Generic convenience functions for testing if an edge is a border edge, if a mesh is triangular, for conversion between models of different FaceGraph concepts, etc.

All functions are in the header file <CGAL/boost/graph/helpers.h>

Functions
template<typename FaceGraph >
bool	CGAL::is_border (typename boost::graph_traits< FaceGraph >::halfedge_descriptor hd, const FaceGraph &g)
	returns `true` if the halfedge `hd` is on a border.

template<typename FaceGraph >
bool	CGAL::is_border_edge (typename boost::graph_traits< FaceGraph >::halfedge_descriptor hd, const FaceGraph &g)
	returns `true` if the halfedge `hd` or the opposite halfedge is on a border.

template<typename FaceGraph >
bool	CGAL::is_border (typename boost::graph_traits< FaceGraph >::edge_descriptor ed, const FaceGraph &g)
	returns `true` if the edge `e` is on a border.

template<typename FaceGraph >
std::optional< typename boost::graph_traits< FaceGraph >::halfedge_descriptor >	CGAL::is_border (typename boost::graph_traits< FaceGraph >::vertex_descriptor vd, const FaceGraph &g)
	returns a halfedge which is on a border and whose target vertex is `vd`, if such a halfedge exists.

template<typename Graph >
bool	CGAL::is_valid_halfedge_graph (const Graph &g, bool verb=false)
	checks the integrity of the graph `g`.

template<typename FaceGraph >
bool	CGAL::is_valid_face_graph (const FaceGraph &g, bool verb=false)
	checks the integrity of the graph `g`.

template<typename Mesh >
bool	CGAL::is_valid_polygon_mesh (const Mesh &g, bool verb=false)
	checks the integrity of the mesh `g`.

template<typename FaceGraph >
bool	CGAL::is_closed (const FaceGraph &g)
	returns `true` if there are no border edges.

template<typename FaceGraph >
bool	CGAL::is_bivalent (typename boost::graph_traits< FaceGraph >::halfedge_descriptor hd, const FaceGraph &g)
	returns `true` if the target of `hd` has exactly two incident edges.

template<typename FaceGraph >
bool	CGAL::is_bivalent_mesh (const FaceGraph &g)
	returns `true` if all vertices have exactly two incident edges.

template<typename FaceGraph >
bool	CGAL::is_trivalent (typename boost::graph_traits< FaceGraph >::halfedge_descriptor hd, const FaceGraph &g)
	returns `true` if the target of `hd` has exactly three incident edges.

template<typename FaceGraph >
bool	CGAL::is_trivalent_mesh (const FaceGraph &g)
	returns `true` if all vertices have exactly three incident edges.

template<typename FaceGraph >
bool	CGAL::is_isolated_triangle (typename boost::graph_traits< FaceGraph >::halfedge_descriptor hd, const FaceGraph &g)
	returns `true` iff the connected component denoted by `hd` is a triangle.

template<typename FaceGraph >
bool	CGAL::is_triangle (typename boost::graph_traits< FaceGraph >::halfedge_descriptor hd, const FaceGraph &g)
	returns `true` iff the face denoted by `hd` is a triangle, that is it has three incident halfedges.

template<typename FaceGraph >
bool	CGAL::is_triangle_mesh (const FaceGraph &g)
	returns `true` if all faces are triangles.

template<typename FaceGraph >
bool	CGAL::is_isolated_quad (typename boost::graph_traits< FaceGraph >::halfedge_descriptor hd, const FaceGraph &g)
	returns `true` iff the connected component denoted by `hd` is a quadrilateral.

template<typename FaceGraph >
bool	CGAL::is_quad (typename boost::graph_traits< FaceGraph >::halfedge_descriptor hd, const FaceGraph &g)
	returns `true` iff the face denoted by `hd` is a quad, that is it has four incident halfedges.

template<typename FaceGraph >
bool	CGAL::is_quad_mesh (const FaceGraph &g)
	returns `true` if all faces are quadrilaterals.

template<typename FaceGraph >
bool	CGAL::is_tetrahedron (typename boost::graph_traits< FaceGraph >::halfedge_descriptor hd, const FaceGraph &g)
	returns `true` iff the connected component denoted by `hd` is a tetrahedron.

