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CGAL 4.8.1 - 2D Visibility
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Visibility_2 Concept Reference
Concepts

Definition

A model of the Visibility_2 concept can be attached to an Arrangement_2 instance to answer visibility queries within the faces of this arrangement.

Has Models:

CGAL::Simple_polygon_visibility_2

CGAL::Rotational_sweep_visibility_2

CGAL::Triangular_expansion_visibility_2

Types

typedef unspecified_type Arrangement_2
 The arrangement type of the input.
 
typedef Arrangement_2::Point_2 Point_2
 The 2D point type used for the queries.
 
typedef
Arrangement_2::Face_const_handle 		Face_const_handle
 The face handle type of the input arrangement.
 
typedef
Arrangement_2::Halfedge_const_handle 		Halfedge_const_handle
 The halfedge handle type of the input arrangement.
 

Tags

typedef unspecified_type Regularization_category
 identifies whether the regularized visibility area is computed (either Tag_true or Tag_false).
 
typedef unspecified_type Supports_general_polygon_category
 identifies whether general polygons (with holes) are supported (either Tag_true or Tag_false). More...
 
typedef unspecified_type Supports_simple_polygon_category
 identifies whether simple polygons are supported (either Tag_true or Tag_false). More...
 

Constructors

 Visibility_2 ()
 Default constructor creates an empty Visibility_2 object that is not attached to any arrangement yet.
 
 Visibility_2 (const Arrangement_2 &arr)
 Constructs a Visibility_2 object that is attached to arr.
 

Functions

bool is_attached () const
 Returns whether an arrangement is attached to the visibility object.
 
void attach (const Arrangement_2 &arr)
 Attaches the given arrangement arr to the visibility object. More...
 
void detach ()
 Detaches the arrangement from the visibility object it is currently attached to.
 
const Arrangement_2 & arrangement_2 () const
 Access to the attached arrangement.
 
template<typename VisibilityArrangement_2 >
Visibility_arrangement_2::Face_handle compute_visibility (const Point_2 &q, const Face_const_handle f, VisibilityArrangement_2 &out_arr) const
 Computes the visibility region for the given query point q in the face \( f \) of the arrangement that is attached to the visibility object. More...
 
template<typename VisibilityArrangement_2 >
Visibility_arrangement_2::Face_handle compute_visibility (const Point_2 &q, const Halfedge_const_handle e, Visibility_arrangement_2 &out_arr) const
 Computes the visibility region in e->face() for the given query point q which must be located on e. More...
 

Member Typedef Documentation

typedef unspecified_type Visibility_2::Supports_general_polygon_category

identifies whether general polygons (with holes) are supported (either Tag_true or Tag_false).

A general polygon is represented by a face \( f \) with no isolated vertex and any edge of \( f \) separates \( f \) from another face. Note that this allows \( f \) to touch a vertex from several sides.

typedef unspecified_type Visibility_2::Supports_simple_polygon_category

identifies whether simple polygons are supported (either Tag_true or Tag_false).

A simple polygon is represented by a face \( f \) with no holes, no isolated vertex and any edge of \( f \) separates \( f \) from another face. Note that this allows \( f \) to touch a vertex from several sides.

Member Function Documentation

void Visibility_2::attach ( const Arrangement_2 &  arr)

Attaches the given arrangement arr to the visibility object.

In case the object is already attached to another arrangement, the visibility object gets detached before being attached to arr.

template<typename VisibilityArrangement_2 >
Visibility_arrangement_2::Face_handle Visibility_2::compute_visibility ( const Point_2 &  q,
const Face_const_handle  f,
VisibilityArrangement_2 &  out_arr 
) const

Computes the visibility region for the given query point q in the face \( f \) of the arrangement that is attached to the visibility object.

The visibility region of q is stored in out_arr, that is, all features but the unbounded face of out_arr represent the visibility region.

Template Parameters
VisibilityArrangement_2is the type of the output arrangement representing the visibility polygon. It must be an instance of CGAL::Arrangement_2, where its CGAL::Arrangement_2::Traits_2 must be mutual convertible to VisibilityArrangement_2::Traits_2.
Parameters
qis the query point
fis the face of the arrangement in which the visibility region is computed
out_arris the output arrangement
Precondition
f is a face of this->arrangement_2()
q is in the interior of the given face f
Returns
the face handle to the face in out_arr that represents interior of the visibility region
template<typename VisibilityArrangement_2 >
Visibility_arrangement_2::Face_handle Visibility_2::compute_visibility ( const Point_2 &  q,
const Halfedge_const_handle  e,
Visibility_arrangement_2 &  out_arr 
) const

Computes the visibility region in e->face() for the given query point q which must be located on e.

If q is an interior point of e, the computed visibility region is restricted to the side indicated by the halfedge e. If q is an endpoint of e, the visibility region is restricted by e and e->next(). The visibility region of q is stored in out_arr, that is, all features but the unbounded face of out_arr represent the visibility region.

Template Parameters
VisibilityArrangement_2is the type of the output arrangement representing the visibility polygon. It must be an instance of CGAL::Arrangement_2, where its CGAL::Arrangement_2::Traits_2 must be mutual convertible to VisibilityArrangement_2::Traits_2.
Parameters
qis the query point
ethe halfedge on which q is located
out_arris the output arrangement
Precondition
e is a halfedge of this->arrangement_2()
q is on e
q equals to e->target()->point() if q is an endpoint of e
Returns
a handle to the face in out_arr that represents the interior of the visibility region