# CenterAnImage

VTKExamples/Cxx/Images/CenterAnImage

### Description

This moves (0,0) from the bottom left corner of the image to the center of the image.

### Code

CenterAnImage.cxx

    #include <vtkSmartPointer.h>

    #include <vtkActor.h>
    #include <vtkBorderRepresentation.h>
    #include <vtkBorderWidget.h>
    #include <vtkCommand.h>
    #include <vtkImageActor.h>
    #include <vtkImageMapper3D.h>
    #include <vtkImageChangeInformation.h>
    #include <vtkImageClip.h>
    #include <vtkImageData.h>
    #include <vtkInteractorStyleImage.h>
    #include <vtkImageReader2Factory.h>
    #include <vtkImageReader2.h>
    #include <vtkMath.h>
    #include <vtkProperty2D.h>
    #include <vtkRenderWindow.h>
    #include <vtkRenderWindowInteractor.h>
    #include <vtkRenderer.h>
    #include <vtkXMLPolyDataReader.h>
    #include <vtkNamedColors.h>

    class vtkBorderCallback : public vtkCommand
    {
    public:
      vtkBorderCallback(){}

      static vtkBorderCallback *New()
      {
        return new vtkBorderCallback;
      }

      virtual void Execute(vtkObject *caller, unsigned long, void*);

      void SetRenderer(vtkSmartPointer<vtkRenderer> renderer)
      {
        this->Renderer = renderer;
      }
      void SetImageActor(vtkSmartPointer<vtkImageActor> actor)
      {
        this->ImageActor = actor;
      }

    private:
      vtkSmartPointer<vtkRenderer>   Renderer;
      vtkSmartPointer<vtkImageActor> ImageActor;
    };

    int main(int argc, char* argv[])
    {
      if ( argc != 2 )
      {
        std::cerr << "Usage: " << argv[0]
                  << " Required parameters: Filename" << std::endl;
        return EXIT_FAILURE;
      }

      // Read the image
      vtkSmartPointer<vtkImageReader2Factory> readerFactory =
        vtkSmartPointer<vtkImageReader2Factory>::New();
      vtkSmartPointer<vtkImageReader2> imageReader =
        readerFactory->CreateImageReader2(argv[1]);
      imageReader->SetFileName(argv[1]);
      imageReader->Update();

      // Shift the image center to (0,0)
      int dims[3];
      imageReader->GetOutput()->GetDimensions(dims);

      vtkSmartPointer<vtkImageChangeInformation> changeInformation =
        vtkSmartPointer<vtkImageChangeInformation>::New();
      changeInformation->SetInputConnection(imageReader->GetOutputPort());
      changeInformation->CenterImageOn();
      changeInformation->Update();

      vtkSmartPointer<vtkImageData> image =
        changeInformation->GetOutput();

      vtkSmartPointer<vtkImageActor> imageActor =
        vtkSmartPointer<vtkImageActor>::New();
      imageActor->GetMapper()->SetInputData(image);

      vtkSmartPointer<vtkRenderWindow> renderWindow =
        vtkSmartPointer<vtkRenderWindow>::New();

      vtkSmartPointer<vtkRenderWindowInteractor> interactor =
        vtkSmartPointer<vtkRenderWindowInteractor>::New();

      vtkSmartPointer<vtkInteractorStyleImage> style =
        vtkSmartPointer<vtkInteractorStyleImage>::New();
      interactor->SetInteractorStyle( style );

      vtkSmartPointer<vtkBorderWidget> borderWidget =
        vtkSmartPointer<vtkBorderWidget>::New();
      borderWidget->SetInteractor(interactor);
      static_cast<vtkBorderRepresentation*>(borderWidget->GetRepresentation())
        ->GetBorderProperty()->SetColor(0,1,0);
      borderWidget->SelectableOff();

      interactor->SetRenderWindow(renderWindow);

      // Setup both renderers
      vtkSmartPointer<vtkNamedColors> colors =
        vtkSmartPointer<vtkNamedColors>::New();
      vtkSmartPointer<vtkRenderer> renderer =
        vtkSmartPointer<vtkRenderer>::New();
      renderer->SetBackground(colors->GetColor3d("Wheat").GetData());
      renderWindow->AddRenderer(renderer);

      renderer->AddActor(imageActor);

      renderer->ResetCamera();

      vtkSmartPointer<vtkBorderCallback> borderCallback =
        vtkSmartPointer<vtkBorderCallback>::New();
      borderCallback->SetRenderer(renderer);
      borderCallback->SetImageActor(imageActor);

      borderWidget->AddObserver(vtkCommand::InteractionEvent,borderCallback);
      borderWidget->On();
      renderWindow->Render();
      interactor->Start();

      return EXIT_SUCCESS;
    }

    void vtkBorderCallback::Execute(vtkObject *caller, unsigned long, void*)
    {

      vtkBorderWidget *borderWidget =
        reinterpret_cast<vtkBorderWidget*>(caller);

      // Get the world coordinates of the two corners of the box
      vtkCoordinate* lowerLeftCoordinate =
        static_cast<vtkBorderRepresentation*>(
          borderWidget->GetRepresentation())->GetPositionCoordinate();
      double* lowerLeft =
        lowerLeftCoordinate->GetComputedWorldValue(this->Renderer);
      std::cout << "Lower left coordinate: "
                << lowerLeft[0] << ", "
                << lowerLeft[1] << ", "
                << lowerLeft[2] << std::endl;

      vtkCoordinate* upperRightCoordinate =
        static_cast<vtkBorderRepresentation*>(
          borderWidget->GetRepresentation())->GetPosition2Coordinate();
      double* upperRight =
        upperRightCoordinate->GetComputedWorldValue(this->Renderer);
      std::cout << "Upper right coordinate: "
                << upperRight[0] << ", "
                << upperRight[1] << ", "
                << upperRight[2] << std::endl;

      double* bounds = this->ImageActor->GetBounds();
      double xmin = bounds[0];
      double xmax = bounds[1];
      double ymin = bounds[2];
      double ymax = bounds[3];

      if( (lowerLeft[0] > xmin) &&
          (upperRight[0] < xmax) &&
          (lowerLeft[1] > ymin) &&
          (upperRight[1] < ymax) )
      {
        //std::cout << "box is inside image" << std::endl;
        //std::cout << "xmin: " << xmin << " xmax: " << xmax << " ymin: " << ymin << " ymax: " << ymax << std::endl;
      }
      else
      {
        std::cout << "box is NOT inside image" << std::endl;
      }
    }

### CMakeLists.txt

    cmake_minimum_required(VERSION 3.3 FATAL_ERROR)

    project(CenterAnImage)

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

### Download and Build CenterAnImage

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

    cd CenterAnImage/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:

    ./CenterAnImage

WINDOWS USERS

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