Added tutorial on deleting geometry

git-svn-id: http://www.openmesh.org/svnrepo/OpenMesh/trunk@156 fdac6126-5c0c-442c-9429-916003d36597

Doc/tutorial_07b.docu

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+/** \page tutorial_07b Deleting geometry elements
+
+This small example shows how to remove faces and vertices from a mesh.
+
+We basically use the geometry created in \ref tutorial_01.
+
+If we want our mesh class to be able to remove vertices, faces or (half-) edges
+we have to extend the default traits for our mesh class.
+Vertices, faces and (half-)edges need the OpenMesh::Attributes::Status attribute
+which is used to hold the flag "deleted" if an element is deleted.
+
+The struct which defines the mesh traits then looks like this:
+
+\dontinclude delete_geometry.cc
+\skipline struct
+\until };
+
+After having created the geometry of the cube one can delete faces and vertices
+by simply calling delete_vertices() (delete_faces() or delete_edges() respectiely).
+
+In this example we delete all faces excpet one and the corresponding vertices.
+The code looks like this
+
+\dontinclude delete_geometry.cc
+\skipline // Delete face 0
+\until mesh.delete_vertex(vhandle[3], false);
+
+Now the deleted faces and vertices are marked as "deleted" internally.
+Call garbage_collection() to definitely remove them from memory.
+
+\dontinclude delete_geometry.cc
+\skipline // Delete all
+\until mesh.garbage_collection();
+
+The full source code of the example:
+
+\include delete_geometry.cc
+
+**/