anchor.diff:  { stdenv, composableDerivation, fetchurl, pkgconfig, xlibsWrapper, inputproto, libXi
   , freeglut, mesa, libjpeg, zlib, libXinerama, libXft, libpng
   , cfg ? {}
  +, darwin, libtiff, freetype
   }:
   
   let inherit (composableDerivation) edf; in
  
positive.code:   meta = {
      description = "A C++ cross-platform lightweight GUI library";
      homepage = http://www.fltk.org;
      platforms = stdenv.lib.platforms.linux;
      license = stdenv.lib.licenses.gpl2;
    };
  
  }
  
  
negative.code:   '';
  
    nativeBuildInputs = [ pkgconfig ];
    propagatedBuildInputs = [ inputproto ]
      ++ (if stdenv.isDarwin
          then (with darwin.apple_sdk.frameworks; [Cocoa AGL GLUT freetype libtiff])
          else [ xlibsWrapper libXi freeglut ]);
  
    enableParallelBuilding = true;
  
  