Merge pull request #5166 from sgiraudot/Arrangement_2-Enhanced_ccb_merge-GF

Arrangement 2: Enhanced CCB Merging for Surface Sweep

Author: lrineau

Arrangement_on_surface_2/include/CGAL/Arr_dcel_base.h

@@ -478,7 +478,18 @@ class Arr_halfedge : public H,
   const Inner_ccb* inner_ccb() const
   {
     CGAL_precondition(is_on_inner_ccb());
-    return (reinterpret_cast<const Inner_ccb*>(_clean_pointer(this->p_comp)));
+
+    const Inner_ccb* out = reinterpret_cast<const Inner_ccb*>(_clean_pointer(this->p_comp));
+    if (out->is_valid())
+      return out;
+
+    // else reduce path and get valid iccb
+    const Inner_ccb* valid = out->next();
+    while (!valid->is_valid())
+      valid = valid->next();
+    const_cast<Inner_ccb*>(out)->set_next(const_cast<Inner_ccb*>(valid));
+    const_cast<Halfedge*>(this)->set_inner_ccb(valid);
+    return valid;
   }
 
   /*! Get an incident inner CCB (non-const version).
@@ -487,11 +498,28 @@ class Arr_halfedge : public H,
   Inner_ccb* inner_ccb()
   {
     CGAL_precondition(is_on_inner_ccb());
-    return (reinterpret_cast<Inner_ccb*>(_clean_pointer(this->p_comp)));
+
+    Inner_ccb* out = reinterpret_cast<Inner_ccb*>(_clean_pointer(this->p_comp));
+    if (out->is_valid())
+      return out;
+
+    // else reduce path and get valid iccb
+    Inner_ccb* valid = out->next();
+    while (!valid->is_valid())
+      valid = valid->next();
+    out->set_next(valid);
+    set_inner_ccb(valid);
+    return valid;
+  }
+
+  Inner_ccb* inner_ccb_no_redirect()
+  {
+    CGAL_precondition(is_on_inner_ccb());
+    return reinterpret_cast<Inner_ccb*>(_clean_pointer(this->p_comp));
   }
 
   /*! Set the incident inner CCB. */
-  void set_inner_ccb(Inner_ccb *ic)
+  void set_inner_ccb(const Inner_ccb *ic)
   {
     // Set the component pointer and set its LSB.
     this->p_comp = _set_lsb(ic);
@@ -768,57 +796,111 @@ class Arr_inner_ccb : public In_place_list_base<Arr_inner_ccb<V,H,F> >
   typedef typename Face::Inner_ccb_iterator  Inner_ccb_iterator;
 
 private:
-  Face* p_f;                  // The face the contains the CCB in its interior.
+  union
+  {
+    Face* f;                  // The face the contains the CCB in its interior.
+    Arr_inner_ccb* icc;       // next inner CCB in chain to valid icc
+  } f_or_icc;
   Inner_ccb_iterator  iter;   // The inner CCB identifier.
-  bool iter_is_not_singular;
+  enum
+  {
+    ITER_IS_SINGULAR,     // singular = default iterator, not initialized
+    ITER_IS_NOT_SINGULAR, // not singular = iterator was assigned and is valid
+    INVALID               // invalid = the inner CCB is invalid and
+                          //           only links to another inner CCB
+                          //           in chain to valid CCB
+  } status;
 
 public:
   /*! Default constructor. */
-  Arr_inner_ccb() : p_f(nullptr), iter_is_not_singular(false) {}
+  Arr_inner_ccb() : status(ITER_IS_SINGULAR) { f_or_icc.f = nullptr; }
 
   /*! Copy constructor. */
   Arr_inner_ccb(const Arr_inner_ccb& other) :
-    p_f(other.p_f), iter_is_not_singular(other.iter_is_not_singular)
-  { if (other.iter_is_not_singular) iter = other.iter; }
+    f_or_icc(other.f_or_icc), status(other.status)
+  { if (other.status == ITER_IS_NOT_SINGULAR) iter = other.iter; }
 
   /*! Get a halfedge along the component (const version). */
-  const Halfedge* halfedge() const { return (*iter); }
+  const Halfedge* halfedge() const
+  {
+    CGAL_assertion (is_valid());
+    return (*iter);
+  }
 
   /*! Get a halfedge along the component (non-const version). */
-  Halfedge* halfedge() { return (*iter); }
+  Halfedge* halfedge()
+  {
+    CGAL_assertion (is_valid());
+    return (*iter);
+  }
 
