WorldEnvironment Glow not working when background is transparent

[Lefl1]

Godot version:
3.1

OS/device including version:
Linux 5.0.5-1-MANJARO
GPU: AMD Radeon R7 260X using AMDGPU driver.

Issue description:
When setting the viewport to have a transparent background, the Glow effect from the WorldEnvironment gets disabled (Possibly other effects to, haven't tested).

Steps to reproduce:

1. Create a scene with a bright object and a WorldEnvironment with Glow enabled.
2. Make the background transparent using get_root().set_transparent_background(true)

Minimal reproduction project:
noglow.zip

[clayjohn]

This comes up periodically. I just stumbled on your issue now. Sorry for the delay. The post-processing effects don't work with a transparent background, this is intentional. Its due to the way the effects are implemented. So this is not so much a bug as a issue with the current implementation.

I don't know if this limitation will be lifted in the Vulkan backend (4.0) but it will be a good thing to look into as that is implemented.

[Ramshell]

Addressing this would be very beneficial for the community since disabling post-process effects in viewports with transparent bg impacts directly in the ability to render more than one camera with different effects. For example, if you want to make a game with a 3d UI, you'll have to decide whether you use the post process effects in the world or in the UI.

[Calinou]

I can still reproduce this as of 4.0.rc2 (Linux, GeForce RTX 4090 with NVIDIA 525.89.02).

Minimal reproduction project (4.0): test_glow_transparent_background.zip

Opaque background	Transparent background

[des1redState]

Ouch, I've just hit this too. My use-case is to overlay a canvas viewport (with own-world & glow) over a 3D scene.