*/
  public void copy (GL dst, int mask) {
    RequestOutputStream o = display.out;
    synchronized (o) {
      o.begin_request (glx.major_opcode, 10, 5);
      o.write_int32 (id);
      o.write_int32 (dst.id);
      o.write_int32 (mask);
      o.write_int32 (tag);
      o.send ();
    }
  }