Arrangement_on_surface_2/unb_planar_vertical_decomposition.cpp

 
// Performing vertical decomposition of an arrangement.
 
#include <list>
 
#include <CGAL/Arr_vertical_decomposition_2.h>
 
#include "arr_linear.h"
 
using Cell_type = std::variant<Vertex_const_handle, Halfedge_const_handle,
                               Face_const_handle>;
using Vert_decomp_type = std::optional<Cell_type>;
using Vert_decomp_pair = std::pair<Vert_decomp_type, Vert_decomp_type>;
using Vert_decomp_entry = std::pair<Vertex_const_handle, Vert_decomp_pair>;
using Vert_decomp_list = std::list<Vert_decomp_entry>;
 
int main() {
  // Construct the arrangement.
  Arrangement arr;
 
  insert_non_intersecting_curve(arr, Segment(Point(1, 1), Point(3, 0)));
  insert_non_intersecting_curve(arr, Segment(Point(1, 1), Point(2, 2)));
  insert_non_intersecting_curve(arr, Segment(Point(2, 2), Point(3, 0)));
  insert_non_intersecting_curve(arr, Segment(Point(2, 2), Point(5, 0)));
  insert_non_intersecting_curve(arr, Segment(Point(3, 2), Point(5, 0)));
  insert_non_intersecting_curve(arr, Segment(Point(2, 3), Point(3, 3)));
  insert_non_intersecting_curve(arr, Segment(Point(0, 3), Point(6, 4)));
  insert_non_intersecting_curve(arr, Segment(Point(4, 4), Point(4, 5)));
 
  // Perform vertical ray-shooting from every vertex and locate the feature
  // that lie below it and the feature that lies above it.
  Vert_decomp_list vd_list;
  CGAL::decompose(arr, std::back_inserter(vd_list));
 
  // Print the results.
  for (auto vd_iter = vd_list.begin(); vd_iter != vd_list.end(); ++vd_iter) {
    const Vert_decomp_pair& curr = vd_iter->second;
    std::cout << "Vertex (" << vd_iter->first->point() << ") : ";
 
    std::cout << " feature below: ";
    if (! curr.first) std::cout << "EMPTY";
    else {
      auto* vh = std::get_if<Vertex_const_handle>(&*(curr.first));;
      if (vh) std::cout << '(' << (*vh)->point() << ')';
      else {
        auto* hh = std::get_if<Halfedge_const_handle>(&*(curr.first));
        if (! (*hh)->is_fictitious())
          std::cout << '[' << (*hh)->curve() << ']';
        else std::cout << "NONE";
      }
    }
 
    std::cout << "   feature above: ";
    if (! curr.second) std::cout << "EMPTY\n";
    else {
      auto* vh = std::get_if<Vertex_const_handle>(&*(curr.second));;
      if (vh) std::cout << '(' << (*vh)->point() << ")\n";
      else {
        auto* hh = std::get_if<Halfedge_const_handle>(&*(curr.second));
        if (! (*hh)->is_fictitious())
          std::cout << '[' << (*hh)->curve() << "]\n";
        else std::cout << "NONE\n";
      }
    }
  }
 
  return 0;
}