new function add_bbox(face_graph) that adds bbox to face graph

the bbox can be :
* triangulated or not
* tight or not

Polygon_mesh_processing/include/CGAL/Polygon_mesh_processing/bbox.h

@@ -15,14 +15,18 @@
 
 #include <CGAL/license/Polygon_mesh_processing/miscellaneous.h>
 
-
 #include <CGAL/Bbox_3.h>
 
-#include <boost/graph/graph_traits.hpp>
+#include <CGAL/Polygon_mesh_processing/polygon_soup_to_polygon_mesh.h>
+#include <CGAL/Polygon_mesh_processing/orient_polygon_soup.h>
+#include <CGAL/boost/graph/copy_face_graph.h>
 
+#include <boost/graph/graph_traits.hpp>
 #include <CGAL/Named_function_parameters.h>
 #include <CGAL/boost/graph/named_params_helper.h>
 
+#include <vector>
+
 namespace CGAL {
 
   namespace Polygon_mesh_processing {
@@ -255,6 +259,83 @@ namespace CGAL {
       }
       return bb;
     }
+
+    /*!
+    * adds a triangulated bounding box to a polygon mesh
+    * @todo add extended bbox factor
+    * @todo add triangulate or not as NP
+    */
+    template<typename PolygonMesh,
+             typename NamedParameters = parameters::Default_named_parameters>
+    void add_bbox(PolygonMesh& pmesh,
+                  const NamedParameters& np = parameters::default_values())
+    {
+      using parameters::choose_parameter;
+      using parameters::get_parameter;
+
+      typedef typename GetGeomTraits<PolygonMesh, NamedParameters>::type GT;
+      GT gt = choose_parameter<GT>(get_parameter(np, internal_np::geom_traits));
+      typedef typename GT::Point_3 Point_3;
+
+      const double factor = 1.1; //todo : add as NP
+      CGAL::Bbox_3 bb = bbox(pmesh);
+      if (factor != 1.0)
+      {
+        const double dx = bb.xmax() - bb.xmin();
+        const double dy = bb.ymax() - bb.ymin();
+        const double dz = bb.zmax() - bb.zmin();
+        const Point_3 center( bb.xmin() + 0.5 * dx,
+                              bb.ymin() + 0.5 * dy,
+                              bb.zmin() + 0.5 * dz );
+        bb = Bbox_3( center.x() - factor * 0.5 * dx,
+                     center.y() - factor * 0.5 * dy,
+                     center.z() - factor * 0.5 * dz,
+                     center.x() + factor * 0.5 * dx,
+                     center.y() + factor * 0.5 * dy,
+                     center.z() + factor * 0.5 * dz );
+      }
+
+      const bool triangulate = true; //todo : add as NP
+
+      const typename GT::Iso_cuboid_3 bbox(bb);
+      std::vector<Point_3> bb_points;
+      for (int i = 0; i < 8; ++i)
+        bb_points.push_back(bbox[i]);
+
+      std::vector<std::vector<std::size_t>> faces;
+      if (!triangulate)
+      {
+        faces.push_back({0, 1, 2, 3});//bottom
+        faces.push_back({4, 5, 6, 7});//top
+        faces.push_back({0, 1, 6, 5});//front
+        faces.push_back({2, 3, 4, 7});//back
+        faces.push_back({1, 2, 7, 6});//right
+        faces.push_back({0, 3, 4, 5});//left
+      }
+      else
+      {
+        faces.push_back({0, 1, 2});//bottom
+        faces.push_back({0, 2, 3});
+        faces.push_back({4, 5, 6});//top
+        faces.push_back({4, 6, 7});
+        faces.push_back({0, 1, 5});//front
+        faces.push_back({1, 5, 6});
+        faces.push_back({2, 3, 4});//back
+        faces.push_back({2, 4, 7});
+        faces.push_back({1, 2, 6});//right
+        faces.push_back({2, 6, 7});
+        faces.push_back({0, 3, 4});//left
+        faces.push_back({0, 4, 5});
+      }
+
+      PolygonMesh bbox_pmesh;
+      orient_polygon_soup(bb_points, faces);
+      polygon_soup_to_polygon_mesh(bb_points, faces, bbox_pmesh);
+
+      CGAL::copy_face_graph(bbox_pmesh, pmesh,
+                            parameters::default_values(),
+                            np);
+    }
   }
 }