Introduction to SourceMod Plugins

This guide will give you a basic introduction to writing a SourceMod plugin. If you are not familiar with the SourcePawn language, it is recommended that you at least briefly read the Introduction to SourcePawn article.

For information on compiling plugins, see Compiling SourceMod Plugins. The author of this article uses Crimson Editor to write plugins. Other possibilities are PSPad, UltraEdit, Notepad++, TextPad, Pawn Studio or any other text editor you're comfortable with.

Plugin Structure

Almost all plugins have the same three elements:

• Includes - Allows you to access the SourceMod API, and if you desire, APIs from external SourceMod extensions and plugins.
• Info - Public information about your plugin.
• Startup - A function which performs start-up routines in your plugin.

A skeletal plugin structure looks like this:

#include <sourcemod>
 
public Plugin:myinfo =
{
	name = "My First Plugin",
	author = "Me",
	description = "My first plugin ever",
	version = "1.0.0.0",
	url = "http://www.sourcemod.net/"
};
 
public OnPluginStart()
{
	// Perform one-time startup tasks ...
}

The information portion is a special syntax construct. You cannot change any of the keywords, or the public Plugin:myinfo declaration. The best idea is to copy and paste this skeletal structure and modify the strings to get started.

Includes

Pawn requires include files, much like C requires header files. Include files list all of the structures, functions, callbacks, and tags that are available. There are three types of include files:

• Core - sourcemod.inc and anything it includes. These are all provided by SourceMod's Core.
• Extension - adds a dependency against a certain extension.
• Plugin - adds a dependency against a certain plugin.

Include files are loaded using the #include compiler directive.

Commands

Our first example will be writing a simple admin command to slap a player. We'll continue to extend this example with more features until we have a final, complete result.

Declaration

First, let's look at what an admin command requires. Admin commands are registered using the RegAdminCmd function. They require a name, a callback function, and default admin flags.

The callback function is what's invoked every time the command is used. Click here to see its prototype. Example:

public OnPluginStart()
{
	RegAdminCmd("sm_myslap", Command_MySlap, ADMFLAG_SLAY);
}
 
public Action:Command_MySlap(client, args)
{
}

Now we've successfully implemented a command -- though it doesn't do anything yet. In fact, it will say "Unknown command" if you use it! The reason is because of the Action tag. Any command that you type in the console, even if it's registered by SourceMod, will be sent to the engine to be processed. Because we have not had SourceMod block this functionality yet, the engine replies with "Unknown command" because it is not a valid engine command.

public Action:Command_MySlap(client, args)
{
	return Plugin_Handled;
}

Now the command will report no error, but it still won't do anything. This is because returning "Plugin_Handled" in a command callback will prevent the engine from processing the command. The engine will never even see that the command was run. This is what you will want to do if you are registering a completely new command through SourceMod.

Implementation

Let's decide what the command will look like. Let's have it act like the default sm_slap command:

sm_myslap <name|#userid> [damage]

To implement this, we'll need a few steps:

• Get the input from the console. For this we use GetCmdArg().
• Find a matching player. For this we use FindTarget().
• Slap them. For this we use SlapPlayer(), which requires including sdktools, an extension bundled with SourceMod.
• Respond to the admin. For this we use ReplyToCommand().

Full example:

#include <sourcemod>
#include <sdktools>
 
public Plugin:myinfo =
{
	name = "My First Plugin",
	author = "Me",
	description = "My first plugin ever",
	version = "1.0.0.0",
	url = "http://www.sourcemod.net/"
}
 
public OnPluginStart()
{
	RegAdminCmd("sm_myslap", Command_MySlap, ADMFLAG_SLAY);
}
 
public Action:Command_MySlap(client, args)
{
	new String:arg1[32], String:arg2[32];
	new damage;
 
	/* Get the first argument */
	GetCmdArg(1, arg1, sizeof(arg1));
 
