cgal/Polyhedron/demo/Polyhedron.old/include/CGAL/self_intersect.h

// compute self-intersection of a CGAL triangle polyhedron mesh
// original code from Lutz Kettner
#ifndef _SELF_INTERSECT_H_
#define _SELF_INTERSECT_H_

#include <CGAL/box_intersection_d.h>
#include <CGAL/intersections.h>
#include <CGAL/Bbox_3.h>

template <class Polyhedron, class Kernel, class OutputIterator>
struct Intersect_facets
{
  typedef typename Kernel::Point_3      Point;
  typedef typename Kernel::Vector_3     Vector;
  typedef typename Kernel::Segment_3    Segment;
  typedef typename Kernel::Triangle_3   Triangle;
  typedef typename Polyhedron::Facet_const_handle       Facet_const_handle;
  typedef typename Polyhedron::Facet_const_iterator     Facet_const_iterator;
  typedef typename Polyhedron::Halfedge_const_handle    Halfedge_const_handle;
  typedef typename CGAL::Box_intersection_d::Box_with_handle_d<double, 3, Facet_const_handle> Box;
  mutable OutputIterator m_iterator;

public:

  Intersect_facets(OutputIterator it)
    : m_iterator(it)
  {
  }

  void operator()(const Box* b,
    const Box* c) const
  {
    Halfedge_const_handle h = b->handle()->halfedge();

    // check for shared egde --> no intersection
    if(h->opposite()->facet() == c->handle() ||
      h->next()->opposite()->facet() == c->handle() ||
      h->next()->next()->opposite()->facet() == c->handle())
      return;

    // check for shared vertex --> maybe intersection, maybe not
    Halfedge_const_handle g = c->handle()->halfedge();
    Halfedge_const_handle v;

    if(h->vertex() == g->vertex())
      v = g;
    if(h->vertex() == g->next()->vertex())
      v = g->next();
    if(h->vertex() == g->next()->next()->vertex())
      v = g->next()->next();

    if(v == Halfedge_const_handle())
    {
      h = h->next();
      if(h->vertex() == g->vertex())
	v = g;
      if(h->vertex() == g->next()->vertex())
	v = g->next();
      if(h->vertex() == g->next()->next()->vertex())
	v = g->next()->next();
      if(v == Halfedge_const_handle())
      {
	h = h->next();
	if(h->vertex() == g->vertex())
	  v = g;
	if(h->vertex() == g->next()->vertex())
	  v = g->next();
	if(h->vertex() == g->next()->next()->vertex())
	  v = g->next()->next();
      }
    }

    if(v != Halfedge_const_handle())
    {
      // found shared vertex: 
      CGAL_assertion(h->vertex() == v->vertex());
      // geometric check if the opposite segments intersect the triangles
      Triangle t1( h->vertex()->point(),
	h->next()->vertex()->point(),
	h->next()->next()->vertex()->point());
      Triangle t2( v->vertex()->point(),
	v->next()->vertex()->point(),
	v->next()->next()->vertex()->point());
      Segment s1( h->next()->vertex()->point(),
	h->next()->next()->vertex()->point());
      Segment s2( v->next()->vertex()->point(),
	v->next()->next()->vertex()->point());

      if(CGAL::do_intersect(t1,s2))
      {
	*m_iterator++ = t1;
	*m_iterator++ = t2;
      }
      else
	if(CGAL::do_intersect(t2,s1))
	{
	  *m_iterator++ = t1;
	  *m_iterator++ = t2;
	}
	return;
    }

    // check for geometric intersection
    Triangle t1( h->vertex()->point(),
      h->next()->vertex()->point(),
      h->next()->next()->vertex()->point());
    Triangle t2( g->vertex()->point(),
      g->next()->vertex()->point(),
      g->next()->next()->vertex()->point());
    if(CGAL::do_intersect(t1, t2))
    {
      *m_iterator++ = t1;
      *m_iterator++ = t2;
    }
  } // end operator ()
}; // end struct Intersect_facets

template <class Polyhedron, class Kernel, class OutputIterator>
void self_intersect(const Polyhedron& polyhedron,
		    OutputIterator out)
{
  typedef CGAL::Bbox_3                  Bbox; // always double
  typedef typename Kernel::Point_3      Point;
  typedef typename Kernel::Vector_3     Vector;
  typedef typename Kernel::Triangle_3   Triangle;
  typedef typename Kernel::Segment_3    Segment;
  typedef typename Polyhedron::Halfedge_const_handle    Halfedge_const_handle;
  typedef typename Polyhedron::Facet_const_iterator     Facet_const_iterator;
  typedef typename Polyhedron::Facet_const_handle       Facet_const_handle;
  typedef typename CGAL::Box_intersection_d::Box_with_handle_d<double, 3, Facet_const_handle> Box;

  // make one box per facet
  std::vector<Box> boxes;
  boxes.reserve(polyhedron.size_of_facets());

  Facet_const_iterator f;
  for(f = polyhedron.facets_begin();
    f != polyhedron.facets_end();
    f++)
    boxes.push_back(Box( f->halfedge()->vertex()->point().bbox() +
    f->halfedge()->next()->vertex()->point().bbox() +
    f->halfedge()->next()->next()->vertex()->point().bbox(),
    f));

  // generate box pointers
  std::vector<const Box*> box_ptr;
  box_ptr.reserve(polyhedron.size_of_facets());
  typename std::vector<Box>::iterator b;
  for(b = boxes.begin();
    b != boxes.end();
    b++)
    box_ptr.push_back(&*b);

  // compute self-intersections filtered out by boxes
  Intersect_facets<Polyhedron,Kernel,OutputIterator> intersect_facets(out);
  std::ptrdiff_t cutoff = 2000;
  CGAL::box_self_intersection_d(box_ptr.begin(), box_ptr.end(),intersect_facets,cutoff);

} // end self_intersect

#endif // _SELF_INTERSECT_H_