anchor.diff:  { lib, stdenv, fetchurl, fetchFromGitHub, fetchpatch, cmake, unzip, zip, file
   , curl, glew , libGL, SDL2, SDL2_image, zlib, freetype, imagemagick
   , openal , opusfile, libogg
  -, Cocoa
  +, Cocoa, libXext
   }:
   
   stdenv.mkDerivation rec {
  
positive.code:   nativeBuildInputs = [ cmake imagemagick unzip zip file ];
  
    buildInputs = [
      freetype SDL2 SDL2_image libGL zlib curl glew opusfile openal libogg
    ] ++ lib.optionals stdenv.hostPlatform.isDarwin [
      Cocoa
    ];
  
negative.code:     homepage    = "https://github.com/yvt/openspades/";
      license     = licenses.gpl3;
      platforms   = platforms.all;
      maintainers = with maintainers; [ abbradar azahi ];
    };
  }
  