Function cmpsl

code/geometry/convex_hull3d.cpp:8–11

  return a.z < b.z; }
point3d slp;
bool cmpsl(const point3d& a, const point3d& b) {
  point3d ad = a-slp, bd = b-slp;
  return atan2(ad.y, sqrt(ad.x*ad.x + ad.z*ad.z)) <
         atan2(bd.y, sqrt(bd.x*bd.x + bd.z*bd.z)); }
set<vi> gift_wrap(vector<point3d> points) {
  int n = points.size(), lowi = 0, lowj = 0;
  set<vi> res; set<ii> vis; queue<ii> q;