Multiplayer Scripting

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This page aims to explain notions and specificities of Multiplayer Scripting and its differences with Singleplayer Scripting.
It features three parts:

  1. Notions and general knowledge
  2. Structuring Multiplayer code
  3. Testing locally


Notions and general knowledge

The basics

  • In Multiplayer, players are connected to a server.
    • The server is a machine that distributes information among clients, such as unit positions, vehicle speeds, etc.
    • The server can be either a dedicated machine, or hosted by a player; in the latter it means the server can have a player unit.
  • A machine connected to a server is called a client.
    • Clients can join a mission after it started: they are considered "JIP" and scripting should be adapted to them. See the Join In Progress chapter for more information.
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In Singleplayer, the game acts as a player-hosted server (isServer returns true).
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Some Multiplayer commands do not work in Singleplayer, such as netId !
The other way around, some Singleplayer commands do not work in Multiplayer (e.g setAccTime).


Locality

Definitions

  • LOCAL is an attribute for the machine where the command/script/function is executed.
    • to check if an argument is local, use the local command
  • REMOTE means non local. All player-controlled soldiers are remote units to a dedicated server, for example.
    • to check if an argument is remote, simply use not local myObject
  • commands arguments and effects can be either local or global:
Template:EffArg a local argument means an argument that is processed on the machine where the command is executed
Template:EffArg a global argument means any argument, even a remote one
Template:EffArg a local effect means that the effect will only happen on the machine where the command is executed
Template:EffArg a global effect means that all the computers will receive it

See Locality in Multiplayer for more information.

Different machines and how to target them

Valid for Arma 3
Machine Conditions Is server Is player Is JIP
Dedicated Server isDedicated Template:task/ Template:task Template:task
Player Server hasInterface && isServer Template:task/ Template:task/ Template:task
Player Client hasInterface && not isServer Template:task Template:task/ Template:task
JIP Player Client hasInterface && didJIP Template:task Template:task/ Template:task/
Headless Client not hasInterface && not isServer Template:task Template:task Template:task
JIP Headless Client not hasInterface && not isServer && didJIP Template:task Template:task Template:task/

For an extended version for all games, click "Show text"

Targeted machine Operation Flashpoint Arma Arma 2 Arma 3
Dedicated Server

A server without a human player behind it

local myLogic && isNull player isServer && player != player isDedicated isDedicated
Player Server

A server hosted by a player

local myLogic && not isNull player isServer && not isDedicated isServer && not isDedicated hasInterface && isServer
Server

Any server, dedicated or hosted

local myLogic isServer isServer isServer
Player Client

A player connected since the lobby

not local myLogic && not isNull player not isServer && not isNull player not isServer && not isNull player hasInterface && not isServer
JIP Client

A player connected in the middle of a mission

N/A not isServer && isNull player not isServer && isNull player hasInterface && didJIP
Headless Client

A client without a human player behind it
(used to offload server calculations)

N/A not hasInterface && not isServer
JIP Headless Client

Headless client connected during the ongoing mission

N/A not hasInterface && not isServer && didJIP
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  • If you want to know if the current machine is a server (Dedicated Server or Player Server), use isServer.
  • If you want to know if the current machine has a player (Player Server included), use hasInterface.
Arma 3
Since Arma 3, a server-only init file is available: initServer.sqf (see Event Scripts)

General information about locality

  • about player:
    • a player's unit is always local to the (human) player's machine
    • a dedicated server doesn't have a player unit (isNull player returns true)
    • to know if a certain unit is a player, use isPlayer
  • groups and AI:
    • an AI group with a player-leader will be local to the player's computer
    • a subordinate player being in a player-lead group will remain local to its computer (see bulletpoint #1)
  • objects:
    • a driven vehicle is always local to the machine of its driver (not the commander's, not the gunner's)
    • terrain objects (buildings, vegetation, roads etc.) are local everywhere (local nearestBuilding player returns true on every client)
    • editor-placed objects and empty vehicles are local to the server
    • editor-placed triggers are created on every machine unless specified otherwise ("Server Only" Eden Editor option ticked)
    • units created with createUnit will be local to the computer that issued the command
    • objects and vehicles created with createVehicle will be local to the computer that issued the command

