# ImageDivergence

VTKExamples/Cxx/Images/ImageDivergence

### Code

ImageDivergence.cxx

    #include <vtkSmartPointer.h>
    #include <vtkImageCast.h>
    #include <vtkImageData.h>
    #include <vtkImageMapper3D.h>
    #include <vtkImageCanvasSource2D.h>
    #include <vtkImageDivergence.h>
    #include <vtkImageGradient.h>
    #include <vtkImageCanvasSource2D.h>
    #include <vtkImageCorrelation.h>
    #include <vtkInteractorStyleImage.h>
    #include <vtkImageActor.h>
    #include <vtkActor.h>
    #include <vtkRenderWindow.h>
    #include <vtkRenderer.h>
    #include <vtkRenderWindowInteractor.h>
    #include <vtkImageMandelbrotSource.h>

    int main(int, char *[])
    {
      // Create an image
      vtkSmartPointer<vtkImageMandelbrotSource> source =
        vtkSmartPointer<vtkImageMandelbrotSource>::New();
      source->Update();

      vtkSmartPointer<vtkImageCast> originalCastFilter =
        vtkSmartPointer<vtkImageCast>::New();
      originalCastFilter->SetInputConnection(source->GetOutputPort());
      originalCastFilter->SetOutputScalarTypeToFloat();
      originalCastFilter->Update();

      // Compute the gradient (to produce a vector field)
      vtkSmartPointer<vtkImageGradient> gradientFilter =
        vtkSmartPointer<vtkImageGradient>::New();
      gradientFilter->SetInputConnection(source->GetOutputPort());
      gradientFilter->Update();

      vtkSmartPointer<vtkImageDivergence> divergenceFilter =
        vtkSmartPointer<vtkImageDivergence>::New();
      divergenceFilter->SetInputConnection(gradientFilter->GetOutputPort());
      divergenceFilter->Update();

      vtkSmartPointer<vtkImageCast> divergenceCastFilter =
        vtkSmartPointer<vtkImageCast>::New();
      divergenceCastFilter->SetInputConnection(divergenceFilter->GetOutputPort());
      divergenceCastFilter->SetOutputScalarTypeToFloat();
      divergenceCastFilter->Update();

      // Create actors
      vtkSmartPointer<vtkImageActor> originalActor =
        vtkSmartPointer<vtkImageActor>::New();
      originalActor->GetMapper()->SetInputConnection(
        originalCastFilter->GetOutputPort());

      vtkSmartPointer<vtkImageActor> divergenceActor =
        vtkSmartPointer<vtkImageActor>::New();
      divergenceActor->GetMapper()->SetInputConnection(
        divergenceCastFilter->GetOutputPort());

      // Define viewport ranges
      // (xmin, ymin, xmax, ymax)
      double leftViewport[4] = {0.0, 0.0, 0.5, 1.0};
      double rightViewport[4] = {0.5, 0.0, 1.0, 1.0};

      // Setup renderers
      vtkSmartPointer<vtkRenderer> originalRenderer =
        vtkSmartPointer<vtkRenderer>::New();
      originalRenderer->SetViewport(leftViewport);
      originalRenderer->AddActor(originalActor);
      originalRenderer->ResetCamera();

      vtkSmartPointer<vtkRenderer> divergenceRenderer =
        vtkSmartPointer<vtkRenderer>::New();
      divergenceRenderer->SetViewport(rightViewport);
      divergenceRenderer->AddActor(divergenceActor);
      divergenceRenderer->ResetCamera();

      // Setup render window
      vtkSmartPointer<vtkRenderWindow> renderWindow =
        vtkSmartPointer<vtkRenderWindow>::New();
      renderWindow->SetSize(600,300);
      renderWindow->AddRenderer(originalRenderer);
      renderWindow->AddRenderer(divergenceRenderer);

      // Setup render window interactor
      vtkSmartPointer<vtkRenderWindowInteractor> renderWindowInteractor =
        vtkSmartPointer<vtkRenderWindowInteractor>::New();
      vtkSmartPointer<vtkInteractorStyleImage> style =
        vtkSmartPointer<vtkInteractorStyleImage>::New();

      renderWindowInteractor->SetInteractorStyle(style);

      // Render and start interaction
      renderWindowInteractor->SetRenderWindow(renderWindow);
      renderWindow->Render();
      renderWindowInteractor->Initialize();

      renderWindowInteractor->Start();

      return EXIT_SUCCESS;
    }

### CMakeLists.txt

    cmake_minimum_required(VERSION 3.3 FATAL_ERROR)

    project(ImageDivergence)

    find_package(VTK COMPONENTS
      vtkCommonCore
      vtkCommonDataModel
      vtkImagingCore
      vtkImagingGeneral
      vtkImagingMath
      vtkImagingSources
      vtkInteractionStyle
      vtkRenderingContextOpenGL2
      vtkRenderingCore
      vtkRenderingFreeType
      vtkRenderingGL2PSOpenGL2
      vtkRenderingOpenGL2 QUIET)
    if (NOT VTK_FOUND)
      message("Skipping ImageDivergence: ${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(ImageDivergence MACOSX_BUNDLE ImageDivergence.cxx )
      target_link_libraries(ImageDivergence PRIVATE ${VTK_LIBRARIES})
    else ()
      # include all components
      add_executable(ImageDivergence MACOSX_BUNDLE ImageDivergence.cxx )
      target_link_libraries(ImageDivergence PRIVATE ${VTK_LIBRARIES})
      # vtk_module_autoinit is needed
      vtk_module_autoinit(
        TARGETS ImageDivergence
        MODULES ${VTK_LIBRARIES}
        )
    endif ()

### Download and Build ImageDivergence

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

    cd ImageDivergence/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:

    ./ImageDivergence

WINDOWS USERS

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