[TRACKER] Vulkan fog and volumetric fog issues

[Calinou]

This issue tracks issues related to standard (non-volumetric) fog in the Vulkan and OpenGL renderers, as well as volumetric fog in the Vulkan Clustered backend.

Bugs

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1. Volumetric Fog texture oddly fills with pitch black when Decal is present in camera frustrum #54496
   archived topic:3d topic:rendering +3
2. Vulkan: FogVolume with volumetric fog temporal reprojection enabled causes the editor to redraw continuously, wasting CPU and GPU resources #54893
   discussion enhancement performance topic:3d topic:rendering +5
3. Vulkan Mobile backend: Fog is only rendered on the background sky, not 3D objects #55870
   bug topic:3d topic:rendering +3
4. Vulkan: SpotLight3D + WorldEnvironment fog causes jaggedness due to clustering issues #59262
   bug confirmed topic:3d topic:rendering +4
5. Vulkan: Flashing Lights through Fog while Alt+Tabbed #61222
   bug confirmed topic:3d topic:rendering +4
6. Vulkan: Volumetric fog without visible FogVolume nodes does not make the editor redraw until it has fully converged #62794
   bug confirmed topic:3d topic:rendering +4
7. Vulkan: viewport flashes white when being resized with volumetric fog enabled #63739
   bug confirmed topic:3d topic:rendering +4
8. Volumetric Fog goes dark on the edges when a Fog shader is used #64634
   documentation enhancement topic:3d topic:rendering +4
9. OpenGL: Environment fog does not affect sky rendering #66456
   bug confirmed good first issue topic:3d topic:rendering +5
10. OpenGL: Fog color is incorrect if one of the components is exactly 0 #66459
    bug topic:3d topic:rendering +3
11. OpenGL: Fog color is inverted if density is exactly 0 #66462
    bug topic:3d topic:rendering +3
12. Vulkan: Volumetric Fog is reflected too much in SSR #66934
    bug confirmed topic:3d topic:rendering +4
13. Vulkan: Volumetric Fog breaks when number of visible VoxelGI nodes changes #69565
    bug confirmed topic:3d topic:rendering +4
14. Volumetric Fog shows artifacts at camera edge at certain angles inside Fog Volumes #74790
    bug confirmed topic:3d topic:rendering +4
15. Vulkan: Volumetric fog glitches out in builds that use optimize=none, but not other optimization levels #76243
    bug needs testing topic:3d topic:rendering +4
16. SpotLight3D turns negative, and creates black boxes on small angles with volumetric fog #78500
    bug confirmed topic:3d topic:rendering +4
17. DirectionalLight3D affecting FogVolume in all VisualInstance3D Layers #82217
    documentation topic:3d topic:rendering +3
18. Volumetric Fog stops working when enabling shadows for positional lights until 3D buffers are recreated #83685
    bug confirmed topic:3d topic:rendering +4
19. Volumetric fog stops taking lights into account when changing scene under specific circumstances #83990
    archived bug topic:3d topic:rendering +4
20. Flashing lights in volumetric fog when attenuation is above 3 #87578
    bug topic:3d topic:rendering +3

Discussions

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1. Vulkan: Environment fog's Sun Scatter isn't fully drawn over the background sky #44466
   archived discussion topic:3d topic:rendering +4
2. Fog volume breaks additive unshaded materials #56374
   confirmed discussion topic:3d topic:rendering +4

Enhancements

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1. Add optional scattering (distance blur) to non-volumetric fog godot-proposals#1698
   topic:3d topic:rendering +2
2. Control fog (both simple and volumetric) from shaders godot-proposals#2643
   topic:3d topic:rendering +2
3. Add a hard cutoff property to Environment fixed fog (for open world fog fading) godot-proposals#3429
   topic:3d topic:rendering +2
4. Allow controlling fog intensity with traditional start/end distance and curve in Godot 4 godot-proposals#4619
   topic:3d topic:rendering +2
5. Add unshaded mode to volumetric fog rendering godot-proposals#5079
   topic:3d topic:rendering +2
6. Make volumetric fog GI Inject take LightmapGI into account godot-proposals#5214
   topic:3d topic:rendering +2