Locality changes

  • if the player-leader dies, the AI is transferred to the machine where the new leader is local (server in case of AI, client in case of another player)
  • joining AI units will change locality to the new leader's computer
  • locality will change from server to client when a player gets in an empty vehicle
  • locality can also change in the event of a Team Switch or usage of selectPlayer
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Since Arma 3 the "Local" Event Handler triggers when an object's locality is changed.

Code examples

Code Argu-ments Effect Description
remoteUnit setDamage 1; Template:EffArg Template:EffArg Any unit (local or remote) will die, and all the computers will know
localUnit addMagazine "30Rnd_556x45_STANAG"; Template:EffArg Template:EffArg Only a local unit can have its inventory edited with this command, but all the machines will be notified: if a player looks into the localUnit inventory, the added magazine will be there
remoteUnit setFace "Miller"; Template:EffArg Template:EffArg Any unit (local or remote) can get its face changed, but the new face will not be propagated through the network. Only the local machine's player will see the effect of the command
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This command should ideally be executed on every machine, for example with: 
[remoteUnit, "Miller"] remoteExec ["setFace", 0, true];
See Remote Execution paragraph for more information.
localCamera cameraEffect ["Internal", "Back"]; Template:EffArg Template:EffArg Only a local camera can be entered, and of course only the local machine will see through this camera


Network ID

Network IDs identify machines and network objects. They can be used to target proper machines with remote execution; see Remote Execution chapter for more information.

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A machine ID (ownerID) is not to be confused with an object's network ID (netId).

Machine network ID

Every machine, including the server, has a network ID.
A server has an ID of 2, every new client has the next number (the first client will be number 3, second client number 4, etc.)

  • To get the current machine's ID, use clientOwner.
  • To get the machine's ID of an object's owner, use owner object (MP only).
  • To get the machine's ID of a group's owner, use groupOwner object (MP only).

Object network ID

Every object synchronised through the network has a network ID, shortened to netId.


Sending information across network

Remote Execution

Since Arma 3 v1.50, remoteExec and remoteExecCall efficient engine network commands are available: 

["Message to everyone, including JIP players!", 0, true] remoteExec ["hint"];

See Arma 3 Remote Execution for more information.

Arma 3 alpha introduced BIS_fnc_MP (obsolete since Arma 3 v1.50, use the above version): 

["Message to everyone, including JIP  players!", "hint", true, true] call BIS_fnc_MP;  // obsolete since Arma 3 v1.50, use remoteExec or remoteExecCall

Arma 2 introduced the Multiplayer framework (not present in Arma 3): 

// Having the Functions module placed in the editor
waitUntil { not isNil "BIS_MPF_InitDone"; };
[nil, nil, rHINT, "Message to everyone!"] call RE;

PublicVariable commands

PublicVariable commands allow to send global variables to specified machines.

  • Network reception is guaranteed
  • Short variable names should be used for network performance
  • These commands shouldn't be used intensely for the same reason
Command Effect JIP synchronised
publicVariable Set/update a variable value from the local machine to all the other machines (including server) Template:task/
publicVariableServer Set/update a variable value from a client to the server Template:task
publicVariableClient Set/update a variable value from the local machine (not necessarily the server) to a specific client Template:task

How it works

The server has the variable ABC_Score to broadcast: 

ABC_Score = 5;				// sets the value
publicVariable "ABC_Score"	// publishes the variable (do not forget the quotes!)

This sends the variable name and value to the clients.

  • If the variable is not yet declared on their machine, it will declare it as well.
  • If the variable already exists, the value is overridden by the server's value.
  • If the variable changes again on the server, it has to be manually publicVariable'd once again!
  • A JIP player will synchronise server's publicVariable'd variables before executing init.sqf. See Initialization Order for more information.
    • A JIP player will not synchronise publicVariableClient-received variables after he disconnects/reconnects. Only server-known public variables sent with publicVariable will be synchronised.

setVariable command

Available since Arma 2 the public version of the setVariable command allows you to store a variable into an object and spread this variable across the network.

