CODEWITHSUNDEEP
network-programmingsystemgame-engine
Alexis Clarembeau
Alexis Clarembeau

Reputation: 2964

MMORPG moving protocol mechanism

I would like to build from scratch a kind of small (extremely small and simple) MMORPG game with click movements inside a given grid (something like an online Pokemon game). When I click on a cell, the player will move to reach the pointed area (using a pathfinding algorithm such as A*). But, I have no idea about how to build the network protocol of the movement system. And, googling the subject doesn't seem to help me a lot. I need to make a choice: - either I send a message to the server each time I move from one cell to another (which isn't efficient at all because if we are in a 100ms latency network, I can only sens 10movements/sec and if I ask the server to acknowledge the movement it can only do 5moves/sec) - either I send a message each time the player wants to change its direction (it clicks on another cell). The client sends periodically its position to the server and it checks if it's coherent with the destination.

The second solution looks a lot better than the first one and I think that a real game systems must implement that strategy. Am I wrong?

Also, how can we build systems based on that solution that doesn't let a modified (hacked) client be able to send fake positions and teleport anywhere they want? Does real systems implement somethink like a "incoherent sent position" system that will try to try to detect and fix those problems?

Or, is there something simpler to implement? Thank you very much

Upvotes: 0

Views: 496

Answers (2)

Alexis Clarembeau
Alexis Clarembeau

Reputation: 2964

Thanks to ScarletMerlin's answers I think there's a simple solution to my problem.

When the player wants to move from one position (for instance 0,0) to another (for instance 10,10), it sends a "MOVE 10 10" message to the server.

Then, only the server will apply the pathfinding algorithm and send after each move the position to the client. (for instance, by message CURRENTLY_ON X Y). Then, the client will update the position of the player.

It's a kind of automatic synchronisation from the server to the client. It also solves the problem of the first solution (one move and one ACK per movement) thanks to pipeling. For instance, if the network has a 1000ms delay and a move is set 50ms, we will just receive messages at time 1000, 1050, 1100, 1150, ... So, we will just feel the lag when the player is changing its direction. The user will also feel some lag when changing from one direction to another but if we assume that the delay is quite low and symetric (it doesn't seems to be a too strong assumption), it won't be so much percepted (as the change direction will often arrive before the sending of the CURRENTLY_ON message and the server can interrupt its current action (going straight on) to handle the new one).

Upvotes: 1

ScarletMerlin
ScarletMerlin

Reputation: 475

In a realtime game I would create a panthing mechanic. I would use a formula such as: Speed * time = distance.

now if you run the same logic in the client and the server you only need to send the movement logic at the beginning and the sever can answer with a finish message when the distance is traveled. (compare at the end to prevent cheating. the server always wins)

Now if the client cancels in the movement to go somewhere else, you send a cancelation of panthing and the time that you traveled. The same goes when changing the panthing (in this case you send a new path staring at a new time and place).

Upvotes: 1

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