[vtkusers] problem with picker->GetCellId() on vtkPolyData structure

[Luboz, Vincent]

Good morning

I am using VTK 5.0 with Visual C++ 2005.
I wrote the following code to display 3D lines and pick them with the left button of the mouse:


// First, I create the renderer and the interactor

vtkRenderer *globalRenderer3D = vtkRenderer::New();
vtkRenderWindow *globalRenWin3D = vtkRenderWindow::New();
        globalRenWin3D->AddRenderer(globalRenderer3D);
               
vtkRenderWindowInteractor *iren3D = vtkRenderWindowInteractor::New();
        iren3D->SetRenderWindow(globalRenWin3D);

// changing the interactor style       
vtkInteractorStyleTrackballCamera *interactSwitch = vtkInteractorStyleTrackballCamera::New();
        iren3D->SetInteractorStyle(interactSwitch);

// function called every time the picker is activated
vtkCallbackCommand *callBackCom = vtkCallbackCommand::New();
        callBackCom->SetCallback(pickingFunction);

// linking the left button to the picking function
iren3D->AddObserver(vtkCommand::LeftButtonReleaseEvent, callBackCom);

// creating the cell picker
vtkCellPicker *picker = vtkCellPicker::New();
iren3D->SetPicker(picker);


// Then I create a polydata and fill it:

//  acquiring the lines
for (int idStruct = 0; idStruct5 < nbStruct; idStruct5++)
{
        //reading the number of lines for this structure
        scanf("%d\n", &nbStructLines);

        // creating a polydata for each structures
        vtkPolyData *polyLine = vtkPolyData::New();
        polyLine->Allocate(nbStructLines, idStruct);

        for (int idLinesPerStruct = 0; idLinesPerStruct < nbStructLines; idLinesPerStruct++)
        {
                // reading the number of nodes for this line
                scanf("%d\n", &nbLineNodes);

                // creating the structures for the points and lines of the current structure
                vtkPoints *points = vtkPoints::New();
                vtkPolyLine *lines = vtkPolyLine::New();
                               
                // setting the number of nodes in the line
                points->SetNumberOfPoints(nbLineNodes);

                // setting the number of indexes in the line                                                                                            lines->GetPointIds()->SetNumberOfIds(nbLineNodes);

                for (int idNodesLine = 0; idNodesLine <= nbLineNodes; idNodesLine++)
                {
                        // reading the index and the coordinates of the current node
                        int id;
                        double x, y, z;                
                        scanf("%d %f %f %f\n", &id, &x, &y, &z);

                        // filling the node’s info
                        points->InsertPoint(idNodesLine, x, y, z);

                        lines->GetPointIds()->SetId(idNodesLine, idNodesLine);
                }
               
                // assigning the line just created in the polydata, after the already created lines
                polyLine->SetPoints(points);
                polyLine->InsertNextCell(lines->GetCellType(), lines->GetPointIds());
        }                                      
       
        // adding each complete polydata to a mapper and displaying it
        vtkDataSetMapper *polyLineMapper = vtkDataSetMapper::New();
                polyLineMapper->SetInput(polyLine);
                                                       
        vtkActor *polyLineActor = vtkActor::New();
                polyLineActor->SetMapper(polyLineMapper);
                               
        globalRenderer3D->AddActor(skeletonPolyLineActor);
}

// displaying the whole scene
globalRenWin3D->Render();



And I have a function to deal with the picking event:

void pickingFunction(vtkObject* obj, unsigned long, void*, void*)
{
        vtkRenderWindowInteractor *iren = reinterpret_cast<vtkRenderWindowInteractor*>(obj);

        // checking if an event happened in the iren window
        if (iren)
        {
                vtkCellPicker *picker = (vtkCellPicker *)iren->GetPicker();

                vtkInteractorStyleTrackballCamera *irenStyle= (vtkInteractorStyleTrackballCamera *)iren->GetInteractorStyle();
                       
                iren->SetKeyCode(int ('p'));
                irenStyle->OnChar();
               
                if (picker->GetCellId() >= 0 )
                {
                        // assigning the values to the editing variables
                        int globalPickedLineId = picker->GetCellId();
                        vtkActor *globalPickedLineActor = vtkActor::New();
                        globalPickedLineActor = picker->GetActor();
                }

                globalRenWin3D->Render();
        }              
}

My problem is that whatever cell of the polydata I click on, the pointer picker->GetCellId() always returns 0!
I checked picker->GetSubId() and it changes. It actually gives me the index of the line in the polydata fine. For example, if I click on the 3rd line of the 2nd polydata having 4 lines, picker->GetCellId() will give me 0 (it should be 1) and picker->GetSubId() will tell me 2 (which is correct).
I tried to change my vtkPolyData into a vtkUnstructuredGrid, but same results

I checked on the vtk website if someone else had the same problem but can not find something to help.
Am I allocating the vtkPolyData the wrong way? Should I also give each polydata an index? (like I am doing for vtkPoints and vtkPolyLines?) Should I not use InsertNextCell for each new line in the vtkPolyData? But then what should I use instead?
Or is there a problem with the picker? Is it not set correctly? Should I not use the cell picker to pick a polydata?

Thank you very much for your help,

Vincent Luboz.
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