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# Picking

VTKEx/Cxx/Interaction/Picking

Question

If you have a simple question about this example contact us at VTKExProject If your question is more complex and may require extended discussion, please use the VTK Discourse Forum

### Code

Picking.cxx

    #include <vtkSmartPointer.h>
    #include <vtkActor.h>
    #include <vtkSphereSource.h>
    #include <vtkRendererCollection.h>
    #include <vtkCellArray.h>
    #include <vtkInteractorStyleTrackballCamera.h>
    #include <vtkObjectFactory.h>
    #include <vtkPlaneSource.h>
    #include <vtkPoints.h>
    #include <vtkPolyData.h>
    #include <vtkPolyDataMapper.h>
    #include <vtkPropPicker.h>
    #include <vtkRenderWindow.h>
    #include <vtkRenderWindowInteractor.h>
    #include <vtkRenderer.h>

    // Handle mouse events
    class MouseInteractorStyle2 : public vtkInteractorStyleTrackballCamera
    {
    public:
      static MouseInteractorStyle2* New();
      vtkTypeMacro(MouseInteractorStyle2, vtkInteractorStyleTrackballCamera);

      virtual void OnLeftButtonDown() override
      {
        int* clickPos = this->GetInteractor()->GetEventPosition();

        // Pick from this location.
        vtkSmartPointer<vtkPropPicker>  picker =
          vtkSmartPointer<vtkPropPicker>::New();
        picker->Pick(clickPos[0], clickPos[1], 0, this->GetDefaultRenderer());

        double* pos = picker->GetPickPosition();
        std::cout << "Pick position (world coordinates) is: "
                  << pos[0] << " " << pos[1]
                  << " " << pos[2] << std::endl;

        std::cout << "Picked actor: " << picker->GetActor() << std::endl;
        //Create a sphere
        vtkSmartPointer<vtkSphereSource> sphereSource =
          vtkSmartPointer<vtkSphereSource>::New();
        sphereSource->SetCenter(pos[0], pos[1], pos[2]);
        sphereSource->SetRadius(0.1);

        //Create a mapper and actor
        vtkSmartPointer<vtkPolyDataMapper> mapper =
          vtkSmartPointer<vtkPolyDataMapper>::New();
        mapper->SetInputConnection(sphereSource->GetOutputPort());

        vtkSmartPointer<vtkActor> actor =
          vtkSmartPointer<vtkActor>::New();
        actor->SetMapper(mapper);

        this->GetDefaultRenderer()->AddActor(actor);
        // Forward events
        vtkInteractorStyleTrackballCamera::OnLeftButtonDown();
      }

    private:

    };

    vtkStandardNewMacro(MouseInteractorStyle2);

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

      // Create a polydata object
      vtkPolyData* polydata = planeSource->GetOutput();

      // Create a mapper
      vtkSmartPointer<vtkPolyDataMapper> mapper =
        vtkSmartPointer<vtkPolyDataMapper>::New();
      mapper->SetInputData ( polydata );

      // Create an actor
      vtkSmartPointer<vtkActor> actor =
        vtkSmartPointer<vtkActor>::New();
      actor->SetMapper ( mapper );

      std::cout << "Actor address: " << actor << std::endl;

      // A renderer and render window
      vtkSmartPointer<vtkRenderer> renderer =
        vtkSmartPointer<vtkRenderer>::New();
      vtkSmartPointer<vtkRenderWindow> renderWindow =
        vtkSmartPointer<vtkRenderWindow>::New();
      renderWindow->AddRenderer ( renderer );

      // An interactor
      vtkSmartPointer<vtkRenderWindowInteractor> renderWindowInteractor =
        vtkSmartPointer<vtkRenderWindowInteractor>::New();
      renderWindowInteractor->SetRenderWindow ( renderWindow );

      // Set the custom stype to use for interaction.
      vtkSmartPointer<MouseInteractorStyle2> style =
        vtkSmartPointer<MouseInteractorStyle2>::New();
      style->SetDefaultRenderer(renderer);

      renderWindowInteractor->SetInteractorStyle( style );

      // Add the actors to the scene
      renderer->AddActor ( actor );
      renderer->SetBackground ( 0,0,1 );

      // Render and interact
      renderWindow->Render();
      renderWindowInteractor->Initialize();
      renderWindowInteractor->Start();

      return EXIT_SUCCESS;
    }

### CMakeLists.txt

    cmake_minimum_required(VERSION 3.3 FATAL_ERROR)

    project(Picking)

    find_package(VTK COMPONENTS
      vtkCommonCore
      vtkCommonDataModel
      vtkFiltersSources
      vtkInteractionStyle
      vtkRenderingContextOpenGL2
      vtkRenderingCore
      vtkRenderingFreeType
      vtkRenderingGL2PSOpenGL2
      vtkRenderingOpenGL2 QUIET)
    if (NOT VTK_FOUND)
      message("Skipping Picking: ${VTK_NOT_FOUND_MESSAGE}")
      return ()
    endif()
    message (STATUS "VTK_VERSION: ${VTK_VERSION}")
    if (VTK_VERSION VERSION_LESS "8.90.0")
      # old system
      include(${VTK_USE_FILE})
      add_executable(Picking MACOSX_BUNDLE Picking.cxx )
      target_link_libraries(Picking PRIVATE ${VTK_LIBRARIES})
    else ()
      # include all components
      add_executable(Picking MACOSX_BUNDLE Picking.cxx )
      target_link_libraries(Picking PRIVATE ${VTK_LIBRARIES})
      # vtk_module_autoinit is needed
      vtk_module_autoinit(
        TARGETS Picking
        MODULES ${VTK_LIBRARIES}
        )
    endif ()

### Download and Build Picking

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

    cd Picking/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:

    ./Picking

WINDOWS USERS

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