anchor.diff:    nativeBuildInputs = [ pkgconfig ]
       ++ optional stdenv.isLinux libcap;
   
  -  propagatedBuildInputs = [ libiconv ]
  -    ++ optionals x11Support [ libXext libICE libXrandr ]
  -    ++ optionals openglSupport [ libGL libGLU ]
  -    ++ optional alsaSupport alsaLib
  -    ++ optional pulseaudioSupport libpulseaudio
  -    ++ optional stdenv.isDarwin Cocoa;
  +  propagatedBuildInputs = [ libiconv ] ++ extraPropagatedBuildInputs;
   
     buildInputs = [ ]
       ++ optional (!stdenv.hostPlatform.isMinGW && alsaSupport) audiofile
  
positive.code: # SDL2 expression too
  
  with stdenv.lib;
  
  stdenv.mkDerivation rec {
    pname = "SDL";
  
negative.code:   postFixup = ''
      for lib in $out/lib/*.so* ; do
        if [[ -L "$lib" ]]; then
          patchelf --set-rpath "$(patchelf --print-rpath $lib):${rpath}" "$lib"
        fi
      done
    '';
  