private void render_3s (int opcode, int p1, int p2, int p3) {
    RequestOutputStream o = display.out;
    synchronized (o) {
      begin_render_request (o, opcode, 12);
      o.write_int16 (p1);
      o.write_int16 (p2);
      o.write_int16 (p3);
      o.write_pad (2);
    }
  }