How to get the scalers of points in my custom VertexShader

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vtkSmartPointer<vtkPolyData> polydata = vtkSmartPointer<vtkPolyData>::New();
polydata = windowedSincFilter->GetOutput();
long numPoints = polydata->GetNumberOfPoints();
int* pointIdArray = new int[numPoints];
std::fill(pointIdArray, pointIdArray + numPoints, 1);
vtkSmartPointer<vtkIntArray> pointIds = vtkSmartPointer<vtkIntArray>::New();
pointIds->SetName("PointIds");
pointIds->SetNumberOfValues(numPoints);
pointIds->SetArray(pointIdArray, numPoints, 1);
polydata->GetPointData()->AddArray(pointIds);

pointIds are set correctly, but I can’t get them in shader using in int PointIds;