ChooseTextColor

VTKExamples/Cxx/Visualization/ChooseTextColor

Description¶

This example uses a simple algorithm to choose a color that "contrasts" with another color. The ChooseContrastingColor procedure converts the input RGB value to HSV using vtkMath::RGBToHSV. If the value is <= .5, the light color is chosen as the contrasting color. Otherwise, the dark color is chosen. The default light color is white and the default dark color is black. Any color from vtkNamedColors can be specified for the light and dark colors.

To run the example with your own arguments:

ChooseTextColor fontFile [background] [lightColor] [darkColor]

Info

VTKNamedColorPatches shows the availabel colors.

Info

The ChooseContrastingColor procedure is reusable, Cut and paste the declarations and code into other examples.

Tip

There are many sources of TrueType fonts. Here is one source.

Code¶

ChooseTextColor.cxx

#include <vtkSmartPointer.h>

#include <vtkTextActor.h>
#include <vtkRenderer.h>
#include <vtkRenderWindow.h>
#include <vtkRenderWindowInteractor.h>
#include <vtkTextProperty.h>
#include <vtkMath.h>

#include <vtksys/SystemTools.hxx>
#include <sstream>
#include <string>

#include <vtkNamedColors.h>
namespace
{
// Given a color, find a contrasting color. If the goven color is "light",
// use the lightColor otherwise use the darkColor
void ChooseContrastingColor(double *rgbIn,
                            double *rgbOut,
                            const double threshold = .5,
                            const std::string lightColor = "white",
                            const std::string darkColor = "black");
}

int main (int argc, char *argv[])
{
  if (argc < 2)
  {
    std::cerr << "Usage: " << argv[0] << " font.ttf [backColor] [lightColor] [darkColor]" << std::endl;
    return EXIT_FAILURE;
  }

  // Defaults
  double threshold(.8);
  std::string backColor = "SlateGray";
  std::string lightColor = "White";
  std::string darkColor = "Black";
  if (argc > 2)
  {
    backColor = argv[2];
  }
  if (argc > 3)
  {
    lightColor = argv[3];
  }
  if (argc > 4)
  {
    darkColor = argv[4];
  }

  std::string fontFile(argv[1]);
  std::stringstream str;
  str << "Font: "
      << vtksys::SystemTools::GetFilenameWithoutExtension(std::string(argv[1]))
      << "\n"
      << "Background: " << backColor
      << "\n"
      << "Light Color: " << lightColor
      << "\n"
      << "Dark Color: " << darkColor;

  int width = 640;
  int height = 480;

  vtkSmartPointer<vtkNamedColors> colors =
    vtkSmartPointer<vtkNamedColors>::New();

  vtkSmartPointer<vtkTextActor> actor =
    vtkSmartPointer<vtkTextActor>::New();
  actor->GetTextProperty()->SetJustificationToCentered();
  actor->GetTextProperty()->SetVerticalJustificationToCentered();
  actor->SetTextScaleModeToViewport();
  actor->SetInput(str.str().c_str());
  actor->SetPosition(width/2, height/2);
  actor->GetTextProperty()->BoldOff();
  actor->GetTextProperty()->SetFontSize(40);
  actor->GetTextProperty()->SetFontFamily(VTK_FONT_FILE);
  actor->GetTextProperty()->SetFontFile(fontFile.c_str());

  vtkSmartPointer<vtkRenderer> renderer =
    vtkSmartPointer<vtkRenderer>::New();
  renderer->SetBackground(colors->GetColor3d(backColor.c_str()).GetData());

  // Compute a good color for text on the renderer background
  double rgb[3];
  ChooseContrastingColor(renderer->GetBackground(),
                         rgb,
                         threshold,
                         lightColor,
                         darkColor);
  std::cout << rgb[0] << "," << rgb[1] << "," << rgb[2] << std::endl;
  actor->GetTextProperty()->SetColor(rgb);

  vtkSmartPointer<vtkRenderWindow> renderWindow =
    vtkSmartPointer<vtkRenderWindow>::New();

  renderWindow->SetSize(width, height);
  renderWindow->AddRenderer(renderer);

  vtkSmartPointer<vtkRenderWindowInteractor> interactor =
    vtkSmartPointer<vtkRenderWindowInteractor>::New();
  interactor->SetRenderWindow(renderWindow);

  renderer->AddActor(actor);

  renderWindow->Render();
  interactor->Initialize();
  interactor->Start();

  return EXIT_SUCCESS;
}

namespace
{
void ChooseContrastingColor(double *rgbIn,
                            double *rgbOut,
                            const double threshold,
                            const std::string lightColor,
                            const std::string darkColor)
{
  vtkSmartPointer<vtkNamedColors> colors =
    vtkSmartPointer<vtkNamedColors>::New();

  double hsv[3];
  // If the value is <= threshold, use a light color, otherwise use a dark color
  vtkMath::RGBToHSV(rgbIn, hsv);
  if (hsv[2] <= threshold)
  {
    colors->GetColor(lightColor.c_str(), rgbOut[0], rgbOut[1], rgbOut[2]);
  }
  else
  {
    colors->GetColor(darkColor.c_str(), rgbOut[0], rgbOut[1], rgbOut[2]);
  }
}
}

CMakeLists.txt¶

cmake_minimum_required(VERSION 3.3 FATAL_ERROR)

project(ChooseTextColor)

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

Download and Build ChooseTextColor¶

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

cd ChooseTextColor/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:

./ChooseTextColor

WINDOWS USERS

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