public static void RecalculateTangents(this Mesh mesh)
{
//speed up math by copying the mesh arrays
int[] triangles = mesh.triangles;
Vector3[] vertices = mesh.vertices;
Vector2[] uv = mesh.uv;
Vector3[] normals = mesh.normals;
//variable definitions
int triangleCount = triangles.Length;
int vertexCount = vertices.Length;
Vector3[] tan1 = new Vector3[vertexCount];
Vector3[] tan2 = new Vector3[vertexCount];
Vector4[] tangents = new Vector4[vertexCount];
for (long a = 0; a < triangleCount; a += 3)
{
long i1 = triangles[a + 0];
long i2 = triangles[a + 1];
long i3 = triangles[a + 2];
Vector3 v1 = vertices[i1];
Vector3 v2 = vertices[i2];
Vector3 v3 = vertices[i3];
Vector2 w1 = uv[i1];
Vector2 w2 = uv[i2];
Vector2 w3 = uv[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 < vertexCount; ++a)
{
Vector3 n = normals[a];
Vector3 t = tan1[a];
//Vector3 tmp = (t - n * Vector3.Dot(n, t)).normalized;
//tangents[a] = new Vector4(tmp.x, tmp.y, tmp.z);
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;
}
mesh.tangents = tangents;
}
