IT/Introduzione allo scripting

Le Resources (Risorse) sono la parte principale di MTA. Essenzialmente, una risorsa è una cartella o un archivio zip che contiene una serie di files ed un file meta che contiene informazioni su come il server deve gestire la risorsa e cosa contengono i suoi componenti. Una risorsa può essere vista come uno dei programmi che girano su un sistema operativo: può essere avviata e fermata, e più risorse possono essere eseguite contemporaneamente.

Tutto ciò che ha a che fare con lo scripting avviene nelle risorse, ciò che una risorsa fà dipende da se si tratta di una gamemode, una mappa o qualsiasi altra cosa.

Creare un semplice script

Innanzitutto, mettiamo caso volessimo creare uno script per aggiungere un comando 'createvehicle' che i giocatori possano usare per far spawnare un veicolo alla loro attuale posizione.

Preparazione

Come detto sopra, una risorsa è una cartella o un archivio zip, quindi prima di tutto dovremo creare una cartella. Il nome della cartella è il nome della risorsa, che viene usato per avviarla o fermarla o come riferimento negli script. Nel nostro esempio la chiameremo commands.

Ciò di cui qualsiasi risorsa ha bisogno è il file meta.xml. Nel nostro caso, vogliamo creare uno script che fornisca determinati comandi ad un giocatore, dobbiamo quindi dire al server di caricare il nostro script, che chiameremo script.lua.

Ecco il contenuto del nostro file meta.xml:

<meta>
     <info author="TuoNome" description="Alcuni semplici comandi" />
     <script src="script.lua" />
</meta>

Creiamo ora il file che conterrà il nostro script: script.lua, nella stessa cartella di meta.xml. Adesso abbiamo i seguenti files:

/commands/meta.xml
/commands/script.lua

Scrivere uno script

Iniziamo a scrivere il contenuto del file script.lua. Come sopra, vogliamo creare un comando per spawnare un veicolo nella posizione di chi esegue il comando stesso. Prima di tutto dobbiamo creare una funzione che possa essere eseguita all'esecuzione dello script, ed un command handler che dica al gioco di eseguire la nostra funzione quando il nostro comando viene chiamato.

-- Creiamo la funzione per spawnare un nuovo veicolo, con gli argomenti "thePlayer", "command" e "vehicle"
function createVehicleForPlayer(thePlayer, command, vehicle)
   -- Qui metteremo le funzioni per creare il veicolo, ottenere la posizione del giocatore eccetera
end

-- Creiamo quindi il "command handler"
addCommandHandler("createvehicle", createVehicleForPlayer)

Nota: Negli esempi di script i nomi delle funzioni sono dei link che portano alla relativa pagina per informazioni sulla funzione stessa.

A proposito dei command handlers

Il primo argomento della funzione addCommandHandler è il nome del comando che il giocatore dovrà eseguire, il secondo argomento è invece la funzione che il comando attiverà, nell'esempio sopra createVehicleForPlayer.

Se hai già un'esperienza di base nello scripting o nella programmazione, saprai già che una funzione si chiama nel seguente modo:

nomeFunzione(argomento1, argomento2, argomento3, ...)

Abbiamo infatti chiamato la funzione addCommandHandler in questo modo, e dato che anche createVehicleForPlayer è una funzione, può essere anche lei chiamat in tale modo. Ma stiamo invece utilizzando un command handler, che la chiama in modo simile internamente ad MTA.

Ad esempio: qualcuno durante il gioco scrive "createvehicle 468" nella console per spawnare una Sanchez, il command handler chiama la funzione createVehicleForPlayer, come se avessimo avuto questa riga di codice nello script:

createVehicleForPlayer(thePlayer,"createvehicle","468") -- thePlayer è l'identificatore del giocatore che ha chiamato la funzione

Come possiamo vedere, contiene diversi argomenti: il giocatore che ha chiamato il comando, il comando che ha chiamato e tutto ciò che ha scritto dopo di esso, in questo caso "468" come id per il veicolo da spawnare, una Sanchez. I primi due parametri sono gli stessi in tutti i command handlers, come puoi vedere nella pagina addEventHandler. Per questo, devi per forza definire almeno questi due parametri prima che MTA possa riconoscerne altri aggiuntivi(ad esempio, in questo caso, l'ID del veicolo).

Nota: Puoi creare un command handler solo DOPO aver creato la funzione che l'handler chiemerà, altrimenti MTA non troverà la funzione e non potrà quindi eseguirla.

