new classes that efficiently handle the union or intersection of multiple polyhedra

OFF_to_nef_3 benefits from the new union

Nef_3/include/CGAL/Nef_3/Nary_intersection.h

@@ -0,0 +1,47 @@
+#ifndef CGAL_NEF_NARY_INTERSECTION_H
+#define CGAL_NEF_NARY_INTERSECTION_H
+
+#include <list>
+
+CGAL_BEGIN_NAMESPACE
+
+template<class Polyhedron>
+class Nary_intersection {
+
+  int inserted;
+  std::list<Polyhedron> queue;
+  typedef typename std::list<Polyhedron>::iterator pit;
+  Polyhedron empty;
+
+ public:
+  Nary_intersection() : inserted(0) {}
+  
+  void unite() {
+    pit i1(queue.begin()), i2(i1);
+    ++i2;
+
+    Polyhedron tmp(*i1 * *i2);
+
+    queue.pop_front();
+    queue.pop_front();
+    queue.push_front(tmp);
+  }
+
+  void add_polyhedron(const Polyhedron& P) {
+    queue.push_front(P);
+    ++inserted;
+    for(int i=2;(inserted%i) == 0; i*=2) {
+      unite();
+    }
+  }
+
+  Polyhedron get_intersection() {
+
+    while(queue.size() > 1)
+      unite();
+    return queue.front();
+  }
+};
+
+CGAL_END_NAMESPACE
+#endif // CGAL_NEF_NARY_INTERSECTION_H

Nef_3/include/CGAL/Nef_3/Nary_union.h

@@ -0,0 +1,47 @@
+#ifndef CGAL_NEF_NARY_UNION_H
+#define CGAL_NEF_NARY_UNION_H
+
+#include <list>
+
+CGAL_BEGIN_NAMESPACE
+
+template<class Polyhedron>
+class Nary_union {
+
+  int inserted;
+  std::list<Polyhedron> queue;
+  typedef typename std::list<Polyhedron>::iterator pit;
+  Polyhedron empty;
+
+ public:
+  Nary_union() : inserted(0) {}
+  
+  void unite() {
+    pit i1(queue.begin()), i2(i1);
+    ++i2;
+
+    Polyhedron tmp(*i1 + *i2);
+
+    queue.pop_front();
+    queue.pop_front();
+    queue.push_front(tmp);
+  }
+
+  void add_polyhedron(const Polyhedron& P) {
+    queue.push_front(P);
+    ++inserted;
+    for(int i=2;(inserted%i) == 0; i*=2) {
+      unite();
+    }
+  }
+
+  Polyhedron get_union() {
+
+    while(queue.size() > 1)
+      unite();
+    return queue.front();
+  }
+};
+
+CGAL_END_NAMESPACE
+#endif // CGAL_NEF_NARY_UNION_H

Nef_3/include/CGAL/OFF_to_nef_3.h

@@ -29,6 +29,7 @@
 #include<CGAL/Cartesian.h>
 #include<CGAL/Homogeneous.h>
 #include<CGAL/Nef_S2/Normalizing.h>
+#include<CGAL/Nef_3/Nary_union.h>
 
 #ifdef CGAL_USE_LEDA
 #include<CGAL/leda_integer.h>
@@ -110,9 +111,7 @@ OFF_to_nef_3 (std::istream &i_st, Nef_3 &nef_union, bool verb=false)
    typedef typename Nef_3::Kernel          Kernel;
    typedef typename Nef_3::Point_3         Point_3;
    typedef typename std::vector<Point_3>   Point_set;
-   typedef std::multimap<typename Nef_3::Size_type,Nef_3> Nef_map;
+   CGAL::Nary_union<Nef_3>                 nary_union;
-   typedef typename Nef_map::iterator      Nef_map_iter;
-
    // input data structure
    typedef double	                   Scan_NT;
    typedef CGAL::Cartesian<Scan_NT>        Scan_kernel;
@@ -131,7 +130,6 @@ OFF_to_nef_3 (std::istream &i_st, Nef_3 &nef_union, bool verb=false)
    // declarations and defaults
    std::size_t discarded_facets=0;
    long idx;
-   Nef_map nef_map; // priority queue
 
 #ifdef CGAL_NEF_OFF_TO_NEF_TIMER
    CGAL::Timer t_convert, t_union;
@@ -190,7 +188,7 @@ OFF_to_nef_3 (std::istream &i_st, Nef_3 &nef_union, bool verb=false)
          // construct and enqueue Nef_polyhedron_3 <Kernel>
          Nef_3 nef (V_f.begin(), V_f.end(), normal, verb);
          if ( !nef.is_empty() )
-         {  nef_map.insert (std::make_pair(nef.number_of_vertices(),nef));
+	   {nary_union.add_polyhedron(nef);
             is_nef = true;
          }
       }
@@ -216,27 +214,18 @@ OFF_to_nef_3 (std::istream &i_st, Nef_3 &nef_union, bool verb=false)
    t_union.start();
 #endif
 
-   while ( nef_map.size() > 1 )
-   {  Nef_map_iter nm=nef_map.begin(), nm2=nef_map.begin();
-      ++nm2;
-      Nef_3 nef_tmp ((nm->second)+(nm2->second));
-      nef_map.insert ( std::make_pair(nef_tmp.number_of_vertices(),nef_tmp));
-      nef_map.erase(nm);
-      nef_map.erase(nm2);
-   }
-
 #ifdef CGAL_NEF_OFF_TO_NEF_TIMER
    t_union.stop();
    std::cout << "time (union): " << t_union.time() << "\n" << std::endl;
 #endif
 
    // return values
-   if ( nef_map.size() == 0 ) nef_union = Nef_3 ();
+   //   if ( nef_map.size() == 0 ) nef_union = Nef_3 ();
-   else
+   //   else
-   {  nef_union = nef_map.begin()->second;
+   nef_union = nary_union.get_union();
    CGAL::Mark_bounded_volumes<Nef_3> mbv (true);
    nef_union.delegate (mbv);
-   }
+
    return discarded_facets;
 }