anchor.diff:  }:
   
   let
  -  inherit (stdenv.lib)
  -    enFlag
  +  inherit (lib)
  +    boolEn
       optionalString;
   in
   stdenv.mkDerivation rec {
  
positive.code:     "--disable-gallium"
      # Only one OpenGL backend may be selected at compile time
      # OpenGL X (gl), or OpenGL ES 2.0 (glesv2)
      (enFlag "gl" (!gles2) null)
      (enFlag "glesv2" gles2 null)
      "--disable-cogl" # recursive dependency
      # FIXME: fix directfb mirroring
      "--disable-directfb"
      "--disable-vg"
      (enFlag "egl" (mesa_noglu != null) null)
      (enFlag "glx" (mesa_noglu != null) null)
      "--disable-wgl"
      "--enable-script"
      "--enable-ft"
  
negative.code:     "--disable-symbol-lookup"
      #"--enable-some-floating-point"
      "--with-x"
      #"--with-skia=yes"
      #"--with-skia-build-type=Release"
      "--without-gallium"
    ];
  
  