anchor.diff:      (opencvFlag "JPEG" enableJPEG)
       (opencvFlag "PNG" enablePNG)
       (opencvFlag "OPENEXR" enableEXR)
  +    (opencvFlag "GSTREAMER" enableGStreamer)
     ];
   
     enableParallelBuilding = true;
  
positive.code: , enableEXR ? (!stdenv.isDarwin), openexr, ilmbase
  , enableJPEG2K ? true, jasper
  , enableFfmpeg ? false, ffmpeg
  , enableGStreamer ? false, gst_all
  , enableEigen ? true, eigen
  , darwin
  }:
  
negative.code:     ++ lib.optionals enableEXR [ openexr ilmbase ]
      ++ lib.optional enableJPEG2K jasper
      ++ lib.optional enableFfmpeg ffmpeg
      ++ lib.optionals enableGStreamer (with gst_all_1; [ gstreamer gst-plugins-base ])
      ++ lib.optional enableEigen eigen
      ++ lib.optionals stdenv.isDarwin (with darwin.apple_sdk.frameworks; [ Cocoa QTKit ])
      ;
  