Mi manual de algoritmos/version_actual/src/geometria/is_inside_convex_polygon.cpp

   1 /*
   2   Returns true if point a is inside convex polygon p.  Note
   3   that if point a lies on the border of p it is considered
   4   outside.
   5
   6   We assume p is convex! The result is useless if p is
   7   concave.
   8  */
   9 bool insideConvexPolygon(const vector<point> &p,
  10                          const point &a){
  11   int mask = 0;
  12   int n = p.size();
  13   for (int i=0; i<n; ++i){
  14     int j = (i+1)%n;
  15     double z = turn(p[i], p[j], a);
  16     if (z < 0.0){
  17       mask |= 1;
  18     }else if (z > 0.0){
  19       mask |= 2;
  20     }else if (z == 0.0) return false;
  21     if (mask == 3) return false;
  22   }
  23   return mask != 0;
  24 }