    **/
    CImgDisplay& set_button() {
      _button = 0;
      _is_event = true;
#if cimg_display==1
      pthread_cond_broadcast(&cimg::X11_attr().wait_event);
#elif cimg_display==2
      SetEvent(cimg::Win32_attr().wait_event);
#endif
      return *this;
Unknown