Metamod:Source Development

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This article is an introduction to coding for Metamod:Source. The main article of importance is SourceHook Development. Additional information can be found in the sample and stub plugins found in the Metamod:Source source code distribution.

If you find this article to be a tough read, you may want to skip over to the Sample Plugins article. See also setting up a Metamod:Source Environment. Note that Metamod:Source is a C++ platform, and you should have an intermediate knowledge of C++ (or, at the least, a strong will to research what's in the SDK).

Differences from Valve Plugins

A Valve Server Plugin has more out-of-box callbacks than a Metamod:Source plugin, but:

  • A Valve Server Plugin cannot opt-out of those callbacks. They must be implemented, even if as empty functions.
  • A Valve Server Plugin cannot hook or override any function not explicitly marked as one of its callbacks. It can do so by using low-level hacks, or by embedding SourceHook, but this sets up a conflict where plugins are vying to alter and override the same memory addresses.

Thus, Metamod:Source has two goals:

  • Resolve the hooking conflicts by creating a centralized, run-time hooking system.
  • Create a standardized, easy, and flexible API to abstract the process of hooking functions.

As an example of this, a Valve Server Plugin has about 13 callbacks, 3 of which can be overridden. A Metamod:Source plugin can safely hook any virtual function in the SDK, and override/supersede each of them as it pleases.

While a stub Metamod:Source plugin may look bare, it is easy to re-implement the functionality provided by IServerPluginCallbacks, and this is done so in the Sample Plugins.

Plugin API

Metamod:Source has two separate APIs:

  • 1.4 API, contained in core-legacy. This is the API you should use if you're building a plugin to run on the following Source engines:
    • Original (The Ship)
    • Episode 1 (Older third party mods).
  • 1.6 API, contained in core. This is the API you should use if you're building against the following Source engines:
    • Orange Box (Garry's Mod, Newer third party mods)
    • Orange Box Valve (Team Fortress, Day of Defeat, CS:S, HL2:DM)
    • Left 4 Dead
    • Left 4 Dead 2
    • Alien Swarm

It is important to get this right. The two APIs are not compatible, and if you wish to write a plugin that work across all engines, you must take special care in your plugin as a few API calls were renamed along the way.

More information is available in the article MM:S API Differences.

Starting a plugin

See Metamod:Source Environment to set up your build environment.

In order to write a plugin, you must implement the ISmmPlugin interface, similar to IServerPluginCallbacks. An example of implementing this can be seen in the stub_mm sample plugin.

Once you've implemented the interface, you must also have a global singleton of your plugin available. There are a few macros to assist you in properly exposing the interface as a DLL and setting up the API states.

  • PLUGIN_GLOBALVARS() - Place in header. Declares the global variables that some API calls require (such as g_SHPtr and g_PLAPI).
  • PLUGIN_EXPOSE(class, singleton) - Place in .cpp file. Declares the external CreateInterface function which exposes the API.
  • PLUGIN_SAVEVARS() - Use first thing in ISmmPlugin::Load(), saves the global variables sent from SourceMM.

Full documentation of each callback is available in the ISmmPlugin.h header file.


Using SourceHook is fully covered in the SourceHook Development article.

Various Macros

  • META_CONPRINT(const char *msg)
  • META_CONPRINTF(const char *fmt, ...)
    • These two functions are equivalent to ConMsg().
  • META_LOG(g_PLAPI, const char *msg, ...)
    • Logs a message through IVEngineServer::LogPrint(). A newline is automatically added, and msg is formatted as a sprintf() style string. Logging is done by the game server and can be enabled by adding log on to server.cfg or typing it in the console. The log files are found in the logs directory of the particular MOD you are running.
    • Registers a ConCommandBase pointer through Metamod:Source.
    • Unregisters a ConCommandBase pointer.

Metamod Events

The Metamod Events System is based on IMetamodListener. By implementing the IMetamodListener class and using g_SMAPI->AddListener, you can watch for certain, low-traffic events. These events are split into three categories:

  • Plugin Events let you listen for plugin pauses and unloads. This is important if you're relying on information from another plugin, as you can handle cases where a live plugin has become invalid.
  • Game Events are simple events that Metamod:Source is already hooking and makes available. These are LevelShutdown and LevelInit right now.
  • Query Events occur when a factory is used. The four main factories (Engine, GameDLL, FileSystem, and Physics) are all overridable. You should simply return a non-NULL result to override, and fill the return code with IFACE_OK if available. There is no way to handle the case of two plugins overriding right now. The final factory is the Metamod Factory, which is the factory that Metamod:Source adds to the runtime space for plugins. By default, it only contains the interfaces for the PluginManager and SourceHook. Plugins can use this to add new interfaces. Other plugins request these interfaces through g_SMAPI->MetaFactory().

Global Variables

These global variables are saved by PLUGIN_EXPOSE and PLUGIN_SAVEVARS. They are declared with PLUGIN_GLOBALVARS.

  • g_PLAPI
    • ISmmPlugin * pointer to your global class singleton.
  • g_PLID
    • The internal PluginId of your plugin.
  • g_SHPtr
    • The SourceHook::ISourceHook * pointer to SourceHook's interface.
  • g_SMAPI
    • The ISmmAPI * pointer to Metamod:Source's interface.

