anchor.diff:      libraw1394
       libtiff
       libwebp
  -    mesa
       #openexr
  +    opengl-dummy
       pango
       #python2Packages.numpy
       #python2Packages.python
  
positive.code: , libraw1394
  , libtiff
  , libwebp
  , mesa
  #, nvidia-cuda-toolkit
  #, openexr
  , pango
  
negative.code:     # WITH_OPENCL_SVM
      #"-DWITH_OPENEXR=${boolOn (openexr != null)}"
      /**/"-DWITH_OPENEXR=OFF"
      "-DWITH_OPENGL=${boolOn (opengl-dummy != null)}"
      # WITH_OPENMP
      # WITH_OPENNI
      # WITH_OPENNI2
  