Visibility_2/simple_polygon_visibility_2.cpp

#include <CGAL/Exact_predicates_exact_constructions_kernel.h>
#include <CGAL/Simple_polygon_visibility_2.h>
#include <CGAL/Arrangement_2.h>
#include <CGAL/Arr_segment_traits_2.h>
#include <CGAL/Arr_naive_point_location.h>
#include <istream>
#include <vector>

typedef CGAL::Exact_predicates_exact_constructions_kernel               Kernel;
typedef Kernel::Point_2                                                 Point_2;
typedef Kernel::Segment_2                                               Segment_2;
typedef CGAL::Arr_segment_traits_2<Kernel>                              Traits_2;
typedef CGAL::Arrangement_2<Traits_2>                                   Arrangement_2;
typedef Arrangement_2::Face_handle                                      Face_handle;
typedef Arrangement_2::Edge_const_iterator                              Edge_const_iterator;
typedef Arrangement_2::Ccb_halfedge_circulator                          Ccb_halfedge_circulator;


int main() {
  //create environment
  Point_2 p1(0,4), p2(0,0), p3(3,2), p4(4,0), p5(4,4), p6(1,2);
  std::vector<Segment_2> segments;
  segments.push_back(Segment_2(p1, p2));
  segments.push_back(Segment_2(p2, p3));
  segments.push_back(Segment_2(p3, p4));
  segments.push_back(Segment_2(p4, p5));
  segments.push_back(Segment_2(p5, p6));
  segments.push_back(Segment_2(p6, p1));

  Arrangement_2 env;
  CGAL::insert_non_intersecting_curves(env,segments.begin(),segments.end());

  // find the face of the query point 
  // (usually you may know that by other means)
  Point_2 q(0.5, 2);
  Arrangement_2::Face_const_handle * face;
  CGAL::Arr_naive_point_location<Arrangement_2> pl(env);
  CGAL::Arr_point_location_result<Arrangement_2>::Type obj = pl.locate(q);
  // The query point locates in the interior of a face
  face = boost::get<Arrangement_2::Face_const_handle> (&obj);
  
  // compute non regularized visibility area  
  // Define visibiliy object type that computes non-regularized visibility area
  typedef CGAL::Simple_polygon_visibility_2<Arrangement_2, CGAL::Tag_false> NSPV;
  Arrangement_2 non_regular_output;
  NSPV non_regular_visibility(env);

  non_regular_visibility.compute_visibility(q, *face, non_regular_output);

  std::cout << "Non-regularized visibility region of q has "
            << non_regular_output.number_of_edges()
            << " edges:" << std::endl;
  for (Edge_const_iterator eit = non_regular_output.edges_begin(); eit != non_regular_output.edges_end(); ++eit)
    std::cout << "[" << eit->source()->point() << " -> " << eit->target()->point() << "]" << std::endl;
   

  // compute non regularized visibility area 
  // Define visibiliy object type that computes regularized visibility area
  typedef CGAL::Simple_polygon_visibility_2<Arrangement_2, CGAL::Tag_true> RSPV;
  Arrangement_2 regular_output;
  RSPV regular_visibility(env);

  regular_visibility.compute_visibility(q, *face, regular_output);

  std::cout << "Regularized visibility region of q has "
            << regular_output.number_of_edges()
            << " edges:" << std::endl;
  for (Edge_const_iterator eit = regular_output.edges_begin(); eit != regular_output.edges_end(); ++eit)
    std::cout << "[" << eit->source()->point() << " -> " << eit->target()->point() << "]" << std::endl;
  
  return 0;
}