detecting-games.md

Detecting games

Since your DLL is loaded on start-up and not when the game you want to mod starts, you need a way to detect when the user launches a specific game. What I and most people do is creating a constantly running loop that will check the title ID of the game currently running to see if it's equal to the title ID of the game we want to mod.

First, we need a few things that will help us detect what game is currently running:

// Enum for game title IDs
typedef enum _TitleId
{
    Title_Dashboard = 0xFFFE07D1,
    Title_MW2 = 0x41560817,
} TitleId;

// Imports from the Xbox libraries
extern "C"
{
    uint32_t XamGetCurrentTitleId();

    uint32_t ExCreateThread(
        HANDLE *pHandle,
        uint32_t stackSize,
        uint32_t *pThreadId,
        void *pApiThreadStartup,
        PTHREAD_START_ROUTINE pStartAddress,
        void *pParameter,
        uint32_t creationFlags
    );
}

We are going to create a function that runs forever and checks if the title ID of the currently running game has changed since the last loop iteration:

bool g_Running = true;

void MonitorTitleId()
{
    uint32_t currentTitleId = 0;

    while (g_Running)
    {
        uint32_t newTitleId = XamGetCurrentTitleId();

        if (newTitleId == currentTitleId)
            continue;

        currentTitleId = newTitleId;

        switch (newTitleId)
        {
        case Title_Dashboard:
            XNotifyQueueUI(0, 0, XNOTIFY_SYSTEM, L"Dashboard", nullptr);
            break;
        case Title_MW2:
            XNotifyQueueUI(0, 0, XNOTIFY_SYSTEM, L"MW2", nullptr);
            break;
        }
    }
}

We can't just call MonitorTitleId when DllMain receives the DLL_PROCESS_ATTACH reason because this will heavily slow down the main thread. That's why we need to run MonitorTitleId in a separate thread. By looking at the signature of ExCreateThread, we see that the function pointer needs to be of type PTHREAD_START_ROUTINE, which is DWORD (WINAPI *PTHREAD_START_ROUTINE)(LPVOID lpThreadParameter);. Which means we need the signature of our MonitorTitleId function to become:

uint32_t MonitorTitleId(void *pThreadParameter)
{
    uint32_t currentTitleId = 0;

    while (g_Running)
    {
        uint32_t newTitleId = XamGetCurrentTitleId();

        if (newTitleId == currentTitleId)
            continue;

        currentTitleId = newTitleId;

        switch (newTitleId)
        {
        case Title_Dashboard:
            XNotifyQueueUI(0, 0, XNOTIFY_SYSTEM, L"Dashboard", nullptr);
            break;
        case Title_MW2:
            XNotifyQueueUI(0, 0, XNOTIFY_SYSTEM, L"MW2", nullptr);
            break;
        }
    }

    return 0;
}

Now, to run MonitorTitleId in a separate thread, simply call ExCreateThread and pass a pointer to MonitorTitleId to it in your main function like so:

int DllMain(HANDLE hModule, DWORD reason, void *pReserved)
{
    switch (reason)
    {
    case DLL_PROCESS_ATTACH:
        // Run MonitorTitleId in separate thread
        ExCreateThread(nullptr, 0, nullptr, nullptr, reinterpret_cast<PTHREAD_START_ROUTINE>(MonitorTitleId), nullptr, 2);
        break;
    case DLL_PROCESS_DETACH:
        g_Running = false;
        // We give the system some time to clean up the thread before exiting
        Sleep(250);
        break;
    }

    return TRUE;
}

You might be wondering why we are using ExCreateThread instead of CreateThread, which is a function provided by Windows in a header file. The reason is that, in order to keep your thread running even when you switch games, you need to pass 2 in the creationFlags argument. Passing 2 to the dwCreationFlags argument of CreateThread does not keep your thread running when you switch games.

Note: The code example shown in this page is available here.

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