anchor.diff:    NIX_CFLAGS_COMPILE = lib.optional enableEXR "-I${ilmbase.dev}/include/OpenEXR";
   
     cmakeFlags = [
  -    "-DBUILD_PROTOBUF=OFF"
  -    "-DPROTOBUF_UPDATE_FILES=ON"
       "-DWITH_OPENMP=ON"
       (opencvFlag "IPP" enableIpp)
       (opencvFlag "TIFF" enableTIFF)
  
positive.code:     dst = ".cache/xfeatures2d/boostdesc";
    };
  
    installExtraFiles = extra : with lib; ''
      mkdir -p "${extra.dst}"
    '' + concatStrings (mapAttrsToList (name : md5 : ''
  
negative.code: { lib, stdenv
  , fetchurl, fetchFromGitHub
  , cmake, pkgconfig, unzip, zlib, pcre, hdf5
  , config
  
  , enableJPEG      ? true, libjpeg
  