[Paraview] Is there a way to reuse the preivous DataSet from RequestData

[Utkarsh Ayachit]

The only way is to cache it in the reader itself. Create a new
vtkUnstructuredGrid and ShallowCopy the contents of your "output" to
it at the end of your RequestData().

Utkarsh

On Mon, Feb 2, 2015 at 2:00 PM, Gonzalo Brito Gadeschi
<g.brito at aia.rwth-aachen.de> wrote:
> In a reader plugin for unstructured grids, after the plugin opens a file,
> and paraview calls RequestData for the first time, I initialize the grid
> like:
>
>  vtkInformation* outInfo = outputVector->GetInformationObject(0);
>  vtkDataSet* output = vtkDataSet::GetData(outInfo);
>  vtk_grid = vtkUnstructuredGrid::SafeDownCast(output);
>
>   vtk_grid->Initialize();
>   vtk_grid->Allocate(0);
>   vtkSmartPointer<vtkPoints> points = vtkSmartPointer<vtkPoints>::New();
>   vtk_grid->SetPoints(points);
>   // create grid points, cells..
>   // load cell data fields (the user can control this via the plugin
> interface)
>
> If the user then decides to load/unload some fields, I would like to reuse
> the loaded points and cells, and just update/add/remove fields.
>
> The problem comes when in subsequent calls to RequestData:
>
>   vtkInformation* outInfo = outputVector->GetInformationObject(0);
>   vtkDataSet* output = vtkDataSet::GetData(outInfo);
>
>   // this asserts works:
>   assert(old_vtk_grid == vtkUnstructuredGrid::SafeDownCast(output));
>  // this assert fails: the number of points is 0..
>   assert(old_number_of_points == vtk_grid->GetNumberOfPoints());
>   // this produces a segmentation fault
>   assert(old_number_of_cells == vtk_grid->GetCells()->GetNumberOfCells());
>
> That is, even tho the grid pointer that gets passed to RequestData points to
> the same memory as before, it seems that the grid is "empty" (number of
> points is 0).
>
> Is there a way to preserve the grid state between calls to RequestData?
>
> Bests,
> Gonzalo
>
> --
> Dipl.-Ing. Gonzalo Brito Gadeschi
> Institute of Aerodynamics and Chair of Fluid Mechanics
> RWTH Aachen University
> Wuellnerstraße 5a
> D-52062 Aachen
> Germany
> Phone: ++49-(0)241-80-94821
> Fax: ++49-(0)241-80-92257
> E-mail:  g.brito at aia.rwth-aachen.de
> Internet: www.aia.rwth-aachen.de
>
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