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

CGAL 4.3 - 2D Arrangements

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Arrangement_on_surface_2/observer.cpp
// Using a simple arrangement observer.
#include <CGAL/Cartesian.h>
#include <CGAL/Quotient.h>
#include <CGAL/MP_Float.h>
#include <CGAL/Arr_segment_traits_2.h>
#include <CGAL/Arrangement_2.h>
#include <CGAL/Arr_observer.h>
typedef CGAL::Quotient<CGAL::MP_Float> Number_type;
typedef CGAL::Cartesian<Number_type> Kernel;
typedef CGAL::Arr_segment_traits_2<Kernel> Traits_2;
typedef Traits_2::Point_2 Point_2;
typedef Traits_2::X_monotone_curve_2 Segment_2;
typedef CGAL::Arrangement_2<Traits_2> Arrangement_2;
// An arrangement observer, used to receive notifications of face splits and
// face mergers.
class My_observer : public CGAL::Arr_observer<Arrangement_2>
{
public:
My_observer (Arrangement_2& arr) :
CGAL::Arr_observer<Arrangement_2> (arr)
{}
virtual void before_split_face (Face_handle,
Halfedge_handle e)
{
std::cout << "-> The insertion of : [ " << e->curve()
<< " ] causes a face to split." << std::endl;
}
virtual void before_merge_face (Face_handle,
Face_handle,
Halfedge_handle e)
{
std::cout << "-> The removal of : [ " << e->curve()
<< " ] causes two faces to merge." << std::endl;
}
};
int main ()
{
// Construct the arrangement containing one diamond-shaped face.
Arrangement_2 arr;
My_observer obs (arr);
Segment_2 s1 (Point_2(-1, 0), Point_2(0, 1));
Segment_2 s2 (Point_2(0, 1), Point_2(1, 0));
Segment_2 s3 (Point_2(1, 0), Point_2(0, -1));
Segment_2 s4 (Point_2(0, -1), Point_2(-1, 0));
insert_non_intersecting_curve (arr, s1);
insert_non_intersecting_curve (arr, s2);
insert_non_intersecting_curve (arr, s3);
insert_non_intersecting_curve (arr, s4);
// Insert a vertical segment dividing the diamond into two, and a
// a horizontal segment further dividing the diamond into four:
Segment_2 s_vert (Point_2(0, -1), Point_2(0, 1));
Arrangement_2::Halfedge_handle
e_vert = insert_non_intersecting_curve (arr, s_vert);
Segment_2 s_horiz (Point_2(-1, 0), Point_2(1, 0));
insert (arr, s_horiz);
std::cout << "The initial arrangement size:" << std::endl
<< " V = " << arr.number_of_vertices()
<< ", E = " << arr.number_of_edges()
<< ", F = " << arr.number_of_faces() << std::endl;
// Now remove a portion of the vertical segment.
remove_edge (arr, e_vert);
std::cout << "The final arrangement size:" << std::endl
<< " V = " << arr.number_of_vertices()
<< ", E = " << arr.number_of_edges()
<< ", F = " << arr.number_of_faces() << std::endl;
return 0;
}