'add_point()' not working with multiple 'plot()'

[eleipi]

Hello,
when using add_point(x, y) in a for-loop to create multiple polygons in a single plot, the polygons get connected to each other and replotted with every plot() command. This happens because the internal list_of_x and list_of_y vectors are not cleared after the plot command creates a GnuplotSeries and adds it to series. To allow the creation of subsequent polygons using add_point(), the plot() command should clear these lists. For example:

  /* Create a plot using the values set with the method `add_point` */
  void plot(const std::string &label = "", LineStyle style = LineStyle::LINES) {
    check_consistency();

    _plot(label, style, false, list_of_x, list_of_y);

    // Clear lists for the next `add_point` usage
    list_of_x.clear();
    list_of_y.clear(); 
  }

[ziotom78]

Hi @eleipi, thanks for the report. I chose to add a new method Gnuplot::clear_list_of_points() instead of automatically empty the list once plot is called, because this would complicate the creation of animations where new points are added progressively.

I have added a new example, examples/src/example-polygons.cpp:

  Gnuplot plt{};

  plt.redirect_to_png("polygons.png", "800,600");

  // Triangle
  plt.add_point(0, 0);
  plt.add_point(1, 0);
  plt.add_point(0, 1);
  plt.add_point(0, 0);
  plt.plot();

  plt.clear_list_of_points();

  // Square

  plt.add_point(3, 0);
  plt.add_point(4, 0);
  plt.add_point(4, 1);
  plt.add_point(3, 1);
  plt.add_point(3, 0);
  plt.plot();

  plt.show();

Here is the result: