anchor.diff:      (enableFeature libxcbshmExtlib "libxcb-shm")
       (enableFeature libxcbxfixesExtlib "libxcb-xfixes")
       (enableFeature libxcbshapeExtlib "libxcb-shape")
  +    (enableFeature (libxml2 != null) "libxml2")
       (enableFeature (xz != null) "lzma")
       (enableFeature nvenc "nvenc")
       (enableFeature (openal != null) "openal")
  
positive.code: , libxcbshapeExtlib ? true # X11 grabbing shape rendering
  , libXv ? null # Xlib support
  , libXext ? null # Xlib support
  , xz ? null # xz-utils
  , nvenc ? !stdenv.isDarwin && !stdenv.isAarch64, nv-codec-headers ? null # NVIDIA NVENC support
  , openal ? null # OpenAL 1.1 capture support
  
negative.code:     bzip2 celt dav1d fontconfig freetype frei0r fribidi game-music-emu gnutls gsm
      libjack2 ladspaH lame libaom libass libbluray libbs2b libcaca libdc1394 libmodplug libmysofa
      libogg libopus librsvg libssh libtheora libvdpau libvorbis libvpx libwebp libX11
      libxcb libXv libXext libxml2 xz openal openjpeg libpulseaudio rav1e svt-av1 rtmpdump opencore-amr
      samba SDL2 soxr speex srt vid-stab vo-amrwbenc x264 x265 xavs xvidcore
      zeromq4 zimg zlib
    ] ++ optionals openglExtlib [ libGL libGLU ]
  