Using 3D or higher simplex noise (for example, using 3D simplex noise in the demo) may be problematic because of [U.S. 6067776](https://www.google.com/patents/US6867776).  (I am not a lawyer.)  Fortunately, the demo doesn't appear to rely on 3D noise and can just use 2D noise instead, which I have done here. Alternatively, the demo can use OpenSimplex noise instead, but that seems too considerable an effort for me to propose for now.