求圓和多邊形的面積交

#include <cstdio>
#include <cstring>
#include <algorithm>
#include <cmath>
#include <cstdlib>
#include <iostream>
#include <ctime>
using namespace std;
#define M 30
#define eps 1e-7
const double PI = acos(-);

class pnt_type
{
public:
    double x,y;
};
class state_type
{
public:
    double angle;
    double CoverArea;
};
pnt_type pnt[M];
pnt_type center;
int n;
double R;
bool read_data()
{
    n = ;
    int i;
    if (cin >> pnt[].x >> pnt[].y)
    {
        for (i=; i<=n; i++) cin >> pnt[i].x >> pnt[i].y;
        cin >> center.x >> center.y >> R;
        return true;
    }
    return false;
}
inline double Area2(pnt_type &a,pnt_type &b,pnt_type &c)
{
    return (b.x - a.x) * (c.y - a.y) - (c.x - a.x) * (b.y - a.y);
}
inline double dot(pnt_type &a,pnt_type &b,pnt_type &c)
{
    return (b.x - a.x) * (c.x - a.x) + (b.y - a.y) * (c.y - a.y);
}
inline double dist(pnt_type &a,pnt_type &b)
{
    return sqrt((b.x - a.x) * (b.x - a.x) + (b.y - a.y) * (b.y - a.y));
}

void init()
{
    int i;
    double temp,sum;
    for (i=; i<n; i++)
    {
        temp = Area2(pnt[],pnt[i],pnt[i + ]);
        sum += temp;
    }
    if (sum < ) reverse(pnt + ,pnt + n + );
    pnt[n + ] = pnt[];
}

inline bool inCircle(pnt_type &s)
{
    return dist(center,s) <= R;
}

bool SameSide(pnt_type a,pnt_type b)
{
    if (dist(a,center) > dist(b,center)) swap(a,b);
    return dot(a,b,center) < eps;
}

double ShadomOnCircle(pnt_type a,pnt_type b)
{
    double flag = Area2(center,a,b),res = ;
    if (fabs(flag) < eps) return ;

    bool ina = inCircle(a),inb = inCircle(b);
    if (ina && inb)
    {
        res = fabs(Area2(center,a,b)) / ;
    }
    else if (!ina && !inb)
    {
        if (SameSide(a,b))
        {
            double theta = acos(dot(center,a,b) / dist(center,a) / dist(center,b));
            res = R * R * theta / ;
        }
        else
        {
            double height = fabs(Area2(center,a,b)) / dist(a,b);
            double theta = acos(dot(center,a,b) / dist(center,a) / dist(center,b));
            if (height >= R)
            {
                res = R * R * theta / ;
            }
            else
            {
                double _theta =  * acos(height / R);
                res = R * R * (theta - _theta) /  + R * R * sin(_theta) / ;
            }
        }
    }
    else
    {
        if (!ina && inb) swap(a,b);
        double height = fabs(Area2(center,a,b)) / dist(a,b);
        double temp = dot(a,center,b);
        double theta = acos(dot(center,a,b) / dist(center,a) / dist(center,b)),theta1,theta2;
        if (fabs(temp) < eps)
        {
            double _theta = acos(height / R);
            res += R * height /  * sin(_theta);
            res += R * R /  * (theta - _theta);
        }
        else
        {
            theta1 = asin(height / R);
            theta2 = asin(height / dist(a,center));
            if (temp > )
            {
                res += dist(center,a) * R /  * sin(PI - theta1 - theta2);
                res += R * R /  * (theta + theta1 + theta2 - PI);
            }
            else
            {
                res += dist(center,a) * R /  * sin(theta2 - theta1);
                res += R * R /  * (theta - theta2 + theta1);
            }
        }
    }
    if (flag < ) return -res;
    else return res;
}
double Cover()
{
    int i;
    double res = ;
    for (i=; i<=n; i++)
        res += ShadomOnCircle(pnt[i],pnt[i + ]);
    return res;
}

int main()
{
    double ans;
    while (read_data())
    {
        init();
        ans = Cover();
        printf("%.2lf\n",ans);
    }
    return ;
}