draw(renderer, viewport) {
		const renderable = this.renderable;
		if (renderable instanceof Renderable) {
			// predraw (apply transforms)
			renderable.preDraw(renderer);

			// draw the object
			renderable.draw(renderer, viewport);

			// postdraw (clean-up);
			renderable.postDraw(renderer);
		}
	}
draw this entity (automatically called by melonJS)
@param {CanvasRenderer|WebGLRenderer} renderer - a renderer instance
@param {Camera2d} [viewport] - the viewport to (re)draw