ENH: Change API of vtkRectilinearGrid::GetPoints()

The method now accepts an instance of vtkPoints that the user must
pre-allocate externally. Since the user explicitely allocates that
object, the responsibility for explicit de-allocation is more obvious
in contrast to the previous API that was implicitely propagating
ownership of the pointer to the caller.

Change-Id: Ia289653d7d9ba2dc784f5851328c321c99e0a72e

Filtering/vtkRectilinearGrid.cxx

@@ -427,18 +427,17 @@ void vtkRectilinearGrid::GetCellBounds(vtkIdType cellId, double bounds[6])
 }
 
 //----------------------------------------------------------------------------
-vtkPoints* vtkRectilinearGrid::GetPoints()
+void vtkRectilinearGrid::GetPoints(vtkPoints *pnts)
 {
-  vtkPoints *pnts = vtkPoints::New();
+  assert("pre: points object should not be NULL" && (pnts !=NULL) );
+
   pnts->Initialize();
   pnts->SetNumberOfPoints( this->GetNumberOfPoints() );
-
   vtkIdType pntIdx = 0;
   for( ; pntIdx < this->GetNumberOfPoints(); ++pntIdx )
     {
     pnts->SetPoint( pntIdx, this->GetPoint(pntIdx) );
     }// END for all points
-  return( pnts );
 }
 
 //----------------------------------------------------------------------------

Filtering/vtkRectilinearGrid.h

@@ -95,8 +95,9 @@ public:
                         vtkIdList *cellIds);
 
   // Description:
-  // Returns the points for this instance of rectilinear grid.
-  vtkPoints* GetPoints();
+  // Given a user-supplied vtkPoints container object, this method fills in all
+  // the points of the RectilinearGrid.
+  void GetPoints(vtkPoints* pnts);
 
   // Description:
   // Set dimensions of rectilinear grid dataset.