[vtkusers] Create a custom valueType vtkArray

[Ruben Di Battista]

Hello, 

At the moment I have some code that reads like this:

        m_H->SetNumberOfValues(nPoints);
        m_G->SetNumberOfValues(nPoints);
        m_C->SetNumberOfValues(nPoints);
        m_SI->SetNumberOfValues(nPoints);

        for ( auto p : this->IterateOver<Point>() ) {
                auto curvatures = p.HG();
                m_H->SetValue(p.Id(), curvatures.H);
                m_G->SetValue(p.Id(), curvatures.G);
                m_C->SetValue(p.Id(), curvatures.C);
                m_SI->SetValue(p.Id(), curvatures.SI);
       }

        m_polyPtr->GetPointData()->AddArray(m_H);
        m_polyPtr->GetPointData()->AddArray(m_G);
        m_polyPtr->GetPointData()->AddArray(m_C);
        m_polyPtr->GetPointData()->AddArray(m_SI);

Where m_polyPtr is a vtkPolyData* and the return type of p.HG() is:
    
     struct Curvatures
    {
        double G; /**< Gauss Curvature */
        double H; /**< Mean Curvature */
        double C; /**< Curvedness */
        double SI; /**< Shape Index */
    };

Now I’m facing a problem where I need to add fields to the structure “Curvatures” and so I need to change code in three different classes. 
Is there a way to create a vtkArray whose (templated?) valueType is `Curvatures` such that I can just modify that struct to allow more fields to be stored and set in a “more abstract way” and that can be appended to the `PointData` of the vtkPolyData in a transparent way?

Any suggestion is appreciated! 

:)


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https://rdb.is
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