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.

Question

If you have a simple question about this example contact us at VTKExamplesProject If your question is more complex and may require extended discussion, please use the VTK Discourse Forum

Code

ChooseTextColor.cxx

#include <vtkSmartPointer.h>

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

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

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");
} // namespace

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;

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

  auto 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());

  auto 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);

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

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

  auto 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)
{
  auto 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]);
  }
}
} // namespace

CMakeLists.txt

cmake_minimum_required(VERSION 3.3 FATAL_ERROR)

project(ChooseTextColor)

find_package(VTK COMPONENTS 
  vtkCommonColor
  vtkCommonCore
  vtkInteractionStyle
  vtkRenderingContextOpenGL2
  vtkRenderingCore
  vtkRenderingFreeType
  vtkRenderingGL2PSOpenGL2
  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.