anchor.diff:      ++ lib.optional enableFfmpeg ffmpeg
       ++ lib.optionals enableGStreamer (with gst_all_1; [ gstreamer gst-plugins-base ])
       ++ lib.optional enableEigen eigen
  -    ++ lib.optional enableCuda [ cudatoolkit gcc5 ]
  +    ++ lib.optionals enableCuda [ cudatoolkit gcc5 ]
  +    ++ lib.optional enableContrib protobuf3_1
       ;
   
     propagatedBuildInputs = lib.optional enablePython pythonPackages.numpy;
  
positive.code: { lib, stdenv, fetchurl, fetchpatch, fetchFromGitHub, cmake, pkgconfig, unzip
  , zlib
  , enableIpp ? false
  , enableContrib ? false
  , enablePython ? false, pythonPackages
  , enableGtk2 ? false, gtk2
  , enableGtk3 ? false, gtk3
  , enableJPEG ? true, libjpeg
  , enablePNG ? true, libpng
  , enableTIFF ? true, libtiff
  , enableWebP ? true, libwebp
  , enableEXR ? true, openexr, ilmbase
  , enableJPEG2K ? true, jasper
  , enableFfmpeg ? false, ffmpeg
  , enableGStreamer ? false, gst_all_1
  , enableEigen ? false, eigen
  , enableCuda ? false, cudatoolkit, gcc5
  }:
  
  let
    version = "3.1.0";
  
    contribSrc = fetchFromGitHub {
      owner = "Itseez";
      repo = "opencv_contrib";
      rev = version;
      sha256 = "153yx62f34gl3zd6vgxv0fj3wccwmq78lnawlda1f6xhrclg9bax";
    };
  
    opencvFlag = name: enabled: "-DWITH_${name}=${if enabled then "ON" else "OFF"}";
  
  in
  
  stdenv.mkDerivation rec {
    name = "opencv-${version}";
    inherit version;
  
    src = fetchFromGitHub {
      owner = "Itseez";
      repo = "opencv";
      rev = version;
      sha256 = "1l0w12czavgs0wzw1c594g358ilvfg2fn32cn8z7pv84zxj4g429";
    };
  
    patches =
      lib.optionals enableCuda [
        (fetchpatch { # Patch for CUDA 8 compatibility
          url = "https://github.com/opencv/opencv/commit/10896129b39655e19e4e7c529153cb5c2191a1db.patch";
          sha256 = "0jka3kxxywgs3prqqgym5kav6p73rrblwj50k1nf3fvfpk194ah1";
        })
        (fetchpatch { # Patch to add CUDA Compute Capability compilation targets up to 6.0
          url = "https://github.com/opencv/opencv/commit/d76f258aebdf63f979a205cabe6d3e81700a7cd8.patch";
          sha256 = "00b3msfgrcw7laij6qafn4b18c1dl96xxpzwx05wxzrjldqb6kqg";
        })
      ]
      ++ lib.optional enablePython (fetchpatch { # Patch to fix FlannBasedMatcher under python
        url = "https://github.com/opencv/opencv/commit/05cfe28612fd8dc8fb0ccb876df945c7b435dd26.patch";
        sha256 = "0niza5lybr1ljzdkyiapr16laa468168qinpy5qn00yimnaygpm6";
      });
  
    preConfigure =
      # By default ippicv gets downloaded by cmake each time opencv is build. See:
      # https://github.com/opencv/opencv/blob/3.1.0/3rdparty/ippicv/downloader.cmake
      # Fortunately cmake doesn't download ippicv if it's already there.
      # So to prevent repeated downloads we store it in the nix store
      # and create a symbolic link to it.
      let version  = "20151201";
          md5      = "808b791a6eac9ed78d32a7666804320e";
          sha256   = "1nph0w0pdcxwhdb5lxkb8whpwd9ylvwl97hn0k425amg80z86cs3";
          rev      = "81a676001ca8075ada498583e4166079e5744668";
          platform = if stdenv.system == "x86_64-linux" || stdenv.system == "i686-linux" then "linux"
                     else throw "ICV is not available for this platform (or not yet supported by this package)";
          name = "ippicv_${platform}_${version}.tgz";
          ippicv = fetchurl {
            url = "https://raw.githubusercontent.com/opencv/opencv_3rdparty/${rev}/ippicv/${name}";
            inherit sha256;
          };
          dir = "3rdparty/ippicv/downloads/${platform}-${md5}";
      in lib.optionalString enableIpp
        ''
          mkdir -p "${dir}"
          ln -s "${ippicv}" "${dir}/${name}"
        '';
  
    buildInputs =
         [ zlib ]
  
negative.code:     (opencvFlag "OPENEXR" enableEXR)
      (opencvFlag "CUDA" enableCuda)
      (opencvFlag "CUBLAS" enableCuda)
    ] ++ lib.optionals enableCuda [ "-DCUDA_FAST_MATH=ON" ]
      ++ lib.optional enableContrib "-DBUILD_PROTOBUF=off";
  
    enableParallelBuilding = true;
  
  