anchor.diff:  
     buildInputs =
          [ zlib pcre hdf5 glog boost google-gflags protobuf ]
  -    ++ lib.optional (!stdenv.isDarwin) caffe
       ++ lib.optional enablePython pythonPackages.python
       ++ lib.optional enableGtk2 gtk2
       ++ lib.optional enableGtk3 gtk3
  
positive.code:     "-DBUILD_PROTOBUF=OFF"
      "-DPROTOBUF_UPDATE_FILES=ON"
      "-DOPENCV_ENABLE_NONFREE=${printEnabled enableUnfree}"
      (opencvFlag "IPP" enableIpp)
      (opencvFlag "TIFF" enableTIFF)
      (opencvFlag "JASPER" enableJPEG2K)
  
negative.code: { lib, stdenv
  , fetchurl, fetchFromGitHub, fetchpatch
  , cmake, pkgconfig, unzip, zlib, pcre, hdf5
  , glog, boost, google-gflags, protobuf
  , config
  
  , enableJPEG      ? true, libjpeg
  