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.