Godot: PhysicalSkyMaterial is black (but ProceduralSky displays normally)

[creikey]

Godot version:

Current Master: a17fba3f21241beb68127d30b8d07db267e65e35

OS/device including version:

Windows 10, Vulkan, iGPU intel 10th gen ( intel hd graphics ):
i5-1035G1 CPU @ 1.00GHz, 1.19GHz

Issue description:

The sky is black from the default PhysicalSkyMaterial, I was expecting the sky to look like a sky.

Steps to reproduce:
Create a WorldEnvironment node, add a sky as the background, then add a PhysicalSkyMaterial.

Minimal reproduction project:

no-sky.zip

[Calinou]

I can confirm this on commit https://github.com/godotengine/godot/commit/25d18e34916ab4a2a5a1281b42549b11cdc8d29c with a GeForce GTX 1080 (NVIDIA 440.100) on Fedora 31.

ProceduralSky doesn't suffer from this issue and displays normally.

[clayjohn]

PhysicalSkyMaterial is a sky material based on the physical interactions of light in the atmosphere. Without a sun, there can be no atmospheric scattering. Therefore, if there is no DirectionalLight in the scene, the sky is black (if you had a night_sky texture set, you would see the stars).

When I initially added the PhysicalSkyMaterial, I was worried this would be confusing for users. Although it makes sense (no sun = no sunlight => only see stars), I can understand why it could be confusing for users.

Earlier I considered 2 solutions, but neither was satisfactory:
1. detect when there are no DirectionalLights in the scene and then add a default sun
This worked well, but it forces a specific behaviour that users may not want (e.g. users may just hide the directional light altogether at nightime as an optimization)

2. show an editor warning when the PhysicalSkyMaterial is added without a DirectionalLight
Similar to the above, this would be fine, but it is troublesome for users that legitimately want a PhysicalSkyMaterial without sunlight.

So, all that is to say, I am open to discussing usability improvements. Clearly this behaviour is confusing, but I don't see any solution that I am happy with.

[soloparatolos]

if there is no DirectionalLight in the scene, the sky is black (if you had a night_sky texture set, you would see the stars)

Could be posible/doable to create a default "procedural night shader" to replace que absence of night_sky texture?

If this was posible, the absence of DirectionalLight would be more clear (and at least it would not feel like a bug).

And yes, I was one of those that thought that the blackness was a bug...

[clayjohn]

@soloparatolos it's a good idea. I initially had a procedural night sky built in. The issue with it is that procedural stars are very hard to get right for all screen resolutions. So either you end up with something that looks pretty and stylized or you do something that looks realistic-ish, but is slow. At the end of the day, I couldn't make something that was general purpose enough to include in the engine.

[name-here]

Alternatively make PhysicalSkyMaterial have a "sun" property that points to the DirectionalLight3D it will use as the sun (or an array if multiple suns are supported in the future). This would make it a bit more obvious that it needs a DirectionalLight3D to have a sun. It also fixes the current problem that, if there is more than one DirectionalLight3D in the scene, PhysicalSkyMaterial only ever seems to use the one higher in the scene tree for the sun's position.

[clayjohn]

@name-here I like that. It also solves another problem I've been tossing around about how to properly support a moon.

I have no idea how we could make it work though. The light is read directly from the shader. The material has no access to it.

[clayjohn]

This will be solved by https://github.com/godotengine/godot-proposals/issues/1599