Is there any way to display Greek letters in the legend?

[allbluelai]

I want to use vpPlot::setLegend to set the title with Greek alphabet. I set in my code:

plotter->setLegend( 0, 0, "W\u0394\u03B8_p1_x" );

Fail to display Greek letters

something like $2\pi$

[fspindle]

This feature is unfortunately not implemented

[s-trinh]

Actually it is possible, at least on Ubuntu/Unix system:

It is with -urw-standard symbols l-medium-r-normal--0-0-0-0-p-0-adobe-fontspecific font. Did not found a better font to mix classical and Greek fonts, but probably there is.

I did different things so I don't know exactly the correct procedure. Anyway, it should be something like:

• to display the available fonts: xlsfonts
• on Ubuntu 18.04, install a font for Greek support
• but I don't know which one, I have installed gsfonts-x11, xfonts-100dpi and fonts-gfs-porson
• in ViSP use plot.setFont()
• there is the xfontsel tool to select the appropriate font also

It gives something like this when playing randomly with it (need to read the doc to understand the meaning of each option):

This link seems to be useful to understand the options.

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Let's convert this issue into a feature request.

• support for font loading and for different OS (Ubuntu/Unix, Windows, MacOS, ...)
• support for font size
• support for font change for vpPlot, vpDisplay, ...
• try to look at stb_truetype.h if it can be useful?

[s-trinh]

Small update.

With https://github.com/lagadic/visp/pull/987 it is now possible to draw text using the font of your choice. But you have to position/handle the text yourself.

Example using https://github.com/googlefonts/Rubik:

---

Quick and dirty code is:

/*! \example tutorial-ibvs-4pts-plotter-continuous-gain-adaptive.cpp */
#include <visp3/core/vpFont.h>
#include <visp3/gui/vpPlot.h>
#include <visp3/gui/vpDisplayX.h>
#include <visp3/robot/vpSimulatorCamera.h>
#include <visp3/visual_features/vpFeatureBuilder.h>
#include <visp3/vs/vpServo.h>

int main()
{
  try {
    vpHomogeneousMatrix cdMo(0, 0, 0.75, 0, 0, 0);
    vpHomogeneousMatrix cMo(0.15, -0.1, 1., vpMath::rad(10), vpMath::rad(-10), vpMath::rad(50));

    vpPoint point[4];
    point[0].setWorldCoordinates(-0.1, -0.1, 0);
    point[1].setWorldCoordinates(0.1, -0.1, 0);
    point[2].setWorldCoordinates(0.1, 0.1, 0);
    point[3].setWorldCoordinates(-0.1, 0.1, 0);

    vpServo task;
    task.setServo(vpServo::EYEINHAND_CAMERA);
    task.setInteractionMatrixType(vpServo::CURRENT);

    vpAdaptiveGain lambda(4, 0.4, 30);
    task.setLambda(lambda);

    vpFeaturePoint p[4], pd[4];
    for (unsigned int i = 0; i < 4; i++) {
      point[i].track(cdMo);
      vpFeatureBuilder::create(pd[i], point[i]);
      point[i].track(cMo);
      vpFeatureBuilder::create(p[i], point[i]);
      task.addFeature(p[i], pd[i]);
    }

    vpHomogeneousMatrix wMc, wMo;
    vpSimulatorCamera robot;
    robot.setSamplingTime(0.040);
    robot.getPosition(wMc);
    wMo = wMc * cMo;

#ifdef VISP_HAVE_DISPLAY
    vpPlot plotter(2, 250 * 2, 500, 100, 200, "Real time curves plotter");
//    plotter.setTitle(0, "Visual features error");
    plotter.setTitle(1, "Camera velocities");

    plotter.initGraph(0, 8);
    plotter.initGraph(1, 6);

    plotter.setLegend(0, 0, "x1");
    plotter.setLegend(0, 1, "y1");
    plotter.setLegend(0, 2, "x2");
    plotter.setLegend(0, 3, "y2");
    plotter.setLegend(0, 4, "x3");
    plotter.setLegend(0, 5, "y3");
    plotter.setLegend(0, 6, "x4");
    plotter.setLegend(0, 7, "y4");

    plotter.setLegend(1, 0, "v_x");
    plotter.setLegend(1, 1, "v_y");
    plotter.setLegend(1, 2, "v_z");
    plotter.setLegend(1, 3, "w_x");
    plotter.setLegend(1, 4, "w_y");
    plotter.setLegend(1, 5, "w_z");

    //TODO:
    vpImage<vpRGBa> customPlotter(plotter.I.getHeight(), plotter.I.getWidth());
    vpDisplayX d;
    d.init(customPlotter, customPlotter.getWidth(), 200, "Graph plotting using manual vpDisplay");
    vpFont font;
#endif

    unsigned int iter = 0;
    while (1) {
      robot.getPosition(wMc);
      cMo = wMc.inverse() * wMo;
      for (unsigned int i = 0; i < 4; i++) {
        point[i].track(cMo);
        vpFeatureBuilder::create(p[i], point[i]);
      }
      vpColVector v = task.computeControlLaw(iter * robot.getSamplingTime());
      robot.setVelocity(vpRobot::CAMERA_FRAME, v);

#ifdef VISP_HAVE_DISPLAY
      plotter.plot(0, iter, task.getError());
      plotter.plot(1, iter, v);

      //TODO:
      vpDisplay::getImage(plotter.I, customPlotter);
      std::string customTitle = "Graphe temps réel : ∑ \u2211 \u221E";
      vpImagePoint titlePos = font.getMeasure(customTitle);
      font.drawText(customPlotter, customTitle, vpImagePoint(15, (500-titlePos.get_u())/2), vpColor::red);
      vpDisplay::display(customPlotter);
      vpDisplay::flush(customPlotter);
#endif
      if ((task.getError()).sumSquare() < 0.0001)
        break;

      vpTime::wait(100);

      iter++;
    }
    std::cout << "Convergence in " << iter << " iterations" << std::endl;

#ifdef VISP_HAVE_DISPLAY
    plotter.saveData(0, "error.dat");
    plotter.saveData(1, "vc.dat");

    //TODO:
    font.drawText(plotter.I, "TEST", vpImagePoint(15, 223), 255);

    vpDisplay::getClick(plotter.I);
#endif
  } catch (const vpException &e) {
    std::cout << "Catch an exception: " << e << std::endl;
  }
}