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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 edges
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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.

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Instead of defining the required attributes via traits on compile-time, it is possible to request
attributes dynamically on run-time by requesting them.
In this example, we want to delete faces, edges and vertices, therefore requesting the status attribute is required.
\note You have to request attributes before you use them, if you don't enable them via traits.
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\dontinclude delete_geometry.cc
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\skipline // the request 
\until mesh.request_vertex_status();
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After having created the geometry of the cube one can delete faces and vertices
by simply calling delete_vertices() (delete_faces() or delete_edges() respectively).

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Note that there is actually no way to directly delete halfedges since they are automatically
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affected when the parent edge is marked as deleted!

The status whether an element is marked as deleted can be requested by

mesh.status(handle).deleted();  // true if element handle is marked as deleted
                                // false otherwise

where handle is either a vertex-, edge- or face-handle.

In this example we delete all faces except one and the corresponding vertices.
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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