anchor.diff:    '';
   
     buildInputs = with stdenv.lib;
  -    [ freetype pkgconfig ]
  +    [ pkgconfig freetype ]
  +    ++ optional fontconfigSupport fontconfig
       ++ optionals x11Support [ libX11 libXext mesa ]
       ++ optional alsaSupport alsaLib
       ++ optional xvSupport libXv
  
positive.code: , useUnfreeCodecs ? false
  }:
  
  assert x11Support -> (libX11 != null && libXext != null && mesa != null);
  assert xineramaSupport -> (libXinerama != null && x11Support);
  assert xvSupport -> (libXv != null && x11Support);
  
negative.code: 
    configureFlags = with stdenv.lib;
      ''
        --enable-freetype
        ${if fontconfigSupport then "--enable-fontconfig" else "--disable-fontconfig"}
        ${if x11Support then "--enable-x11 --enable-gl" else "--disable-x11 --disable-gl"}
        ${if xineramaSupport then "--enable-xinerama" else "--disable-xinerama"}
        ${if xvSupport then "--enable-xv" else "--disable-xv"}
  