Arma 3
In Arma 3 it is possible to broadcast the nil value, thus deleting the variable from the target.


Player connection events

The following commands will execute given code when a player is connecting or disconnecting. This code will run for players connecting in the lobby and for JIP players!

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Client state

A client state is the client's connection state. It can be obtained with getClientState and getClientStateNumber commands on both server and clients.

getClientStateNumber getClientState Description
0 "NONE" No client (or singleplayer)
1 "CREATED" Client is created
2 "CONNECTED" Client is connected to server, message formats are registered
3 "LOGGED IN" Identity is created
4 "MISSION SELECTED" Mission is selected
5 "MISSION ASKED" Server was asked to send / not send mission
6 "ROLE ASSIGNED" Role was assigned (and confirmed)
7 "MISSION RECEIVED" Mission received
8 "GAME LOADED" Island loaded, vehicles received
9 "BRIEFING SHOWN" Briefing was displayed
10 "BRIEFING READ" Ready to play mission
11 "GAME FINISHED" Game was finished
12 "DEBRIEFING READ" Debriefing read, ready to continue with next mission


Join In Progress

A JIP player will have many information synchronised by the game before accessing the mission itself. JIP was introduced in Arma.

Information Arma 1 Arma 2 Arma 3
date/time Template:task/ Template:task/ Template:task/
date/time + setDate/skipTime Template:task Template:task Template:task/
weather (overcast, fog) Template:task Template:task/ Template:task/
weather + setOvercast/setFog/setRain/setLightnings Template:task Template:task Template:task/
time passed since mission start (time command) unknown unknown Template:task/
publicVariable-sent variables (Number, String, Text, Array, Code) Template:task/ Template:task/ Template:task/
publicVariable-sent variables (nil) Template:task Template:task Template:task/
setVariable-assigned variables (when alternative syntax's public parameter is set to true) N/A Template:task/ Template:task/
remoteExec- and remoteExecCall-executed code if JIP prerequisites are met N/A N/A Template:task/

See Join In Progress for more information.


See also


Structuring Multiplayer code

Template:wip


Responsibilities

Server

The Server must be considered as the one ruler of the mission. He is the game's referee and all the decisions should come from it. All the values on the server should be considered as true.
Consider the server as a powerful machine where you can put all the mission conditions and heavy scripting on. In case of a very heavy mission, the server can be assisted by Headless Clients (this involves a per-mission specific design).

Server-side code must gather or wait all the variables (potentially from client-side scripts and publicVariableServer) and take and broadcast its decisions accordingly using publicVariable.

Client

The Client must be considered as an average machine that can leave the game at any moment. No mission-vital code must be executed on its side and no decisions must be taken client-side.
Again, one must expect that any client can disconnect at any moment.

The client executes all the (local) UI code (Post process effects, Dialogs, etc.)


See also


Testing locally

To properly test MP scripting locality issues, it is recommended to run a dedicated server and connect with two clients. In order to do so: 

	loopback = true;	// force LAN-only server
	kickDuplicate = 0;	// disable duplicate Arma kick

	// needed in case of Headless Client test only
	headlessClients[]	= { "127.0.0.1" };
	localClient[]		= { "127.0.0.1" };
  • Run Arma 3 twice from Steam and connect each (with -showScriptErrors flag)
    • If you use one screen for the first client and the other screen for the second client, use -noPause -window launcher options. This will not pause render if the window doesn't have focus.
  • Try your mission and check for script errors:
  • To ensure all cases, your mission should ideally work properly:
    • in Singleplayer
    • in Player-hosted Multiplayer
    • in a Dedicated Server-hosted game
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Of course, nothing prevents you to invite friends to play your mission and report bugs!


See Also

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