private void CalcSideNormal()
{
sideNormal = new Vector( 0, 0 );
double dx = p3.X - p2.X;
double dy = p3.Y - p2.Y;
sideNormal.Set( dy, -dx );
sideNormal.Normalize();
}
private void CalcFaceNormal()
{
faceNormal = new Vector( 0, 0 );
double dx = p2.X - p1.X;
double dy = p2.Y - p1.Y;
faceNormal.Set( dy, -dx );
faceNormal.Normalize();
}