# ObserverMemberFunction

VTKExamples/Cxx/Interaction/ObserverMemberFunction

### Description

You must use the git version of VTK from at least 10/11/2010 to use this functionality.

### Code

ObserverMemberFunction.cxx

    #include <vtkPolyDataMapper.h>
    #include <vtkObjectFactory.h>
    #include <vtkCommand.h>
    #include <vtkActor.h>
    #include <vtkSmartPointer.h>
    #include <vtkRenderWindow.h>
    #include <vtkRenderer.h>
    #include <vtkRenderWindowInteractor.h>
    #include <vtkInteractorStyle.h>
    #include <vtkPolyData.h>
    #include <vtkSphereSource.h>
    #include <vtkInteractorStyleTrackballCamera.h>

    // A class not derived from vtkObjectBase
    class MyClass
    {
      public:
        void KeypressCallbackFunction(vtkObject*,
                                      long unsigned int vtkNotUsed(eventId),
                                      void* vtkNotUsed(callData))
        {
        std::cout << "Caught event in MyClass" << std::endl;
        }

    };

    // A class that is derived from vtkObjectBase
    class MyInteractorStyle : public vtkInteractorStyleTrackballCamera
    {
    public:
      static MyInteractorStyle* New();
      vtkTypeMacro(MyInteractorStyle, vtkInteractorStyleTrackballCamera);

      void KeypressCallbackFunction(vtkObject*,
                                    long unsigned int vtkNotUsed(eventId),
                                    void* vtkNotUsed(callData) )
      {
        std::cout << "Caught event in MyInteractorStyle" << std::endl;
      }

    };
    vtkStandardNewMacro(MyInteractorStyle);

    int main(int, char *[])
    {
      // Create a sphere
      vtkSmartPointer<vtkSphereSource> sphereSource =
        vtkSmartPointer<vtkSphereSource>::New();
      sphereSource->SetCenter(0.0, 0.0, 0.0);
      sphereSource->SetRadius(5.0);
      sphereSource->Update();

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

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

      // 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);

      MyClass myClass;
      renderWindowInteractor->AddObserver(vtkCommand::KeyPressEvent, &myClass, &MyClass::KeypressCallbackFunction);

      vtkSmartPointer<MyInteractorStyle> style =
        MyInteractorStyle::New();
      renderWindowInteractor->AddObserver(vtkCommand::KeyPressEvent, style, &MyInteractorStyle::KeypressCallbackFunction);

      vtkSmartPointer<MyInteractorStyle> style2 =
        vtkSmartPointer<MyInteractorStyle>::New();
      renderWindowInteractor->AddObserver(vtkCommand::KeyPressEvent, style2, &MyInteractorStyle::KeypressCallbackFunction);

      renderer->AddActor(actor);
      renderer->SetBackground(1,1,1); // Background color white
      renderWindow->Render();
      renderWindowInteractor->Start();

      return EXIT_SUCCESS;
    }

### CMakeLists.txt

    cmake_minimum_required(VERSION 3.3 FATAL_ERROR)

    project(ObserverMemberFunction)

    find_package(VTK COMPONENTS
      vtkCommonCore
      vtkCommonDataModel
      vtkFiltersSources
      vtkInteractionStyle
      vtkRenderingCore
      vtkRenderingFreeType
      vtkRenderingOpenGL2 QUIET)
    if (NOT VTK_FOUND)
      message("Skipping ObserverMemberFunction: ${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(ObserverMemberFunction MACOSX_BUNDLE ObserverMemberFunction.cxx )
      target_link_libraries(ObserverMemberFunction PRIVATE ${VTK_LIBRARIES})
    else ()
      # include all components
      add_executable(ObserverMemberFunction MACOSX_BUNDLE ObserverMemberFunction.cxx )
      target_link_libraries(ObserverMemberFunction PRIVATE ${VTK_LIBRARIES})
      # vtk_module_autoinit is needed
      vtk_module_autoinit(
        TARGETS ObserverMemberFunction
        MODULES ${VTK_LIBRARIES}
        )
    endif ()

### Download and Build ObserverMemberFunction

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

    cd ObserverMemberFunction/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:

    ./ObserverMemberFunction

WINDOWS USERS

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