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84 lines
4.7 KiB
Markdown
84 lines
4.7 KiB
Markdown
# Nishita Sky With Volumetric Clouds
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This is a Nishita sky shader for Godot 4.0, with [Clay John's volumetric clouds](https://github.com/clayjohn/godot-volumetric-cloud-demo) based on [a tutorial by scratch pixel](https://www.scratchapixel.com/lessons/procedural-generation-virtual-worlds/simulating-sky/simulating-colors-of-the-sky.html).
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## Screenshots
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| Day | Sunset |
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| --- | --- |
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| Cloudy Sky | Partial Eclipse |
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| --- | --- |
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| Full Eclipse | Blood Moon |
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| --- | --- |
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| Night Sky | Night Sky Without Clouds |
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| --- | --- |
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| Earth From Above | Earth From Above Sunset |
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## Features
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* Game-ready asset
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* Raymarched sky
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* Raymarched clouds that move with the camera
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* Different times of day by rotating the "NishitaSky" node
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* Realistic lighting at different altitudes
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* A night sky, with Milky Way texture
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* A directional light that takes on the color of the sun in the shader
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* All elements interact with each other: the night sky is blocked by the clouds and attenuated by the atmosphere
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* Ability to configure quality of the shader and turn the clouds on/off
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* Moon
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* Realistically lit moon influenced by the sun, resulting in different moon phases, including Earth blocking moon (new moon phase, and blood moon)
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* Support for moon and ground textures, accurate textures included
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* Performance optimizations
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## Bonus Features
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* Raising the camera high on the Y axis brings the moon closer
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* Moving the camera on the XZ axis (very far) changes the sky and ground texture position
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## Limitations
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* Performance heavy, especially with clouds on
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* The camera must remain below the clouds (but is clamped to cloud height if it goes higher), since the clouds do not actually exist
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## Improvements
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* For the sky precompute the optical depth between the sun and an arbitrary point along the ray (from Nishita's paper)
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* Add multiple scattering to clouds and sky
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* Physical raytraced clouds, with better lighting (currently the clouds are evenly lit)
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* Better cloud density textures
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* Use cloud sample distance for cloud fog (currently uses distance to clouds)
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* Physically accurate ground material (currently the brightness is just a dot product to the sun)
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* Better sun color saturation (currently some hacks are necessary to get the expected sun brightness and saturation)
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## How to Use
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To implement this sky into a project
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1. Copy the "NishitaSky" node from the main scene into the project
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2. 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
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3. Create an "WorldEnvironment" node, set the sky material to the "nishita_sky" material
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4. 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**
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5. Set the correct "sun_ground_height" on the "NishitaSky" node, this is the height of objects on the ground
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6. After adjusting all settings as needed click the "Compute Gradient Toggle" to precompute the sun color gradient
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7. It may be necessary to reload the scene to make the sky work in the editor
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8. If the sky is very slow try changing the process mode to "High-Quality Incremental" in the Sky settings in the WorldEnvironment
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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.
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## Todo
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* Fix clouds "jumping" after some time
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* Clean up code
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* Rework sun saturation
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* Set WorldEnvironment fog color based on sky color
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* Make stars move with the sun
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* Position sun, stars, and moon using a real world date/time
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## Images
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* Moon albedo was rendered from [NASA](https://svs.gsfc.nasa.gov/cgi-bin/details.cgi?aid=4720)
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* Night sky HDRI was underexposed and compressed to webp from [NASA](https://svs.gsfc.nasa.gov/4851#media_group_5169)
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* Earth image was color corrected and compressed to webp from [NASA](https://visibleearth.nasa.gov/images/74142/september-blue-marble-next-generation/74159l)
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