About

This is where I try to refine and improve on everything I've learned in my Procedural planets generator. The idea is that someday this will be license free Earth sized comprehensive Unity GPU-mostly procedural planets and procedural universe generator. So people can #MakeGamesNotProceduralPlanets

It's not production ready !

Key technological points

A base (planetary) height map is provided or generated, which defines the basic planet shape
Uses chunked LOD quad tree
Chunk normal maps are in model space
Each chunk is located on planet inside area of 4 direction unit vectors

Features

Floating scene origin
Procedural space skybox

Chunk generation steps

GPU: generate chunk height map from base planetary height map using bicubic sampling
GPU: generate chunk slope map from chunk height map
GPU: chunk height map: add noise based on chunk slope map
GPU: fill array of chunk mesh vertices from chunk height map
GPU: generate chunk slope map from chunk height map
GPU: generate chunk diffuse map based on chunk slope map
GPU: generate chunk normal map based on chunk height map
GPU->CPU: download chunk mesh vertices from GPU to CPU
CPU: move edge vertices down to create skirt to hide cracks on differend LODs boundary (optional)
CPU: create chunk mesh (and mesh collider) from downloaded chunk mesh vertices

Chunk mesh vertices could be generated on CPU only, so it can be used on dedicated servers. Things generated on GPU should be only to add eye candy. Currently everything is generated on GPU.

Todo

Fix normal map artefacts if planet has radius over 10k.
Better biomes, per biome compute shader, that outputs: weight, color and adjusts height.
Noise channels (Outerra), that adds octaves as chunk depth increases, so we wont't need to calculate 30 octaves every time.

Planet detail subdivision (chunked LOD quad tree)

You can use either squares or triangles for chunks shape. Triangles appear to have better mesh, but it's finicky to figure out their texturing coordinates, plus you use only half of texture for each tringular chunk. Root triangular chunks are made out of icosahedron. Root square chunks are made out of cube.

Naive cube to sphere function is:

unitSphere = normalize(unitCube);

this however brings in distortions, better distortion-less unit cube to unit sphere is:

// -1 <= unitCube.x && unitCube.x <= 1
// -1 <= unitCube.y && unitCube.y <= 1
// -1 <= unitCube.z && unitCube.z <= 1
// uses math from http://mathproofs.blogspot.cz/2005/07/mapping-cube-to-sphere.html
// implementation license: public domain
float3 unitCubeToUnitSphere(float3 unitCube)
{
	float3 unitCubePow2 = unitCube * unitCube;
	float3 unitCubePow2Div2 = unitCubePow2 / 2;
	float3 unitCubePow2Div3 = unitCubePow2 / 3;
	return unitCube * sqrt(1 - unitCubePow2Div2.yzx - unitCubePow2Div2.zxy + unitCubePow2.yzx * unitCubePow2Div3.zxy);
}

/// <summary>
/// transforms unitCube position into unitSphere,
/// implementation license: public domain,
/// uses math from http://mathproofs.blogspot.cz/2005/07/mapping-cube-to-sphere.html
/// </summary>
/// <param name="unitCube">unitCube.xyz is in inclusive range [-1, 1]</param>
/// <returns></returns>
public static Vector3 UnitCubeToUnitSphere(Vector3 unitCube)
{
	var unitCubePow2 = new Vector3(unitCube.x * unitCube.x, unitCube.y * unitCube.y, unitCube.z * unitCube.z);
	var unitCubePow2Div2 = unitCubePow2 / 2;
	var unitCubePow2Div3 = unitCubePow2 / 3;
	var unitSphere = new Vector3(
		unitCube.x * Mathf.Sqrt(1 - unitCubePow2Div2.y - unitCubePow2Div2.z + unitCubePow2.y * unitCubePow2Div3.z),
		unitCube.y * Mathf.Sqrt(1 - unitCubePow2Div2.z - unitCubePow2Div2.x + unitCubePow2.z * unitCubePow2Div3.x),
		unitCube.z * Mathf.Sqrt(1 - unitCubePow2Div2.x - unitCubePow2Div2.y + unitCubePow2.x * unitCubePow2Div3.y)
	);
	return unitSphere;
}

Chunk height maps

Chunk height maps can have adjusted min max, based on the range they need. That is what the FindTextureMinMax is for.

float chunkMapHeight = (realPlanetHeight - _heightMin) / (_heightMax - _heightMin);

float realPlanetHeight = chunkMapHeight * (_heightMax - _heightMin) + _heightMin;

Child chunk height map is based off of parent chunk height map