code: public void registerMapAddon(MapAddon addon) {
  		if (addon != null && !addons.containsKey(addon.getId())) {
  			addons.put(addon.getId(), addon);
  		}
  		if (graphics.isReady() && mapModelRenderer.isReadyToDraw()) {
  			addon.setMapSize(getWidth(), getHeight());
  			render(addon, RenderGroup.SCREEN, RenderStatus.UPDATE);
  			addon.onDraw();
  		}
  	}
docs: Register a certain <code>MapAddon</code> to be placed on the map. Map add-ons are fixed position entities on a
  map with possibly additional functionality. Examples are the scale bar, and navigation buttons.
  
  @param addon
  The new add-on to be added to the map.