Networking gampeplay - Sending controller inputs vs. sending game actions

Question

I'm reading about techniques for implementing game networking.

Some of the resources i've read state that it is a common practice (at least for some games) to send the actual controller input across the network, to be fed into the remote game's loop for processing.

This seems a bit odd to me and i'd like to know what are the benefits of using such a method?

To me, it seems that controller input is merely a way to gather data to be fed into the game, which in turn determines how to translate these into specific game actions.

Why would i want to send the control data and not the game actions themselves?

Answer 1

Sending Input to the Game Server

Pros

• The computation for all players is done at once on one machine.
• Each player receives the same game state.

Cons

• The player has to wait for the server's response to his/her input.

Sending Game Actions to the Game Server

Pros

• The player will not experience any latency relating to his/her own actions.

Cons

• The server has to stitch together and arrange multiple events from multiple players to be sent back out to the players.

Summary

It takes more work for a server to listen to multiple players' actions than it is to just take their input, calculate the result, and return a game state for all players.

Answer 2

In general, yes, you send desired actions, not raw inputs. Sanity-check on the server, though (otherwise players could run at twice the max speed, etc).

I've written a series of articles detailing how all this works, some people have found it useful: http://www.gabrielgambetta.com/fpm2.html.

Answer 3

The problem comes from cheaters. You might want to read some about the so called authoritative game server. It is very well explained in this article by Gabriel Gambetta.

But lets think about the following example.

You have an online shooter game, which can be either ammo or cooldown based. Your client is a nasty hacker. By accepting game actions (events) from the client, the client can feed the server with new bullets fired, even when he is out of ammo, or his weapon on cooldown. By collecting user input, you need to do the maths and all the checkings on the server side but in return your game is kinda cheat safe. Using an aimbot also gets a lot easier for hackers if you simply accept game events on server side.

You could of course validate the events sent by the client, but sending game events can be heavier on bandwidth.

Have fun implementing your game.

Answer 4

Depends on your game more specific...

Action/Event based System

• Strategy Game
• Turn based games
• ...

you need to send the actions which the players do because the server don't care about the realtime informations

Live/Streamed System

• Realtime games

the server need to know as fast as possible what the input of each user is to update gameworld objects.

For example if i hold the forward button of a racer game the client should send on every network tick the state of all buttons so the server can simulate the world in realtime.

You could also realisize this with an event based system, but you need more bits to encode the event for a button change which is not that good.

Answer 5

I know this thread is 7 years old but for anyone looking in here and wondering one big advantage is that its practicaly hacker safe. Online game hacking happens when a player can moddify the packets sent to the server in ways you shouldnt but if you only send key inputs there cant be any combination of input controlls that are concidered cheating. but if you send for example the player movements you can modify them so that the player for example is flying even if he isnt allowed to, wich isnt possible if all the math is done by the actuall server.