if (p1.X != p2.X)
            {
                a = (p2.Y - p1.Y) / (p2.X - p1.X);
                state |= 1;
            }
            if (p3.X != p4.X)
            {
                b = (p4.Y - p3.Y) / (p4.X - p3.X);
                state |= 2;
            }
            switch (state)
            {
                case 0: //L1與L2都平行Y軸
                    {
                        if (p1.X == p3.X)
                        {
                            throw new Exception("兩條直線互相重合，且平行于Y軸，無法計(jì)算交點(diǎn)。");
                        }
                        else
                        {
                            throw new Exception("兩條直線互相平行，且平行于Y軸，無法計(jì)算交點(diǎn)。");
                        }
                    }
                case 1: //L1存在斜率, L2平行Y軸
                    {
                        float x = p3.X;
                        float y = a * x - a * p1.X + p1.Y;
                        return new PointF(x, y);
                    }
                case 2: //L1 平行Y軸，L2存在斜率
                    {
                        float x = p1.X;
                        float y = b * x + b * p3.X + p3.Y;
                        return new PointF(x, y);
                    }
                case 3: //L1，L2都存在斜率
                    {
                        if (a == b)
                        {
                            throw new Exception("兩條直線平行或重合，無法計(jì)算交點(diǎn)。");
                        }
                        float x = (a * p1.X - b * p3.X - p1.Y + p3.Y) / (a - b);
                        float y = a * x - a * p1.X + p1.Y;
                        return new PointF(x, y);
                    }
            }
            throw new Exception("不可能發(fā)生的情況");
        }