private void render_4f(int opcode, float p1, float p2, float p3,
                         float p4) {
    RequestOutputStream o = display.out;
    synchronized (o) {
      begin_render_request (o, opcode, 20);
      o.write_float (p1);
      o.write_float (p2);
      o.write_float (p3);
      o.write_float (p4);
    }
  }