CGAL 4.11 - Halfedge Data Structures
CGAL::HalfedgeDS_items_decorator< HDS > Class Template Reference

#include <CGAL/HalfedgeDS_items_decorator.h>

Inherited by CGAL::HalfedgeDS_const_decorator< HDS >, and CGAL::HalfedgeDS_decorator< HDS > [private].

## Definition

The class CGAL::HalfedgeDS_items_decorator<HDS> provides additional functions for vertices, halfedges, and faces of a halfedge data structure without knowing the containing halfedge data structure.

The class CGAL::HalfedgeDS_decorator<HDS> stores a reference to the halfedge data structure and provides functions that modify the halfedge data structure, for example Euler-operators. The class CGAL::HalfedgeDS_const_decorator<HDS> stores a const reference to the halfedge data structure. It contains non-modifying functions, for example the test for validness of the data structure.

All these additional functions take care of the different capabilities a halfedge data structure may have or may not have. The functions evaluate the type tags of the halfedge data structure to decide on the actions. If a particular feature is not supported nothing is done. Note that for example the creation of new halfedges is mandatory for all halfedge data structures and will not appear here again.

CGAL::HalfedgeDS_decorator<HDS>
CGAL::HalfedgeDS_const_decorator<HDS>

Example

The following program fragment illustrates how a refined halfedge class for a polyhedron can make use of the find_prev() member function to implement a prev() member function that works regardless of whether the halfedge data structure HDS provides a prev() member function for its halfedges or not. In the case that not, the implementation given here runs in time proportional to the size of the incident face. For const-correctness a second implementation with signature Halfedge_const_handle prev() const; is needed.

Note also the use of the static member function HalfedgeDS::halfedge_handle() of the halfedge data structure. It converts a pointer to the halfedge into a halfedge handle. This conversion encapsulates possible adjustments for hidden data members in the true halfedge type, such as linked-list pointers.

struct Polyhedron_halfedge {
// ...
return decorator.find_prev( HDS::halfedge_handle(this));
}
};

## Types

The respective const_handle's and const_iterator's are available as well.

typedef unspecified_type HalfedgeDS
halfedge data structure.

typedef unspecified_type Vertex
vertex type of HalfedgeDS.

typedef unspecified_type Halfedge
halfedge type of HalfedgeDS.

typedef unspecified_type Face
face type of HalfedgeDS.

typedef unspecified_type Vertex_handle

typedef unspecified_type Halfedge_handle

typedef unspecified_type Face_handle

typedef unspecified_type Vertex_iterator

typedef unspecified_type Halfedge_iterator

typedef unspecified_type Face_iterator

typedef unspecified_type size_type

typedef unspecified_type difference_type

typedef unspecified_type iterator_category

typedef unspecified_type Supports_vertex_halfedge

typedef unspecified_type Supports_halfedge_prev

typedef unspecified_type Supports_halfedge_vertex

typedef unspecified_type Supports_halfedge_face

typedef unspecified_type Supports_face_halfedge

typedef unspecified_type Supports_removal

## Creation

HalfedgeDS_items_decorator ()
default constructor.

## Access Functions

Corresponding member functions for const_handle's are provided as well.

Halfedge_handle get_vertex_halfedge (Vertex_handle v)
returns the incident halfedge of v if supported, Halfedge_handle() otherwise.

Vertex_handle get_vertex (Halfedge_handle h)
returns the incident vertex of h if supported, Vertex_handle() otherwise.

Halfedge_handle get_prev (Halfedge_handle h)
returns the previous halfedge of h if supported, Halfedge_handle() otherwise.

Halfedge_handle find_prev (Halfedge_handle h)
returns the previous halfedge of h. More...

Halfedge_handle find_prev_around_vertex (Halfedge_handle h)
returns the previous halfedge of h. More...

Face_handle get_face (Halfedge_handle h)
returns the incident face of h if supported, Face_handle() otherwise.

Halfedge_handle get_face_halfedge (Face_handle f)
returns the incident halfedge of f if supported, Halfedge_handle() otherwise.