template<typename FaceGraph >
bool	CGAL::is_hexahedron (typename boost::graph_traits< FaceGraph >::halfedge_descriptor hd, const FaceGraph &g)
	returns `true` iff the connected component denoted by `hd` is a hexahedron.

template<typename FaceGraph >
void	CGAL::remove_all_elements (FaceGraph &g)
	removes all vertices, faces and halfedges from a graph.

template<typename FaceGraph >
void	CGAL::clear (FaceGraph &g)
	removes all vertices, faces and halfedges from a graph.

template<typename FaceGraph >
bool	CGAL::is_empty (const FaceGraph &g)
	checks whether the graph is empty, by checking that it does not contain any vertex.

template<typename Graph >
int	CGAL::vertex_index_in_face (const typename boost::graph_traits< Graph >::vertex_descriptor vd, const typename boost::graph_traits< Graph >::face_descriptor fd, const Graph &g)
	returns the number of calls to `next()` one has to apply to the halfedge `hd` for `source(hd, mesh) == vd` to be true, starting from `hd = halfedge(fd, tm)`.

template<typename Graph >
int	CGAL::halfedge_index_in_face (typename boost::graph_traits< Graph >::halfedge_descriptor he, const Graph &g)
	returns the number of calls to `next(hd, tm)` one has to apply to `hd` for `hd == he` to be true, starting from `hd = halfedge(face(he, tm), tm)`.

template<typename SourceMesh , typename TargetMesh , typename NamedParameters1 = parameters::Default_named_parameters, typename NamedParameters2 = parameters::Default_named_parameters>
void	CGAL::copy_face_graph (const SourceMesh &sm, TargetMesh &tm, const NamedParameters1 &np1=parameters::default_values(), const NamedParameters2 &np2=parameters::default_values())
	copies a source model of `FaceListGraph` into a target model of a `FaceListGraph`.

Function Documentation

◆ clear()

template<typename FaceGraph >

void CGAL::clear ( FaceGraph & g )

#include <CGAL/boost/graph/helpers.h>

removes all vertices, faces and halfedges from a graph.

Calls remove_vertex(), remove_edge(), and remove_face(), for each vertex, edge, and face.

If the graph has a member function clear(), it will be called instead.

Warning: If it exists, the clear() function of a graph might do more than simply remove elements. For example, CGAL::Surface_mesh::clear() collects garbage and removes all property maps added by a call to CGAL::Surface_mesh::add_property_map() for all simplex types.

Template Parameters

FaceGraph model of MutableHalfedgeGraph and MutableFaceGraph

Parameters

g	the graph to clear

See also: CGAL::remove_all_elements()

◆ copy_face_graph()

template<typename SourceMesh , typename TargetMesh , typename NamedParameters1 = parameters::Default_named_parameters, typename NamedParameters2 = parameters::Default_named_parameters>

void CGAL::copy_face_graph	(	const SourceMesh &	sm,
		TargetMesh &	tm,
		const NamedParameters1 &	np1 = `parameters::default_values()`,
		const NamedParameters2 &	np2 = `parameters::default_values()`
	)

#include <CGAL/boost/graph/copy_face_graph.h>

copies a source model of FaceListGraph into a target model of a FaceListGraph.

OutputIterators can be provided to produce a mapping between source and target elements. The target graph is not cleared.

Template Parameters

SourceMesh	a model of `FaceListGraph`. The descriptor types `boost::graph_traits<SourceMesh>::vertex_descriptor` and `boost::graph_traits<SourceMesh>::face_descriptor` must be models of `Hashable`.
TargetMesh	a model of `FaceListGraph`
NamedParameters1	a sequence of Named Parameters
NamedParameters2	a sequence of Named Parameters

The types sm_vertex_descriptor and sm_face_descriptor must be models of the concept Hashable.

