sclass AnimatedLine > Animation {
  int maxSpeed = 1;
  int y, speed;
  
  void start {
    y = random(h);
    newSpeed();
  }
  
  void newSpeed {
    speed = random_incl(-maxSpeed, maxSpeed);
  }
  
  void paint {
    fillRect(g, 0, 0, w, h, Color.white);
    drawLine(g, 0, y, w, y, Color.black);
  }
  
  void nextFrame {
    if (oneIn(20)) newSpeed();
    y = clamp(y+speed, 0, h-1);
  }
}