Add a NP for orientation requirement

Polygon_mesh_processing/include/CGAL/Polygon_mesh_processing/measure.h

@@ -34,6 +34,7 @@
 #include <boost/dynamic_bitset.hpp>
 
 #include <utility>
+#include <algorithm>
 
 #ifdef DOXYGEN_RUNNING
 #define CGAL_PMP_NP_TEMPLATE_PARAMETERS NamedParameters
@@ -51,7 +52,20 @@ public:
 };
 
 namespace Polygon_mesh_processing {
-
+namespace pmp_internal {
+void rearrange_face_ids(boost::container::small_vector<std::size_t, 4>& ids, bool orientation_counts)
+{
+  if(!orientation_counts)
+  {
+    std::sort(ids.begin(), ids.end());
+  }
+  else
+  {
+    auto min_elem = std::min_element(ids.begin(), ids.end());
+    std::rotate(ids.begin(), min_elem, ids.end());
+  }
+}
+}//end pmp_internal
 /**
   * \ingroup measure_grp
   * computes the length of an edge of a given polygon mesh.
@@ -827,7 +841,6 @@ centroid(const TriangleMesh& tmesh)
   * \ingroup measure_grp
   * given two meshes, separates the faces that are only in one, the faces
   * that are only in the other one, and the faces that are common to both.
-  * The orientation of the faces is ignored during the comparison.
   *
   * @tparam PolygonMesh a model of `HalfedgeListGraph` and `FaceListGraph`
   * @tparam OutputFaceIterator model of `OutputIterator`
@@ -867,6 +880,14 @@ centroid(const TriangleMesh& tmesh)
   *                     or using an external map. The latter might result in  - slightly - worsened performance
   *                     in case of non-constant complexity for index access.}
   *   \cgalParamNEnd
+  *   \cgalParamNBegin{require_same_orientation}
+  *   \cgalParamDescription{Parameter (np1 only) to indicate if face orientation should be taken
+  *                        into account when determining whether two faces are duplicates,
+  *                        that is, whether e.g. the triangles `0,1,2` and `0,2,1` are duplicates.}
+  *  \cgalParamType{Boolean}
+  *  \cgalParamDefault{`false`}
+  *\cgalParamNEnd
+
   * \cgalNamedParamsEnd
   *
  */
@@ -887,6 +908,7 @@ void compare_meshes(const PolygonMesh& m1, const PolygonMesh& m2,
                                       get_const_property_map(vertex_point, m2));
   VIMap1 vim1 = get_initialized_vertex_index_map(m1, np1);
   VIMap1 vim2 = get_initialized_vertex_index_map(m2, np2);
+  const bool same_orientation = choose_parameter(get_parameter(np1, internal_np::require_same_orientation), false);
   typedef typename boost::property_traits<VPMap2>::value_type Point_3;
   typedef typename boost::graph_traits<PolygonMesh>::face_descriptor face_descriptor;
 
@@ -935,7 +957,7 @@ void compare_meshes(const PolygonMesh& m1, const PolygonMesh& m2,
     }
     if(all_shared)
     {
-      std::sort(ids.begin(), ids.end());
+      pmp_internal::rearrange_face_ids(ids, same_orientation);
       m1_faces_map.insert({ids, f});
     }
     else
@@ -957,7 +979,7 @@ void compare_meshes(const PolygonMesh& m1, const PolygonMesh& m2,
     }
     if(all_shared)
     {
-      std::sort(ids.begin(), ids.end());
+      pmp_internal::rearrange_face_ids(ids, same_orientation);
       auto it = m1_faces_map.find(ids);
       if(it != m1_faces_map.end())
       {

Polyhedron/demo/Polyhedron/Plugins/Operations_on_polyhedra/Diff_between_meshes_plugin.cpp

@@ -75,6 +75,14 @@ void Polyhedron_demo_diff_between_meshes_plugin::diff()
   typedef CGAL::Face_filtered_graph<SMesh> Filtered_graph;
 
   QCursor c(Qt::WaitCursor);
+
+  QMessageBox msgBox;
+  msgBox.setText("Require the Same Orientation ?");
+  msgBox.setInformativeText("Should face orientation count for duplicate detection ?");
+  msgBox.setStandardButtons(QMessageBox::Yes| QMessageBox::No);
+  msgBox.setDefaultButton(QMessageBox::No);
+  int ret = msgBox.exec();
+  bool same_orientation = (ret == QMessageBox::Yes);
   CGAL::Three::Three::CursorScopeGuard guard(c);
 
   //Get the two meshes. No need to check their existance, applicable()
@@ -88,7 +96,13 @@ void Polyhedron_demo_diff_between_meshes_plugin::diff()
       m2=*m2_item->face_graph();
   std::vector<face_descriptor> m1_only, m2_only;
   std::vector<std::pair<face_descriptor, face_descriptor> > common;
-  CGAL::Polygon_mesh_processing::compare_meshes(m1, m2, std::back_inserter(common), std::back_inserter(m1_only), std::back_inserter(m2_only));
+  CGAL::Polygon_mesh_processing::compare_meshes(
+        m1,
+        m2,
+        std::back_inserter(common),
+        std::back_inserter(m1_only),
+        std::back_inserter(m2_only),
+        CGAL::parameters::require_same_orientation(same_orientation));
 
   Filtered_graph filter1(m1, m1_only);
   SMesh mesh1_only, mesh2_only, common_mesh;