anchor.diff:  
     buildInputs =
          [ zlib ]
  -    ++ lib.optional enablePython python2Packages.python
       ++ lib.optional enableGtk2 gtk2
       ++ lib.optional enableJPEG libjpeg
       ++ lib.optional enablePNG libpng
  
positive.code:     ++ lib.optional enableEigen eigen
      ++ lib.optionals stdenv.isDarwin [ Cocoa QTKit ]
      ;
  
    propagatedBuildInputs = lib.optional enablePython python2Packages.numpy;
  
    nativeBuildInputs = [ cmake pkg-config unzip ];
  
  
negative.code:     sed -i $dev/lib/pkgconfig/opencv.pc -e "s|includedir_new=.*|includedir_new=$dev/include|"
    '';
  
    meta = with lib; {
      description = "Open Computer Vision Library with more than 500 algorithms";
      homepage = "https://opencv.org/";
  