CGAL 5.5.2 - 2D Arrangements
Arrangement_on_surface_2/observer.cpp
// Using a simple arrangement observer.
#include <CGAL/basic.h>
#include <CGAL/Arr_observer.h>
#include "arr_exact_construction_segments.h"
#include "arr_print.h"
// An observer that receives notifications of face splits and face mergers.
class My_observer : public CGAL::Arr_observer<Arrangement> {
public:
My_observer(Arrangement& arr) : CGAL::Arr_observer<Arrangement>(arr) {}
virtual void before_split_face(Face_handle, Halfedge_handle e) {
std::cout << "-> The insertion of : [ " << e->curve()
<< " ] causes a face to split.\n";
}
virtual void before_merge_face(Face_handle, Face_handle, Halfedge_handle e) {
std::cout << "-> The removal of : [ " << e->curve()
<< " ] causes two faces to merge.\n";
}
};
int main() {
// Construct the arrangement containing one diamond-shaped face.
Arrangement arr;
My_observer obs(arr);
insert_non_intersecting_curve(arr, Segment(Point(-1, 0), Point(0, 1)));
insert_non_intersecting_curve(arr, Segment(Point(0, 1), Point(1, 0)));
insert_non_intersecting_curve(arr, Segment(Point(1, 0), Point(0, -1)));
insert_non_intersecting_curve(arr, Segment(Point(0, -1), Point(-1, 0)));
// Insert a vertical segment dividing the diamond into two, and a
// a horizontal segment further dividing the diamond into four.
Segment s_v(Point(0, -1), Point(0, 1));
Halfedge_handle e_v = insert_non_intersecting_curve(arr, s_v);
insert(arr, Segment(Point(-1, 0), Point(1, 0))); /* \label{lst:observer:insertion} */
print_arrangement_size(arr);
// Now remove a portion of the vertical segment.
remove_edge(arr, e_v); // the observer will make a notification
print_arrangement_size(arr);
return 0;
}