    **/
    CImgDisplay& set_key() {
      std::memset((void*)_keys,0,128*sizeof(unsigned int));
      std::memset((void*)_released_keys,0,128*sizeof(unsigned int));
      _is_keyESC = _is_keyF1 = _is_keyF2 = _is_keyF3 = _is_keyF4 = _is_keyF5 = _is_keyF6 = _is_keyF7 = _is_keyF8 =
        _is_keyF9 = _is_keyF10 = _is_keyF11 = _is_keyF12 = _is_keyPAUSE = _is_key1 = _is_key2 = _is_key3 = _is_key4 =
        _is_key5 = _is_key6 = _is_key7 = _is_key8 = _is_key9 = _is_key0 = _is_keyBACKSPACE = _is_keyINSERT =
        _is_keyHOME = _is_keyPAGEUP = _is_keyTAB = _is_keyQ = _is_keyW = _is_keyE = _is_keyR = _is_keyT = _is_keyY =
        _is_keyU = _is_keyI = _is_keyO = _is_keyP = _is_keyDELETE = _is_keyEND = _is_keyPAGEDOWN = _is_keyCAPSLOCK =
        _is_keyA = _is_keyS = _is_keyD = _is_keyF = _is_keyG = _is_keyH = _is_keyJ = _is_keyK = _is_keyL =
        _is_keyENTER = _is_keySHIFTLEFT = _is_keyZ = _is_keyX = _is_keyC = _is_keyV = _is_keyB = _is_keyN =
        _is_keyM = _is_keySHIFTRIGHT = _is_keyARROWUP = _is_keyCTRLLEFT = _is_keyAPPLEFT = _is_keyALT = _is_keySPACE =
        _is_keyALTGR = _is_keyAPPRIGHT = _is_keyMENU = _is_keyCTRLRIGHT = _is_keyARROWLEFT = _is_keyARROWDOWN =
        _is_keyARROWRIGHT = _is_keyPAD0 = _is_keyPAD1 = _is_keyPAD2 = _is_keyPAD3 = _is_keyPAD4 = _is_keyPAD5 =
        _is_keyPAD6 = _is_keyPAD7 = _is_keyPAD8 = _is_keyPAD9 = _is_keyPADADD = _is_keyPADSUB = _is_keyPADMUL =
        _is_keyPADDIV = false;
      _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