anchor.diff:  { stdenv, lib, fetchFromGitHub, makeWrapper, cmake, pkgconfig
  -, boost, cereal, curl, expat, glew, libpng, tbb, wxGTK30
  +, boost, cereal, curl, eigen, expat, glew, libpng, tbb, wxGTK30
   , gtest, nlopt, xorg, makeDesktopItem
   }:
   let
  
positive.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;
  
    prePatch = ''
      # In nix ioctls.h isn't available from the standard kernel-headers package
  
negative.code:     pkgconfig
    ];
  
    buildInputs = [
      boost
      cereal
      curl
      eigen
      expat
      glew
      libpng
  