Parameters

sm	the source mesh
tm	the target mesh
np1	an optional sequence of Named Parameters among the ones listed below

Optional Named Parameters

a property map associating points to the vertices of `sm` Type: a class model of `ReadWritePropertyMap` with `boost::graph_traits<SourceMesh>::vertex_descriptor` as key type and `Point_3` as value type Default: `boost::get(CGAL::vertex_point, sm)` Extra: If this parameter is omitted, an internal property map for `CGAL::vertex_point_t` must be available in `SourceMesh`.
an `OutputIterator` containing the pairs source-vertex, target-vertex. Type: a class model of `OutputIterator` accepting `std::pair<`boost::graph_traits<SourceMesh>::vertex_descriptor, `boost::graph_traits<TargetMesh>::vertex_descriptor>` Default: `Emptyset_iterator` Extra: If this parameter is given, then `vertex_to_vertex_map` cannot be used.
an `OutputIterator` containing the pairs source-halfedge, target-halfedge. Type: a class model of `OutputIterator` accepting `std::pair<`boost::graph_traits<SourceMesh>::halfedge_descriptor, `boost::graph_traits<TargetMesh>::halfedge_descriptor>` Default: `Emptyset_iterator` Extra: If this parameter is given, then `halfedge_to_halfedge_map` cannot be used.
an `OutputIterator` containing the pairs source-face, target-face. Type: a class model of `OutputIterator` accepting `std::pair<`boost::graph_traits<SourceMesh>::face_descriptor, `boost::graph_traits<TargetMesh>::face_descriptor>` Default: `Emptyset_iterator` Extra: If this parameter is given, then `face_to_face_map` cannot be used.
a property map storing for each vertex of a source mesh the corresponding vertex of another mesh Type: a class model of `ReadWritePropertyMap` with `boost::graph_traits<SourceMesh>::vertex_descriptor` as key type and `boost::graph_traits<TargetMesh>::vertex_descriptor` as value type. Default: unused Extra: A typical use case is mapping the vertices from a source mesh to its copy's after a `copy_face_graph()` operation.
a property map storing for each halfedge of a source mesh the corresponding halfedge of another mesh Type: a class model of `ReadWritePropertyMap` with `boost::graph_traits<SourceMesh>::halfedge_descriptor` as key type and `boost::graph_traits<TargetMesh>::halfedge_descriptor` as value type Default: unused Extra: A typical use case is mapping the halfedges from a source mesh to its copy's after a `copy_face_graph()`operation.
a property map storing for each face of a source mesh the corresponding face of another mesh Type: a class model of `ReadWritePropertyMap` with `boost::graph_traits<SourceMesh>::face_descriptor` as key type and `boost::graph_traits<TargetMesh>::face_descriptor` as value type Default: unused Extra: A typical use case is mapping the faces from a source mesh to its copy's after a `copy_face_graph()` operation

Parameters

np2	an optional sequence of Named Parameters among the ones listed below

Optional Named Parameters

a property map associating points to the vertices of tm
Type: a class model of ReadWritePropertyMap with boost::graph_traits<TargetMesh>::vertex_descriptor as key type and Point_3 as value type
Default: boost::get(CGAL::vertex_point, tm)
Extra: If this parameter is omitted, an internal property map for CGAL::vertex_point_t must be available in TargetMesh.

The points from sm to tm are converted using CGAL::Cartesian_converter<SourceKernel, TargetKernel>. SourceKernel and TargetKernel are deduced using CGAL::Kernel_traits from the value types of the vertex point maps.

Other properties are not copied.

Examples: BGL_polyhedron_3/copy_polyhedron.cpp, BGL_surface_mesh/surface_mesh_partition.cpp, and Surface_mesh_segmentation/extract_segmentation_into_mesh_example.cpp.

◆ halfedge_index_in_face()

template<typename Graph >

int CGAL::halfedge_index_in_face	(	typename boost::graph_traits< Graph >::halfedge_descriptor	he,
		const Graph &	g
	)

#include <CGAL/boost/graph/helpers.h>

returns the number of calls to next(hd, tm) one has to apply to hd for hd == he to be true, starting from hd = halfedge(face(he, tm), tm).

Template Parameters

Graph a model of FaceGraph.

Parameters

he	a halfedge of `g` whose index in `face(he, tm)` is sought
g	an object of type `Graph`

◆ is_empty()

template<typename FaceGraph >

bool CGAL::is_empty ( const FaceGraph & g )

#include <CGAL/boost/graph/helpers.h>

checks whether the graph is empty, by checking that it does not contain any vertex.

