Different times of day by rotating the "NishitaSky" node
Realistic lighting at different altitudes
A night sky, with Milky Way texture
A directional light that takes on the color of the sun in the shader
All elements interact with each other: the night sky is blocked by the clouds and attenuated by the atmosphere
Ability to configure quality of the shader and turn the clouds on/off
Moon
Realistically lit moon influenced by the sun, resulting in different moon phases, including Earth blocking moon (new moon phase, and blood moon)
Support for moon and ground textures, accurate textures included
Performance optimizations
Bonus Features
Raising the camera high on the Y axis brings the moon closer
Moving the camera on the XZ axis (very far) changes the sky and ground texture position
Limitations
Performance heavy, especially with clouds on
The camera must remain below the clouds (but is clamped to cloud height if it goes higher), since the clouds do not actually exist
Improvements
For the sky precompute the optical depth between the sun and an arbitrary point along the ray (from Nishita's paper)
Add multiple scattering to clouds and sky
Physical raytraced clouds, with better lighting (currently the clouds are evenly lit)
Better cloud density textures
Use cloud sample distance for cloud fog (currently uses distance to clouds)
Physically accurate ground material (currently the brightness is just a dot product to the sun)
Better sun color saturation (currently some hacks are necessary to get the expected sun brightness and saturation)
How to Use
To implement this sky into a project
Copy the "NishitaSky" node from the main scene into the project
In the "NishitaSky" node set "sun_object_path" variable to the desired directional light, do not make this directional light a child of the "NishitaSky" node
Create an "WorldEnvironment" node, set the sky material to the "nishita_sky" material
Click copy on the sky section of the "WorldEnvironment" node, and paste it into the "sky_material" section of the "NishitaSky" node. THE MATERIALS MUST BE LINKED FOR THE SKY PARAMETERS TO BE THE SAME ON THE SCRIPT AND THE SHADER
Set the correct "sun_ground_height" on the "NishitaSky" node, this is the height of objects on the ground
After adjusting all settings as needed click the "Compute Gradient Toggle" to precompute the sun color gradient
It may be necessary to reload the scene to make the sky work in the editor
If the sky is very slow try changing the process mode to "High-Quality Incremental" in the Sky settings in the WorldEnvironment
To understand what the shader settings do, read the comments in the nishita_sky.gdshader file. The variables prefixed with precomputed_ are set by the NishitaSky.gd script, they cannot be modified.
Todo
Fix clouds "jumping" after some time
Clean up code
Rework sun saturation
Set WorldEnvironment fog color based on sky color
Make stars move with the sun
Position sun, stars, and moon using a real world date/time