	/* If there are 2 or more arguments, and the second argument fetch 
	 * is successful, convert it to an integer.
	 */
	if (args >= 2 && GetCmdArg(2, arg2, sizeof(arg2)))
	{
		damage = StringToInt(arg2);
	}
 
	/* Try and find a matching player */
	new target = FindTarget(client, arg1);
	if (target == -1)
	{
		/* FindTarget() automatically replies with the 
		 * failure reason.
		 */
		return Plugin_Handled;
	}
 
	SlapPlayer(target, damage);
 
	new String:name[MAX_NAME_LENGTH];
 
	GetClientName(target, name, sizeof(name));
	ReplyToCommand(client, "[SM] You slapped %s for %d damage!", name, damage);
 
	return Plugin_Handled;
}

For more information on what %s and %d are, see Format Class Functions. Note that you never need to unregister or remove your admin command. When a plugin is unloaded, SourceMod cleans it up for you.

ConVars

ConVars, also known as cvars, are global console variables in the Source engine. They can have integer, float, or string values. ConVar accessing is done through Handles. Since ConVars are global, you do not need to close ConVar Handles (in fact, you cannot).

The handy feature of ConVars is that they are easy for users to configure. They can be placed in any .cfg file, such as server.cfg or sourcemod.cfg. To make this easier, SourceMod has an AutoExecConfig() function. This function will automatically build a default .cfg file containing all of your cvars, annotated with comments, for users. It is highly recommend that you call this if you have customizable ConVars.

Let's extend your example from earlier with a new ConVar. Our ConVar will be sm_myslap_damage and will specify the default damage someone is slapped for if no damage is specified.

new Handle:sm_myslap_damage = INVALID_HANDLE
 
public OnPluginStart()
{
	RegAdminCmd("sm_myslap", Command_MySlap, ADMFLAG_SLAY);
 
	sm_myslap_damage = CreateConVar("sm_myslap_damage", "5", "Default slap damage");
	AutoExecConfig(true, "plugin_myslap");
}
 
public Action:Command_MySlap(client, args)
{
	new String:arg1[32], String:arg2[32];
	new damage = GetConVarInt(sm_myslap_damage);
 
	/* The rest remains unchanged! */

Showing Activity, Logging

Almost all admin commands should log their activity, and some admin commands should show their activity to in-game clients. This can be done via the LogAction() and ShowActivity2() functions. The exact functionality of ShowActivity2() is determined by the sm_show_activity cvar.

For example, let's rewrite the last few lines of our slap command:

	SlapPlayer(target, damage);
 
	new String:name[MAX_NAME_LENGTH];
 
	GetClientName(target, name, sizeof(name));
 
	ShowActivity2(client, "[SM] ", "Slapped %s for %d damage!", name, damage);
	LogAction(client, target, "\"%L\" slapped \"%L\" (damage %d)", client, target, damage);
 
	return Plugin_Handled;
}

Multiple Targets

To fully complete our slap demonstration, let's make it support multiple targets. SourceMod's targeting system is quite advanced, so using it may seem complicated at first.

The function we use is ProcessTargetString(). It takes in input from the console, and returns a list of matching clients. It also returns a noun that will identify either a single client or describe a list of clients. The idea is that each client is then processed, but the activity shown to all players is only processed once. This reduces screen spam.

This method of target processing is used for almost every admin command in SourceMod, and in fact FindTarget() is just a simplified version.

Full, final example:

#include <sourcemod>
#include <sdktools>
 
new Handle:sm_myslap_damage = INVALID_HANDLE
 
public Plugin:myinfo =
{
	name = "My First Plugin",
	author = "Me",
	description = "My first plugin ever",
	version = "1.0.0.0",
	url = "http://www.sourcemod.net/"
}
 
public OnPluginStart()
{
	LoadTranslations("common.phrases");
	RegAdminCmd("sm_myslap", Command_MySlap, ADMFLAG_SLAY);
 
	sm_myslap_damage = CreateConVar("sm_myslap_damage", "5", "Default slap damage");
	AutoExecConfig(true, "plugin_myslap");
}
 
public Action:Command_MySlap(client, args)
{
	new String:arg1[32], String:arg2[32];
	new damage = GetConVarInt(sm_myslap_damage);
 
