In 3dsmax I've used a blend material (rock and snow) using falloff as a mask set to World Z, Towards/Away (so it lands on the tops of the objects). If you set it up right it will obey the bumps. http://www.docstoc.com/docs/13492996/Making-Snow-in-3d-Studio-Max This is also handy for getting dirt and dust on the tops of…