OMI_environment_sky

[aaronfranke]

Preview: https://github.com/aaronfranke/gltf-extensions/tree/OMI_environment_sky/extensions/2.0/OMI_environment_sky

This is a work-in-progress extension for specifying a skybox in glTF data, allowing for glTF scenes to have skyboxes, and defines how the sky provides environment lighting.

The sky can be a gradient, panorama, physical sky, or plain sky. The sky can be used to light the scene, provide a background, or both. To add suns to the sky, use the KHR_lights_punctual extension to define directional lights.

• Gradient skies use color gradients to define the sky colors: top, horizon, and bottom colors. The sun angle can be defined, but the sun color comes from the directional light. The blending between these colors is controlled by the curve values. Also, gradient skies can be used for plain color skies when a visual sun is required.
  

• Physical skies use a physically-based model to simulate the scattering of light in the atmosphere, including rayleigh and mie scattering colors and parameters. The default values are for Earth, and can be tweaked for other planets.
  

• Panorama skies use a texture or set of textures to represent the sky. It can be either a single equirectangular texture (more common, recommended) or a cubemap texture (supported by some engines).
  

• Plain color skies have the entire skybox as one color. They do not have a sun or any special decorations. Here is a test scene with an aggressively cyan sky as a test.
  

There is a Godot implementation here: omigroup/omi-godot#15