   /*! Set a representative halfedge for the component. */
-  void set_halfedge(Halfedge *he) { *iter = he; }
+  void set_halfedge(Halfedge *he)
+  {
+    CGAL_assertion (is_valid());
+    *iter = he;
+  }
 
   /*! Get the incident face (const version). */
-  const Face* face() const { return (p_f); }
+  const Face* face() const
+  {
+    CGAL_assertion (status != INVALID);
+    return f_or_icc.f;
+  }
 
   /*! Get the incident face (non-const version). */
-  Face* face() { return (p_f); }
+  Face* face()
+  {
+    CGAL_assertion (status != INVALID);
+    return f_or_icc.f;
+  }
 
   /*! Set the incident face. */
-  void set_face(Face* f) { p_f = f; }
+  void set_face(Face* f)
+  {
+    CGAL_assertion (status != INVALID);
+    f_or_icc.f = f;
+  }
 
   /*! Get the iterator (const version). */
   Inner_ccb_iterator iterator() const
   {
-    CGAL_assertion(iter_is_not_singular);
+    CGAL_assertion(status == ITER_IS_NOT_SINGULAR);
     return (iter);
   }
 
   /*! Get the iterator (non-const version). */
   Inner_ccb_iterator iterator()
   {
-    CGAL_assertion(iter_is_not_singular);
+    CGAL_assertion(status == ITER_IS_NOT_SINGULAR);
     return (iter);
   }
 
   /*! Set the inner CCB iterator. */
   void set_iterator(Inner_ccb_iterator it)
   {
+    CGAL_assertion (is_valid());
     iter = it;
-    iter_is_not_singular = true;
+    status = ITER_IS_NOT_SINGULAR;
+  }
+
+  /*! Check validity */
+  bool is_valid() const { return (status != INVALID); }
+
+  /*! Get the next CCB to primary chain. */
+  Arr_inner_ccb* next() const
+  {
+    CGAL_assertion (status == INVALID);
+    return f_or_icc.icc;
   }
+
+  /*! Set the next CCB to primary chain. */
+  void set_next(Arr_inner_ccb* next)
+  {
+    status = INVALID;
+    f_or_icc.icc = next;
+  }
+
 };
 
 /*! \class
@@ -942,6 +1024,7 @@ class Arr_dcel_base {
   typedef typename Face_list::iterator                Face_iterator;
   typedef CGAL::N_step_adaptor_derived<Halfedge_iterator, 2>
                                                       Edge_iterator;
+  typedef typename Inner_ccb_list::iterator           Inner_ccb_iterator;
 
   // Definitions of const iterators.
   typedef typename Vertex_list::const_iterator        Vertex_const_iterator;
@@ -1018,6 +1101,9 @@ class Arr_dcel_base {
   {
     return make_prevent_deref_range(edges_begin(), edges_end());
   }
+
+  Inner_ccb_iterator inner_ccbs_begin() { return in_ccbs.begin(); }
+  Inner_ccb_iterator inner_ccbs_end()   { return in_ccbs.end(); }
   //@}
 
   /// \name Obtaining constant iterators.

Arrangement_on_surface_2/include/CGAL/Arrangement_2/Arrangement_on_surface_2_impl.h

@@ -2739,14 +2739,24 @@ _insert_at_vertices(DHalfedge* he_to,
       he1->set_inner_ccb(ic1);
       he2->set_inner_ccb(ic1);
 
-      // Make all halfedges along ic2 to point to ic1.
-      DHalfedge* curr;
-
-      for (curr = he2->next(); curr != he1; curr = curr->next())
-        curr->set_inner_ccb(ic1);
+      if (m_sweep_mode)
+      {
+        // Inner CCB are obtained using Halfedge::inner_ccb() which
+        // performs path reduction and always return valid iCCB
+        CGAL_assertion(ic1->is_valid());
+        CGAL_assertion(ic2->is_valid());
+        ic2->set_next(ic1);
+      }
+      else
+      {
+        // Make all halfedges along ic2 to point to ic1.
+        DHalfedge* curr;
+        for (curr = he2->next(); curr != he1; curr = curr->next())
+          curr->set_inner_ccb(ic1);
 
-      // Delete the redundant inner CCB.
-      _dcel().delete_inner_ccb(ic2);
+        // Delete the redundant inner CCB.
+        _dcel().delete_inner_ccb(ic2);
+      }
 
       // Notify the observers that we have merged the two inner CCBs.
       _notify_after_merge_inner_ccb(fh, (Halfedge_handle(he1))->ccb());

Arrangement_on_surface_2/include/CGAL/Arrangement_on_surface_2.h

@@ -909,6 +909,14 @@ class Arrangement_on_surface_2 {
   bool                    m_own_traits;    // inidicates whether the geometry
                                            // traits should be freed up.
 
