計算幾何 圓 二維模板

#include#include#include#include#include#define fir first

#define sec second
using namespace std;
const double eps = 1e-8;
const double pi = acos(-1.0);
int dcmp(double x)
//兩圓求公切線
//a[i] 為第i條切線與圓a的交點
int get_tangents(circle a, circle b, pnode *a, pnode *b)
double d = sqrt((a.x - b.x) * (a.x - b.x) + (a.y - b.y) * (a.y - b.y));     //圓心距
double rdiff = a.r - b.r;      //兩圓半徑差
double rsum  = a.r + b.r;       //兩圓半徑和
if(dcmp(d - rdiff) < 0)
return 0;        //1.內含
double base = atan2(b.y - a.y, b.x - a.x);      //向量ab的極角
if(dcmp(d) == 0) return -1;        //2.重合
if(dcmp(d - rdiff) == 0)
double ang = acos((a.r - b.r) / d);
a[cnt] = a.point(base + ang); b[cnt] = b.point(base + ang); cnt++;      //4.相交（外切、外離的外公切線也在此求出）
a[cnt] = a.point(base - ang); b[cnt] = b.point(base - ang); cnt++;      //兩條外公切線的切點
if(dcmp(d - rsum) == 0)
else if(dcmp(d - rsum) > 0)
return cnt;
}int main()

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