在win8中根据触摸点位置删除最近的笔画墨迹

假设已知笔画墨迹的起始点坐标,触摸点的坐标很容易获取,下面就是找到要删除的墨迹的核心代码!

 private bool lineInterCircle(Point ptStart, Point ptEnd, Point ptCenter)//ptCenter目标坐标点
        {
            double eraserRadius = 17;
            double fDis = Math.Sqrt((ptEnd.X - ptStart.X) * (ptEnd.X - ptStart.X) + (ptEnd.Y - ptStart.Y) * (ptEnd.Y - ptStart.Y));
            if (fDis == 0)
            {
                // 点重叠，则判断该点群到橡皮擦的距离是否大于圆的半径
                double d = Math.Sqrt((double)(Math.Pow(Math.Abs(ptStart.X - ptCenter.X), 2) + Math.Pow(Math.Abs(ptStart.Y - ptCenter.Y), 2)));
                return (d < eraserRadius) ? true : false;
            }
            Point dPoint = new Point();
            dPoint.X = (int)((ptEnd.X - ptStart.X) / fDis);
            dPoint.Y = (int)((ptEnd.Y - ptStart.Y) / fDis);
            Point ePoint = new Point();
            ePoint.X = ptCenter.X - ptStart.X;
            ePoint.Y = ptCenter.Y - ptStart.Y;
            double a = ePoint.X * dPoint.X + ePoint.Y * dPoint.Y;
            double a2 = a * a;
            double e2 = ePoint.X * ePoint.X + ePoint.Y * ePoint.Y;
            double r2 = eraserRadius * eraserRadius;
            if ((r2 - e2 + a2) < 0)
            {
                return false;
            }
            else
            {
                //求交点
                double f = Math.Sqrt(r2 - e2 + a2);
                double t = a - f;
                if (((t - 0.0) > -0.00001) && (t - fDis) < 0.00001)
                {
                    return true;
                }
                t = a + f;
                if (((t - 0.0) > -0.00001) && (t - fDis) < 0.00001)
                {
                    return true;
                }
            }
            return false;
        }