Writing the function

In order to fill the function we created, we need to think about what we have to do:

• Get the players position, so we know where to spawn the vehicle (we want it to appear right beside the player)
• Calculate the position we want to spawn the vehicle at (we don't want it to appear in the player)
• Spawn the vehicle
• Check if it has been spawned successfully, or output a message

In order to achieve our goals, we have to use several functions. To find function we need to use, we should visit the Server Functions List. First we need a function to get the players position. Since players are Elements, we first jump to the Element functions where we find the getElementPosition function. By clicking on the function name in the list, you get to the function description. There we can see the syntax, what it returns and usually an example. The syntax shows us what arguments we can or have to submit.

For getElementPosition, the syntax is:

float, float, float getElementPosition ( element theElement )

The three float in front of the function name are the return type. In this case it means the function returns three floating point numbers. Within the parentheses, you can see what arguments you have to submit. In this case only the element whose position you want to get, which is the player in our example.

function createVehicleForPlayer(thePlayer, command, vehicleModel)
	-- get the position and put it in the x,y,z variables
	-- (local means, the variables only exist in the current scope, in this case, the function)
	local x,y,z = getElementPosition(thePlayer)
end

Next we want to ensure that the vehicle won't spawn directly in the player, so we add a few units to the x variable, which will make it spawn east from the player.

function createVehicleForPlayer(thePlayer, command, vehicleModel)
	local x,y,z = getElementPosition(thePlayer) -- get the position of the player
	x = x + 5 -- add 5 units to the x position
end

Now we need another function, one to spawn a vehicle. We once again search for it on the Server Functions List, this time - since we are talking about vehicles - in the Vehicle functions section, where we will choose createVehicle. In this function's syntax, we only have one return type (which is more common), a vehicle element that points to the vehicle we just created. Also, we see that some arguments are enclosed within [ ] which means that those are optional.

We already have all arguments we need for createVehicle in our function: The position we just calculated in the x,y,z variables and the model id that we provided through the command ("createvehicle 468") and can access in the function as vehicleModel variable.

function createVehicleForPlayer(thePlayer, command, vehicleModel)
	local x,y,z = getElementPosition(thePlayer) -- get the position of the player
	x = x + 5 -- add 5 units to the x position
	-- create the vehicle and store the returned vehicle element in the ''createdVehicle'' variable
	local createdVehicle = createVehicle(tonumber(vehicleModel),x,y,z)
end

Of course this code can be improved in many ways, but at least we want to add a check whether the vehicle was created successfully or not. As we can read on the createVehicle page under Returns, the function returns false when it was unable to create the vehicle. Thus, we check the value of the createVehicle variable.

Now we have our complete script:

function createVehicleForPlayer(thePlayer, command, vehicleModel)
	local x,y,z = getElementPosition(thePlayer) -- get the position of the player
	x = x + 5 -- add 5 units to the x position
	local createdVehicle = createVehicle(tonumber(vehicleModel),x,y,z)
	-- check if the return value was ''false''
	if (createdVehicle == false) then
		-- if so, output a message to the chatbox, but only to this player.
		outputChatBox("Failed to create vehicle.",thePlayer)
	end
end
addCommandHandler("createvehicle", createVehicleForPlayer)

As you can see, we introduced another function with outputChatBox. By now, you should be able to explore the function's documentation page yourself.

What you need to know

You already read some things about resources, command handlers and finding functions in the documentation in the first paragraph, but there is much more to learn. This section will give you a rather short overview over some of these things, while linking to related pages if possible.

Clientside and Serverside scripts

You may have already noticed these or similiar terms (Server/Client) somwhere on this wiki, mostly in conjunction with functions. MTA not only supports scripts that run on the server and provide commands (like the one we wrote above) or other features, but also scripts that run on the MTA client the players use to connect to the server. The reason for this is, that some features MTA provides have to be clientside (like a GUI - Graphical User Interface), others should be because they work better and still others are better off to be serverside or just don't work clientside.

Most scripts you will make (gamemodes, maps) will probably be serverside, like the one we wrote in the first section. If you run into something that can't be solved serverside, you will probably have to make it clientside. For a clientside script for example, you would create a ordinary script file (for example called client.lua) and specify it in the meta.xml, like this:

<script src="client.lua" type="client" />

The type attribute defaults to 'server', so you only need to specify it for clientside scripts. When you do this, the clientside script will be downloaded to the player's computer once he connects to the server. Read more about Client side scripts.

