# DrawOnAnImage

VTKExamples/Cxx/Images/DrawOnAnImage

### Description

This example draws a circle in the center of the input image using {{class|vtkImageCanvasSource2D}}'s `DrawCircle` method.

### Code

DrawOnAnImage.cxx

    #include <vtkSmartPointer.h>

    #include <vtkRenderWindow.h>
    #include <vtkRenderWindowInteractor.h>
    #include <vtkRenderer.h>
    #include <vtkJPEGReader.h>
    #include <vtkImageData.h>
    #include <vtkImageMapper3D.h>
    #include <vtkImageViewer2.h>
    #include <vtkImageCanvasSource2D.h>
    #include <vtkImageBlend.h>

    int main ( int argc, char* argv[] )
    {
      //Verify input arguments
      if ( argc != 2 )
      {
        std::cout << "Usage: " << argv[0]
                  << " InputFilename(jpg)" << std::endl;
        return EXIT_FAILURE;
      }

      // Parse input arguments
      std::string inputFilename = argv[1];

      // Read the image
      vtkSmartPointer<vtkJPEGReader> jPEGReader =
        vtkSmartPointer<vtkJPEGReader>::New();
      jPEGReader->SetFileName ( inputFilename.c_str() );
      jPEGReader->Update();

      vtkImageData* image = jPEGReader->GetOutput();

      // Find center of image
      int center[2];
      center[0] = (image->GetExtent()[1] + image->GetExtent()[0]) / 2;
      center[1] = (image->GetExtent()[3] + image->GetExtent()[2]) / 2;

      // Pick a radius for the circle
      int radius;
      radius = (image->GetExtent()[1] < image->GetExtent()[3]) ?
        image->GetExtent()[1] * 2 / 5 : image->GetExtent()[3] * 2 / 5;

      // Draw a circle in the center of the image
      vtkSmartPointer<vtkImageCanvasSource2D> drawing =
        vtkSmartPointer<vtkImageCanvasSource2D>::New();
      drawing->SetNumberOfScalarComponents(3);
      drawing->SetScalarTypeToUnsignedChar();
      drawing->SetExtent(image->GetExtent());
      drawing->SetDrawColor(0.0, 0.0, 0.0);
      drawing->FillBox(image->GetExtent()[0], image->GetExtent()[1],
        image->GetExtent()[2], image->GetExtent()[3]);
      drawing->SetDrawColor(255.0, 255.0, 255.0);
      drawing->DrawCircle(center[0], center[1], radius);

      // Combine the images (blend takes multiple connections on the 0th
      // input port)
      vtkSmartPointer<vtkImageBlend> blend =
        vtkSmartPointer<vtkImageBlend>::New();
      blend->AddInputConnection(jPEGReader->GetOutputPort());
      blend->AddInputConnection(drawing->GetOutputPort());
      blend->SetOpacity(0,.6);
      blend->SetOpacity(1,.4);

      // Display the result
      vtkSmartPointer<vtkRenderWindowInteractor> renderWindowInteractor =
        vtkSmartPointer<vtkRenderWindowInteractor>::New();

      vtkSmartPointer<vtkImageViewer2> imageViewer =
        vtkSmartPointer<vtkImageViewer2>::New();
      imageViewer->SetInputConnection(blend->GetOutputPort());
      imageViewer->SetSize(640, 512);
      imageViewer->SetupInteractor(renderWindowInteractor);
      imageViewer->GetRenderer()->ResetCamera();
      imageViewer->GetRenderer()->SetBackground(1,0,0); //red

      renderWindowInteractor->Initialize();
      renderWindowInteractor->Start();

      return EXIT_SUCCESS;
    }

### CMakeLists.txt

    cmake_minimum_required(VERSION 2.8)

    PROJECT(DrawOnAnImage)

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

    add_executable(DrawOnAnImage MACOSX_BUNDLE DrawOnAnImage.cxx )

    target_link_libraries(DrawOnAnImage ${VTK_LIBRARIES})

### Download and Build DrawOnAnImage

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

    cd DrawOnAnImage/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:

    ./DrawOnAnImage

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.