Template Parameters

FaceGraph model of FaceGraph

Parameters

g	the graph to test

◆ is_isolated_triangle()

template<typename FaceGraph >

bool CGAL::is_isolated_triangle	(	typename boost::graph_traits< FaceGraph >::halfedge_descriptor	hd,
		const FaceGraph &	g
	)

#include <CGAL/boost/graph/helpers.h>

returns true iff the connected component denoted by hd is a triangle.

Precondition: g must be valid.

◆ is_valid_face_graph()

template<typename FaceGraph >

bool CGAL::is_valid_face_graph	(	const FaceGraph &	g,
		bool	verb = `false`
	)

#include <CGAL/boost/graph/helpers.h>

checks the integrity of the graph g.

The graph g is a valid face graph if it is a valid halfedge graph, and if it follows the rules of the FaceListGraph concept and all of its associations are reciprocal (for example, face(halfedge(f,g),g) must be f).

Parameters

g	the graph to test
verb	if `true`, the details of the check will be written in the standard output

Template Parameters

FaceGraph a model of FaceListGraph and HalfedgeListGraph

Returns: true if g is valid, false otherwise.

See also: is_valid_halfedge_graph()

◆ is_valid_halfedge_graph()

template<typename Graph >

bool CGAL::is_valid_halfedge_graph	(	const Graph &	g,
		bool	verb = `false`
	)

#include <CGAL/boost/graph/helpers.h>

checks the integrity of the graph g.

The graph g is valid if it follows the rules of the HalfedgeListGraph concept and all of its associations are reciprocal (for example, prev(next(h, g), g) must be h, and next(prev(h, g), g) must be h).

Parameters

g	the graph to test
verb	if `true`, the details of the check will be written in the standard output.

Template Parameters

Graph a model of HalfedgeListGraph

Returns: true if g is valid, false otherwise.

◆ is_valid_polygon_mesh()

template<typename Mesh >

bool CGAL::is_valid_polygon_mesh	(	const Mesh &	g,
		bool	verb = `false`
	)

#include <CGAL/boost/graph/helpers.h>

checks the integrity of the mesh g.

The mesh g is a valid polygon mesh if it is a valid face graph and if it follows the rules defined in PolygonMesh.

Parameters

g	the `Mesh` to test
verb	if `true`, the details of the check will be written in the standard output

Template Parameters

Mesh	a model of `FaceListGraph` and `HalfedgeListGraph`

Returns: true if g is valid, false otherwise.

See also: is_valid_face_graph(); is_valid_halfedge_graph()

Examples: BGL_polyhedron_3/copy_polyhedron.cpp.

◆ remove_all_elements()

template<typename FaceGraph >

void CGAL::remove_all_elements ( FaceGraph & g )

#include <CGAL/boost/graph/helpers.h>

removes all vertices, faces and halfedges from a graph.

Calls remove_vertex(), remove_edge(), and remove_face(), for each vertex, edge, and face.

Note that some graphs have a specialized version of this function to improve complexity.

Warning: This function does not perform anything more than what is advertised above. It is up to the user to e.g. clean garbage or remove internal property maps (if relevant, and desired).

Template Parameters

FaceGraph model of MutableHalfedgeGraph and MutableFaceGraph

Parameters

g	the graph whose elements will be removed

See also: CGAL::clear()

◆ vertex_index_in_face()

template<typename Graph >

int CGAL::vertex_index_in_face	(	const typename boost::graph_traits< Graph >::vertex_descriptor	vd,
		const typename boost::graph_traits< Graph >::face_descriptor	fd,
		const Graph &	g
	)

#include <CGAL/boost/graph/helpers.h>

returns the number of calls to next() one has to apply to the halfedge hd for source(hd, mesh) == vd to be true, starting from hd = halfedge(fd, tm).

Template Parameters

Graph a model of FaceGraph

Parameters

vd	a vertex of `g` whose index is sought
fd	a face of `g` in which the index of `vd` is sought
g	a mesh of type `Graph`

Precondition: vd is a vertex of fd.

Functions

Function Documentation

◆ clear()

◆ copy_face_graph()

◆ halfedge_index_in_face()

◆ is_empty()

◆ is_isolated_triangle()

◆ is_valid_face_graph()

◆ is_valid_halfedge_graph()

◆ is_valid_polygon_mesh()

◆ remove_all_elements()

◆ vertex_index_in_face()