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SonicD007

Passing information between gamestates

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Hi,  I'm using the gamestate sample from: http://gamedevgeek.com/tutorials/managing-game-states-in-c/  and I want to pass information from one gamestate to another gamestate.  In particular, I'm thinking of creating a LogIn state in which it will connect to a server, verify/login, then grab the character data.  I then want to pass the character data to the next gamestate (PlayGameState or something) and use that data to do whatever game logic I need done.  What would be the best way to do this?  Would I need to change the Init class to have another parameter in which I can pass a generic object of some sort similar to how C# forms use the Tag property to exchange data with other forms?  How would you do this?

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I would pass the data as a structure parameter in the state's Instance function. If you design your game well, you should not need to pass a lot of structures between states. If you were to successfully login, it could pass the character data to a loading screen state. The data could contain information on where the character was last in the game, and based on that information, load that part of the world for the game for the state following the loading screen.

Also consider what data you want to be persistent throughout the run of the program, not just when you're actually playing the game.

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There's no reason not to think of game state classes as very different from any other class. Like any other class, if there's information you want to pass to an object as you create it, then you can make it a parameter of the constructor.

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I don't see why you have to pass character data from one state to the next (in this case), because "logging in" and "getting character data" are two distinct activities, which can be executed in two distinct states: In your log-in state, you're trying to authenticate, and if you do, you transition into the "load" state, where you can get the relevant data from the network.

 

Some general comments relating to state machines: There are many cases where you don't really need to have a convoluted class hierarchy, and where setting a function pointer will work just fine.

 

I actually wrote a small Tetris game in C, where states, and state transitions, are just as simple as that.

 

You can see the code on my github, specifically in this file: states.c.

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I don't see why you have to pass character data from one state to the next (in this case), because "logging in" and "getting character data" are two distinct activities, which can be executed in two distinct states: In your log-in state, you're trying to authenticate, and if you do, you transition into the "load" state, where you can get the relevant data from the network.

 

Even if I do it that way, wouldn't I only be pushing the transfer of data between states to the load state?  

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As a side not on the original state system I would ditch the singleton behaviour from all the states, you can have different instances of the same state in a game. Some information shouldn't be stored in the states itself they only indicate in which state the game is. We stored player information for example in a player profile which was globally accesseable through a resource class that was passed in the constructor of a state. You then had multiple states to check whether the player had signed into a profile on the console, and then other states to check other things in the profile when needed.

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Even if I do it that way, wouldn't I only be pushing the transfer of data between states to the load state?  

 

You would no longer need to have a system for transferring data between states, because each state would be responsible for getting the data it actually requires.

 

If other states need to access this data somewhere along the line, they should be able to get it from some globally visible data structure.

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