public Geometry GetCurrentGeometry()
        {
            两圆轨迹 轨迹线 = 当前轨迹线;

            return(new PathGeometry(new PathFigure[]
            {
                new PathFigure(轨迹线.四边形的点集[0], new PathSegment[]
                {
                    new PolyLineSegment(轨迹线.四边形的点集, true),
                }, true),
            }));
        }
        public void Move(Point point, double 半径 = 75)
        {
            _eraserElement.Width  = 半径 * 2;
            _eraserElement.Height = 半径 * 2;

            var x = point.X - 半径;
            var y = point.Y - 半径;

            //EraserEllipse.Margin = new Thickness(x, y, 0, 0);
            EraserTranslate.X = x;
            EraserTranslate.Y = y;

            _currentPoint = point;
            this.半径       = 半径;

            当前落点的圆 = new 圆(_currentPoint, 半径);
            两圆轨迹 轨迹线 = 前一个落点圆.求两圆轨迹线(当前落点的圆);

            当前轨迹线 = 轨迹线;
        }