When B actually received A's bullet message, B was at a different position, so no hit was propagated.Īn important step in implementing the game and ensuring that every player will be able to see the same simulation accurately is the identification of relevant actions. For example, player A shoots and locally sees the bullet hitting B's ship, but nothing happens that's because A's view of B is delayed due to network lag. In a perfect world, there would be no network latency, so messages would come and go instantly and the simulation would be extremely accurate.Īs the latency increases, however, the simulation becomes inaccurate. All other players will receive messages from A informing about his actions and they will react accordingly, so if A's bullet got C's ship, then C will broadcast a message informing it was destroyed.Īs a consequence, each player will see all other ships (and their actions) according to the received messages. This means that, if the game has four players - say A, B, C and D - player A is the only one able to inform where ship A is, if it got hit, if it fired a bullet or dropped a bomb, and so on. In order to keep the simulation accurate, every peer is responsible for propagating only the information about its ship, not the others. Those messages take time to travel over the network from one computer to another, so when the player receives an information saying an opponent's ship is at (x, y), it's probably not there any more - that's why it's a simulation:Ĭommunication delay caused by the network. For the movement of all the other ships, the player must receive a network message from every opponent informing where their ships are. The player's ship's movement and actions are guided by local input, so the player's game state is updated almost instantly. Opponent ships are simulated based on network communication. As a consequence, the player sees two scenarios simultaneously: his ship moving according to his input and a simulation of all other ships controlled by the opponents: Tip: the authoritative approach is more secure against cheating, because the server fully controls the game state and can ignore any suspicious message, like an entity saying it moved 200 pixels when it could only have moved 10.Ī non-authoritative multiplayer game has no central entity to control the game state, so every peer must control its own game state, communicating any changes and important actions to the others. The game and the networking code are abstracted as much as possible for the sake of simplification. I'm going to focus on the communication and synchronization of peer states. The game is a deathmatch arena where each player controls a ship able to shoot and drop bombs. In this tutorial I present the implementation of a multiplayer game played over the network using a non-authoritative P2P approach. Non-authoritative implementation using P2P architecture. In a peer-to-peer (P2P) approach, a peer sends data to all other peers and receives data from them, assuming that information is reliable and correct (cheating-free): In the non-authoritative group, there is no central entity and every peer (game) controls its game state. After that it propagates the information to all clients, so they can update their game state accordingly. The server checks whether the information is correct, then updates its game state. If a client performs an action, such as moving from one point to another, that information is sent to the server. It's a bit like watching TV.Īuthoritative implementation using client-server architecture. Every client connected to the server constantly receives data, locally creating a representation of the game state. In the authoritative group, the most common approach is the client-server architecture, where a central entity (the authoritative server) controls the whole game. Controls: arrows or WASD to move, Space to shoot, B to deploy a bomb.Īrt from Remastered Tyrian Graphics, Iron Plague and Hard Vacuum by Daniel Cook ( Lost Garden).Ī multiplayer game played over the network can be implemented using several different approaches, which can be categorized into two groups: authoritative and non-authoritative. If you want to find unique resources for your own game, check out the selection of game assets over on Envato Market. You can download or fork the final code from the GitHub repo or the zipped source files. You must have a basic understanding of networking communication. Note: Although this tutorial is written using AS3 and Flash, you should be able to use the same techniques and concepts in almost any game development environment. This tutorial presents the implementation of a multiplayer game played over the network using a non-authoritative peer-to-peer (P2P) approach. Instead of beating AI-controlled opponents, the player must face strategies created by another human being. Playing a multiplayer game is always fun.
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