+  bool                    m_sweep_mode = false;
+                                           // sweep mode efficiently
+                                           // merges inner CCB but
+                                           // keeps invalid inner CCB
+                                           // and memory overhead that
+                                           // should be cleaned
+                                           // afterwards
+
 public:
   /// \name Constructors.
   //@{
@@ -939,6 +947,9 @@ class Arrangement_on_surface_2 {
   /*! Destructor. */
   virtual ~Arrangement_on_surface_2();
 
+  /*! Change mode. */
+  void set_sweep_mode (bool mode) { m_sweep_mode = mode; }
+
   /*! Clear the arrangement. */
   virtual void clear();
   //@}
@@ -1516,6 +1527,39 @@ class Arrangement_on_surface_2 {
 
   //@}
 
+  /*!
+   * Cleans the inner CCB if sweep mode was used, by removing all
+   * non-valid inner CCBs
+   */
+  void clean_inner_ccbs_after_sweep()
+  {
+    for (DHalfedge_iter he = _dcel().halfedges_begin();
+         he != _dcel().halfedges_end(); ++ he)
+    {
+      if (!he->is_on_inner_ccb())
+        continue;
+
+      DInner_ccb* ic1 = he->inner_ccb_no_redirect();
+      if (ic1->is_valid())
+        continue;
+
+      // Calling Halfedge::inner_ccb() reduces the path and makes the
+      // halfedge point to a correct CCB
+      DInner_ccb* ic2 = he->inner_ccb();
+      CGAL_USE(ic2);
+      CGAL_assertion (ic2->halfedge()->is_on_inner_ccb()
+                      && ic2->halfedge()->inner_ccb_no_redirect() == ic2);
+    }
+
+    typename Dcel::Inner_ccb_iterator it = _dcel().inner_ccbs_begin();
+    while (it != _dcel().inner_ccbs_end())
+    {
+      typename Dcel::Inner_ccb_iterator current = it ++;
+      if (!current->is_valid())
+        _dcel().delete_inner_ccb(&*current);
+    }
+  }
+
 protected:
   /// \name Determining the boundary-side conditions.
   //@{

Arrangement_on_surface_2/include/CGAL/Surface_sweep_2/Arr_construction_ss_visitor.h

@@ -142,6 +142,9 @@ class Arr_construction_ss_visitor :
   /* A notification issued before the sweep process starts. */
   inline void before_sweep();
 
+  /* A notification issued after the sweep process stops. */
+  inline void after_sweep();
+
   /*!
    * A notification invoked before the sweep-line starts handling the given
    * event.
@@ -267,7 +270,21 @@ class Arr_construction_ss_visitor :
 // Notifies the helper that the sweep process now starts.
 template <typename Hlpr, typename Vis>
 void Arr_construction_ss_visitor<Hlpr, Vis>::before_sweep()
-{ m_helper.before_sweep(); }
+{
+  m_helper.before_sweep();
+  m_arr->set_sweep_mode(true);
+}
+
+
+//-----------------------------------------------------------------------------
+// A notification issued after the sweep process stops.
+template <typename Hlpr, typename Vis>
+void Arr_construction_ss_visitor<Hlpr, Vis>::after_sweep()
+{
+  m_arr->clean_inner_ccbs_after_sweep();
+  m_arr->set_sweep_mode(false);
+}
+
 
 //-----------------------------------------------------------------------------
 // A notification invoked before the sweep-line starts handling the given

Arrangement_on_surface_2/include/CGAL/Surface_sweep_2/Arr_overlay_ss_visitor.h

@@ -552,6 +552,8 @@ Arr_overlay_ss_visitor<OvlHlpr, OvlTr, Vis>::update_event(Event* e,
 template <typename OvlHlpr, typename OvlTr, typename Vis>
 void Arr_overlay_ss_visitor<OvlHlpr, OvlTr, Vis>::after_sweep()
 {
+  Base::after_sweep();
+
   // Notify boundary vertices:
   typename Vertex_map::iterator it;
   for (it = m_vertices_map.begin(); it != m_vertices_map.end(); ++it) {