Assignment 3

Discuss the applicability of visibility-based interest management (VIM) to MMORPG and FPS games.


  • VIM only filters visual-type information. Position updates still need to be sent in order to compute visibility. In FPS games, movements of players are fast and frequent -- position updates are therefore much more frequent compared to visual-type data (players change weapon/jump/crouch). The savings obtained by VIM would be insignificant.
  • The paper did not elaborate on how visual-type data are filtered. It is unlikely that multicast (IP or application-level) is used since it would require that each entity to be its own multicast source (one group per entity). Further, since in FPS, players view changes frequently, there will be many join/leave requests. The other possiblity is for the server to filter the messages when forwarding to other players. In this case, players need to update the server frequently about the entities visible. Either way the overhead is large and the savings is small for FPS.
  • For MMORPG, most games uses side scrolling or third person view. VIM can still be applied here with minor tweak -- we compute the visibility from the view of the human player on screen rather than the avatar. In MMORPG, the changes in visibility is less frequent compared to FPS. Further, visual-type updates are more frequent compared to FPS, as gesture, costume, etc are more meaningful for MMORPG than FPS.

Common Mistakes

  • "VIM is expensive at client." Not true -- The whole point of using visibility information is that it is readily available from the rendering engine. So little additional computation is required.
  • "Using VIM eliminates the need for a server." Not true -- Yes, interest management is now computed locally but server is still needed for many other things. VIM alone does not eliminate the server -- a combinations of techniques (synchronization protocols, etc.) is needed.
  • "If A shoots B from behind, B will filter out this event since B cannot see A." Not true -- Shooting is not be a visual-type event and should not be filtered.
  • "VIM can leads to cheating since players' position is needed to compute visibility." True -- but this is not an issue with VIM specifically. Players positions are exchanged during games anyway regardless of visibility (if region-based IM is used, then positions of players within the same region are exchanged).


  • Write succintly and to the point. No need to summarize the paper and discuss its pro and cons (unless it is related to the method applicability to FPS and MMORPG).
  • Focus on issues related specifically to the discussed techniques only.
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