HeightmapSample GetSampleInPlanetSpace(HeightmapDefinition definition, int column, int row)
{
// Check out "Textures and Modelling - A Procedural Approach" by Ken Musgaves
// We have several different reference frames to deal with here:
// "Quad grid" coordinates which is the column and row index of the vertex in the mesh grid
// "Unit plane" coordinates which is the coordinates of the vertex on the unit plane of this quadtree
// "Unit sphere" coordinates which is the coordinates of the vertex on the unit sphere arc of this quadtree
// "Planet space" coordinates which is the coordinates of the vertex in real units relative to the planet center
// We start with quad grid coordinates. We first convert the quad coordinates into a unit plane vector that
// points to the equivalent point on the quadtree's plane. Then we project the unit plane to its equivalent unit
// sphere vector. We then calculate the terrain height for the vertex and use that information to extend the unit
// sphere vector to the proper length for the real-space size of our planet.
var unitPlaneVector = ConvertToUnitPlaneVector(definition, column, row);
var unitSphereVector = unitPlaneVector.ProjectUnitPlaneToUnitSphere();
var terrainHeight = _heightGenerator.GetHeight(unitSphereVector, definition.QuadLevel, 8000);
var planetSpaceVector = ConvertToPlanetSpace(definition, unitSphereVector, terrainHeight);
return(new HeightmapSample()
{
Height = terrainHeight,
Vector = planetSpaceVector
});
}
DoubleVector3 ConvertToUnitPlaneVector(HeightmapDefinition definition, int column, int row)
{
var uDelta = definition.UVector * (definition.Extents.North + (row * definition.Stride));
var vDelta = definition.VVector * (definition.Extents.West + (column * definition.Stride));
var convertedVector = definition.PlaneNormalVector + uDelta + vDelta;
return(convertedVector);
}
public HeightmapSample[] GenerateHeightmapSamples(HeightmapDefinition definition)
{
var samples = new HeightmapSample[definition.GridSize * definition.GridSize];
for (int row = 0; row < definition.GridSize; row++)
{
for (int column = 0; column < definition.GridSize; column++)
{
var sample = GetSampleInPlanetSpace(definition, column, row);
samples[row * definition.GridSize + column] = sample;
}
}
return(samples);
}
DoubleVector3 ConvertToPlanetSpace(HeightmapDefinition definition, DoubleVector3 sphereUnitVector, double terrainHeight)
{
return(sphereUnitVector * (definition.PlanetRadius + terrainHeight));
}