face_handles.hpp

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//=======================================================================
// Copyright (c) Aaron Windsor 2007
//
// 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)
//=======================================================================

#ifndef __FACE_HANDLES_HPP__
#define __FACE_HANDLES_HPP__


#include <list>
#include <boost/graph/graph_traits.hpp>
#include <boost/shared_ptr.hpp>


// A "face handle" is an optimization meant to serve two purposes in
// the implementation of the Boyer-Myrvold planarity test: (1) it holds
// the partial planar embedding of a particular vertex as it's being
// constructed, and (2) it allows for efficient traversal around the
// outer face of the partial embedding at that particular vertex. A face
// handle is lightweight, just a shared pointer to the actual implementation,
// since it is passed around/copied liberally in the algorithm. It consists
// of an "anchor" (the actual vertex it's associated with) as well as a
// sequence of edges. The functions first_vertex/second_vertex and
// first_edge/second_edge allow fast access to the beginning and end of the
// stored sequence, which allows one to traverse the outer face of the partial
// planar embedding as it's being created. 
//
// There are some policies below that define the contents of the face handles:
// in the case no embedding is needed (for example, if one just wants to use
// the Boyer-Myrvold algorithm as a true/false test for planarity, the
// no_embedding class can be passed as the StoreEmbedding policy. Otherwise,
// either std_list (which uses as std::list) or recursive_lazy_list can be
// passed as this policy. recursive_lazy_list has the best theoretical
// performance (O(n) for a sequence of interleaved concatenations and reversals
// of the underlying list), but I've noticed little difference between std_list
// and recursive_lazy_list in my tests, even though using std_list changes
// the worst-case complexity of the planarity test to O(n^2)
//
// Another policy is StoreOldHandlesPolicy, which specifies whether or not
// to keep a record of the previous first/second vertex/edge - this is needed
// if a Kuratowski subgraph needs to be isolated.


namespace boost { namespace graph { namespace detail {


  //face handle policies
  
  //EmbeddingStorage policy
  struct store_embedding {};
  struct recursive_lazy_list : public store_embedding {};
  struct std_list : public store_embedding {};
  struct no_embedding {};

  //StoreOldHandlesPolicy
  struct store_old_handles {};
  struct no_old_handles {};




  template<typename DataType>
  struct lazy_list_node
  {
    typedef shared_ptr< lazy_list_node<DataType> > ptr_t;

    lazy_list_node(const DataType& data) :
      m_reversed(false),
      m_data(data),
      m_has_data(true)
    {}
    
    lazy_list_node(ptr_t left_child, ptr_t right_child) :
      m_reversed(false),
      m_has_data(false),
      m_left_child(left_child),
      m_right_child(right_child)
    {}

    bool m_reversed;
    DataType m_data;
    bool m_has_data;
    shared_ptr<lazy_list_node> m_left_child;
    shared_ptr<lazy_list_node> m_right_child;
  };
  


  template <typename StoreOldHandlesPolicy, typename Vertex, typename Edge>
  struct old_handles_storage;

  template <typename Vertex, typename Edge>
  struct old_handles_storage<store_old_handles, Vertex, Edge>
  {
    Vertex first_vertex;
    Vertex second_vertex;
    Edge first_edge;
    Edge second_edge;
  };

  template <typename Vertex, typename Edge>
  struct old_handles_storage<no_old_handles, Vertex, Edge>
  {};






  template <typename StoreEmbeddingPolicy, typename Edge>
  struct edge_list_storage;





  template <typename Edge>
  struct edge_list_storage<no_embedding, Edge>
  {
    typedef void type;

    void push_back(Edge) {}
    void push_front(Edge) {}
    void reverse() {}
    void concat_front(edge_list_storage<no_embedding,Edge>) {}
    void concat_back(edge_list_storage<no_embedding,Edge>) {}
    template <typename OutputIterator>
    void get_list(OutputIterator) {}
  };





  template <typename Edge>
  struct edge_list_storage<recursive_lazy_list, Edge>
  {
    typedef lazy_list_node<Edge> node_type;
    typedef shared_ptr< node_type > type;
    type value;

    void push_back(Edge e)
    {
      type new_node(new node_type(e));
      value = type(new node_type(value, new_node));
    }

    void push_front(Edge e)
    {
      type new_node(new node_type(e));
      value = type(new node_type(new_node, value));
    }

    void reverse()
    {
      value->m_reversed = !value->m_reversed;
    }

    void concat_front(edge_list_storage<recursive_lazy_list, Edge> other)
    {
      value = type(new node_type(other.value, value));
    }

