计算几何之判断线段相交

#include <iostream>
#include <math.h>
using namespace std;

#define COUNTER_CLOCKWISE -1 //逆时针
#define CLOCKWISE 1          //顺时针
#define ONLINE_BACK -2       //p2 p0 p1依次排列在一条直线上
#define ONLINE_FRONT 2       //p0 p1 p2依次排列在一条直线上
#define ON_SEGMENT 0         //p2在线段p0p1上

#define EPS 1E-8

class Point
{
public:
    double x, y;
    Point()
    {
    }
    Point(double x, double y)
    {
        (*this).x = x;
        (*this).y = y;
    }

    double operator^(const Point &p) const //叉乘
    {
        return x * p.y - y * p.x;
    }

    double operator*(const Point &p) const //点乘
    {
        return x * p.x + y * p.y;
    }

    Point operator*(const double &d) const
    {
        return Point(x * d, y * d);
    }

    Point operator/(const double &d) const
    {
        return Point(x / d, y / d);
    }

    Point operator-(const Point &p) const
    {
        return Point(x - p.x, y - p.y);
    }

    Point operator+(const Point &p) const
    {
        return Point(x + p.x, y + p.y);
    }

    double sqr()
    {
        return x * x + y * y;
    }
    double abs()
    {
        return sqrt(sqr());
    }

    double distance(const Point &p)
    {
        return fabs((*this - p).abs());
    }

    /*
    void print()
    {

        printf("%.10lf %.10lf\n", x, y);
    }
    */
};

class Line
{
public:
    Point p1, p2;
    Line()
    {
        
    }
    Line(Point p1, Point p2)
    {
        (*this).p1 = p1;
        (*this).p2 = p2;
    }
};

int ccw(Point p0, Point p1, Point p2) //判断p2与线段p0p1的关系
{
    Point vec1 = p1 - p0;
    Point vec2 = p2 - p0;

    if ((vec1 ^ vec2) > EPS)
        return COUNTER_CLOCKWISE; //p0、p1、p2逆时针
    else if ((vec1 ^ vec2) < -EPS)
        return CLOCKWISE; //p0 p1 p2顺时针
    else                  //p0 p1 p2在一条线上
    {
        if (vec1 * vec2 < -EPS)
            return ONLINE_BACK;
        else
        {
            if (vec1.abs() - vec2.abs() < -EPS)
                return ONLINE_FRONT;
            else
                return ON_SEGMENT;
        }
    }
}

bool intersect(Line l1, Line l2) //判断线段是否相交。
//如果两条线段都符合“另一条线段的两个端点分别位于当前线段的顺时针和逆时针方向”，那么两条线段相交
{
    return (ccw(l1.p1, l1.p2, l2.p1) * ccw(l1.p1, l1.p2, l2.p2) <= 0 &&
            ccw(l2.p1, l2.p2, l1.p1) * ccw(l2.p1, l2.p2, l1.p2) <= 0);
}

int main()
{
    ios::sync_with_stdio(false);
    cin.tie(0);
    cout.tie(0);

    int q;
    cin >> q;

    while (q--)
    {
        Line l[2];
        cin >> l[0].p1.x >> l[0].p1.y >> l[0].p2.x >> l[0].p2.y;
        cin >> l[1].p1.x >> l[1].p1.y >> l[1].p2.x >> l[1].p2.y;

        cout << intersect(l[0], l[1]) << endl;
        }
}