docs: def draw_circle(ctx, x, y, radius, cairo_color):
      """
      Draw a circle.
      :param radius: radius in pixels
      :param cairo_color: normalized rgb color
      """
      ctx.new_path()
      ctx.set_source_rgb(cairo_color.red, cairo_color.green, cairo_color.blue)
      ctx.arc(x, y, radius, 0, 2 * pi)
      ctx.fill()