# ImageText

VTKExamples/Cxx/Images/ImageText

### Description

This example demonstrates how to draw text onto an image vtkImageData. It uses vtkImageBlend to blend the text and the image. For another example using vtkImageBlend, see CombineImages.

Seealso

DrawText for an example of drawing text, also in 2D, but into the render window rather than into a vtkImageData object.

### Code

ImageText.cxx

    #include <vtkImageBlend.h>
    #include <vtkImageData.h>
    #include <vtkPointData.h>
    #include <vtkPNGWriter.h>
    #include <vtkSmartPointer.h>
    #include <vtkFreeTypeUtilities.h>
    #include <vtkTextProperty.h>
    #include <vtkImageCanvasSource2D.h>

    // must build VTK with VTK_USE_SYSTEM_FREETYPE=ON

    int main(int argc, char* argv[])
    {
      // Create a black image with a red circle of radius 50 centered at (60, 60)
      vtkSmartPointer<vtkImageCanvasSource2D> drawing =
        vtkSmartPointer<vtkImageCanvasSource2D>::New();
      drawing->SetScalarTypeToUnsignedChar(); // PNGWriter requires unsigned char (or unsigned short)
      drawing->SetNumberOfScalarComponents(3);
      drawing->SetExtent(0, 150, 0, 120, 0, 0); // xmin, xmax, ymin, ymax, zmin, zmax
      drawing->SetDrawColor(255, 0, 0); // red
      drawing->DrawCircle(60, 60, 50); // parameters: x, y, radius

      // Create an image of text
      vtkSmartPointer<vtkFreeTypeUtilities> freeType = vtkSmartPointer<vtkFreeTypeUtilities>::New();
      vtkSmartPointer<vtkTextProperty> textProperty = vtkSmartPointer<vtkTextProperty>::New();
      textProperty->SetColor(1.0, 1.0, 0.0); // yellow
      textProperty->SetFontSize(24);
      vtkSmartPointer<vtkImageData> textImage = vtkSmartPointer<vtkImageData>::New();
      freeType->RenderString(textProperty, "Test String", textImage);

      // Combine the images
      vtkSmartPointer<vtkImageBlend> blend =
        vtkSmartPointer<vtkImageBlend>::New();
      blend->AddInputConnection(drawing->GetOutputPort());
      blend->AddInputData(textImage);
      blend->SetOpacity(0, 0.5); // background image: 50% opaque
      blend->SetOpacity(1, 1.0); // text: 100% opaque
      blend->Update();

      vtkSmartPointer<vtkPNGWriter> writer =
        vtkSmartPointer<vtkPNGWriter>::New();
      writer->SetFileName("output.png");
      writer->SetInputConnection(blend->GetOutputPort());
      writer->Write();

      return EXIT_SUCCESS;
    }

### CMakeLists.txt

    cmake_minimum_required(VERSION 3.3 FATAL_ERROR)

    project(ImageText)

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

### Download and Build ImageText

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

    cd ImageText/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:

    ./ImageText

WINDOWS USERS

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