private unsafe MeshVertex CreateVertex(CyCoord coords, float dTheta)
{
Vector3 *pos = stackalloc Vector3[3];
CyCoord tcoord = coords;
for (int i = 0; i < 3; i++)
{
//compute 3 positions for computing the derivate respect theta
pos[i] = tcoord.ToCartesian();
tcoord.Theta += dTheta;
}
var tangent = Vector3.Normalize(Numerics.DerivateForward1(pos, dTheta));
var normal = Vector3.Normalize(Vector3.Cross(tangent, new Vector3(0, -1, 0)));
var texCoord = new Vector2(coords.Theta / Numerics.TwoPI, 0.5f - coords.Y / height);
return(new MeshVertex(pos[0], normal, tangent, texCoord));
}
private void Generate()
{
vertices = new MeshVertex[slices + 1];
float step = Numerics.TwoPI / slices;
CyCoord coords = new CyCoord(Numerics.PIover2, 0, radius);
for (int i = 0; i <= slices; i++)
{
coords.Theta = i * step;
vertices[i] = new MeshVertex(position: coords.ToCartesian());
}
indices = new ushort[slices * 2];
for (int i = 0; i < slices; i++)
{
indices[2 * i] = (ushort)i;
indices[2 * i + 1] = (ushort)(i + 1);
}
}