원과 직선의 교점

// mydelTest.cpp : 콘솔 응용 프로그램에 대한 진입점을 정의합니다.
//
#include "stdafx.h"
#include <float.h>
#include <math.h>

class Point2
{
public:
    float x, y;

    Point2() :  x(0.0f), y(0.0f)
    {
    }
    Point2(float x, float y) : x(x), y(y)
    {
    }

    const float& operator[] (int i) const
    {
       return ((&x)[i]);
    }

    float& operator[] (int i)
    {
       return ((&x)[i]);
    }

    Point2& operator =(const Point2& v)
    {
        x = v.x;
        y = v.y;
        return (*this);
    }

    Point2 operator +(const Point2& v) const
    {
        return Point2(x + v.x, y + v.y);
    }

    Point2 operator *(float num) const
    {
        return Point2(x * num, y * num);
    }
};

// Find the points of intersection. output intersection1, intersection2
int FindLineCircleIntersections(float cx, float cy, float radius,
                                            Point2 point1, Point2 point2,
                                            Point2& intersection1, Point2& intersection2)
{
    float dx, dy, A, B, C, det, t;

    dx = point2.x - point1.x;
    dy = point2.y - point1.y;

    A = dx * dx + dy * dy;
    B = 2 * (dx * (point1.x - cx) + dy * (point1.y - cy));
    C = (point1.x - cx) * (point1.x - cx) + (point1.y - cy) * (point1.y - cy) - radius * radius;

    det = B * B - 4 * A * C;
    if ((A <= 0.0000001) || (det < 0))
    {
        // No real solutions.
        intersection1 = Point2(-FLT_MAX, -FLT_MAX);
        intersection2 = Point2(-FLT_MAX, -FLT_MAX);
        return 0;
    }
    else if (det == 0)
    {
        // One solution.
        t = -B / (2 * A);
        intersection1 = Point2(point1.x + t * dx, point1.y + t * dy);
        intersection2 = Point2(-FLT_MAX, -FLT_MAX);
        return 1;
    }
    else
    {
        // Two solutions.
        t = (float)((-B + sqrt(det)) / (2 * A));
        intersection1 = Point2(point1.x + t * dx, point1.y + t * dy);
        t = (float)((-B - sqrt(det)) / (2 * A));
        intersection2 = Point2(point1.x + t * dx, point1.y + t * dy);
        return 2;
    }
}

int _tmain(int argc, _TCHAR* argv[])
{
    Point2 pt1 = Point2(6, -5);
    Point2 pt2 = Point2(3, -2);
    Point2 out1, out2;
    int count = FindLineCircleIntersections(3, -5, 3, pt1, pt2, out1, out2);
    //count1 = 2,  out1 = 3, -2,      out2 = 6, -5

    //y = -x - 1/2
    //(x-2)^2 + (y+3)^2 = 4
    Point2 pt3 = Point2(0, -0.5f);
    Point2 pt4 = Point2(10, -10.5);
    Point2 out3, out4;
    int count2 = FindLineCircleIntersections(2, -3, 2, pt3, pt4, out3, out4);

    //count2 = 2, out3 = 3.64, -4.14   out4 = 0.85, -1.35
    return 0;
}