VTK/Examples/Cxx/Images/ImageText

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 VTK/Examples/Cxx/Images/CombineImages.

See also VTK/Examples/Cxx/Visualization/DrawText for an example of drawing text, also in 2D, but into the render window rather than into a vtkImageData object.

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;
}

Please try the new VTKExamples website.

CMakeLists.txt

cmake_minimum_required(VERSION 2.8)

PROJECT(ImageText)

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

add_executable(ImageText MACOSX_BUNDLE ImageText.cxx)

if(VTK_LIBRARIES)
  target_link_libraries(ImageText ${VTK_LIBRARIES})
else()
  target_link_libraries(ImageText vtkHybrid vtkWidgets)
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 PLEASE NOTE: Be sure to add the VTK bin directory to your path. This will resolve the VTK dll's at run time.