anchor.diff:  , enableEigen     ? false, eigen
   , enableOpenblas  ? false, openblas
   , enableCuda      ? false, cudatoolkit, gcc5
  +, enableTesseract ? false, tesseract, leptonica
   , AVFoundation, Cocoa, QTKit
   }:
   
  
positive.code:     (opencvFlag "CUDA" enableCuda)
      (opencvFlag "CUBLAS" enableCuda)
    ] ++ lib.optionals enableCuda [ "-DCUDA_FAST_MATH=ON" ]
      ++ lib.optional enableContrib "-DBUILD_PROTOBUF=off"
      ++ lib.optionals stdenv.isDarwin ["-DWITH_OPENCL=OFF" "-DWITH_LAPACK=OFF"];
  
    enableParallelBuilding = true;
  
negative.code:     sha256 = "11dsq8dwh1k6f7zglbc26xwsjw184ggf2531mhf7v77kd72k19fm";
    };
  
    # Contrib must be built in order to enable Tesseract support:
    buildContrib = enableContrib || enableTesseract;
  
    vggFiles = fetchFromGitHub {
      owner  = "opencv";
      repo   = "opencv_3rdparty";
  