# CallData

VTKExamples/Cxx/Interaction/CallData

### Description

This example demonstrates the use of 'calldata' in a vtkCallbackCommand. Here, we create a custom VTK filter to invoke an event to which we attach a value (the 'calldata'). We use a timer to modify and update the filter so that the event is triggered repeatedly, demonstrating the pass-via-calldata.

### Code

CallData.cxx

    #include <vtkObjectFactory.h>
    #include <vtkCommand.h>
    #include <vtkCallbackCommand.h>
    #include <vtkStreamingDemandDrivenPipeline.h>
    #include <vtkInformationVector.h>
    #include <vtkInformation.h>
    #include <vtkDataObject.h>
    #include <vtkSmartPointer.h>
    #include <vtkAppendPolyData.h>
    #include <vtkSphereSource.h>
    #include <vtkPolyDataAlgorithm.h>
    #include <vtkRenderer.h>
    #include <vtkRenderWindow.h>
    #include <vtkRenderWindowInteractor.h>

    class vtkMyTestFilter : public vtkPolyDataAlgorithm
    {
    public:
      vtkTypeMacro(vtkMyTestFilter,vtkPolyDataAlgorithm);
      static vtkMyTestFilter *New();

      int RefreshEvent;

    protected:
      vtkMyTestFilter()
      {
        this->SetNumberOfInputPorts(0);

        this->RefreshEvent = vtkCommand::UserEvent + 1;

        this->Counter = 0;
      }

      int RequestData(vtkInformation *, vtkInformationVector **, vtkInformationVector *)
      {
          this->InvokeEvent(this->RefreshEvent, &this->Counter);
          this->Counter++;
          return 1;
      }

    private:
      vtkMyTestFilter(const vtkMyTestFilter&);  // Not implemented.
      void operator=(const vtkMyTestFilter&);  // Not implemented.

      unsigned int Counter;
    };

    vtkStandardNewMacro(vtkMyTestFilter);

    static void CallbackFunction(vtkObject* caller,
                    long unsigned int eventId,
                    void* clientData,
                    void* callData );

    class vtkTimerCallback : public vtkCommand
    {
      public:
        static vtkTimerCallback *New()
        {
          vtkTimerCallback *cb = new vtkTimerCallback;

          return cb;
        }

        virtual void Execute(vtkObject *vtkNotUsed(caller),
                             unsigned long vtkNotUsed(eventId),
                             void *vtkNotUsed(callData))
        {
            TestFilter->Modified();
            TestFilter->Update();
        }

        vtkMyTestFilter* TestFilter;

    };

    int main(int, char *[])
    {
      // Create a renderer, render window, and interactor
      vtkSmartPointer<vtkRenderer> renderer =
        vtkSmartPointer<vtkRenderer>::New();
      vtkSmartPointer<vtkRenderWindow> renderWindow =
        vtkSmartPointer<vtkRenderWindow>::New();
      renderWindow->AddRenderer(renderer);
      vtkSmartPointer<vtkRenderWindowInteractor> renderWindowInteractor =
        vtkSmartPointer<vtkRenderWindowInteractor>::New();
      renderWindowInteractor->SetRenderWindow(renderWindow);

      vtkSmartPointer<vtkMyTestFilter> testFilter =
        vtkSmartPointer<vtkMyTestFilter>::New();

      vtkSmartPointer<vtkCallbackCommand> callback =
        vtkSmartPointer<vtkCallbackCommand>::New();
      callback->SetCallback(CallbackFunction );
      testFilter->AddObserver(testFilter->RefreshEvent, callback);
      testFilter->Update();

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

      // Sign up to receive TimerEvent
      vtkSmartPointer<vtkTimerCallback> timerCallback =
        vtkSmartPointer<vtkTimerCallback>::New();
      timerCallback->TestFilter = testFilter;

      renderWindowInteractor->AddObserver(vtkCommand::TimerEvent, timerCallback);

      renderWindowInteractor->CreateRepeatingTimer(100);

      renderWindowInteractor->Start();

      return EXIT_SUCCESS;
    }

    void CallbackFunction(vtkObject* vtkNotUsed(caller),
                          long unsigned int vtkNotUsed(eventId),
                          void* vtkNotUsed(clientData),
                          void* callData )
    {
      unsigned int* callDataCasted = reinterpret_cast<unsigned int*>(callData);
      std::cout << *callDataCasted << std::endl;
    }

### CMakeLists.txt

    cmake_minimum_required(VERSION 3.3 FATAL_ERROR)

    project(CallData)

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

### Download and Build CallData

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

    cd CallData/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:

    ./CallData

WINDOWS USERS

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