/// <summary>
/// Calculates a tangent.
/// </summary>
/// <param name="vertex1">Vertex one.</param>
/// <param name="vertex2">Vertex two.</param>
/// <param name="vertex3">Vertex three.</param>
/// <param name="normal">The normal of the face.</param>
/// <returns>The calculate tangent.</returns>
public static Vector3 CalculateTangent(ref TangentNormalTexture vertex1,
ref TangentNormalTexture vertex2, ref TangentNormalTexture vertex3, ref Vector3 normal)
{
Vector3 tangent = Vector3.Zero;
Vector3 edge1 = vertex3.Position - vertex1.Position;
Vector3 edge2 = vertex2.Position - vertex1.Position;
Vector2 texEdge1 = vertex3.TextureCoord - vertex1.TextureCoord;
Vector2 texEdge2 = vertex2.TextureCoord - vertex1.TextureCoord;
edge1.Normalize();
edge2.Normalize();
texEdge1.Normalize();
texEdge2.Normalize();
float det = (texEdge1.X * texEdge2.Y) - (texEdge1.Y * texEdge2.X);
Vector3 t;
if ((float)Math.Abs(det) < 1e-6f)
{
t = Vector3.UnitX;
}
else
{
det = 1.0f / det;
t.X = (texEdge2.Y * edge1.X - texEdge1.Y * edge2.X) * det;
t.Y = (texEdge2.Y * edge1.Y - texEdge1.Y * edge2.Y) * det;
t.Z = (texEdge2.Y * edge1.Z - texEdge1.Y * edge2.Z) * det;
t.Normalize();
}
tangent.X = t.X;
tangent.Y = t.Y;
tangent.Z = t.Z;
return(tangent);
}
/// <summary>
/// Used to set both the noprm and the tangent of the face.
/// </summary>
/// <param name="vertices">The vertices that make up the face.</param>
public void SetNormalTangent(List <TangentNormalTexture> vertices)
{
TangentNormalTexture[] vert = new TangentNormalTexture[]
{
vertices[indices[0]],
vertices[indices[1]],
vertices[indices[2]]
};
Vector3 normal = VertexHelper.CalculateNormal(
ref vert[0].Position, ref vert[1].Position, ref vert[2].Position);
Vector3 tangent = VertexHelper.CalculateTangent(
ref vert[0], ref vert[1], ref vert[2], ref normal);
for (int i = 0; i < vert.Length; i++)
{
vert[i].Normal += normal;
vert[i].Normal.Normalize();
vert[i].Tangent += tangent;
vert[i].EvaluateTangent();
vertices[indices[i]] = vert[i];
}
}
