anchor.diff:      pkgconfig
     ];
   
  -  # We could add Eigen, but it doesn't currently compile with the version in
  -  # nixpkgs.
     buildInputs = [
       boost
       cereal
       curl
  +    eigen
       expat
       glew
       libpng
  
positive.code: { stdenv, lib, fetchFromGitHub, makeWrapper, cmake, pkgconfig
  , boost, cereal, curl, expat, glew, libpng, tbb, wxGTK30
  , gtest, nlopt, xorg, makeDesktopItem
  }:
  let
  
negative.code:   # for finding the nlopt library, which doesn't pick up the package in the nix store.
    # We need to set the path via the NLOPT environment variable instead.
    NLOPT = nlopt;
  
    # Disable compiler warnings that clutter the build log
    # It seems to be a known issue for Eigen:
    # http://eigen.tuxfamily.org/bz/show_bug.cgi?id=1221
    NIX_CFLAGS_COMPILE = "-Wno-ignored-attributes";
  
    prePatch = ''
      # In nix ioctls.h isn't available from the standard kernel-headers package
  