// If the mesh is a topological disk, extract its longest border,
// else compute a very simple cut to make it homeomorphic to a disk.
// Return the border of this region (empty on error)
//
// CAUTION: this cutting algorithm is very naive. Write your own!
static Seam cut_mesh(Parameterization_polyhedron_adaptor& mesh_adaptor)
{
// Helper class to compute genus or extract borders
typedef CGAL::Parameterization_mesh_feature_extractor<Parameterization_polyhedron_adaptor>
Mesh_feature_extractor;
Seam seam; // returned list
// Get reference to Polyhedron_3 mesh
Polyhedron& mesh = mesh_adaptor.get_adapted_mesh();
// Extract mesh borders and compute genus
Mesh_feature_extractor feature_extractor(mesh_adaptor);
int nb_borders = feature_extractor.get_nb_borders();
int genus = feature_extractor.get_genus();
// If mesh is a topological disk
if (genus == 0 && nb_borders > 0)
{
// Pick the longest border
seam = feature_extractor.get_longest_border();
}
else // if mesh is *not* a topological disk, create a virtual cut
{
const int CUT_LENGTH = 6;
// Build consecutive halfedges array
Polyhedron::Halfedge_handle seam_halfedges[CUT_LENGTH];
seam_halfedges[0] = mesh.halfedges_begin();
if (seam_halfedges[0] == NULL)
return seam; // return empty list
int i;
for (i=1; i<CUT_LENGTH; i++)
{
seam_halfedges[i] = seam_halfedges[i-1]->next()->opposite()->next();
if (seam_halfedges[i] == NULL)
return seam; // return empty list
}
// Convert halfedges array to two-ways vertices list
for (i=0; i<CUT_LENGTH; i++)
seam.push_back(seam_halfedges[i]->vertex());
for (i=CUT_LENGTH-1; i>=0; i--)
seam.push_back(seam_halfedges[i]->opposite()->vertex());
}
return seam;
}
// Cut the mesh to make it homeomorphic to a disk
// or extract a region homeomorphic to a disc.
// Return the border of this region (empty on error)
//
// CAUTION:
// This method is provided "as is". It is very buggy and simply part of this example.
// Developers using this package should implement a more robust cut algorithm!
static Seam cut_mesh(Parameterization_polyhedron_adaptor& mesh_adaptor)
{
// Helper class to compute genus or extract borders
typedef CGAL::Parameterization_mesh_feature_extractor<Parameterization_polyhedron_adaptor_ex>
Mesh_feature_extractor;
typedef Mesh_cutter::Backbone Backbone;
Seam seam; // returned list
// Get refererence to Polyhedron_3 mesh
Polyhedron& mesh = mesh_adaptor.get_adapted_mesh();
// Extract mesh borders and compute genus
Mesh_feature_extractor feature_extractor(mesh_adaptor);
int nb_borders = feature_extractor.get_nb_borders();
int genus = feature_extractor.get_genus();
// If mesh is a topological disk
if (genus == 0 && nb_borders > 0)
{
// Pick the longest border
seam = feature_extractor.get_longest_border();
}
else // if mesh is *not* a topological disk, create a virtual cut
{
Backbone seamingBackbone; // result of cutting
Backbone::iterator he;
// Compute a cutting path that makes the mesh a "virtual" topological disk
mesh.compute_facet_centers();
Mesh_cutter cutter(mesh);
if (genus == 0)
{
// no border, we need to cut the mesh
assert (nb_borders == 0);
cutter.cut(seamingBackbone); // simple cut
}
else // genus > 0 -> cut the mesh
{
cutter.cut_genus(seamingBackbone);
}
// The Mesh_cutter class is quite buggy
// => we check that seamingBackbone is valid
//
// 1) Check that seamingBackbone is not empty
if (seamingBackbone.begin() == seamingBackbone.end())
return seam; // return empty list
//
// 2) Check that seamingBackbone is a loop and
// count occurences of seam halfedges
mesh.tag_halfedges(0); // Reset counters
for (he = seamingBackbone.begin(); he != seamingBackbone.end(); he++)
{
// Get next halfedge iterator (looping)
Backbone::iterator next_he = he;
next_he++;
if (next_he == seamingBackbone.end())
next_he = seamingBackbone.begin();
// Check that seamingBackbone is a loop: check that
// end of current HE == start of next one
if ((*he)->vertex() != (*next_he)->opposite()->vertex())
return seam; // return empty list
// Increment counter (in "tag" field) of seam halfedges
(*he)->tag( (*he)->tag()+1 );
}
//
// 3) check that the seamingBackbone is a two-way list
for (he = seamingBackbone.begin(); he != seamingBackbone.end(); he++)
{
// Counter of halfedge and opposite halfedge must be 1
if ((*he)->tag() != 1 || (*he)->opposite()->tag() != 1)
return seam; // return empty list
}
// Convert list of halfedges to a list of vertices
for (he = seamingBackbone.begin(); he != seamingBackbone.end(); he++)
seam.push_back((*he)->vertex());
}
return seam;
}