MARKUS

        /// move control point has same location of given pt along given delta

        /// </summary>

        /// <author>humkyung</author>

        /// <date>2019.06.20</date>

        /// <param name="pt"></param>

        /// <param name="dx"></param>

        /// <param name="dy"></param>

        public override void OnMoveCtrlPoint(Point pt, double dx, double dy)

        {

            IPath path = (this as IPath);

            Point selected = MathSet.getNearPoint(path.PointSet, pt);

            selected.X += dx;

            selected.Y += dy;

            int i = 0;

            for (i = 0; i < (this as IPath).PointSet.Count; i++)

            {

                if (pt.Equals((this as IPath).PointSet[i]))

                {

                    path.PointSet[i] = selected;

                    break;

                }

            }

            var ReverseP = (i + path.PointSet.Count / 2) % path.PointSet.Count;

            var PreviousP = (i + (path.PointSet.Count - 1)) % path.PointSet.Count;

            var NextP = (i + 1) % path.PointSet.Count;

            var distance = MathSet.DistanceTo(path.PointSet[ReverseP], path.PointSet[i]);

            var PreviousV = MathSet.GetNormVectorBetween(path.PointSet[ReverseP], path.PointSet[PreviousP]);

            var l = MathSet.DotProduct(PreviousV.X, PreviousV.Y, path.PointSet[i].X - path.PointSet[ReverseP].X,

                path.PointSet[i].Y - path.PointSet[ReverseP].Y);

            path.PointSet[PreviousP] = new Point(path.PointSet[ReverseP].X + PreviousV.X * l, path.PointSet[ReverseP].Y + PreviousV.Y * l);

            var NextV = MathSet.GetNormVectorBetween(path.PointSet[ReverseP], path.PointSet[NextP]);

            l = MathSet.DotProduct(NextV.X, NextV.Y, path.PointSet[i].X - path.PointSet[ReverseP].X, path.PointSet

                [i].Y - path.PointSet[ReverseP].Y);

            path.PointSet[NextP] = new Point(path.PointSet[ReverseP].X + NextV.X * l, path.PointSet[ReverseP].Y + NextV.Y * l);

            this.updateControl();

        }

        /// <summary>