PowerToys/src/runner/lowlevel_keyboard_event.cpp

#include "pch.h"
#include "lowlevel_keyboard_event.h"
#include "powertoys_events.h"

namespace
{
    HHOOK hook_handle = nullptr;
    HHOOK hook_handle_copy = nullptr; // make sure we do use nullptr in CallNextHookEx call
    LRESULT CALLBACK hook_proc(int nCode, WPARAM wParam, LPARAM lParam)
    {
        LowlevelKeyboardEvent event;
        if (nCode == HC_ACTION)
        {
            event.lParam = reinterpret_cast<KBDLLHOOKSTRUCT*>(lParam);
            event.wParam = wParam;
            if (powertoys_events().signal_event(ll_keyboard, reinterpret_cast<intptr_t>(&event)) != 0)
            {
                return 1;
            }
        }
        return CallNextHookEx(hook_handle_copy, nCode, wParam, lParam);
    }
}

// Prevent system-wide input lagging while paused in the debugger
//#define DISABLE_LOWLEVEL_KBHOOK_WHEN_DEBUGGED

void start_lowlevel_keyboard_hook()
{
#if defined(_DEBUG) && defined(DISABLE_LOWLEVEL_KBHOOK_WHEN_DEBUGGED)
    if (IsDebuggerPresent())
    {
        return;
    }
#endif

    if (!hook_handle)
    {
        hook_handle = SetWindowsHookEx(WH_KEYBOARD_LL, hook_proc, GetModuleHandle(NULL), NULL);
        hook_handle_copy = hook_handle;
        if (!hook_handle)
        {
            throw std::runtime_error("Cannot install keyboard listener");
        }
    }
}

void stop_lowlevel_keyboard_hook()
{
    if (hook_handle)
    {
        UnhookWindowsHookEx(hook_handle);
        hook_handle = nullptr;
    }
}