anchor.diff:  , pulseSupport ? false, pulseaudio ? null
   # For screenshots
   , libpngSupport ? true, libpng ? null
  +, useUnfreeCodecs ? false
   }:
   
   assert x11Support -> (libX11 != null && libXext != null && mesa != null);
  
positive.code:       cp -prv * $out
      '';
  
      meta = {
        license = "unfree";
      };
    } else null;
  
  in
  
negative.code:     '';
  
    NIX_LDFLAGS = stdenv.lib.optionalString x11Support "-lX11 -lXext";
  
    enableParallelBuilding = true;
  
    # Provide a reasonable standard font.  Maybe we should symlink here.
    postInstall =
  