求直線和圓的關係 c#

/// <summary>
        /// 王月，6月2日
        /// 求直線和圓的關係，若相交或相切則求出交點。直線方程：ax+by+c=0
        /// </summary>
        /// <param name="p">圓心</param>
        /// <param name="r">半徑</param>
        /// <param name="a">直線參數a</param>
        /// <param name="b">直線參數b</param>
        /// <param name="c">直線參數c</param>
        /// <param name="rp1">交點</param>
        /// <param name="rp2">交點</param>
        /// <returns>0----相離 1----相切 2----相交 </returns>
        int clpoint(PointF p, double r, double a, double b, double c, ref PointF rp1, ref PointF rp2)
        {
            int res = 0;

            c = c + a * p.X + b * p.Y;
            double tmp;
            if (a == 0 && b != 0)
            {
                tmp = -c / b;
                if (r * r < tmp * tmp)
                    res = 0;
                else if (r * r == tmp * tmp)
                {
                    res = 1;
                    rp1.Y = Convert.ToSingle(tmp);
                    rp1.X = 0;
                }
                else
                {
                    res = 2;
                    rp1.Y = rp2.Y = Convert.ToSingle(tmp);
                    rp1.X = Convert.ToSingle(Math.Sqrt(r * r - tmp * tmp));
                    rp2.X = -rp1.X;
                }
            }
            else if (a != 0 && b == 0)
            {
                tmp = -c / a;
                if (r * r < tmp * tmp)
                    res = 0;
                else if (r * r == tmp * tmp)
                {
                    res = 1;
                    rp1.X = Convert.ToSingle(tmp);
                    rp1.Y = 0;
                }
                else
                {
                    res = 2;
                    rp1.X = rp2.X = Convert.ToSingle(tmp);
                    rp1.Y = Convert.ToSingle(Math.Sqrt(r * r - tmp * tmp));
                    rp2.Y = -rp1.Y;
                }
            }
            else if (a != 0 && b != 0)
            {
                double delta;
                delta = b * b * c * c - (a * a + b * b) * (c * c - a * a * r * r);
                if (delta < 0)
                    res = 0;
                else if (delta == 0)
                {
                    res = 1;
                    rp1.Y = Convert.ToSingle(-b * c / (a * a + b * b));
                    rp1.X = Convert.ToSingle((-c - b * rp1.Y) / a);
                }
                else
                {
                    res = 2;
                    rp1.Y = Convert.ToSingle((-b * c + Math.Sqrt(delta)) / (a * a + b * b));
                    rp2.Y = Convert.ToSingle((-b * c - Math.Sqrt(delta)) / (a * a + b * b));
                    rp1.X = Convert.ToSingle((-c - b * rp1.Y) / a);
                    rp2.X = Convert.ToSingle((-c - b * rp2.Y) / a);
                }
            }
            rp1.X += p.X;
            rp1.Y += p.Y;
            rp2.X += p.X;
            rp2.Y += p.Y;
            return res;
        }