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CGAL 4.8 - Halfedge Data Structures

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CGAL::HalfedgeDS_items_decorator< HDS > Class Template Reference
Decorators

`#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.

See Also
  `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 {
// ...
Halfedge_handle prev() {
CGAL::HalfedgeDS_items_decorator<HDS> decorator;
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()`.