sinterface Renderable extends MakesBufferedImage, G2Drawable {
  void renderOn(Graphics2D g, int w, int h);
  
  default Pt preferredSize() { ret pt(640, 480); }
  
  default int getWidth() { ret preferredSize().x; }
  default int getHeight() { ret preferredSize().y; }
  
  default BufferedImage getBufferedImage aka render() {
    ret renderableToImage(this);
  }
  
  // unknown size
  default void drawOn(Graphics2D g) {
    renderOn(g, -1, -1);
  }
}