fix: conditions on *itr to skip its further processing

(after RW's observation)

Arrangement_on_surface_2/include/CGAL/Sweep_line_2/Arr_construction_sl_visitor.h

@@ -96,6 +96,8 @@ protected:
                                           // subcurves that emarge from event
                                           // points with only right curves). 
 
+  Halfedge_handle          m_last_he;     // the last halfedge at the top
+
   std::vector<Halfedge_handle>
                            m_sc_he_table; // A table that maps a subcurve
                                           // index to its halfedge handle,
@@ -286,7 +288,7 @@ void Arr_construction_sl_visitor<Hlpr>::before_handle_event (Event* event)
 {
   // We just have to notify the helper class on the event.
   m_helper.before_handle_event (event);
-
+  m_last_he = Halfedge_handle();
   return;
 }
 
@@ -335,22 +337,39 @@ bool Arr_construction_sl_visitor<Hlpr>::after_handle_event
 
     // In case of a finite event that has no incident left curves, it is
     // associated with a point that may be the leftmost one in a hole.
-    // We give index to the topmost subcurve from the right, and add this
-    // vertex indices list of the curve the event "sees" from below.
-    m_sc_counter++;
-    (*(event->right_curves_rbegin()))->set_index (m_sc_counter);
+    // The last inserted halfedge belongs to this event. We have to check
+    // whether it really can pose a hole, i.e., whether the inserted halfedge
+    // is on an inner ccb.
 
-    if (iter != this->status_line_end())
+    std::cout << "m_sc_counter++: " << (m_sc_counter + 1) << std::endl;
+
+    const Halfedge_handle invalid_he;
+    //CGAL_assertion(m_last_he->direction() == CGAL::RIGHT_TO_LEFT);
+    if (m_last_he != invalid_he && m_last_he->is_on_inner_ccb()) 
     {
-      // The vertex "sees" the subcurve of the given position from below.
-      Subcurve *sc_above = *iter;
-      sc_above->add_halfedge_index(m_sc_counter);
-    }
-    else
-    {
-      // The vertex is not located below any valid curve, so we use the helper
-      // class to mark that this index should belong to the current top face.
-      m_helper.add_subcurve_in_top_face (m_sc_counter);
+      // We give index to the topmost subcurve from the right, and add this
+      // vertex indices list of the curve the event "sees" from below.
+      m_sc_counter++;
+      (*(event->right_curves_rbegin()))->set_index (m_sc_counter);
+      
+      if (iter != this->status_line_end())
+      {
+        // The vertex "sees" the subcurve of the given position from below.
+        Subcurve *sc_above = *iter;
+        sc_above->add_halfedge_index(m_sc_counter);
+      }
+      else
+      {
+        // The vertex is not located below any valid curve, 
+        // so we use the helper class to mark that this index 
+        // should belong to the current top face.
+        m_helper.add_subcurve_in_top_face (m_sc_counter);
+      }
+    } else {
+        if (m_last_he != invalid_he) {
+            std::cout << "Valid, but not inner: " 
+                      << m_last_he->curve() << std::endl;
+        }
     }
   }
   
@@ -397,6 +416,8 @@ template <class Hlpr>
 void Arr_construction_sl_visitor<Hlpr>::add_subcurve
     (const X_monotone_curve_2& cv, Subcurve* sc)
 {
+    std::cout << "Add subcurve: " << cv << std::endl;
+
   // Obtain all information to perform the insertion of the subcurve into
   // the arrangement.
   Event           *last_event = last_event_on_subcurve(sc);
@@ -456,14 +477,31 @@ void Arr_construction_sl_visitor<Hlpr>::add_subcurve
   if (res->direction() != LEFT_TO_RIGHT)
     res = res->twin();
 
+  std::cout << "resI: " << res->is_on_inner_ccb() << std::endl;
+  std::cout << "resTI: " << res->twin()->is_on_inner_ccb() << std::endl;
+
+  if (res->is_on_inner_ccb()) {
+      std::cout << "resF: " << &(*res->inner_ccb()->face()) << std::endl;
+  } else {
+      std::cout << "resF: " << &(*res->outer_ccb()->face()) << std::endl;
+  }
+
+  if (res->twin()->is_on_inner_ccb()) {
+      std::cout << "res->twinF: " << &(*res->twin()->inner_ccb()->face()) << std::endl;
+  } else {
+      std::cout << "res->twinF: " << &(*res->twin()->outer_ccb()->face()) << std::endl;
+  }
+
+  m_last_he = res;
+  
   // Update the last event with the inserted halfegde (if necessary)
   // and check if we have to update the auxiliary information on the location 
   // of holes.
   if (last_event->number_of_left_curves() == 0 &&  
       last_event->is_curve_largest((Subcurve*)sc))
   {
-      if (last_event->vertex_handle() == m_invalid_vertex)
-          last_event->set_halfedge_handle(res->twin());
+    if (last_event->vertex_handle() == m_invalid_vertex)
+        last_event->set_halfedge_handle(res->twin());
     
     // If sc has valid index, insert its index to m_sc_he_table.
     if(sc->has_valid_index())
@@ -856,7 +894,7 @@ void Arr_construction_sl_visitor<Hlpr>::relocate_in_new_face
         continue;
      
       Halfedge_handle he_on_face = m_sc_he_table[*itr];
-          
+
       if(he_on_face == invalid_he)
       {
         // If the halfedge handle is invalis, then we have an index for an
@@ -904,6 +942,8 @@ void Arr_construction_sl_visitor<Hlpr>::_map_new_halfedge
     (unsigned int i, Halfedge_handle he)
 {
   CGAL_assertion (i != 0);
+
+  std::cout << "Assign " << i << " to " << he->curve() << std::endl;
   
   if(i >= m_sc_he_table.size())
     // Resize the index table if we reached it capacity.