CGAL users discussion list

[Jo <>]

Ben Supnik's first hint using the "Arr_bfs_scanner" class.
I'm not sure the result. 1 polygon to have 3 holes.

#include <CGAL/Gmpq.h>
#include <CGAL/Lazy_exact_nt.h>
#include <CGAL/Cartesian.h>
#include <CGAL/Arrangement_2.h>
#include <CGAL/Boolean_set_operations_2/Gps_default_dcel.h>
#include <CGAL/Gps_segment_traits_2.h>
#include <CGAL/General_polygon_set_2.h>
#include <CGAL/General_polygon_with_holes_2.h>
#include <list>

typedef CGAL::Gmpq                                                     
Number_type;
typedef CGAL::Lazy_exact_nt<Number_type>                               
Lazy_exact_nt;
typedef CGAL::Cartesian<Lazy_exact_nt>                                  
Kernel;
typedef Kernel::Point_2                                                
Point_2;
typedef Kernel::Segment_2                                              
Segment_2;
typedef CGAL::Gps_segment_traits_2<Kernel>                             
Traits_2;
typedef CGAL::Gps_default_dcel<Traits_2>                                Dcel;
typedef CGAL::Arrangement_2<Traits_2, Dcel>                            
Arrangement2;
typedef CGAL::General_polygon_set_2<Traits_2>                          
Polygon_set_2;
typedef Traits_2::General_polygon_with_holes_2                         
Polygon_with_holes_2;
typedef std::back_insert_iterator<std::list<Polygon_with_holes_2> >    
OutputIterator;
typedef CGAL::Arr_bfs_scanner<Arrangement2, OutputIterator>            
Arr_bfs_scanner;

int main()
{
    Arrangement2 arr;
    std::list<Segment_2> segments;

    segments.push_back(Segment_2(Point_2(0,0), Point_2(50,0)));
    segments.push_back(Segment_2(Point_2(50,0), Point_2(50,30)));
    segments.push_back(Segment_2(Point_2(50,30), Point_2(30,30)));
    segments.push_back(Segment_2(Point_2(30,30), Point_2(30,10)));
    segments.push_back(Segment_2(Point_2(30,10), Point_2(10,10)));
    segments.push_back(Segment_2(Point_2(10,10), Point_2(10,40)));
    segments.push_back(Segment_2(Point_2(10,40), Point_2(20,40)));
    segments.push_back(Segment_2(Point_2(20,40), Point_2(20,20)));
    segments.push_back(Segment_2(Point_2(20,20), Point_2(40,20)));
    segments.push_back(Segment_2(Point_2(40,20), Point_2(40,50)));
    segments.push_back(Segment_2(Point_2(40,50), Point_2(0,50)));
    segments.push_back(Segment_2(Point_2(0,50), Point_2(0,0)));

    insert(arr, segments.begin(), segments.end());

    Polygon_set_2 s;
    std::list<Polygon_with_holes_2> res;
    OutputIterator out = std::back_inserter(res);

    Traits_2 trait;
    Arr_bfs_scanner scanner(&trait, out);
    scanner.scan(arr);
    
    std::cout<<std::endl;
    std::cout<<"Number of polygon : "<<res.size()<<std::endl;
    std::list<Polygon_with_holes_2>::const_iterator it;
    int i=1;
    for (it=res.begin(); it!=res.end(); ++it, ++i)
        std::cout<<"#"<<i<<" Number of holes :
"<<it->number_of_holes()<<std::endl;

    return 0;
}

I hope that somebody draw the shapes on a screen to confirm the result.
Thans.