Polygon.cpp


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#include "Polygon.h"
#include <math.h>


double Polygon::area() const {
  double d = 0.0;
  
  for(const_iterator it = begin(); it != end(); it++) {
    const_iterator it2 = it+1;
    if(it2 == end()) it2 = begin();
    
    d += (it2->getX()+it->getX())*(it2->getY()-it->getY());
  }
  
  return fabs(d/2);
}

double Polygon::perimeter() const {
  double d = 0.0;
  
  for(const_iterator it = begin(); it != end(); it++) {
    const_iterator it2 = it+1;
    if(it2 == end()) it2 = begin();
    
    d += it->distance(*it2);
  }
  
  return d;
}

int Polygon::quadrant(const Vertex &v) const {
  if(v.getX() > 0 && v.getY() >= 0) return 1;
  if(v.getX() >= 0 && v.getY() < 0) return 2;
  if(v.getX() < 0 && v.getY() <= 0) return 3;
  if(v.getX() <= 0 && v.getY() > 0) return 4;
  
  return 0;
}

bool Polygon::contains(const Vertex &v) const {
  const Line d1(-1, -1, 1, 1);
  const Line d2(-1, 1, 1, -1);
  int d = 0;
  int q, ql, q2;
  Line l;
  Vertex v2;
  
  
  if(empty()) return false;
  
  v2 = back() - v;
  q = quadrant(v2);
  
  if(q == 0) return true;
  
  for(const_iterator it = begin(); it != end(); it++) {
    ql = q;
    
    v2 = *it - v;
    q = quadrant(v2);
    
    if(q == 0) return true;
    
    switch(q-ql) {
      case 0:
        break;
      case 1:
      case -3:
        d++;
        break;
      case 3:
      case -1:
        d--;
        break;
      default:
        l.setVertex1(((it == begin()) ? back() : *(it-1)) - v);
        l.setVertex2(v2);
        
        if(q == 1 || q == 3) {
          if(!(l.intersects(d2, &v2) & INTERSECTION_LINE)) return false;
          
          q2 = quadrant(v2);
          if(q2 == 0) return true;
          
          if((q == 1 && q2 == 2) || (q == 3 && q2 == 4)) d -= 2;
          else d += 2;
        }
        else {
          if(!(l.intersects(d1, &v2) & INTERSECTION_LINE)) return false;
          
          q2 = quadrant(v2);
          if(q2 == 0) return true;
          
          if((q == 2 && q2 == 3) || (q == 4 && q2 == 1)) d -= 2;
          else d += 2;
        }
    }
  }
  
  return (d != 0);
}

bool Polygon::intersects(const Line &l) const {
  Line line;
  
  for(Polygon::const_iterator it = begin(); it != end(); it++) {
    Polygon::const_iterator it2 = it+1;
    if(it2 == end()) it2 = begin();
    
    line.setVertex1(*it);
    line.setVertex2(*it2);
    
    if(l.intersects(line, NULL) == INTERSECTION_SEGMENT_SEGMENT)
      return true;
  }
  
  return false;
}