// darkscope.cpp : Defines the entry point for the console application.// // darkscope.cpp : Defines the entry point for the console application.// #include "stdafx.h"#include #include #include #include const double eps=1e-8;const double pi=3.1415926535897;using namespace std;struct point                    //点{
         	double x,y;	point()	{
         }	point(double xx,double yy)	{
         		x=xx;y=yy;	}};struct vect                    //向量{
         	double x,y;	vect()	{
         }	vect(double xx,double yy)	{
         		x=xx;		y=yy;	}	vect(point a,point b)	{
         		x=b.x-a.x;		y=b.y-a.y;	}};double dot_product(vect a,vect b)			//点积{
         	return a.x*b.x+a.y*b.y;}double cha_product(vect a,vect b)				//叉积{
         	return a.x*b.y-b.x*a.y;}bool cross(point a,point b,point c,point d)			//线段ab，cd是否相交,不含边界{
         	return cha_product(vect(a,c),vect(a,d))*cha_product(vect(b,c),vect(b,d))0?1:-1;}double square_of_polygan(vector a)  //计算多边形面积，a是顺时针或者逆时针的点集{
         	a.push_back(a[0]);	double ans=0;	for (int i=1;i k;	k.push_back(a);k.push_back(c);k.push_back(d);	double sacd=square_of_polygan(k);	k.clear();k.push_back(b);k.push_back(c);k.push_back(d);	double sbcd=square_of_polygan(k);	point ans=point(a.x*sbcd/(sacd+sbcd)+b.x*sacd/(sacd+sbcd),a.y*sbcd/(sacd+sbcd)+b.y*sacd/(sacd+sbcd));	return ans;}double angle_of_vector(vect a,vect b)                 //求两个向量的夹角，返回值为弧度数，如果要度数需要ans*180/pi{
         	return acos((a.x*b.x+a.y*b.y)/(sqrt(a.x*a.x+a.y*a.y)*sqrt(b.x*b.x+b.y*b.y)));}