\( \newcommand{\E}{\mathrm{E}} \) \( \newcommand{\A}{\mathrm{A}} \) \( \newcommand{\R}{\mathrm{R}} \) \( \newcommand{\N}{\mathrm{N}} \) \( \newcommand{\Q}{\mathrm{Q}} \) \( \newcommand{\Z}{\mathrm{Z}} \) \( \def\ccSum #1#2#3{ \sum_{#1}^{#2}{#3} } \def\ccProd #1#2#3{ \sum_{#1}^{#2}{#3} }\)

CGAL 4.8 - 2D Visibility

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Visibility_2/general_polygon_example.cpp
#include <CGAL/Exact_predicates_exact_constructions_kernel.h>
#include <CGAL/Triangular_expansion_visibility_2.h>
#include <CGAL/Arr_segment_traits_2.h>
#include <CGAL/Arrangement_2.h>
#include <iostream>
#include <vector>
// Define the used kernel and arrangement
typedef CGAL::Exact_predicates_exact_constructions_kernel Kernel;
typedef Kernel::Point_2 Point_2;
typedef Kernel::Segment_2 Segment_2;
typedef CGAL::Arr_segment_traits_2<Kernel> Traits_2;
typedef CGAL::Arrangement_2<Traits_2> Arrangement_2;
typedef Arrangement_2::Halfedge_const_handle Halfedge_const_handle;
typedef Arrangement_2::Face_handle Face_handle;
// Define the used visibility class
typedef CGAL::Triangular_expansion_visibility_2<Arrangement_2> TEV;
int main() {
// Defining the input geometry
Point_2 p1(1,2), p2(12, 3), p3(19,-2), p4(12,6), p5(14,14), p6( 9,5);
Point_2 h1(8,3), h2(10, 3), h3( 8, 4), h4(10,6), h5(11, 6), h6(11,7);
std::vector<Segment_2> segments;
segments.push_back(Segment_2(p1,p2));
segments.push_back(Segment_2(p2,p3));
segments.push_back(Segment_2(p3,p4));
segments.push_back(Segment_2(p4,p5));
segments.push_back(Segment_2(p5,p6));
segments.push_back(Segment_2(p6,p1));
segments.push_back(Segment_2(h1,h2));
segments.push_back(Segment_2(h2,h3));
segments.push_back(Segment_2(h3,h1));
segments.push_back(Segment_2(h4,h5));
segments.push_back(Segment_2(h5,h6));
segments.push_back(Segment_2(h6,h4));
// insert geometry into the arrangement
Arrangement_2 env;
CGAL::insert_non_intersecting_curves(env,segments.begin(),segments.end());
//Find the halfedge whose target is the query point.
//(usually you may know that already by other means)
Point_2 query_point = p4;
Halfedge_const_handle he = env.halfedges_begin();
while (he->source()->point() != p3 || he->target()->point() != p4)
he++;
//visibility query
Arrangement_2 output_arr;
TEV tev(env);
Face_handle fh = tev.compute_visibility(query_point, he, output_arr);
//print out the visibility region.
std::cout << "Regularized visibility region of q has "
<< output_arr.number_of_edges()
<< " edges." << std::endl;
std::cout << "Boundary edges of the visibility region:" << std::endl;
Arrangement_2::Ccb_halfedge_circulator curr = fh->outer_ccb();
std::cout << "[" << curr->source()->point() << " -> " << curr->target()->point() << "]" << std::endl;
while (++curr != fh->outer_ccb())
std::cout << "[" << curr->source()->point() << " -> " << curr->target()->point() << "]"<< std::endl;
return 0;
}