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<TITLE>Planar Face Visitor Concept</TITLE>
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<H1>Planar Face Visitor Concept</H1>

This concept defines the visitor interface for 
<a href="./planar_face_traversal.html"><tt>planar_face_traversal</tt></a>. 
Users can define a class with the Planar Face Visitor interface and pass an 
object of the class to <tt>planar_face_traversal</tt>, thereby augmenting the 
actions taken during the traversal. Note that objects passed to 
<tt>planar_face_traversal</tt> are passed by reference.

<h3>Notation</h3>

<table>
<tbody><tr>
<td><tt>V</tt></td>
<td>A type that is a model of Planar Face Visitor.</td>
</tr>

<tr>
<td><tt>vis</tt></td>
<td>An object of type <tt>V</tt>.</td>
</tr>

<tr>
<td><tt>G</tt></td>
<td>A type that is a model of Graph.</td>
</tr>

<tr>
<td><tt>e</tt></td>
<td>An object of type <tt>boost::graph_traits&lt;G&gt;::edge_descriptor</tt>.
</td>
</tr>

<tr>
<td><tt>v</tt></td>
<td>An object of type <tt>boost::graph_traits&lt;G&gt;::vertex_descriptor</tt>.
</td>
</tr>

</tbody></table>


<h3>Valid Expressions</h3>

<table border="1">
<tbody><tr>
<th>Name</th><th>Expression</th><th>Return Type</th><th>Description</th>
</tr>

<tr>
<td>Begin Traversal</td>
<td><tt>vis.begin_traversal()</tt></td>
<td><tt>void</tt></td>
<td>
This is invoked once per traversal, before the traversal begins.
</td>
</tr>

<tr>
<td>Begin Face</td>
<td><tt>vis.begin_face()</tt></td>
<td><tt>void</tt></td>
<td>
This is invoked once for each face, before any vertices or edges on the face 
are visited. 
</td>
</tr>

<tr>
<td>Next Vertex</td>
<td><tt>vis.next_vertex(v)</tt></td>
<td><tt>void</tt></td>
<td>
This is invoked when a vertex is encountered while traversing a face.
</td>
</tr>


<tr>
<td>Next Edge</td>
<td><tt>vis.next_edge(e)</tt></td>
<td><tt>void</tt></td>
<td>
This is invoked when an edge is encountered while traversing a face.
</td>
</tr>

<tr>
<td>End Face</td>
<td><tt>vis.end_face()</tt></td>
<td><tt>void</tt></td>
<td>
This is invoked once for each face, after all vertices and edges on the face 
are visited.
</td>
</tr>


<tr>
<td>End Traversal</td>
<td><tt>vis.end_traversal()</tt></td>
<td><tt>void</tt></td>
<td>
This is invoked once per traversal, after the traversal ends.
</td>
</tr>

</tbody></table>

<h3>Models</h3>

<ul>
 <li> The file <a href="../../../boost/graph/planar_face_traversal.hpp">
<tt>planar_face_traversal.hpp</tt></a> contains a class 
<tt>planar_face_traversal_visitor</tt> that implements empty actions for
all event points of a Planar Face Visitor. In the case where only a few of the 
event points of Planar Face Visitor need to be implemented, one can derive from
<tt>planar_face_traversal_visitor</tt> and only implement the necessary event 
points. <li> The implementation of <a href="./make_maximal_planar.html">
<tt>make_maximal_planar</tt></a> uses a <tt>triangulation_visitor</tt> that is 
a model of Planar Face Visitor.
</li>
</ul>

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Copyright &copy; 2007 Aaron Windsor (<a href="mailto:aaron.windsor@gmail.com">
aaron.windsor@gmail.com</a>)
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