anchor.diff:  , mpg123
   , twolame
   , gtkSupport ? false, gtk3 ? null
  +, raspiCameraSupport ? false, libraspberrypi ? null
   , enableJack ? true, libjack2
   , libXdamage
   , libXext
  
positive.code: }:
  
  assert gtkSupport -> gtk3 != null;
  
  let
    inherit (stdenv.lib) optionals;
  
negative.code:     xorg.libXfixes
      xorg.libXdamage
      wavpack
    ] ++ optionals raspiCameraSupport [
      libraspberrypi
    ] ++ optionals gtkSupport [
      # for gtksink
      gtk3
  