# CheckerboardWidget

VTKExamples/Cxx/Widgets/CheckerboardWidget

### Description

Compare two images with a checkerboard. The widget permits interactive control of the number of checkers in the x/y directions. Checkerboards are often used to compare the results of image registration. For an alternative image comparison widget try the RectilinearWipeWidget.

### Code

CheckerboardWidget.cxx

    #include <vtkSmartPointer.h>
    #include <vtkCheckerboardWidget.h>
    #include <vtkCheckerboardRepresentation.h>
    #include <vtkJPEGReader.h>
    #include <vtkImageCheckerboard.h>
    #include <vtkImageActor.h>
    #include <vtkImageMapper3D.h>
    #include <vtkImageData.h>
    #include <vtkRenderer.h>
    #include <vtkRenderWindow.h>
    #include <vtkRenderWindowInteractor.h>
    #include <vtkProperty2D.h>
    #include <vtkCommand.h>
    #include <vtkObjectFactory.h>
    #include <vtkInteractorStyleImage.h>

    int main( int argc, char *argv[] )
    {
      if ( argc < 3 )
      {
        std::cerr << "Usage: " << argv[0]
                  << " Input1Filename Input2Filename" << std::endl;
        return EXIT_FAILURE;
      }

      //Read the images
      vtkSmartPointer<vtkJPEGReader> reader1 =
        vtkSmartPointer<vtkJPEGReader>::New();
      reader1->SetFileName ( argv[1] );

      vtkSmartPointer<vtkJPEGReader> reader2 =
        vtkSmartPointer<vtkJPEGReader>::New();
      reader2->SetFileName ( argv[2] );

      // Create a checker pipeline
      vtkSmartPointer<vtkImageCheckerboard> checker =
        vtkSmartPointer<vtkImageCheckerboard>::New();
      checker->SetInputConnection(0,reader1->GetOutputPort());
      checker->SetInputConnection(1,reader2->GetOutputPort());
      checker->SetNumberOfDivisions(3,3,1);

      // Create the RenderWindow, Renderer and both Actors
      //
      vtkSmartPointer<vtkRenderer> ren1 =
        vtkSmartPointer<vtkRenderer>::New();
      vtkSmartPointer<vtkRenderWindow> renWin =
        vtkSmartPointer<vtkRenderWindow>::New();
      renWin->AddRenderer(ren1);

      vtkSmartPointer<vtkRenderWindowInteractor> iren =
        vtkSmartPointer<vtkRenderWindowInteractor>::New();
      iren->SetRenderWindow(renWin);

      vtkSmartPointer<vtkImageActor> checkerActor =
        vtkSmartPointer<vtkImageActor>::New();
      checkerActor->GetMapper()->SetInputConnection(checker->GetOutputPort());

      // VTK widgets consist of two parts: the widget part that handles
      // event processing; and the widget representation that defines how
      // the widget appears in the scene
      // (i.e., matters pertaining to geometry).
      vtkSmartPointer<vtkCheckerboardWidget> checkerWidget =
        vtkSmartPointer<vtkCheckerboardWidget>::New();
      checkerWidget->SetInteractor(iren);

      vtkCheckerboardRepresentation *checkerWidgetRep=
        static_cast<vtkCheckerboardRepresentation *>
        (checkerWidget->GetRepresentation());

      checkerWidgetRep->SetImageActor(checkerActor);
      checkerWidgetRep->SetCheckerboard(checker);

      // Add the actors to the renderer, set the background and size
      //
      ren1->AddActor(checkerActor);
      ren1->SetBackground(0.1, 0.2, 0.4);
      renWin->SetSize(300, 300);

      // render the image
      //
      iren->Initialize();
      renWin->Render();
      checkerWidget->On();
      iren->Start();

      return EXIT_SUCCESS;
    }

### CMakeLists.txt

    cmake_minimum_required(VERSION 2.8)

    PROJECT(CheckerboardWidget)

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

    add_executable(CheckerboardWidget MACOSX_BUNDLE CheckerboardWidget.cxx )

    target_link_libraries(CheckerboardWidget ${VTK_LIBRARIES})

### Download and Build CheckerboardWidget

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

    cd CheckerboardWidget/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:

    ./CheckerboardWidget

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.