add the possibility to use an external region map

Shape_detection/doc/Shape_detection/PackageDescription.txt

@@ -60,7 +60,7 @@ Classified Reference Manual for the Region Growing shape detection component.
 - `RegionType`
 
 # Algorithm #
-- `CGAL::Shape_detection::Region_growing<%NeighborQuery, %RegionType>`
+- `CGAL::Shape_detection::Region_growing<%NeighborQuery, %RegionType, RegionMap>`
 
 # Point Set #
 ## Neighbord Query Classes ##

Shape_detection/include/CGAL/Polygon_mesh_processing/region_growing.h

@@ -106,7 +106,7 @@ region_growing_of_planes_on_faces(const PolygonMesh& mesh,
   using Neighbor_query = RG_PM::One_ring_neighbor_query<PolygonMesh>;
   using Region_type = RG_PM::Least_squares_plane_fit_region<Traits, PolygonMesh, VPM>;
   using Sorting = RG_PM::Least_squares_plane_fit_sorting<Traits, PolygonMesh, Neighbor_query, VPM>;
-  using Region_growing = CGAL::Shape_detection::Region_growing<Neighbor_query, Region_type>;
+  using Region_growing = CGAL::Shape_detection::Region_growing<Neighbor_query, Region_type, RegionMap>;
 
   Neighbor_query neighbor_query(mesh);
   Region_type region_type(mesh, np);
@@ -115,12 +115,9 @@ region_growing_of_planes_on_faces(const PolygonMesh& mesh,
 
   std::vector<typename Region_growing::Primitive_and_region> regions;
   Region_growing region_growing(
-    faces(mesh), sorting.ordered(), neighbor_query, region_type);
+    faces(mesh), sorting.ordered(), neighbor_query, region_type, region_map);
   region_growing.detect(CGAL::Emptyset_iterator());
 
-  for (face_descriptor f : faces(mesh))
-    put(region_map, f, get(region_growing.region_map(), f));
-
   return region_growing.number_of_regions_detected();
 }
 

Shape_detection/include/CGAL/Shape_detection/Region_growing/Region_growing.h

@@ -48,10 +48,14 @@ namespace Shape_detection {
 
     \tparam RegionType
     a model of `RegionType`
+
+    \tparam RegionMap a model of `ReadWritePropertyMap` whose key type is `Item`
+    and value type is `std::size_t`.
   */
   template<
     typename NeighborQuery,
-    typename RegionType >
+    typename RegionType,
+    typename RegionMap = typename RegionType::Region_index_map>
   class Region_growing {
 
   public:
@@ -69,7 +73,7 @@ namespace Shape_detection {
     using Primitive_and_region = std::pair<typename Region_type::Primitive, Region>;
 
     /// Item to region property map.
-    using Region_map = typename Region_type::Region_index_map;
+    using Region_map = RegionMap;
 
   private:
     using Running_queue = std::queue<Item>;
@@ -90,7 +94,7 @@ namespace Shape_detection {
         either `CGAL::Dereference_property_map` or `CGAL::Identity_property_map`.
 
       \param input_range
-      a range of input items for region growing
+      a range of input items for region growing. `input_range` must not be empty.
 
       \param neighbor_query
       an instance of `NeighborQuery` that is used internally to
@@ -102,15 +106,15 @@ namespace Shape_detection {
 
       \param item_map
         an instance of the property map to retrieve items from input values
-
-      \pre `input_range.size() > 0`
     */
     template<typename InputRange, typename ItemMap = Default>
     Region_growing(
       const InputRange& input_range,
       NeighborQuery& neighbor_query,
       RegionType& region_type,
-      ItemMap item_map = ItemMap()) :
+      ItemMap item_map = ItemMap(),
+      std::enable_if_t<std::is_same<RegionMap, typename Region_type::Region_index_map>::value>* = 0
+      ) :
       m_neighbor_query(neighbor_query),
       m_region_type(region_type),
       m_region_map(region_type.region_index_map()),
@@ -130,6 +134,34 @@ namespace Shape_detection {
       clear(input_range, item_map_);
     }
 
+    /// \copydoc Region_growing()
+    /// \param rm external property map that will be filled when calling `detect()`
+    template<typename InputRange, typename ItemMap = Default>
+    Region_growing(
+      const InputRange& input_range,
+      NeighborQuery& neighbor_query,
+      RegionType& region_type,
+      Region_map rm,
+      ItemMap item_map = ItemMap()) :
+      m_neighbor_query(neighbor_query),
+      m_region_type(region_type),
+      m_region_map(rm),
+      m_visited(m_visited_map)
+    {
+      CGAL_precondition(input_range.size() > 0);
+      m_seed_range.resize(input_range.size());
+
+      using Item_helper = internal::Item_map_helper<ItemMap, Item, typename InputRange::const_iterator>;
+      using Item_map = typename Item_helper::type;
+      Item_map item_map_ = Item_helper::get(item_map);
+
+      std::size_t idx = 0;
+      for (auto it = input_range.begin(); it != input_range.end(); it++)
+        m_seed_range[idx++] = get(item_map_, it);
+
+      clear(input_range, item_map_);
+    }
+
     /*!
       \brief initializes the region growing algorithm.
 
@@ -208,8 +240,8 @@ namespace Shape_detection {
 
       \return past-the-end position in the output sequence
     */
-    template<typename PrimitiveAndRegionOutputIterator>
-    PrimitiveAndRegionOutputIterator detect(PrimitiveAndRegionOutputIterator region_out) {
+    template<typename PrimitiveAndRegionOutputIterator = Emptyset_iterator>
+    PrimitiveAndRegionOutputIterator detect(PrimitiveAndRegionOutputIterator region_out = PrimitiveAndRegionOutputIterator()) {
 //      clear(); TODO: this is not valid to comment this clear()
       m_visited_map.clear(); // tmp replacement for the line above