void ComputeNormal()
{
Vector3 v0 = vertex[ 0 ].commonVertex.position;
Vector3 v1 = vertex[ 1 ].commonVertex.position;
Vector3 v2 = vertex[ 2 ].commonVertex.position;
// Cross-product 2 edges
Vector3 e1 = v1 - v0;
Vector3 e2 = v2 - v1;
normal = e1.Cross( e2 );
normal.Normalize();
}
internal void ReplaceVertex( PMFaceVertex vold, PMFaceVertex vnew )