    void concat_back(edge_list_storage<recursive_lazy_list, Edge> other)
    {
      value = type(new node_type(value, other.value));
    }

    template <typename OutputIterator>
    void get_list(OutputIterator out)
    {
      get_list_helper(out, value);
    }

  private:

    template <typename OutputIterator>
    void get_list_helper(OutputIterator o_itr, 
                         type root,
                         bool flipped = false
                         )
    {
      if (!root)
        return;
      
      if (root->m_has_data)
        *o_itr = root->m_data;
      
      if ((flipped && !root->m_reversed) ||
          (!flipped && root->m_reversed)
          )
        {
          get_list_helper(o_itr, root->m_right_child, true);
          get_list_helper(o_itr, root->m_left_child, true);
        }
      else
        {
          get_list_helper(o_itr, root->m_left_child, false);
          get_list_helper(o_itr, root->m_right_child, false);
        }
      
    }
    
  };





  template <typename Edge>
  struct edge_list_storage<std_list, Edge>
  {
    typedef std::list<Edge> type;
    type value;

    void push_back(Edge e)
    {
      value.push_back(e);
    }

    void push_front(Edge e)
    {
      value.push_front(e);
    }

    void reverse()
    {
      value.reverse();
    }

    void concat_front(edge_list_storage<std_list,Edge> other)
    {
      value.splice(value.begin(), other.value);
    }

    void concat_back(edge_list_storage<std_list, Edge> other)
    {
      value.splice(value.end(), other.value);
    }

    template <typename OutputIterator>
    void get_list(OutputIterator out)
    {
      std::copy(value.begin(), value.end(), out);
    }

  };






  
  template<typename Graph, 
           typename StoreOldHandlesPolicy, 
           typename StoreEmbeddingPolicy           
           >
  struct face_handle_impl
  {
    typedef typename graph_traits<Graph>::vertex_descriptor vertex_t;
    typedef typename graph_traits<Graph>::edge_descriptor edge_t;
    typedef typename edge_list_storage<StoreEmbeddingPolicy, edge_t>::type 
      edge_list_storage_t;


    face_handle_impl() : 
      cached_first_vertex(graph_traits<Graph>::null_vertex()),
      cached_second_vertex(graph_traits<Graph>::null_vertex()),
      true_first_vertex(graph_traits<Graph>::null_vertex()),
      true_second_vertex(graph_traits<Graph>::null_vertex()),
      anchor(graph_traits<Graph>::null_vertex())
    {
      initialize_old_vertices_dispatch(StoreOldHandlesPolicy());
    }

    void initialize_old_vertices_dispatch(store_old_handles)
    {
      old_handles.first_vertex = graph_traits<Graph>::null_vertex();
      old_handles.second_vertex = graph_traits<Graph>::null_vertex();
    }

    void initialize_old_vertices_dispatch(no_old_handles) {}

    vertex_t cached_first_vertex;
    vertex_t cached_second_vertex;
    vertex_t true_first_vertex;
    vertex_t true_second_vertex;
    vertex_t anchor;
    edge_t cached_first_edge;
    edge_t cached_second_edge;

    edge_list_storage<StoreEmbeddingPolicy, edge_t> edge_list;
    old_handles_storage<StoreOldHandlesPolicy, vertex_t, edge_t> old_handles;

  };











  template <typename Graph, 
            typename StoreOldHandlesPolicy = store_old_handles, 
            typename StoreEmbeddingPolicy = recursive_lazy_list
            >
  class face_handle 
  {
  public:
    typedef typename graph_traits<Graph>::vertex_descriptor vertex_t;
    typedef typename graph_traits<Graph>::edge_descriptor edge_t;
    typedef face_handle_impl
      <Graph, StoreOldHandlesPolicy, StoreEmbeddingPolicy> impl_t;
    typedef face_handle
      <Graph, StoreOldHandlesPolicy, StoreEmbeddingPolicy> self_t;

    face_handle(vertex_t anchor = graph_traits<Graph>::null_vertex()) :
      pimpl(new impl_t())
    {
      pimpl->anchor = anchor;
    }

    face_handle(vertex_t anchor, edge_t initial_edge, const Graph& g) :
      pimpl(new impl_t())
    {
      vertex_t s(source(initial_edge,g));
      vertex_t t(target(initial_edge,g));
      vertex_t other_vertex = s == anchor ? t : s;
      pimpl->anchor = anchor;
      pimpl->cached_first_edge = initial_edge;
      pimpl->cached_second_edge = initial_edge;
      pimpl->cached_first_vertex = other_vertex;
      pimpl->cached_second_vertex = other_vertex;
      pimpl->true_first_vertex = other_vertex;
      pimpl->true_second_vertex = other_vertex;

      pimpl->edge_list.push_back(initial_edge);
      store_old_face_handles_dispatch(StoreOldHandlesPolicy());
    }

