anchor.diff: -{ stdenv, fetchurl
  +{ stdenv, fetchFromGitHub, autoreconfHook, libtool
   , threadingSupport ? true # multi-threading
   , openglSupport ? false, freeglut ? null, libGL ? null, libGLU ? null # OpenGL (required for vwebp)
   , pngSupport ? true, libpng ? null # PNG image format
  
positive.code:     (mkFlag libwebpdecoderSupport "libwebpdecoder")
    ];
  
    buildInputs = [ ]
      ++ optionals openglSupport [ freeglut libGL libGLU ]
      ++ optional pngSupport libpng
  
negative.code: with stdenv.lib;
  stdenv.mkDerivation rec {
    pname = "libwebp";
    version = "1.1.0";
  
    src = fetchFromGitHub {
      owner  = "webmproject";
      repo   = pname;
      rev    = version;
      sha256 = "1kl6qqa29ygqb2fpv140y59v539gdqx4vcf3mlaxhca2bks98qgm";
    };
  
    prePatch = "patchShebangs .";
  
    configureFlags = [
      (mkFlag threadingSupport "threading")
  