# ExtractVisibleCells

VTKExamples/Cxx/Filtering/ExtractVisibleCells

### Code

ExtractVisibleCells.cxx

    #include <vtkSphereSource.h>
    #include <vtkPolyData.h>
    #include <vtkSmartPointer.h>
    #include <vtkPolyDataMapper.h>
    #include <vtkActor.h>
    #include <vtkRenderWindow.h>
    #include <vtkRenderer.h>
    #include <vtkRenderWindowInteractor.h>
    #include <vtkHardwareSelector.h>
    #include <vtkInteractorStyleTrackballCamera.h>
    #include <vtkObjectFactory.h>
    #include <vtkRendererCollection.h>
    #include <vtkDataSetMapper.h>
    #include <vtkExtractSelection.h>
    #include <vtkSelection.h>
    #include <vtkProperty.h>

    // Define interaction style
    class KeyPressInteractorStyle : public vtkInteractorStyleTrackballCamera
    {
      public:
        static KeyPressInteractorStyle* New();
        vtkTypeMacro(KeyPressInteractorStyle, vtkInteractorStyleTrackballCamera);

        virtual void OnKeyPress()
        {
          // Get the keypress
          std::string key = this->Interactor->GetKeySym();

          // "s" for "s"elect
          if(key.compare("s") == 0)
          {
            vtkSmartPointer<vtkHardwareSelector> selector =
              vtkSmartPointer<vtkHardwareSelector>::New();
            selector->SetRenderer(this->Interactor->GetRenderWindow()->GetRenderers()->GetFirstRenderer());
            int* temp = this->Interactor->GetRenderWindow()->GetSize();
            unsigned int windowSize[4];
            windowSize[0] = temp[2];
            windowSize[1] = temp[3];
            windowSize[2] = temp[0];
            windowSize[3] = temp[1];
            /*
            for(unsigned int i = 0; i < 4; i++)
              {
              windowSize[i] = temp[i];
              }
            */
            selector->SetArea(windowSize);
            selector->SetFieldAssociation(vtkDataObject::FIELD_ASSOCIATION_CELLS);
            vtkSelection* selection = selector->Select();
            std::cout << "Selection has " << selection->GetNumberOfNodes() << " nodes." << std::endl;

            vtkSmartPointer<vtkExtractSelection> extractSelection =
              vtkSmartPointer<vtkExtractSelection>::New();
            extractSelection->SetInputData(0, this->Data);
            extractSelection->SetInputData(1, selection);
            extractSelection->Update();

            vtkSmartPointer<vtkDataSetMapper> mapper =
              vtkSmartPointer<vtkDataSetMapper>::New();
            mapper->SetInputConnection(extractSelection->GetOutputPort());

            vtkSmartPointer<vtkActor> actor =
              vtkSmartPointer<vtkActor>::New();
            actor->SetMapper(mapper);
            actor->GetProperty()->SetColor(1,0,0);
            this->Renderer->AddActor(actor);

          }

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

        vtkPolyData* Data;
        vtkRenderer* Renderer;

    };
    vtkStandardNewMacro(KeyPressInteractorStyle);

    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();

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

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

      // Create a renderer, render window, and interactor
      vtkSmartPointer<vtkRenderer> renderer =
        vtkSmartPointer<vtkRenderer>::New();
      vtkSmartPointer<vtkRenderWindow> renderWindow =
        vtkSmartPointer<vtkRenderWindow>::New();
      renderWindow->SetMultiSamples(0); // Turn off anti-aliasing
      renderWindow->AddRenderer(renderer);
      vtkSmartPointer<vtkRenderWindowInteractor> renderWindowInteractor =
        vtkSmartPointer<vtkRenderWindowInteractor>::New();
      renderWindowInteractor->SetRenderWindow(renderWindow);

      vtkSmartPointer<KeyPressInteractorStyle> style =
        vtkSmartPointer<KeyPressInteractorStyle>::New();
      style->Renderer = renderer;
      renderWindowInteractor->SetInteractorStyle(style);
      style->SetCurrentRenderer(renderer);
      style->Data = sphereSource->GetOutput();

      // Add the actor to the scene
      renderer->AddActor(actor);
      renderer->SetBackground(.3, .6, .3); // Background color green

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

      return EXIT_SUCCESS;
    }

### CMakeLists.txt

    cmake_minimum_required(VERSION 3.3 FATAL_ERROR)

    project(ExtractVisibleCells)

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

### Download and Build ExtractVisibleCells

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

    cd ExtractVisibleCells/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:

    ./ExtractVisibleCells

WINDOWS USERS

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