Powder.h existed in the old The Powder Toy - which was about a few years ago. Since then, we've moved over to a rewrite in C++ and a more object-oriented and MVC fashion, which is internally called TPT++. This source has been the main source for a long time, and the way you create elements on TPT++ has changed a bit. See http://boxmein.x10.mx/tptelements/#cpp , or https://github.com/simtr/The-Powder-Toy/tree/master/src/simulation/elements .