Boost C++ Libraries

libs/graph/example/make_maximal_planar.cpp

//=======================================================================
// Copyright 2007 Aaron Windsor
//
// Distributed under the Boost Software License, Version 1.0. (See
// accompanying file LICENSE_1_0.txt or copy at
// http://www.boost.org/LICENSE_1_0.txt)
//=======================================================================
#include <iostream>
#include <boost/graph/adjacency_list.hpp>
#include <boost/graph/properties.hpp>
#include <boost/graph/graph_traits.hpp>
#include <boost/property_map/property_map.hpp>
#include <boost/ref.hpp>
#include <vector>

#include <boost/graph/make_biconnected_planar.hpp>
#include <boost/graph/make_maximal_planar.hpp>
#include <boost/graph/planar_face_traversal.hpp>
#include <boost/graph/boyer_myrvold_planar_test.hpp>

// This example shows how to start with a connected planar graph
// and add edges to make the graph maximal planar (triangulated.)
// Any maximal planar simple graph on n vertices has 3n - 6 edges and
// 2n - 4 faces, a consequence of Euler's formula.

using namespace boost;

// This visitor is passed to planar_face_traversal to count the
// number of faces.
struct face_counter : public planar_face_traversal_visitor
{
    face_counter() : count(0) {}
    void begin_face() { ++count; }
    int count;
};

int main(int argc, char** argv)
{

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

    // Create the graph - a straight line
    graph g(10);
    add_edge(0, 1, g);
    add_edge(1, 2, g);
    add_edge(2, 3, g);
    add_edge(3, 4, g);
    add_edge(4, 5, g);
    add_edge(5, 6, g);
    add_edge(6, 7, g);
    add_edge(7, 8, g);
    add_edge(8, 9, g);

    std::cout << "Since the input graph is planar with " << num_vertices(g)
              << " vertices," << std::endl
              << "The output graph should be planar with "
              << 3 * num_vertices(g) - 6 << " edges and "
              << 2 * num_vertices(g) - 4 << " faces." << std::endl;

    // Initialize the interior edge index
    property_map< graph, edge_index_t >::type e_index = get(edge_index, g);
    graph_traits< graph >::edges_size_type edge_count = 0;
    graph_traits< graph >::edge_iterator ei, ei_end;
    for (boost::tie(ei, ei_end) = edges(g); ei != ei_end; ++ei)
        put(e_index, *ei, edge_count++);

    // Test for planarity; compute the planar embedding as a side-effect
    typedef std::vector< graph_traits< graph >::edge_descriptor > vec_t;
    std::vector< vec_t > embedding(num_vertices(g));
    if (boyer_myrvold_planarity_test(boyer_myrvold_params::graph = g,
            boyer_myrvold_params::embedding = &embedding[0]))
        std::cout << "Input graph is planar" << std::endl;
    else
        std::cout << "Input graph is not planar" << std::endl;

    make_biconnected_planar(g, &embedding[0]);

    // Re-initialize the edge index, since we just added a few edges
    edge_count = 0;
    for (boost::tie(ei, ei_end) = edges(g); ei != ei_end; ++ei)
        put(e_index, *ei, edge_count++);

    // Test for planarity again; compute the planar embedding as a side-effect
    if (boyer_myrvold_planarity_test(boyer_myrvold_params::graph = g,
            boyer_myrvold_params::embedding = &embedding[0]))
        std::cout << "After calling make_biconnected, the graph is still planar"
                  << std::endl;
    else
        std::cout << "After calling make_biconnected, the graph is not planar"
                  << std::endl;

    make_maximal_planar(g, &embedding[0]);

    // Re-initialize the edge index, since we just added a few edges
    edge_count = 0;
    for (boost::tie(ei, ei_end) = edges(g); ei != ei_end; ++ei)
        put(e_index, *ei, edge_count++);

    // Test for planarity one final time; compute the planar embedding as a
    // side-effect
    std::cout << "After calling make_maximal_planar, the final graph ";
    if (boyer_myrvold_planarity_test(boyer_myrvold_params::graph = g,
            boyer_myrvold_params::embedding = &embedding[0]))
        std::cout << "is planar." << std::endl;
    else
        std::cout << "is not planar." << std::endl;

    std::cout << "The final graph has " << num_edges(g) << " edges."
              << std::endl;

    face_counter count_visitor;
    planar_face_traversal(g, &embedding[0], count_visitor);
    std::cout << "The final graph has " << count_visitor.count << " faces."
              << std::endl;

    return 0;
}