fall back to dummy implementation for calc_face_normal on meshes with non-3D points

src/OpenMesh/Core/Mesh/PolyMeshT.cc

@@ -61,6 +61,7 @@
 
 #include <OpenMesh/Core/Mesh/PolyMeshT.hh>
 #include <OpenMesh/Core/Geometry/LoopSchemeMaskT.hh>
+#include <OpenMesh/Core/Utils/GenProg.hh>
 #include <OpenMesh/Core/Utils/vector_cast.hh>
 #include <OpenMesh/Core/System/omstream.hh>
 #include <vector>
@@ -97,8 +98,18 @@ uint PolyMeshT<Kernel>::find_feature_edges(Scalar _angle_tresh)
 
 template <class Kernel>
 typename PolyMeshT<Kernel>::Normal
-PolyMeshT<Kernel>::
+PolyMeshT<Kernel>::calc_face_normal(FaceHandle _fh) const
-calc_face_normal(FaceHandle _fh) const
+{
+  return calc_face_normal_impl(_fh, typename GenProg::IF<
+    PolyMeshT<Kernel>::Point::size() == 3,
+    PointIs3DTag,
+    PointIsNot3DTag
+  >::Result());
+}
+
+template <class Kernel>
+typename PolyMeshT<Kernel>::Normal
+PolyMeshT<Kernel>::calc_face_normal_impl(FaceHandle _fh, PointIs3DTag) const
 {
   assert(this->halfedge_handle(_fh).is_valid());
   ConstFaceVertexIter fv_it(this->cfv_iter(_fh));
@@ -139,8 +150,15 @@ calc_face_normal(FaceHandle _fh) const
           : Normal(0, 0, 0);
 }
 
-//-----------------------------------------------------------------------------
+template <class Kernel>
+typename PolyMeshT<Kernel>::Normal
+PolyMeshT<Kernel>::calc_face_normal_impl(FaceHandle, PointIsNot3DTag) const
+{
+  // Dummy fallback implementation
+  return Normal(0);
+}
 
+//-----------------------------------------------------------------------------
 
 template <class Kernel>
 typename PolyMeshT<Kernel>::Normal
@@ -148,6 +166,21 @@ PolyMeshT<Kernel>::
 calc_face_normal(const Point& _p0,
      const Point& _p1,
      const Point& _p2) const
+{
+  return calc_face_normal_impl(_p0, _p1, _p2, typename GenProg::IF<
+    PolyMeshT<Kernel>::Point::size() == 3,
+    PointIs3DTag,
+    PointIsNot3DTag
+  >::Result());
+}
+
+template <class Kernel>
+typename PolyMeshT<Kernel>::Normal
+PolyMeshT<Kernel>::
+calc_face_normal_impl(const Point& _p0,
+     const Point& _p1,
+     const Point& _p2,
+     PointIs3DTag) const
 {
 #if 1
   // The OpenSG <Vector>::operator -= () does not support the type Point
@@ -174,6 +207,14 @@ calc_face_normal(const Point& _p0,
 #endif
 }
 
+template <class Kernel>
+typename PolyMeshT<Kernel>::Normal
+PolyMeshT<Kernel>::
+calc_face_normal_impl(const Point&, const Point&, const Point&, PointIsNot3DTag) const
+{
+    return Normal(0);
+}
+
 //-----------------------------------------------------------------------------
 
 template <class Kernel>

src/OpenMesh/Core/Mesh/PolyMeshT.hh

@@ -520,6 +520,13 @@ public:
   inline void split(EdgeHandle _eh, VertexHandle _vh)
   { Kernel::split_edge(_eh, _vh); }
   
+private:
+  struct PointIs3DTag {};
+  struct PointIsNot3DTag {};
+  Normal calc_face_normal_impl(FaceHandle, PointIs3DTag) const;
+  Normal calc_face_normal_impl(FaceHandle, PointIsNot3DTag) const;
+  Normal calc_face_normal_impl(const Point&, const Point&, const Point&, PointIs3DTag) const;
+  Normal calc_face_normal_impl(const Point&, const Point&, const Point&, PointIsNot3DTag) const;
 };
 
 /**