More complex resources

The previous section showed briefly how to add clientside scripts to the resource, but there is also much more possible. As mentioned at the very top of this page, resources can be pretty much everything. Their purpose is defined by what they do. Let's have some theoretical resources, by looking at the files it contains, the meta.xml and what they might do:

First example - A utility script

/admin_commands
	/meta.xml
	/commands.lua
	/client.lua

<meta>
	<info author="Someguy" description="admin commands" />
	<script src="commands.lua" />
	<script src="client.lua" type="client" />
</meta>

• The commands.lua provides some admin commands, like banning a player, muting or something else that can be used to admin the server
• The client.lua provides a GUI to be able to perform the mentioned actions easily

This example might be running all the time (maybe even auto-started when the server starts) as it's useful during the whole gaming experience and also wont interfere with the gameplay, unless an admin decides to take some action of course.

Second example - A gamemode

/counterstrike
	/meta.xml
	/counterstrike.lua
	/buymenu.lua

<meta>
	<info author="Someguy" description="Counterstrike remake" type="gamemode" />
	<script src="counterstrike.lua" />
	<script src="buymenu.lua" type="client" />
</meta>

• The counterstrike.lua contains similiar to the following features:
  • Let players choose their team and spawn them
  • Provide them with weapons, targets and instructions (maybe read from a Map, see below)
  • Define the game's rules, e.g. when does the round end, what happens when a player dies
  • .. and maybe some more
• The buymenu.lua is a clientside script and creates a menu to buy weapons

This example can be called a gamemode, since it not only intereferes with the gameplay, but actually defines the rules of it. The type attribute indicates that this example works with the Map manager, yet another resource that was written by the QA Team to manage gamemodes and map loading. It is highly recommended that you base your gamemodes on the techniques it provides.

This also means that the gamemode probably won't run without a map. Gamemodes should always be as generic as possible. An example for a map is stated in the next example.

Third example - A Map

/cs-airport
	/meta.xml
	/airport.map
	/airport.lua

<meta>
	<info author="Someguy" description="Counterstrike airport map" type="map" gamemodes="counterstrike" />
	<map src="airport.map" />
	<script src="airport.lua" />
</meta>

• The airport.map in a XML file that provides information about the map to the gamemode, these may include:
  • Where the players should spawn, with what weapons, what teams there are
  • What the targets are
  • Weather, World Time, Timelimit
  • Provide vehicles
• The airport.lua might contain map-specific features, that may include:
  • Opening some door/make something explode when something specific happens
  • Create or move some custom objects, or manipulate objects that are created through the .map file
  • .. anything else map-specific you can think of

As you can see, the type attribute changed to 'map', telling the Map manager that this resource is a map, while the gamemodes attribute tells it for which gamemodes this map is valid, in this case the gamemode from the above example. What may come as a surprise is that there is also a script in the Map resource. Of course this is not necessarily needed in a map, but opens a wide range of possibilities for map makers to create their own world within the rules of the gamemode they create it for.

The airport.map file might look similiar to this:

<map mode="deathmatch" version="1.0">
	<terrorists>
		<spawnpoint posX="2332.23" posY="-12232.33" posZ="4.42223" skins="23-40" />
	</terrorists>
	<counterterrorists>
		<spawnpoint posX="2334.23443" posY="-12300.233" posZ="10.2344" skins="40-50" />
	</counterterrorists>

	<bomb posX="23342.23" posY="" posZ="" />
	
	<vehicle posX="" posY="" posZ="" model="602" />	
	<vehicle posX="" posY="" posZ="" model="603" />	
</map>

When a gamemode is started with a map, the map resources is automatically started by the mapmanager and the information it contains can be read by the gamemode resource. When the map changes, the current map resource is stopped and the next map resource is started.

Events

Events are the way MTA tells scripts about things that happen. For example when a player dies, the onPlayerWasted event is triggered. In order to perform any actions when a player dies, you have to prepare yourself similiar to adding a command handler, as shown in the first chapter.

This example will output a message with the name of the player who died:

function playerDied(totalAmmo, killer, killerWeapon, bodypart)
	outputChatBox(getClientName(source).." died!")
end
addEventHandler("onPlayerWasted",getRootElement(),playerDied)

Instead of showing what arguments are needed, the documentation page for Events shows what parameters are passed to the handler function, similiar to the way a command handler does, just that it is different from event to event. Another important point is the source variable, that exists in handler functions. It doesn't have to be added to the parameter list of the function, but it still exists. It has a different value from event to event, for player events (as in the example above) it is the player element.

Where to go from here

You should now be familiar with the most basic aspects of MTA scripting and also a bit with the documentation. The Main Page provides you with links to more information, Tutorials and References that allow a deeper look into the topics you desire to learn about.