Re: plotted circle is regular decagon on opengl graphics

[Andreas Weber]

Hi Tatsuro,

Am 11.08.2016 um 08:17 schrieb Tatsuro MATSUOKA:
> Graphics tool kit: qt and fltk
> plot (1:1, 'o', 'markersize', 24)
> print -depsc circle.eps
> plotted circle is regular decagon (ugly).

The code to draw the markers with OpenGL is in gl-render.cc
opengl_renderer::make_marker_list

    case 'o':
      {
        double ang_step = M_PI / 5;

        glBegin ((filled ? GL_POLYGON : GL_LINE_LOOP));
        for (double ang = 0; ang < (2*M_PI); ang += ang_step)
          glVertex2d (sz*cos (ang)/2, sz*sin (ang)/2);
        glEnd ();
      }

As you can see the decagon is hardcoded. AFAIK there is no "draw circle"
command in OpenGL so the only way to get a smoother circle would be to
increase the numer of segments.

-- Andy