geode/loader/launcher/windows/proxyLoader.cpp

#include <Windows.h>
#include <string>

struct XINPUT_STATE;
struct XINPUT_CAPABILITIES;

constexpr static auto MAX_PATH_CHARS = 32768u;

static HMODULE getXInput() {
    static auto xinput = []() -> HMODULE {
        std::wstring path(MAX_PATH_CHARS, L'\0');
        auto size = GetSystemDirectoryW(const_cast<wchar_t*>(path.data()), path.size());
        if (size) {
            path.resize(size);
            return LoadLibraryW((path + L"\\XInput1_4.dll").c_str());
        }
        return NULL;
    }();

    return xinput;
}

static FARPROC getFP(const std::string& sym) {
    if (auto xinput = getXInput())
        return GetProcAddress(xinput, sym.c_str());

    return NULL;
}

#pragma comment(linker, "/export:XInputGetState,@2")
extern "C" DWORD XInputGetState(DWORD dwUserIndex, XINPUT_STATE *pState) {
    static auto fp = getFP("XInputGetState");
    if (fp) {
        using FPType = decltype(&XInputGetState);
        return reinterpret_cast<FPType>(fp)(dwUserIndex, pState);
    }

    return ERROR_DEVICE_NOT_CONNECTED;
}

#pragma comment(linker, "/export:XInputGetCapabilities,@4")
extern "C" DWORD XInputGetCapabilities(DWORD dwUserIndex, DWORD dwFlags, XINPUT_CAPABILITIES *pCapabilities) {
    static auto fp = getFP("XInputGetCapabilities");
    if (fp) {
        using FPType = decltype(&XInputGetCapabilities);
        return reinterpret_cast<FPType>(fp)(dwUserIndex, dwFlags, pCapabilities);
    }

    return ERROR_DEVICE_NOT_CONNECTED;
}

static std::wstring getErrorString() {
    return L"Could not load Geode. Error code: " + std::to_wstring(GetLastError());
}

BOOL WINAPI DllMain(HINSTANCE module, DWORD reason, LPVOID _) {
    if (reason == DLL_PROCESS_ATTACH) {
        DisableThreadLibraryCalls(module);

        // This is UB.
        if (LoadLibraryW(L"Geode.dll") == NULL)
            MessageBoxW(NULL, getErrorString().c_str(), L"Load failed" , MB_OK | MB_ICONWARNING);
    }

    return TRUE;
}