    //default copy construction, assignment okay.
    
    void push_first(edge_t e, const Graph& g) 
    { 
      pimpl->edge_list.push_front(e);
      pimpl->cached_first_vertex = pimpl->true_first_vertex = 
        source(e, g) == pimpl->anchor ? target(e,g) : source(e,g);
      pimpl->cached_first_edge = e;
    }
  
    void push_second(edge_t e, const Graph& g) 
    { 
      pimpl->edge_list.push_back(e);
      pimpl->cached_second_vertex = pimpl->true_second_vertex = 
        source(e, g) == pimpl->anchor ? target(e,g) : source(e,g);
      pimpl->cached_second_edge = e;
    }

    inline void store_old_face_handles()
    {
      store_old_face_handles_dispatch(StoreOldHandlesPolicy());
    }

    inline vertex_t first_vertex() const
    { 
      return pimpl->cached_first_vertex;
    }
    
    inline vertex_t second_vertex() const 
    { 
      return pimpl->cached_second_vertex;
    }

    inline vertex_t true_first_vertex() const 
    { 
      return pimpl->true_first_vertex;
    }

    inline vertex_t true_second_vertex() const 
    { 
      return pimpl->true_second_vertex;
    }

    inline vertex_t old_first_vertex() const
    {
      return pimpl->old_handles.first_vertex;
    }

    inline vertex_t old_second_vertex() const
    {
      return pimpl->old_handles.second_vertex;
    }

    inline edge_t old_first_edge() const
    {
      return pimpl->old_handles.first_edge;
    }

    inline edge_t old_second_edge() const
    {
      return pimpl->old_handles.second_edge;
    }

    inline edge_t first_edge() const
    {
      return pimpl->cached_first_edge;
    }
  
    inline edge_t second_edge() const
    {
      return pimpl->cached_second_edge;
    }
    
    inline vertex_t get_anchor() const
    {
      return pimpl->anchor;
    }
  
    void glue_first_to_second
      (face_handle<Graph,StoreOldHandlesPolicy,StoreEmbeddingPolicy>& bottom)
    {
      pimpl->edge_list.concat_front(bottom.pimpl->edge_list);
      pimpl->true_first_vertex = bottom.pimpl->true_first_vertex;
      pimpl->cached_first_vertex = bottom.pimpl->cached_first_vertex;
      pimpl->cached_first_edge = bottom.pimpl->cached_first_edge;
    }
    
    void glue_second_to_first
      (face_handle<Graph,StoreOldHandlesPolicy,StoreEmbeddingPolicy>& bottom)
    {
      pimpl->edge_list.concat_back(bottom.pimpl->edge_list);
      pimpl->true_second_vertex = bottom.pimpl->true_second_vertex;
      pimpl->cached_second_vertex = bottom.pimpl->cached_second_vertex;
      pimpl->cached_second_edge = bottom.pimpl->cached_second_edge;
    }
  
    void flip()
    {
      pimpl->edge_list.reverse();
      std::swap(pimpl->true_first_vertex, pimpl->true_second_vertex);
      std::swap(pimpl->cached_first_vertex, pimpl->cached_second_vertex);
      std::swap(pimpl->cached_first_edge, pimpl->cached_second_edge);
    }
    
    template <typename OutputIterator>
    void get_list(OutputIterator o_itr)
    {
      pimpl->edge_list.get_list(o_itr);
    }

    void reset_vertex_cache()
    {
      pimpl->cached_first_vertex = pimpl->true_first_vertex;
      pimpl->cached_second_vertex = pimpl->true_second_vertex;
    }

    inline void set_first_vertex(vertex_t v)
    {
      pimpl->cached_first_vertex = v;
    }

    inline void set_second_vertex(vertex_t v)
    {
      pimpl->cached_second_vertex = v;
    }

  private:

    void store_old_face_handles_dispatch(store_old_handles)
    {
      pimpl->old_handles.first_vertex = pimpl->true_first_vertex;
      pimpl->old_handles.second_vertex = pimpl->true_second_vertex;
      pimpl->old_handles.first_edge = pimpl->cached_first_edge;
      pimpl->old_handles.second_edge = pimpl->cached_second_edge;
    }
  
    void store_old_face_handles_dispatch(no_old_handles) {}



    boost::shared_ptr<impl_t> pimpl;

  };


} /* namespace detail */ } /* namespace graph */ } /* namespace boost */


#endif //__FACE_HANDLES_HPP__