[Boost-users] Newbie: BGL & planar graphs

Subject: [Boost-users] Newbie: BGL & planar graphs
From: ano kato (nchatz314_at_[hidden])
Date: 2017-12-03 01:29:03

Hello everyone!

I am using BGL to test for the planarity of drawings of graphs. The
coordinates are hardcoded into the source code. Here's what the graph
should look like: <https://i.imgur.com/UGA0mRB.png>. This definitely isn't
planar and yet is_straight_line_drawing() returns 1! I'm quite confused. Am
I doing something wrong? Thank you to anyone who replies.

#include <iostream>
#include <vector>
#include <boost/graph/adjacency_list.hpp>
#include <boost/property_map/property_map.hpp>
#include <boost/graph/is_straight_line_drawing.hpp>

using namespace boost;

typedef struct { size_t x,y; } coord_t;

int main(void) {

  typedef adjacency_list<vecS,
             vecS,
             undirectedS,
             property<vertex_index_t, int>
             > graph;

  graph Moser(7);
  add_edge(0,1,Moser);
  add_edge(0,6,Moser);
  add_edge(0,4,Moser);
  add_edge(1,6,Moser);
  add_edge(1,2,Moser);
  add_edge(2,6,Moser);
  add_edge(2,5,Moser);
  add_edge(2,3,Moser);
  add_edge(3,4,Moser);
  add_edge(4,5,Moser);

  graph G(Moser);
  int k = num_vertices(G);

  typedef std::vector<coord_t> cvec;
  typedef boost::iterator_property_map
    <cvec::iterator,
     property_map<graph, vertex_index_t>::type // ?
     >
    foo_t;

  cvec v(num_vertices(G));
  foo_t drawing(v.begin(), get(vertex_index, G));

  coord_t x[k];
  x[0].x = 20; x[0].y = 10;
  x[1].x = 50; x[1].y = 10;
  x[2].x = 58; x[2].y = 52;
  x[3].x = 00; x[3].y = 30;
  x[4].x = 35; x[4].y = 50;
  x[5].x = 12; x[5].y = 51;
  x[6].x = 70; x[6].y = 30;

  graph_traits<graph>::vertex_iterator vi, vi_end;
  for(boost::tie(vi, vi_end) = vertices(G); vi != vi_end; ++vi)
      put(drawing, *vi, x[*vi]);
  if(is_straight_line_drawing(G,drawing))
    std::cout << "This is a straight line planar drawing!" << std::endl;
  return 0;
}