add virtual functions to Sliver_criterion and use them :

- get_max_value() to be able to keep the abstract class and derivatives properly
- get_perturbation_unit() to replace "delta" in Sliver_perturber (progressive version of perturber is running for bound = i*delta for i >= 1)

Mesh_3/include/CGAL/Mesh_3/C3T3_helpers.h

@@ -2420,7 +2420,7 @@ min_sliver_value(const Cell_vector& cells,
   using boost::make_transform_iterator;
   
   if ( cells.empty() )
-    return SliverCriterion::max_value;
+    return criterion.get_max_value();
   
   if ( ! use_cache )
   { 
@@ -2428,10 +2428,21 @@ min_sliver_value(const Cell_vector& cells,
   }
   
   // Return min dihedral angle
-  Sliver_criterion_value<SliverCriterion> sc_value(tr_,criterion);
-  
-  return *(std::min_element(make_transform_iterator(cells.begin(),sc_value),
-                            make_transform_iterator(cells.end(),sc_value)));
+  //Sliver_criterion_value<SliverCriterion> sc_value(tr_,criterion);
+  //
+  //return *(std::min_element(make_transform_iterator(cells.begin(),sc_value),
+  //                          make_transform_iterator(cells.end(),sc_value)));
+  FT min = criterion.get_max_value();
+  FT sliver_value = 0.;
+  for(typename Cell_vector::const_iterator it = cells.begin(); 
+      it != cells.end(); 
+      ++it)
+  {
+    sliver_value = criterion(c3t3_.triangulation().tetrahedron(*it));
+    if( sliver_value < min )
+	    min = sliver_value;
+  } 
+  return min;
 }
   
   

Mesh_3/include/CGAL/Mesh_3/Sliver_perturber.h

@@ -237,8 +237,7 @@ public:
    * The perturber runs step by step, using delta as step size. 
    */
   Mesh_optimization_return_code
-  operator()(const FT& delta = FT(1.),
-             Visitor visitor = Visitor());
+  operator()(Visitor visitor = Visitor());
   
   /**
    * Adds a perturbation at the end of the perturbation queue
@@ -388,7 +387,7 @@ Sliver_perturber(C3T3& c3t3,
 template <typename C3T3, typename Md, typename Sc, typename V_>
 Mesh_optimization_return_code
 Sliver_perturber<C3T3,Md,Sc,V_>::
-operator()(const FT& delta, Visitor visitor)
+operator()(Visitor visitor)
 {
   // Reset sliver value cache
   helper_.reset_cache();
@@ -413,6 +412,7 @@ operator()(const FT& delta, Visitor visitor)
             << "(#vertices in pqueue, #iterations, #fails)" << std::endl;
 #endif
   
+  const FT& delta = sliver_criterion_.get_perturbation_unit();
   FT current_bound = delta;
   bool perturbation_ok = true;
   while ( current_bound <= sliver_bound() && perturbation_ok)

Mesh_3/include/CGAL/Mesh_3/sliver_criteria.h

@@ -37,6 +37,11 @@ class Sliver_criterion
 {
   typedef typename K::Tetrahedron_3 Tetrahedron_3;
   
+public:
+  virtual const double get_max_value() const = 0;
+  //Sliver_perturber performs perturbation "unit-per-unit"
+  // so it needs to know how much is a unit for each criterion
+  virtual const double get_perturbation_unit() const = 0;
 public:
   virtual double operator()(const Tetrahedron_3& t) const = 0;
 };
@@ -50,7 +55,10 @@ public:
   static double default_value;
   static double max_value;
   static double min_value;
-  
+
+  virtual const double get_max_value() const { return 90.; }
+  virtual const double get_perturbation_unit() const { return 1.; }
+
   double operator()(const Tetrahedron_3& t) const
   {
     return CGAL::to_double(minimum_dihedral_angle(t, K()));
@@ -71,7 +79,10 @@ public:
   static double default_value;
   static double max_value;
   static double min_value;
-  
+
+  virtual const double get_max_value() const { return 1.; }
+  virtual const double get_perturbation_unit() const { return 0.05; }
+
   double operator()(const Tetrahedron_3& t) const
   {
     return CGAL::to_double(radius_ratio(t, K()));