Networked Games - Game Programming Algorithms and Techniques - page 314

game is only sending a relatively small number of actions per minute, as even the
best RTS player is not going to have more than 300-400 commands per minute.
Because in a peer-to-peer setup, every peer might be simulating part of the game
world, the game state must be 100% deterministic. This can make it difficult to
have gameplay based on chance; if a Zealot in StarCraft II could do a variable
amount of damage based on virtual dice rolls, this might result in one peer sim-
ulating a round of combat differently than another peer. This doesn't mean that
random elements are entirely impossible in a peer-to-peer game (as in Company
of Heroes ), but that further effort must be taken to guarantee synchronization
between peers.
Though RTS is arguably the main genre that sees peer-to-peer use, there are def-
initely other games that do so. One notable example is the Halo series, which uses
a peer-to-peer model for its multiplayer. But that being said, it's fair to say that
peer-to-peer does not see nearly as much use in games as server/client does.
Cheating
A major consideration in any networked game is to ensure that the players have
an even playing field. It's the unfortunate truth that some players will do whatever
they can to win, even if it involves breaking the rules of the game. In a networked
multiplayer game, there are many ways rules can potentially be broken, and so
whenever possible, networked games must be designed to prevent players from
cheating.
Information Cheats
An information cheat is one where a player is able to get additional information
that players normally are not intended to have. Suppose you are playing a game
such as Team Fortress 2 , which has a character that can use stealth to hide from
other players. Normally, when the spy character goes into stealth mode, that char-
acter becomes invisible to all opposing players. But we already know that every
so often, the server is going to be sending positional information of the other play-
ers. If the server is still sending the location information of the hidden character,
it would not be that challenging for an experienced hacker to keep the spy visible,
even in stealth mode.
Theeasiestwaytostopinformationcheatsisbylimitingwhatinformationisavail-
able. In the case of the spy character, the solution would be to have the server stop
sending position information for a character when in stealth mode. In this manner,