anchor.diff:  
     src =  fetchurl {
       url = "ftp://ftp.freedesktop.org/pub/mesa/${version}/MesaLib-${version}.tar.bz2";
  -    sha256 = "0h2sq8h0l7415vsqfkb7mn1rxm62m2anpi9swlca69fbpr9bavpz";
  +    sha256 = "1c4qcz7zi3qvdcxa56yxl6kps5amk4zq2xlhqlgcpzqzv0777bpk";
     };
   
     prePatch = "patchShebangs .";
  
positive.code: */
  
  let
    version = "10.0.4";
    # this is the default search path for DRI drivers
    driverLink = "/run/opengl-driver" + stdenv.lib.optionalString stdenv.isi686 "-32";
  in
  
negative.code:     ;
    buildInputs = with xorg; [
      autoreconfHook intltool expat libxml2Python llvm
      glproto dri2proto dri3proto presentproto
      libX11 libXext libxcb libXt libXfixes libxshmfence
      libffi wayland libvdpau libelf
    ] ++ optionals enableExtraFeatures [ /*libXvMC*/ ]
      ++ optional stdenv.isLinux udev
  