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.

Question

If you have a question about this example, please use the VTK Discourse Forum

Code¶

ImageText.cxx

#include <vtkFreeTypeTools.h>
#include <vtkImageActor.h>
#include <vtkImageBlend.h>
#include <vtkImageCanvasSource2D.h>
#include <vtkImageData.h>
#include <vtkImageMapper3D.h>
#include <vtkInteractorStyleImage.h>
#include <vtkNamedColors.h>
#include <vtkNew.h>
#include <vtkPointData.h>
#include <vtkRenderWindow.h>
#include <vtkRenderWindowInteractor.h>
#include <vtkRenderer.h>
#include <vtkStdString.h>
#include <vtkTextProperty.h>

#include <array>

int main(int argc, char* argv[])
{
  vtkNew<vtkNamedColors> colors;

  std::array<double, 3> drawColor1{0, 0, 0};
  std::array<double, 3> drawColor2{0, 0, 0};
  auto color1 = colors->GetColor3ub("Blue").GetData();
  auto color2 = colors->GetColor3ub("Red").GetData();
  for (auto i = 0; i < 3; ++i)
  {
    drawColor1[i] = color1[i];
    drawColor2[i] = color2[i];
  }
  // Create a blue image with a red circle of radius 50 centered at (60, 60).
  vtkNew<vtkImageCanvasSource2D> drawing;
  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(drawColor1.data());
  drawing->FillBox(0, 150, 0, 120);
  drawing->SetDrawColor(drawColor2.data());
  drawing->DrawCircle(60, 60, 50); // parameters: x, y, radius
  // Create an image of text.
  vtkFreeTypeTools* freeType = vtkFreeTypeTools::GetInstance();
  vtkNew<vtkTextProperty> textProperty;
  textProperty->SetColor(colors->GetColor3d("Yellow").GetData());
  textProperty->SetJustificationToLeft();
  textProperty->SetFontSize(24);
  textProperty->SetOrientation(25);
  vtkStdString text("   Test String");
  vtkNew<vtkImageData> textImage;
  freeType->RenderString(textProperty, text, 70, textImage.GetPointer());

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

  vtkNew<vtkImageActor> blendActor;
  blendActor->GetMapper()->SetInputConnection(blend->GetOutputPort());

  vtkNew<vtkRenderer> blendRenderer;
  blendRenderer->AddActor(blendActor);
  blendRenderer->ResetCamera();
  blendRenderer->SetBackground(colors->GetColor3d("DodgerBlue").GetData());

  vtkNew<vtkRenderWindow> renderWindow;
  renderWindow->SetSize(300, 300);
  renderWindow->AddRenderer(blendRenderer);
  renderWindow->SetWindowName("ImageText");

  vtkNew<vtkRenderWindowInteractor> renderWindowInteractor;
  vtkNew<vtkInteractorStyleImage> style;

  renderWindowInteractor->SetInteractorStyle(style);

  renderWindowInteractor->SetRenderWindow(renderWindow);
  renderWindow->Render();
  renderWindowInteractor->Initialize();

  renderWindowInteractor->Start();

  return EXIT_SUCCESS;
}

CMakeLists.txt¶

cmake_minimum_required(VERSION 3.12 FATAL_ERROR)

project(ImageText)

find_package(VTK COMPONENTS 
)

if (NOT VTK_FOUND)
  message(FATAL_ERROR "ImageText: Unable to find the VTK build folder.")
endif()

# Prevent a "command line is too long" failure in Windows.
set(CMAKE_NINJA_FORCE_RESPONSE_FILE "ON" CACHE BOOL "Force Ninja to use response files.")
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}
)

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.