public void RecalculateTangents()
{
if (HasUVs() == false)
{
UVs.Resize(Vertices.Count);
}
//partialy stolen from http://www.opengl-tutorial.org/intermediate-tutorials/tutorial-13-normal-mapping/
int verticesNum = Vertices.Count;
int indiciesNum = TriangleIndicies.Count;
int[] counts = new int[verticesNum];
Tangents.Clear();
Tangents.Capacity = verticesNum;
for (int i = 0; i < verticesNum; i++)
{
counts[i] = 0;
Tangents.Add(Vector3.Zero);
}
for (int i = 0; i <= indiciesNum - 3; i += 3)
{
int ai = TriangleIndicies[i];
int bi = TriangleIndicies[i + 1];
int ci = TriangleIndicies[i + 2];
if (ai < verticesNum && bi < verticesNum && ci < verticesNum)
{
Vector3 av = Vertices[ai];
Vector3 deltaPos1 = Vertices[bi] - av;
Vector3 deltaPos2 = Vertices[ci] - av;
Vector2 auv = UVs[ai];
Vector2 deltaUV1 = UVs[bi] - auv;
Vector2 deltaUV2 = UVs[ci] - auv;
float r = 1.0f / (deltaUV1.X * deltaUV2.Y - deltaUV1.Y * deltaUV2.X);
Vector3 t = (deltaPos1 * deltaUV2.Y - deltaPos2 * deltaUV1.Y) * r;
Tangents[ai] += t;
Tangents[bi] += t;
Tangents[ci] += t;
counts[ai]++;
counts[bi]++;
counts[ci]++;
}
}
for (int i = 0; i < verticesNum; i++)
{
Tangents[i] /= counts[i];
}
}