将多边形点按照逆时针排序

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Point center;bool PointCmp(const Point &a,const Point &b){    if (a.x >= 0 && b.x < 0)        return true;    if (a.x == 0 && b.x == 0)        return a.y > b.y;    //向量OA和向量OB的叉积    int det = (a.x - center.x) * (b.y - center.y) - (b.x - center.x) * (a.y - center.y);    if (det < 0)        return true;    if (det > 0)        return false;    //向量OA和向量OB共线，以距离判断大小    int d1 = (a.x - center.x) * (a.x - center.x) + (a.y - center.y) * (a.y - center.y);    int d2 = (b.x - center.x) * (b.x - center.y) + (b.y - center.y) * (b.y - center.y);    return d1 > d2;}bool Cmp(const Point &a,const Point &b){    return !PointCmp(a,b);}

Point Gravity(Point *p, int n) {  //返回多边形的重心    double area = 0;    Point center;    center.x = 0;    center.y = 0;    for (int i = 0; i < n-1; i++) {        area += (p[i].x*p[i+1].y - p[i+1].x*p[i].y)/2;        center.x += (p[i].x*p[i+1].y - p[i+1].x*p[i].y) * (p[i].x + p[i+1].x);        center.y += (p[i].x*p[i+1].y - p[i+1].x*p[i].y) * (p[i].y + p[i+1].y);    }    area += (p[n-1].x*p[0].y - p[0].x*p[n-1].y)/2;    center.x += (p[n-1].x*p[0].y - p[0].x*p[n-1].y) * (p[n-1].x + p[0].x);    center.y += (p[n-1].x*p[0].y - p[0].x*p[n-1].y) * (p[n-1].y + p[0].y);    center.x /= 6*area;    center.y /= 6*area;    return center;}void ClockwiseSortPoints(Point* vPoints, int n){    //计算重心    center=Gravity(vPoints,n);    sort(vPoints,vPoints+n,Cmp);}

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