## Modifying Functions (Composed)

void close_tip (Halfedge_handle h) const
makes h->opposite() the successor of h.

void close_tip (Halfedge_handle h, Vertex_handle v) const
makes h->opposite() the successor of h and sets the incident vertex of h to v.

void insert_tip (Halfedge_handle h, Halfedge_handle v) const
inserts the tip of the edge h into the halfedges around the vertex pointed to by v. More...

void remove_tip (Halfedge_handle h) const
removes the edge h->next()->opposite() from the halfedge circle around the vertex referred to by h. More...

void insert_halfedge (Halfedge_handle h, Halfedge_handle f) const
inserts the halfedge h between f and f->next(). More...

void remove_halfedge (Halfedge_handle h) const
removes edge h->next() from the halfedge circle around the face referred to by h. More...

void set_vertex_in_vertex_loop (Halfedge_handle h, Vertex_handle v) const
loops around the vertex incident to h and sets all vertex pointers to v. More...

void set_face_in_face_loop (Halfedge_handle h, Face_handle f) const
loops around the face incident to h and sets all face pointers to f. More...

Halfedge_handle flip_edge (Halfedge_handle h) const
performs an edge flip. More...

## Modifying Functions (Primitives)

void set_vertex_halfedge (Vertex_handle v, Halfedge_handle g) const
sets the incident halfedge of v to g.

void set_vertex_halfedge (Halfedge_handle h) const
sets the incident halfedge of the vertex v to h.

void set_vertex (Halfedge_handle h, Vertex_handle v) const
sets the incident vertex of h to v.

void set_prev (Halfedge_handle h, Halfedge_handle g) const
sets the previous link of h to g.

void set_face (Halfedge_handle h, Face_handle f) const
sets the incident face of h to f.

void set_face_halfedge (Face_handle f, Halfedge_handle g) const
sets the incident halfedge of f to g.

void set_face_halfedge (Halfedge_handle h) const
sets the incident halfedge of the face f to h.

## Member Function Documentation

template<typename HDS>
 Halfedge_handle CGAL::HalfedgeDS_items_decorator< HDS >::find_prev ( Halfedge_handle h)

returns the previous halfedge of h.

Uses the prev() method if supported or performs a search around the face using next().

template<typename HDS>
 Halfedge_handle CGAL::HalfedgeDS_items_decorator< HDS >::find_prev_around_vertex ( Halfedge_handle h)

returns the previous halfedge of h.

Uses the prev() method if supported or performs a search around the vertex using next().

template<typename HDS>
 Halfedge_handle CGAL::HalfedgeDS_items_decorator< HDS >::flip_edge ( Halfedge_handle h) const

performs an edge flip.

It returns h after rotating the edge h one vertex in the direction of the face orientation.

Precondition
h != Halfedge_handle() and both incident faces of h are triangles.
template<typename HDS>
 void CGAL::HalfedgeDS_items_decorator< HDS >::insert_halfedge ( Halfedge_handle h, Halfedge_handle f ) const

inserts the halfedge h between f and f->next().

The face of h will be the one f refers to if faces are supported.

template<typename HDS>
 void CGAL::HalfedgeDS_items_decorator< HDS >::insert_tip ( Halfedge_handle h, Halfedge_handle v ) const

inserts the tip of the edge h into the halfedges around the vertex pointed to by v.

Halfedge h->opposite() is the new successor of v and h->next() will be set to v->next(). The vertex of h will be set to the vertex v refers to if vertices are supported.

template<typename HDS>
 void CGAL::HalfedgeDS_items_decorator< HDS >::remove_halfedge ( Halfedge_handle h) const

removes edge h->next() from the halfedge circle around the face referred to by h.

The new successor of h will be h->next()->next().

template<typename HDS>
 void CGAL::HalfedgeDS_items_decorator< HDS >::remove_tip ( Halfedge_handle h) const

removes the edge h->next()->opposite() from the halfedge circle around the vertex referred to by h.

The new successor halfedge of h will be h->next()->opposite()->next().

template<typename HDS>
 void CGAL::HalfedgeDS_items_decorator< HDS >::set_face_in_face_loop ( Halfedge_handle h, Face_handle f ) const

loops around the face incident to h and sets all face pointers to f.

Precondition
h != Halfedge_handle().
template<typename HDS>
 void CGAL::HalfedgeDS_items_decorator< HDS >::set_vertex_in_vertex_loop ( Halfedge_handle h, Vertex_handle v ) const

loops around the vertex incident to h and sets all vertex pointers to v.

Precondition
h != Halfedge_handle().