anchor.diff:  
   assert fontconfigSupport -> (fontconfig != null);
   assert (!fontconfigSupport) -> (freefont_ttf != null);
  +assert fribidiSupport -> (fribidi != null);
   assert x11Support -> (libX11 != null && libXext != null && mesa != null);
   assert xineramaSupport -> (libXinerama != null && x11Support);
   assert xvSupport -> (libXv != null && x11Support);
  
positive.code:       ${if pulseSupport then "--enable-pulse" else "--disable-pulse"}
        ${optionalString (useUnfreeCodecs && codecs != null) "--codecsdir=${codecs}"}
        ${optionalString (stdenv.isi686 || stdenv.isx86_64) "--enable-runtime-cpudetection"}
        --disable-xanim
        --disable-ivtv
        --disable-xvid --disable-xvid-lavc
  
negative.code:   buildInputs = with stdenv.lib;
      [ pkgconfig freetype ]
      ++ optional fontconfigSupport fontconfig
      ++ optional fribidiSupport fribidi
      ++ optionals x11Support [ libX11 libXext mesa ]
      ++ optional alsaSupport alsaLib
      ++ optional xvSupport libXv
  