anchor.diff:  { stdenv, fetchurl, pkgconfig, gtk, libXinerama, libSM, libXxf86vm, xf86vidmodeproto
  -, gstreamer, gst_plugins_base, GConf
  +, gstreamer, gst_plugins_base, GConf, libX11, cairo
   , withMesa ? true, mesa ? null, compat24 ? false, compat26 ? true, unicode ? true,
   }:
   
  
positive.code:     sha256 = "1l1w4i113csv3bd5r8ybyj0qpxdq83lj6jrc5p7cc10mkwyiagqz";
    };
  
    buildInputs = [ gtk libXinerama libSM libXxf86vm xf86vidmodeproto gstreamer gst_plugins_base GConf ]
      ++ optional withMesa mesa;
  
    nativeBuildInputs = [ pkgconfig ];
  
negative.code:     + optionalString withMesa "${mesa}/lib ";
  
    # Work around a bug in configure.
    NIX_CFLAGS_COMPILE = [ "-DHAVE_X11_XLIB_H=1" "-lX11" "-lcairo" ];
  
    preConfigure = "
      substituteInPlace configure --replace 'SEARCH_INCLUDE=' 'DUMMY_SEARCH_INCLUDE='
  