private PointD DeCasteljau(int i, double t)
{
PointD P0 = ControlPoints[i];
PointD P1 = ControlPoints[i + 1];
PointD P2 = ControlPoints[i + 2];
//
P0 = P0.Lerp(P1, t);
P1 = P1.Lerp(P2, t);
P2 = P2.Lerp(ControlPoints[i + 3], t);
//
P0 = P0.Lerp(P1, t);
P1 = P1.Lerp(P2, t);
//
return(P0.Lerp(P1, t));
}