\( \newcommand{\E}{\mathrm{E}} \) \( \newcommand{\A}{\mathrm{A}} \) \( \newcommand{\R}{\mathrm{R}} \) \( \newcommand{\N}{\mathrm{N}} \) \( \newcommand{\Q}{\mathrm{Q}} \) \( \newcommand{\Z}{\mathrm{Z}} \) \( \def\ccSum #1#2#3{ \sum_{#1}^{#2}{#3} } \def\ccProd #1#2#3{ \sum_{#1}^{#2}{#3} }\)
CGAL - Halfedge Data Structures
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HalfedgeDS/hds_prog_compact.cpp
#include <CGAL/HalfedgeDS_items_2.h>
#include <CGAL/HalfedgeDS_vector.h>
#include <CGAL/HalfedgeDS_decorator.h>
#include <cstddef>
// Define a new halfedge class. We assume that the Halfedge_handle can
// be created from a pointer (e.g. the HalfedgeDS is based here on the
// In_place_list or a std::vector with such property) and that halfedges
// are allocated in pairs. We encode the opposite pointer in a single bit,
// which is stored in the lower bit of the next-pointer. We use the
// static member function HDS::halfedge_handle to translate pointer to
// handles.
template <class Refs>
class My_halfedge {
public:
typedef Refs HDS;
typedef My_halfedge<Refs> Base_base;
typedef My_halfedge<Refs> Base;
typedef My_halfedge<Refs> Self;
typedef CGAL::Tag_false Supports_halfedge_prev;
typedef CGAL::Tag_true Supports_halfedge_vertex;
typedef CGAL::Tag_true Supports_halfedge_face;
typedef typename Refs::Vertex_handle Vertex_handle;
typedef typename Refs::Vertex_const_handle Vertex_const_handle;
typedef typename Refs::Halfedge Halfedge;
typedef typename Refs::Halfedge_handle Halfedge_handle;
typedef typename Refs::Halfedge_const_handle Halfedge_const_handle;
typedef typename Refs::Face_handle Face_handle;
typedef typename Refs::Face_const_handle Face_const_handle;
private:
std::ptrdiff_t nxt;
public:
My_halfedge() : nxt(0), f( Face_handle()) {}
Halfedge_handle opposite() {
// Halfedge could be different from My_halfedge (e.g. pointer for
// linked list). Get proper handle from 'this' pointer first, do
// pointer arithmetic, then convert pointer back to handle again.
Halfedge_handle h = HDS::halfedge_handle(this); // proper handle
if ( nxt & 1)
return HDS::halfedge_handle( &* h + 1);
return HDS::halfedge_handle( &* h - 1);
}
Halfedge_const_handle opposite() const { // same as above
Halfedge_const_handle h = HDS::halfedge_handle(this); // proper handle
if ( nxt & 1)
return HDS::halfedge_handle( &* h + 1);
return HDS::halfedge_handle( &* h - 1);
}
Halfedge_handle next() {
return HDS::halfedge_handle((Halfedge*)(nxt & (~ std::ptrdiff_t(1))));
}
Halfedge_const_handle next() const {
return HDS::halfedge_handle((const Halfedge*)
(nxt & (~ std::ptrdiff_t(1))));
}
void set_opposite( Halfedge_handle h) {
CGAL_precondition(( &* h - 1 == &* HDS::halfedge_handle(this)) ||
( &* h + 1 == &* HDS::halfedge_handle(this)));
if ( &* h - 1 == &* HDS::halfedge_handle(this))
nxt |= 1;
else
nxt &= (~ std::ptrdiff_t(1));
}
void set_next( Halfedge_handle h) {
CGAL_precondition( ((std::ptrdiff_t)(&*h) & 1) == 0);
nxt = ((std::ptrdiff_t)(&*h)) | (nxt & 1);
}
private: // Support for the Vertex_handle.
Vertex_handle v;
public:
// the incident vertex.
Vertex_handle vertex() { return v; }
Vertex_const_handle vertex() const { return v; }
void set_vertex( Vertex_handle w) { v = w; }
private:
Face_handle f;
public:
Face_handle face() { return f; }
Face_const_handle face() const { return f; }
void set_face( Face_handle g) { f = g; }
bool is_border() const { return f == Face_handle(); }
};
// Replace halfedge in the default items type.
struct My_items : public CGAL::HalfedgeDS_items_2 {
template <class Refs, class Traits>
struct Halfedge_wrapper {
typedef My_halfedge<Refs> Halfedge;
};
};
struct Traits { typedef int Point_2; };
int main() {
HDS hds(1,2,2);
Decorator decorator(hds);
decorator.create_loop();
CGAL_assertion( decorator.is_valid());
return 0;
}