Interface Searching

ISmmAPI::VInterfaceMatch() can be used for searching for an interface.. This simplified version corrects the design flaw in InterfaceSearch() whereby passing an unmodified INTERFACEVERSION string would only search interfaces later than or equal to that version. For example, INTERFACEVERSION_SERVERGAMEDLL being "ServerGameDLL005" would not find a GameDLL using ServerGameDLL004.

VInterfaceMatch() removes the "max" parameter from InterfaceSearch() and adds an optional "chop" parameter, which specifices whether or not the interface should be searched from the beginning (default) or from the current version.

VSP Interface Hooking

Metamod:Source can provide a "virtual" Valve Server Plugin plugin interface. This is useful for providing an IServerPluginCallbacks pointer to certain routines, or hooking functions it has.

Example: (Note that GetVSPInfo is for Metamod:Source 1.6+)

SH_DECL_HOOK2(IServerPluginCallbacks, NetworkIDValidated, SH_NOATTRIB, 0, PLUGIN_RESULT, const char *, const char *);
IServerPluginCallbacks *vsp_iface = NULL;
bool Plugin::Load(PluginId id, ISmmAPI *ismm, char *error, size_t maxlen, bool late)
    if ((vsp_iface = ismm->GetVSPInfo(NULL)) == NULL)
      ismm->AddListener(this, this);
void Plugin::OnVSPListening(IServerPluginCallbacks *iface)
    SH_ADD_HOOK_MEMFUNC(IServerPluginCallbacks, NetworkIDValidated, iface, &g_Plugin, &Plugin::NetworkIDValidated, false);
    vsp_iface = iface;
PLUGIN_RESULT Plugin::NetworkIDValidated(const char *pszUserName, const char *pszNetworkID)
    META_CONPRINTF("%s has been validated with Network ID %s\n", pszUserName, pszNetworkID);

User Message Enumeration

API functions have also been added for the purpose of enumerating user messages. These serve to replace IServerGameDLL::GetUserMessageInfo() which can crash the server upon passing an invalid message index. The new functions include:

  • GetUserMessageCount()
  • FindUserMessage()
  • GetUserMessage()

Here is a quick example of how to use them:

// Get index of 'SayText' message
int msgSayText = g_SMAPI->FindUserMessage("SayText");
// Get number of user messages in GameDLL
int count = g_SMAPI->GetUserMessageCount();
const char *name;
int size;
// Print list of user message names and sizes
for (int i = 0; i < count; i++)
    name = g_SMAPI->GetUserMessage(i, &size);
    META_CONPRINTF("Message %d: (name \"%s\") (size %d)\n", i, name, size);



See Sample Plugins and Metamod:Source Environment for getting sample Makefiles and setting up your build environment.

There are a few GCC flags that you should not remove, or if you're writing a new Makefile, you should consider using:

  • -Wall and -Werror - These help ensure a minimal amount of accidental coding mistakes. Unless you absolutely refuse to fix warnings, it is a good idea to make sure your code compiles flawlessly. Note that Valve does not build with these options, and many mistakes are masked in the SDK because of it. If you use Valve's SDK instead of our fixed copy, you will not be able to use -Werror.
  • -Wno-non-virtual-dtor - This is kind of a useless warning from GCC (not all classes need destructors).
  • -fno-exceptions - You should not use exceptions because this creates a libstdc++ dependency.
  • -fno-strict-aliasing - By default, GCC does not allow certain type casts which were perfectly legal in previous versions, and are perfectly legal in almost every other C/C++ compiler. These type casts are prevalent and without this option, GCC will generate incorrect code.

There are a few flags you should generally not add, ever:

  • -lstdc++ (same as using g++) - Even if you use the exact same compiler build as Valve, linking against the libstdc++ will be painful. Not all Linux distributions use the same version, and in general ABI compatibility on this library is frequently broken. You will find that users report load failures or even crashes, and the problem may be very difficult to trace. As such, you should avoid using exceptions or any part of the Standard Template Library (STL). Valve provides many abstractions that should suffice, and SourceHook provides some as well.
    • Note: Statically linking to libstdc++ is not an option. It will cause many problems.
  • -m64 - Don't try to build 64-bit software off the SDK. Valve doesn't even have a 64-bit port of the server yet.


For Visual Studio, there are a few project options which are required. All of these settings are in the "Project Properties" dialog (under the Project menu).

  • Configuration Properties -> General
    • "Character Set" should be "Use Multi-Byte Character Set," not Unicode.
  • Configuration Properties -> C/C++
    • General
      • "Detect 64-bit Portability Issues" should be "No," unless you like (mostly) pointless warnings.
    • Preprocessor
      • "Processor Defines" -- You should add _CRT_SECURE_NO_DEPRECATE and _CRT_NONSTDC_NO_DEPRECATE to the semicolon-delimited list. Microsoft decided to "deprecate" a bunch of Standard C API calls, apparently not noticing that people like to use them. Use these macros to stop the compiler from throwing a hissy-fit.
    • Code Generation
      • "Runtime" Library should be "Multi-threaded Debug" or "Multi-threaded" depending on the configuration. You should not use the DLL version, as this will link against MSVCRT80[D], which is part of the redistributable framework (and not packaged with Windows).

For sample linking and include folders, you should see Sample Plugins (Metamod:Source). Sample Visual Studio project files are provided with everything you'd need.