Enabling Scalability by Partitioning Virtual Environments Using Frontier Sets

We present a class of partitioning scheme that we have called frontier sets. Frontier sets build on the notion of a potentially visible set (PVS) (Airey, Rohlf & Brooks, 1990) (Teller & Sequin, 1991). In a PVS, a world is sub-divided into cells and for each cell all the other cells that can be seen are computed. In contrast, a frontier set considers pairs of cells, A and B. For each pair, it lists two sets of cells (two frontiers), FAB and FBA. By definition, from no cell in FAB is any cell in FBA visible and vice-versa. Our initial use of frontier sets has been to enable scalability in distributed networking. This is possible because, for example, if at time t0 Player1 is in cell A and Player2 is in cell B, as long as they stay in their respective frontiers, they do not need to send update information to each other. In this paper we describe two strategies for building frontier sets. Both strategies are dynamic and computer frontiers only as necessary at run-time. The first is distance-based frontiers. This strategy requires pre-computation of an enhanced potentially visible set. The second is greedy frontiers. This strategy is computationally more expensive to compute at run-time, however leads to larger and thus more efficient frontiers. Network simulations using code based on the Quake II engine show that frontiers have significant promise and may allow a new class of scalable peer-to-peer game infrastructures to emerge.