code: func (imd *IMDraw) Polygon(thickness float64) {
  	if thickness == 0 {
  		imd.fillPolygon()
  	} else {
  		imd.polyline(thickness, true)
  	}
  }
docs: // Polygon draws a polygon from the Pushed points. If the thickness is 0, the convex polygon will be
  // filled. Otherwise, an outline of the specified thickness will be drawn. The outline does not have
  // to be convex.
  //
  // Note, that the filled polygon does not have to be strictly convex. The way it's drawn is that a
  // triangle is drawn between each two adjacent points and the first Pushed point. You can use this
  // property to draw certain kinds of concave polygons.