MARKUS

            if (bAxisLocked)

            {

                double _dx = pt.X - this.StartPoint.X;

                double _dy = pt.Y - this.StartPoint.Y;

                double dist = Math.Max(Math.Abs(_dx), Math.Abs(_dy));

                var dir = new Vector(_dx, _dy);

                dir.Normalize();

                this.LeftBottomPoint = new Point(this.StartPoint.X, this.StartPoint.Y + (dir.Y > 0 ? 1 : -1) * dist);

                this.TopRightPoint = new Point(this.StartPoint.X + (dir.X > 0 ? 1 : -1) * dist, this.StartPoint.Y);

                this.EndPoint = new Point(this.TopRightPoint.X, this.LeftBottomPoint.Y);

            }

            else

            {

                this.EndPoint = pt;

                this.LeftBottomPoint = new Point(this.StartPoint.X, this.EndPoint.Y);

                this.TopRightPoint = new Point(this.EndPoint.X, this.StartPoint.Y);

            }