JUCE/modules/juce_audio_plugin_client/utility/juce_WindowsHooks.h

/*
  ==============================================================================

   This file is part of the JUCE library.
   Copyright (c) 2020 - Raw Material Software Limited

   JUCE is an open source library subject to commercial or open-source
   licensing.

   By using JUCE, you agree to the terms of both the JUCE 6 End-User License
   Agreement and JUCE Privacy Policy (both effective as of the 16th June 2020).

   End User License Agreement: www.juce.com/juce-6-licence
   Privacy Policy: www.juce.com/juce-privacy-policy

   Or: You may also use this code under the terms of the GPL v3 (see
   www.gnu.org/licenses).

   JUCE IS PROVIDED "AS IS" WITHOUT ANY WARRANTY, AND ALL WARRANTIES, WHETHER
   EXPRESSED OR IMPLIED, INCLUDING MERCHANTABILITY AND FITNESS FOR PURPOSE, ARE
   DISCLAIMED.

  ==============================================================================
*/

#if JUCE_WINDOWS

namespace juce
{

// This function is in juce_win32_Windowing.cpp
extern bool offerKeyMessageToJUCEWindow (MSG&);

static HHOOK mouseWheelHook = nullptr, keyboardHook = nullptr;
static int numHookUsers = 0;

struct WindowsHooks
{
    WindowsHooks()
    {
        if (numHookUsers++ == 0)
        {
            mouseWheelHook = SetWindowsHookEx (WH_MOUSE, mouseWheelHookCallback,
                                               (HINSTANCE) juce::Process::getCurrentModuleInstanceHandle(),
                                               GetCurrentThreadId());

            keyboardHook = SetWindowsHookEx (WH_GETMESSAGE, keyboardHookCallback,
                                             (HINSTANCE) juce::Process::getCurrentModuleInstanceHandle(),
                                             GetCurrentThreadId());
        }
    }

    ~WindowsHooks()
    {
        if (--numHookUsers == 0)
        {
            if (mouseWheelHook != nullptr)
            {
                UnhookWindowsHookEx (mouseWheelHook);
                mouseWheelHook = nullptr;
            }

            if (keyboardHook != nullptr)
            {
                UnhookWindowsHookEx (keyboardHook);
                keyboardHook = nullptr;
            }
        }
    }

    static LRESULT CALLBACK mouseWheelHookCallback (int nCode, WPARAM wParam, LPARAM lParam)
    {
        if (nCode >= 0 && wParam == WM_MOUSEWHEEL)
        {
            // using a local copy of this struct to support old mingw libraries
            struct MOUSEHOOKSTRUCTEX_  : public MOUSEHOOKSTRUCT  { DWORD mouseData; };

            auto& hs = *(MOUSEHOOKSTRUCTEX_*) lParam;

            if (auto* comp = Desktop::getInstance().findComponentAt ({ hs.pt.x, hs.pt.y }))
                if (comp->getWindowHandle() != nullptr)
                    return PostMessage ((HWND) comp->getWindowHandle(), WM_MOUSEWHEEL,
                                        hs.mouseData & 0xffff0000, (hs.pt.x & 0xffff) | (hs.pt.y << 16));
        }

        return CallNextHookEx (mouseWheelHook, nCode, wParam, lParam);
    }

    static LRESULT CALLBACK keyboardHookCallback (int nCode, WPARAM wParam, LPARAM lParam)
    {
        MSG& msg = *(MSG*) lParam;

        if (nCode == HC_ACTION && wParam == PM_REMOVE
             && offerKeyMessageToJUCEWindow (msg))
        {
            zerostruct (msg);
            msg.message = WM_USER;
            return 1;
        }

        return CallNextHookEx (keyboardHook, nCode, wParam, lParam);
    }
};

} // namespace juce

#endif