Fog obscures unshaded materials in GLES2, also affects Gizmos.

[EzraT]

Godot version:
Godot_v3.1-beta7
Also tested in 3.1-RC1, still present.

OS/device including version:
Linux Mint 19.1
NVIDIA GP106 [GeForce GTX 1060 6GB], Driver version: 415.27

Issue description:

As the title says, unshaded objects get obscured by fog in GLES2.
I'm not sure what the correct behaviour is here, but the GLES3 backend always renders unshaded meshes the same way, whether fog is enabled in the scene or not.

Steps to reproduce:

1. Switch to GLES2.
2. Enable fog in WorldEnvironment node.
3. Add a MeshInstance with an unshaded material to the scene.
4. View the mesh from a greater distance by zooming out.
5. Compare to GLES3.

Screenshots:
GLES3:

GLES2:

[EzraT]

This same problem also happens to Gizmo's, I'm guessing they use the same unshaded render mode. (?)
Look at the camera gizmo turning dark when zooming out:

[EzraT]

@akien-mga Can this issue be re-opened? This still affects editor gizmo's in GLES2:

They turn black when fog is enabled, even when the fog color is set to something different than black.
This happens in the official 3.1 build.

[clayjohn]

Could be related to #31019

Can you rebuild from master but delete the ".gen.h" files from drivers/gles2/shaders first?

[EzraT]

I'm not using a self compiled build of Godot at the moment, but I will re-test this as you described.

[akien-mga]

I'm not using a self compiled build of Godot at the moment, but I will re-test this as you described.

What version are you using then? This issue was fixed in the master branch in May, the fix is not in any stable release yet.

[akien-mga]

I see you added

This happens in the official 3.1 build.

So it's normal, this was fixed in master, and cherry-picked for 3.1.2. The issue's milestone tells you which main branch will include the fix (3.2).