多边形相交面积计算模版

/*
    类型：多边形相交面积模板
*/

#include
#include
#include
#include
#include
using namespace std;
#define maxn 510
const double eps=1E-8;
int sig(double d){
    return(d>eps)-(d<-eps);
}
struct Point{
    double x,y; Point(){}
    Point(double x,double y):x(x),y(y){}
    bool operator==(const Point&p)const{
        return sig(x-p.x)==0&&sig(y-p.y)==0;
    }
};
double cross(Point o,Point a,Point b){
    return(a.x-o.x)*(b.y-o.y)-(b.x-o.x)*(a.y-o.y);
}
double area(Point* ps,int n){
    ps[n]=ps[0];
    double res=0;
    for(int i=0;i0) pp[m++]=p[i];
        if(sig(cross(a,b,p[i]))!=sig(cross(a,b,p[i+1])))
            lineCross(a,b,p[i],p[i+1],pp[m++]);
    }
    n=0;
    for(int i=0;i1&&p[n-1]==p[0])n--;
}
//---------------华丽的分隔线-----------------//
//返回三角形oab和三角形ocd的有向交面积,o是原点//
double intersectArea(Point a,Point b,Point c,Point d){
    Point o(0,0);
    int s1=sig(cross(o,a,b));
    int s2=sig(cross(o,c,d));
    if(s1==0||s2==0)return 0.0;//退化，面积为0
    if(s1==-1) swap(a,b);
    if(s2==-1) swap(c,d);
    Point p[10]={o,a,b};
    int n=3;
    polygon_cut(p,n,o,c);
    polygon_cut(p,n,c,d);
    polygon_cut(p,n,d,o);
    double res=fabs(area(p,n));
    if(s1*s2==-1) res=-res;return res;
}
//求两多边形的交面积
double intersectArea(Point*ps1,int n1,Point*ps2,int n2){
    if(area(ps1,n1)<0) reverse(ps1,ps1+n1);
    if(area(ps2,n2)<0) reverse(ps2,ps2+n2);
    ps1[n1]=ps1[0];
    ps2[n2]=ps2[0];
    double res=0;
    for(int i=0;i