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If each player has their own avatar, that can move, jump, and do actions to entities in the world (let's say, boxes). How is it handled? Is clients sending commands to the server and getting the current state of the world in response a viable design?

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closed as off topic by Mark Trapp Aug 3 '11 at 2:18

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It is viable. But do note that you have a trade-off. If you only send the information about the part of the world that is currently visible, latency and interactivity get hurt. If you send updates about the local area, usability is better but you face the possibility of people breaking your protocol and using it to generate compromised clients that can do things like see around corners. –  btilly Aug 3 '11 at 0:54
    
I think this question would get better answers on gamedev.stackexchange. Is there a mod around to move it? :) –  Tyanna Aug 3 '11 at 1:49
    
GameDev.SE would be where this is on-topic, but it's a pretty broad question. You should look at their multiplayer tag to see if your question is answered there before asking a more specific question. –  user8 Aug 3 '11 at 2:20
    
What does the "design patterns" item refer to in the faq then? –  Tamás Szelei Aug 3 '11 at 11:12

2 Answers 2

Is clients sending commands to the server and getting the current state of the world in response a viable design?

Broadly speaking, yes. Now, that changes a bit when you start talking about peer-to-peer systems, or real-time-strategy games with exponentially more entities and states to account for.

I highly recommend browsing some of the published documentation for Valve's Source engine as a starting point:

Notable features/optimizations include:

  • Client-side prediction
  • Interpolation of entities
  • Lag-compensation for instant-travel attacks
  • Using geometry information in the world to avoid sending data about things that are "out of sight".
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Depending on your game you are going to need some communication between the client and the server. If your game doesn't need to be real-time then asking the state of the server from the client is a viable alternative.
If, however, you need more real-time capabilities you are going to want to look in to Socket Programming, especially using a language where the Sockets can send events.

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