From acb96cba86842093ea6d975df04750c46dbffb95 Mon Sep 17 00:00:00 2001
From: Simon Giraudot <simon.giraudot@geometryfactory.com>
Date: Wed, 12 Aug 2020 15:56:46 +0200
Subject: [PATCH] Get rid of index using pointer squatting + before/after
 functions

---
 .../include/CGAL/Arr_dcel_base.h              |  7 ++-
 .../include/CGAL/Arr_overlay_2.h              | 62 ++++++++++++++-----
 .../CGAL/No_intersection_surface_sweep_2.h    |  2 +
 3 files changed, 53 insertions(+), 18 deletions(-)

diff --git a/Arrangement_on_surface_2/include/CGAL/Arr_dcel_base.h b/Arrangement_on_surface_2/include/CGAL/Arr_dcel_base.h
index 76f490663f0..2c685385abc 100644
--- a/Arrangement_on_surface_2/include/CGAL/Arr_dcel_base.h
+++ b/Arrangement_on_surface_2/include/CGAL/Arr_dcel_base.h
@@ -90,6 +90,11 @@ public:
   /*! Destructor. */
   virtual ~Arr_vertex_base() {}
 
+  // Access/modification for pointer squatting
+  void* inc() const { return p_inc; }
+  void set_inc(void * inc) const
+  { const_cast<Arr_vertex_base&>(*this).p_inc = inc; }
+
   /*! Check if the point pointer is nullptr. */
   bool has_null_point() const { return (p_pt == nullptr); }
 
@@ -287,8 +292,6 @@ public:
   typedef Arr_halfedge<V,H,F>         Halfedge;
   typedef Arr_isolated_vertex<V,H,F>  Isolated_vertex;
 
-  mutable std::size_t index;
-
   /*! Default constructor. */
   Arr_vertex() {}
 
diff --git a/Arrangement_on_surface_2/include/CGAL/Arr_overlay_2.h b/Arrangement_on_surface_2/include/CGAL/Arr_overlay_2.h
index 569d6e66d93..d6b55cffd2c 100644
--- a/Arrangement_on_surface_2/include/CGAL/Arr_overlay_2.h
+++ b/Arrangement_on_surface_2/include/CGAL/Arr_overlay_2.h
@@ -40,24 +40,31 @@
 
 namespace CGAL {
 
-template <typename Curve>
+template <typename Arr1, typename Arr2, typename Curve>
 class Indexed_sweep_accessor
 {
-  std::size_t nbv;
+  const Arr1& arr1;
+  const Arr2& arr2;
+  mutable std::vector<void*> backup_inc;
 
 public:
-  Indexed_sweep_accessor (std::size_t nbv) : nbv(nbv) { }
 
-  std::size_t nb_vertices() const { return nbv; }
+  Indexed_sweep_accessor (const Arr1& arr1, const Arr2& arr2)
+    : arr1(arr1), arr2(arr2) { }
+
+  std::size_t nb_vertices() const
+  {
+    return arr1.number_of_vertices() + arr2.number_of_vertices();
+  }
 
   std::size_t source_index (const Curve& c) const
   {
-    return halfedge(c)->target()->index;
+    return reinterpret_cast<std::size_t>(halfedge(c)->target()->inc());
   }
 
   std::size_t target_index (const Curve& c) const
   {
-    return halfedge(c)->source()->index;
+    return reinterpret_cast<std::size_t>(halfedge(c)->source()->inc());
   }
 
   const Curve& curve (const Curve& c) const
@@ -65,6 +72,35 @@ public:
     return c;
   }
 
+  void before_init() const
+  {
+    std::size_t idx = 0;
+    backup_inc.reserve (nb_vertices());
+    for (typename Arr1::Vertex_const_iterator vit = arr1.vertices_begin();
+         vit != arr1.vertices_end(); ++vit, ++idx)
+    {
+      backup_inc[idx] = vit->inc();
+      vit->set_inc (reinterpret_cast<void*>(idx));
+    }
+    for (typename Arr2::Vertex_const_iterator vit = arr2.vertices_begin();
+         vit != arr2.vertices_end(); ++vit, ++idx)
+    {
+      backup_inc[idx] = vit->inc();
+      vit->set_inc (reinterpret_cast<void*>(idx));
+    }
+  }
+
+  void after_init() const
+  {
+    std::size_t idx = 0;
+    for (typename Arr1::Vertex_const_iterator vit = arr1.vertices_begin();
+         vit != arr1.vertices_end(); ++vit, ++idx)
+      vit->set_inc (backup_inc[idx]);
+    for (typename Arr2::Vertex_const_iterator vit = arr2.vertices_begin();
+         vit != arr2.vertices_end(); ++vit, ++idx)
+      vit->set_inc (backup_inc[idx]);
+  }
+
 private:
 
   typename Curve::Halfedge_handle halfedge (const Curve& c) const
@@ -168,15 +204,6 @@ overlay(const Arrangement_on_surface_2<GeometryTraitsA_2, TopologyTraitsA>& arr1
   CGAL_precondition(((void*)(&arr) != (void*)(&arr1)) &&
                     ((void*)(&arr) != (void*)(&arr2)));
 
-  // Index vertices for indexed sweep
-  std::size_t idx = 0;
-  for (typename Arr_a::Vertex_const_iterator vit = arr1.vertices_begin();
-       vit != arr1.vertices_end(); ++vit, ++idx)
-    vit->index = idx;
-  for (typename Arr_b::Vertex_const_iterator vit = arr2.vertices_begin();
-       vit != arr2.vertices_end(); ++vit, ++idx)
-    vit->index = idx;
-
   // Prepare a vector of extended x-monotone curves that represent all edges
   // in both input arrangements. Each curve is associated with a halfedge
   // directed from right to left.
@@ -231,7 +258,10 @@ overlay(const Arrangement_on_surface_2<GeometryTraitsA_2, TopologyTraitsA>& arr1
   if (total_iso_verts == 0) {
     // Clear the result arrangement and perform the sweep to construct it.
     arr.clear();
-    surface_sweep.indexed_sweep (xcvs_vec, Indexed_sweep_accessor<Ovl_x_monotone_curve_2>(idx));
+    surface_sweep.indexed_sweep (xcvs_vec,
+                                 Indexed_sweep_accessor
+                                 <Arr_a, Arr_b, Ovl_x_monotone_curve_2>
+                                 (arr1, arr2));
     xcvs_vec.clear();
     return;
   }
diff --git a/Surface_sweep_2/include/CGAL/No_intersection_surface_sweep_2.h b/Surface_sweep_2/include/CGAL/No_intersection_surface_sweep_2.h
index 659624f48b7..34bd84ce139 100644
--- a/Surface_sweep_2/include/CGAL/No_intersection_surface_sweep_2.h
+++ b/Surface_sweep_2/include/CGAL/No_intersection_surface_sweep_2.h
@@ -314,7 +314,9 @@ public:
                       const Accessor& accessor)
   {
     m_visitor->before_sweep();
+    accessor.before_init();
     _init_indexed_sweep(edges, accessor);
+    accessor.after_init();
     _sweep();
     _complete_sweep();
     m_visitor->after_sweep();