	/* Get the first argument */
	GetCmdArg(1, arg1, sizeof(arg1));
 
	/* If there are 2 or more arguments, and the second argument fetch 
	 * is successful, convert it to an integer.
	 */
	if (args >= 2 && GetCmdArg(2, arg2, sizeof(arg2)))
	{
		damage = StringToInt(arg2);
	}
 
	/**
	 * target_name - stores the noun identifying the target(s)
	 * target_list - array to store clients
	 * target_count - variable to store number of clients
	 * tn_is_ml - stores whether the noun must be translated
	 */
	new String:target_name[MAX_TARGET_LENGTH];
	new target_list[MAXPLAYERS], target_count;
	new bool:tn_is_ml;
 
	if ((target_count = ProcessTargetString(
			arg1,
			client,
			target_list,
			MAXPLAYERS,
			COMMAND_FILTER_ALIVE, /* Only allow alive players */
			target_name,
			sizeof(target_name),
			tn_is_ml)) <= 0)
	{
		/* This function replies to the admin with a failure message */
		ReplyToTargetError(client, target_count);
		return Plugin_Handled;
	}
 
	for (new i = 0; i < target_count; i++)
	{
		SlapPlayer(target_list[i], damage);
		LogAction(client, target_list[i], "\"%L\" slapped \"%L\" (damage %d)", client, target_list[i], damage);
	}
 
	if (tn_is_ml)
	{
		ShowActivity2(client, "[SM] ", "Slapped %t for %d damage!", target_name, damage);
	}
	else
	{
		ShowActivity2(client, "[SM] ", "Slapped %s for %d damage!", target_name, damage);
	}
 
	return Plugin_Handled;
}

Client and Entity Indexes

One major point of confusion with Half-Life 2 is the difference between the following things:

• Client index
• Entity index
• Userid

The first answer is that clients are entities. Thus, a client index and an entity index are the same thing. When a SourceMod function asks for an entity index, a client index can be specified. When a SourceMod function asks for a client index, usually it means only a client index can be specified.

A fast way to check if an entity index is a client is checking whether it's between 1 and GetMaxClients() (inclusive). If a server has N client slots maximum, then entities 1 through N are always reserved for clients. Note that 0 is a valid entity index; it is the world entity (worldspawn).

A userid, on the other hand, is completely different. The server maintains a global "connection count" number, and it starts at 1. Each time a client connects, the connection count is incremented, and the client receives that new number as their userid.

For example, the first client to connect has a userid of 2. If he exits and rejoins, his userid will be 3 (unless another client joins in-between). Since clients are disconnected on mapchange, their userids change as well. Userids are a handy way to check if a client's connection status has changed.

SourceMod provides two functions for userids: GetClientOfUserId() and GetClientUserId().

Events

Events are informational notification messages passed between objects in the server. Many are also passed from the server to the client. They are defined in .res files under the hl2/resource folder and resource folders of specific mods. For a basic listing, see Source Game Events.

It is important to note a few concepts about events:

• They are almost always informational. That is, blocking player_death will not stop a player from dying. It may block a HUD or console message or something else minor.
• They almost always use userids instead of client indexes.
• Just because it is in a resource file does not mean it is ever called, or works the way you expect it to. Mods are notorious at not properly documenting their event functionality.

An example of finding when a player dies:

public OnPluginStart()
{
   HookEvent("player_death", Event_PlayerDeath);
}
 
public Event_PlayerDeath(Handle:event, const String:name[], bool:dontBroadcast)
{
   new victim_id = GetEventInt(event, "userid");
   new attacker_id = GetEventInt(event, "attacker");
 
   new victim = GetClientOfUserId(victim_id);
   new attacker = GetClientOfUserId(attacker_id);
 
   /* CODE */
}

Callback Orders and Pairing

SourceMod has a number of builtin callbacks about the state of the server and plugin. Some of these are paired in special ways which is confusing to users.

