in Proceedings of the ACM SIGGRAPH Symposium on Interactive 3D Graphics and Games 2012 (I3D'12) Morgan McGuire, NVIDIA and Williams College Padraic Hennessy, Vicarious Visions Michael Bukowski, Vicarious Visions Brian Osman, Vicarious Visions ACM Copyright Notice Copyright by the Association for Computing Machinery, Inc. Permission to make digital or hard copies of part or all of this work for per