public static void CalculateTangents(ProBuilderMesh mesh)
{
int vc = mesh.vertexCount;
if (!mesh.HasArrays(MeshArrays.Tangent))
{
mesh.tangentsInternal = new Vector4[vc];
}
if (!mesh.HasArrays(MeshArrays.Position) || !mesh.HasArrays(MeshArrays.Texture0))
{
return;
}
// http://answers.unity3d.com/questions/7789/calculating-tangents-vector4.html
Vector3[] normals = mesh.GetNormals();
var positions = mesh.positionsInternal;
var textures = mesh.texturesInternal;
var tan1 = new Vector3[vc];
var tan2 = new Vector3[vc];
var tangents = mesh.tangentsInternal;
foreach (var face in mesh.facesInternal)
{
int[] triangles = face.indexesInternal;
for (int a = 0, c = triangles.Length; a < c; a += 3)
{
long i1 = triangles[a + 0];
long i2 = triangles[a + 1];
long i3 = triangles[a + 2];
Vector3 v1 = positions[i1];
Vector3 v2 = positions[i2];
Vector3 v3 = positions[i3];
Vector2 w1 = textures[i1];
Vector2 w2 = textures[i2];
Vector2 w3 = textures[i3];
float x1 = v2.x - v1.x;
float x2 = v3.x - v1.x;
float y1 = v2.y - v1.y;
float y2 = v3.y - v1.y;
float z1 = v2.z - v1.z;
float z2 = v3.z - v1.z;
float s1 = w2.x - w1.x;
float s2 = w3.x - w1.x;
float t1 = w2.y - w1.y;
float t2 = w3.y - w1.y;
float r = 1.0f / (s1 * t2 - s2 * t1);
Vector3 sdir = new Vector3((t2 * x1 - t1 * x2) * r, (t2 * y1 - t1 * y2) * r, (t2 * z1 - t1 * z2) * r);
Vector3 tdir = new Vector3((s1 * x2 - s2 * x1) * r, (s1 * y2 - s2 * y1) * r, (s1 * z2 - s2 * z1) * r);
tan1[i1] += sdir;
tan1[i2] += sdir;
tan1[i3] += sdir;
tan2[i1] += tdir;
tan2[i2] += tdir;
tan2[i3] += tdir;
}
}
for (long a = 0; a < vc; ++a)
{
Vector3 n = normals[a];
Vector3 t = tan1[a];
Vector3.OrthoNormalize(ref n, ref t);
tangents[a].x = t.x;
tangents[a].y = t.y;
tangents[a].z = t.z;
tangents[a].w = (Vector3.Dot(Vector3.Cross(n, t), tan2[a]) < 0.0f) ? -1.0f : 1.0f;
}
}
