if (Constraint == VertexConstraint.Angle)
            {
                if ((crossProduct > 0 && Angle < 0) ||
                    (crossProduct < 0 && Angle > 0))
                    Angle = -Angle;
                if (Math.Abs(Angle - CalculateAngle()) > Constants.Eps)
                {
                    Point RotatePoint(Point p, double angle, Point center)
                    {
                        double s = Math.Sin(angle);
                        double c = Math.Cos(angle);

                        double cx = center.X;
                        double cy = center.Y;

                        // translate point back to origin:
                        p.X -= cx;
                        p.Y -= cy;

                        // rotate point
                        double xnew = p.X * c - p.Y * s;
                        double ynew = p.X * s + p.Y * c;

                        // translate point back:
                        p.X = xnew + cx;
                        p.Y = ynew + cy;
                        return p;
                    }
                    //if (PrevConstraint != SideConstraint.None || startVertex == Prev)
                    //    CorrectAngle(Prev, this, Next);
                    //else if (Prev.PrevConstraint != SideConstraint.None && Next.NextConstraint != SideConstraint.None && startVertex != this)
                    //{
                    //    void CorrentAngleThisPoint()
                    //    {
                    //        Vector delta = Point.Subtract(Next.ToPoint(), Prev.ToPoint()) / 2;
                    //        double tan = Math.Tan(Angle / 2);
                    //        Vector x = delta / tan;
                    //        double xProduct = (X - Prev.X) * (Next.Y - Prev.Y) - (Next.X - Prev.X) * (Y - Prev.Y);
                    //        if (xProduct < 0)
                    //        {
                    //            x.X *= -1;
                    //            x.Y *= -1;
                    //        }
                    //        delta.X += -x.Y;
                    //        delta.Y += x.X;

                    //        X = Prev.X + delta.X;
                    //        Y = Prev.Y + delta.Y;
                    //    }
                    //    CorrentAngleThisPoint();
                    //}
                    //else
                    //{
                    //    Angle = -Angle;
                    //    CorrectAngle(Next, this, Prev);
                    //    Angle = -Angle;