enable writing of primitive data to paraview

dune/fem-dg/algorithm/caller/sub/datawriter.hh

@@ -77,8 +77,7 @@ namespace Fem
           consLF.evaluate( qp, cons );
 
           // it is useful to visualize better suited quantities
-          bool forVisual = true;
-          alg->model().conservativeToPrimitive( tp.time(), xgl, cons, prim, forVisual );
+          alg->paraview( tp.time(), xgl, cons, prim );
 
           prim *=  qp.weight();
           primLF.axpy( qp, prim );

dune/fem-dg/algorithm/sub/interface.hh

@@ -287,6 +287,17 @@ namespace Fem
       return model_.problem().exactSolution( time );
     }
 
+    template< class DomainType, class InRangeType, class OutRangeType >
+    decltype(auto) paraview( const double time,
+                             const DomainType& xgl,
+                             const InRangeType& cons,
+                             OutRangeType& result,
+                             bool forVisual = true )
+    {
+      return model_.conservativeToPrimitive( time, xgl, cons, result, forVisual );
+    }
+
+
   protected:
     virtual bool doCheckSolutionValid ( const int loop, TimeProviderType& tp ) const { return true; }
     /**