Visibility_2 Concept Reference

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

Supports_general_polygon_category

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.

Supports_simple_polygon_category

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

attach()

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.

compute_visibility() [1/2]

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_2

is 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

q	is the query point
f	is the face of the arrangement in which the visibility region is computed
out_arr	is 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

compute_visibility() [2/2]

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_2

is 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

q	is the query point
e	the halfedge on which q is located
out_arr	is 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