Pairing

Pairing is SourceMod terminology. Examples of it are:

• OnMapEnd() cannot be called without an OnMapStart(), and if OnMapStart() is called, it cannot be called again without an OnMapEnd().
• OnClientConnected(N) for a given client N will only be called once, until an OnClientDisconnected(N) for the same client N is called (which is guaranteed to happen).

There is a formal definition of SourceMod's pairing. For two functions X and Y, both with input A, the following conditions hold:

• If X is invoked with input A, it cannot be invoked again with the same input unless Y is called with input A.
• If X is invoked with input A, it is guaranteed that Y will, at some point, be called with input A.
• Y cannot be invoked with any input A unless X was called first with input A.
• The relationship is described as, "X is paired with Y," and "Y is paired to X."

General Callbacks

These callbacks are listed in the order they are called, in the lifetime of a plugin and the server.

• AskPluginLoad() - Called once, immediately after the plugin is loaded from the disk.
• OnPluginStart() - Called once, after the plugin has been fully initialized and can proceed to load. Any run-time errors in this function will cause the plugin to fail to load. This is paired with OnPluginEnd().
• OnMapStart() - Called every time the map loads. If the plugin is loaded late, and the map has already started, this function is called anyway after load, in order to preserve pairing. This function is paired with OnMapEnd().
• OnConfigsExecuted() - Called once per map-change after servercfgfile (usually server.cfg), sourcemod.cfg, and all plugin config files have finished executing. If a plugin is loaded after this has happened, the callback is called anyway, in order to preserve pairing. This function is paired with OnMapEnd().
• At this point, most game callbacks can occur, such as events and callbacks involving clients (or other things, like OnGameFrame).
• OnMapEnd() - Called when the map is about to end. At this point, all clients are disconnected, but TIMER_NO_MAPCHANGE timers are not yet destroyed. This function is paired to OnMapStart().
• OnPluginEnd() - Called once, immediately before the plugin is unloaded. This function is paired to OnPluginStart().

Client Callbacks

These callbacks are listed in no specific order, however, their documentation holds for both fake and real clients.

• OnClientConnect() - Called when a player initiates a connection. This is paired with OnClientDisconnect() for successful connections only.
• OnClientAuthorized() - Called when a player gets a Steam ID. It is important to note that this may never be called. It may occur any time in between connect and disconnect. Do not rely on it unless you are writing something that needs Steam IDs, and even then you should use OnClientPostAdminCheck().
• OnClientPutInServer() - Signifies that the player is in-game and IsClientInGame() will return true.
• OnClientPostAdminCheck() - Called after the player is both authorized and in-game. That is, both OnClientAuthorized() and OnClientPutInServer() have been invoked. This is the best callback for checking administrative access after connect.
• OnClientDisconnect() - Called when a player's disconnection ends. This is paired to OnClientConnect().

Frequently Asked Questions

Are plugins reloaded every mapchange?

Plugins, by default, are not reloaded on mapchange unless their timestamp changes. This is a feature so plugin authors have more flexibility with the state of their plugins.

Do I need to call CloseHandle in OnPluginEnd?

No. SourceMod automatically closes your Handles when your plugin is unloaded, in order to prevent memory errors.

Do I need to #include every individual .inc?

No. #include <sourcemod> will give you 95% of the .incs. Similarly, #include <sdktools> includes everything starting with <sdktools>.

Why don't some events fire?

There is no guarantee that events will fire. The event listing is not a specification, it is a list of the events that a game is capable of firing. Whether the game actually fires them is up to Valve or the developer.

Do I need to CloseHandle timers?

No. In fact, doing so may cause errors. Timers naturally die on their own unless they are infinite timers, in which case you can use KillTimer() or die gracefully by returning Plugin_Stop in the callback.

Are clients disconnected on mapchange?

All clients are fully disconnected before the map changes. They are all reconnected after the next map starts.

Further Reading

For further reading, see the "Scripting" section at the SourceMod Documentation.

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