: