# CellPicking

VTKExamples/Cxx/Picking/CellPicking

### Description

This example demonstrates how to get the coordinates of the point on an actor that is clicked with the left mouse button. It also indicates which cell the selected point belongs to by highlighting the edges of that cell.

### Code

CellPicking.cxx

    #include <vtkVersion.h>
    #include <vtkSmartPointer.h>
    #include <vtkRendererCollection.h>
    #include <vtkDataSetMapper.h>
    #include <vtkUnstructuredGrid.h>
    #include <vtkIdTypeArray.h>
    #include <vtkTriangleFilter.h>
    #include <vtkPolyDataMapper.h>
    #include <vtkActor.h>
    #include <vtkCommand.h>
    #include <vtkRenderWindow.h>
    #include <vtkRenderer.h>
    #include <vtkRenderWindowInteractor.h>
    #include <vtkPolyData.h>
    #include <vtkPoints.h>
    #include <vtkCellArray.h>
    #include <vtkPlaneSource.h>
    #include <vtkCellPicker.h>
    #include <vtkInteractorStyleTrackballCamera.h>
    #include <vtkProperty.h>
    #include <vtkSelectionNode.h>
    #include <vtkSelection.h>
    #include <vtkExtractSelection.h>
    #include <vtkObjectFactory.h>

    // Catch mouse events
    class MouseInteractorStyle : public vtkInteractorStyleTrackballCamera
    {
      public:
      static MouseInteractorStyle* New();

      MouseInteractorStyle()
      {
        selectedMapper = vtkSmartPointer<vtkDataSetMapper>::New();
        selectedActor = vtkSmartPointer<vtkActor>::New();
      }

        virtual void OnLeftButtonDown()
        {
          // Get the location of the click (in window coordinates)
          int* pos = this->GetInteractor()->GetEventPosition();

          vtkSmartPointer<vtkCellPicker> picker =
            vtkSmartPointer<vtkCellPicker>::New();
          picker->SetTolerance(0.0005);

          // Pick from this location.
          picker->Pick(pos[0], pos[1], 0, this->GetDefaultRenderer());

          double* worldPosition = picker->GetPickPosition();
          std::cout << "Cell id is: " << picker->GetCellId() << std::endl;

          if(picker->GetCellId() != -1)
          {

            std::cout << "Pick position is: " << worldPosition[0] << " " << worldPosition[1]
                      << " " << worldPosition[2] << endl;

            vtkSmartPointer<vtkIdTypeArray> ids =
              vtkSmartPointer<vtkIdTypeArray>::New();
            ids->SetNumberOfComponents(1);
            ids->InsertNextValue(picker->GetCellId());

            vtkSmartPointer<vtkSelectionNode> selectionNode =
              vtkSmartPointer<vtkSelectionNode>::New();
            selectionNode->SetFieldType(vtkSelectionNode::CELL);
            selectionNode->SetContentType(vtkSelectionNode::INDICES);
            selectionNode->SetSelectionList(ids);

            vtkSmartPointer<vtkSelection> selection =
              vtkSmartPointer<vtkSelection>::New();
            selection->AddNode(selectionNode);

            vtkSmartPointer<vtkExtractSelection> extractSelection =
              vtkSmartPointer<vtkExtractSelection>::New();
    #if VTK_MAJOR_VERSION <= 5
            extractSelection->SetInput(0, this->Data);
            extractSelection->SetInput(1, selection);
    #else
            extractSelection->SetInputData(0, this->Data);
            extractSelection->SetInputData(1, selection);
    #endif
            extractSelection->Update();

            // In selection
            vtkSmartPointer<vtkUnstructuredGrid> selected =
              vtkSmartPointer<vtkUnstructuredGrid>::New();
            selected->ShallowCopy(extractSelection->GetOutput());

            std::cout << "There are " << selected->GetNumberOfPoints()
                      << " points in the selection." << std::endl;
            std::cout << "There are " << selected->GetNumberOfCells()
                      << " cells in the selection." << std::endl;

    #if VTK_MAJOR_VERSION <= 5
            selectedMapper->SetInputConnection(
              selected->GetProducerPort());
    #else
            selectedMapper->SetInputData(selected);
    #endif

            selectedActor->SetMapper(selectedMapper);
            selectedActor->GetProperty()->EdgeVisibilityOn();
            selectedActor->GetProperty()->SetEdgeColor(1,0,0);
            selectedActor->GetProperty()->SetLineWidth(3);

            this->Interactor->GetRenderWindow()->GetRenderers()->GetFirstRenderer()->AddActor(selectedActor);

          }
          // Forward events
          vtkInteractorStyleTrackballCamera::OnLeftButtonDown();
        }

        vtkSmartPointer<vtkPolyData> Data;
        vtkSmartPointer<vtkDataSetMapper> selectedMapper;
        vtkSmartPointer<vtkActor> selectedActor;

    };

    vtkStandardNewMacro(MouseInteractorStyle);

    int main (int, char *[])
    {
      vtkSmartPointer<vtkPlaneSource> planeSource =
        vtkSmartPointer<vtkPlaneSource>::New();
      planeSource->Update();

      vtkSmartPointer<vtkTriangleFilter> triangleFilter =
        vtkSmartPointer<vtkTriangleFilter>::New();
      triangleFilter->SetInputConnection(planeSource->GetOutputPort());
      triangleFilter->Update();

      vtkSmartPointer<vtkPolyDataMapper> mapper =
        vtkSmartPointer<vtkPolyDataMapper>::New();
      mapper->SetInputConnection(triangleFilter->GetOutputPort());

      vtkSmartPointer<vtkActor> actor =
        vtkSmartPointer<vtkActor>::New();
      actor->GetProperty()->SetColor(0,1,0); //green
      actor->SetMapper(mapper);

      vtkSmartPointer<vtkRenderer> renderer =
        vtkSmartPointer<vtkRenderer>::New();
      vtkSmartPointer<vtkRenderWindow> renderWindow =
        vtkSmartPointer<vtkRenderWindow>::New();
      renderWindow->AddRenderer(renderer);

      vtkSmartPointer<vtkRenderWindowInteractor> renderWindowInteractor =
        vtkSmartPointer<vtkRenderWindowInteractor>::New();
      renderWindowInteractor->SetRenderWindow(renderWindow);
      renderWindowInteractor->Initialize();

      // Set the custom stype to use for interaction.
      vtkSmartPointer<MouseInteractorStyle> style =
        vtkSmartPointer<MouseInteractorStyle>::New();
      style->SetDefaultRenderer(renderer);
      style->Data = triangleFilter->GetOutput();

      renderWindowInteractor->SetInteractorStyle(style);

      renderer->AddActor(actor);
      renderer->ResetCamera();

      renderer->SetBackground(0,0,1); // Blue

      renderWindow->Render();
      renderWindowInteractor->Start();

      return EXIT_SUCCESS;
    }

### CMakeLists.txt

    cmake_minimum_required(VERSION 2.8)

    PROJECT(CellPicking)

    find_package(VTK REQUIRED)
    include(${VTK_USE_FILE})

    add_executable(CellPicking MACOSX_BUNDLE CellPicking.cxx)

    target_link_libraries(CellPicking ${VTK_LIBRARIES})

### Download and Build CellPicking

Click here to download CellPicking and its CMakeLists.txt file. Once the tarball CellPicking.tar has been downloaded and extracted,

    cd CellPicking/build

If VTK is installed:

    cmake ..

If VTK is not installed but compiled on your system, you will need to specify the path to your VTK build:

    cmake -DVTK_DIR:PATH=/home/me/vtk_build ..

Build the project:

    make

and run it:

    ./CellPicking

WINDOWS USERS PLEASE NOTE: Be sure to add the VTK bin directory to your path. This will resolve the VTK dll's at run time.