Editing Software Plugins and Codes (section)

====Copy your data to the output, instead of connecting the output to a VTK filter====

I don't understand why this is sometimes required, but using ShallowCopy seems be necessary in certain cases.  Note there should in theory be no performance impact to using ShallowCopy (no new copy of the data will be made in memory).

Here is an example.

<source lang="c">
int vtkAIMReaderPlugin::RequestData (vtkInformation*,
                                     vtkInformationVector**,
                                     vtkInformationVector* outputVector)
{
  // Make sure FileName is set
  if (!this->FileName)
    {
    vtkErrorMacro("A Filename must be specified");
    return 0;
    }

  vtkSmartPointer<vtkAIMReader> reader = vtkSmartPointer<vtkAIMReader>::New();
  reader->SetFileName (FileName);
  reader->UpdateInformation();   // Not sure if this is redundant
  reader->Update();
  vtkImageData* data = reader->GetOutput();

  vtkImageData* out = vtkImageData::GetData (outputVector);
  if (!out)
  {
    return 0;
  }
  // Not sure why we need a temporary object for the caster, but without it,
  // an error occurs in paraview.
  vtkSmartPointer<vtkImageData> temp = vtkSmartPointer<vtkImageData>::New();
  // Convert to float, regardless of original type
  vtkSmartPointer<vtkImageCast> caster = vtkSmartPointer<vtkImageCast>::New();
  caster->SetInput (data);
  caster->SetOutput (temp);
  caster->SetOutputScalarType (VTK_FLOAT);
  caster->Update();

  out->ShallowCopy(temp);

  // Must have a name for the scalar data otherwise paraview can do nothing
  // with it.
  out->GetPointData()->GetScalars()->SetName("AIMData");

  return 1;
}
</source>

This is the error that you will get if you fail to use ShallowCopy and just set the output of caster in the above example to 'out':

 ERROR: In /home/eric/source/paraview-3.6.1/Servers/Common/vtkPVDataInformation.cxx, line 586
 vtkPVDataInformation (0x2c391a0): Could not cast object to a known data set: vtkAlgorithmOutput


[[Image:Redirect.jpg|15px]] [[#top|''Return to Contents'']] or [[Main_Page|''Return to Main Page'']]