Scripting Introduction

Resources are a key part of MTA. A resource is essentially a folder or zip file that contains a collection of files, plus a meta file that describes to the server how the resource should be loaded and what files it does contain. A resource can be seen as being partly equivalent to a program running in an operating system - it can be started and stopped, and multiple resources can run at once.

Everything that has to do with scripting happens in resources, what a resource does defines if it is a gamemode, a map or anything else.

Creating a simple script

Firstly, we want to write something that adds a 'createvehicle' command players can use to spawn a vehicle beside their position.

Preparations

As decribed above, a resource is a folder or zip file, so first you should create a folder. The folder name is the name of the resource, that is used to start or stop it or reference in scripts. In our example, we shall call it commands.

What every resource has and needs is the meta.xml file. In our case, we want to create a script that provides some simple commands to the user, thus we need to tell the server to load a script file, we name script.lua in our case.

<meta>
  <info author="YourName" description="A few simple commands" />
  <script src="script.lua" />
 </meta>

Now we have to create the script.lua file we defined above in the same directory as the meta.xml. Now we have the both files:

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

Writing the script

Let's start with the contents of the script.lua file. As mentioned above, we want to provide a command to create a vehicle beside your current position in the game. Firstly we need to create a function we want to call and a command handler that creates the command the player will be able to enter in the console.

-- create the function the command handler calls, with the arguments: thePlayer, command, vehicle
function createVehicleForPlayer(thePlayer, command, vehicle)
   -- create a vehicle and stuff
end

-- create a command handler
addCommandHandler("createvehicle", createVehicleForPlayer)

Note: Function names are clickable in code examples on the wiki and linked to the functions' documentation.

About command handlers

The first argument of addCommandHandler is the name of the command the player will be able to enter, the second argument is the function this will call, in this case createVehicleForPlayer.

If you have already experience in scripting, you will know that you call a function like this:

functionName(argument1, argument2, argument3, ..)

We called the addCommandHandler function this way already and since createVehicleForPlayer is a function too, it can be called that way as well. But we are using a command handler for that, which calls it in a similiar manner, internally.

For example: Someone types "createvehicle 468" ingame in the console to spawn a Sanchez, the command handler calls the createVehicleForPlayer function, as if we would have this line of code in the script:

createVehiceForPlayer(thePlayer,"createvehicle","468") -- thePlayer is the player element of the player who entered the command

As we can see, it provides several parameters: the player who called the command, the command he entered and whatever text he had after that, in this case "468" as vehicle id for the Sanchez. The first two parameters are the same with all command handlers, which you can read on the addEventHandler page. For this fact, you always have to define at least those two parameters to use any after that (for example to process text that was entered after the command, like in our example the vehicle model id).

Note: You have to add the command handler AFTER you defined the handler function, else it can't find it. The order of execution matters.

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 functions' 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 theoratical 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">
	<meta>
		<author>someguy</author>
		<name>Airport</name>
		<description>Prevent the terrorist from planting a bomb on the airport</description>
	</meta>

	<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.