linjam/JuceLibraryCode/modules/juce_events/native/juce_win32_HiddenMessageWindow.h

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

   This file is part of the JUCE library.
   Copyright (c) 2017 - ROLI Ltd.

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

   The code included in this file is provided under the terms of the ISC license
   http://www.isc.org/downloads/software-support-policy/isc-license. Permission
   To use, copy, modify, and/or distribute this software for any purpose with or
   without fee is hereby granted provided that the above copyright notice and
   this permission notice appear in all copies.

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

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

namespace juce
{

//==============================================================================
class HiddenMessageWindow
{
public:
    HiddenMessageWindow (const TCHAR* const messageWindowName, WNDPROC wndProc)
    {
        String className ("JUCE_");
        className << String::toHexString (Time::getHighResolutionTicks());

        HMODULE moduleHandle = (HMODULE) Process::getCurrentModuleInstanceHandle();

        WNDCLASSEX wc = { 0 };
        wc.cbSize         = sizeof (wc);
        wc.lpfnWndProc    = wndProc;
        wc.cbWndExtra     = 4;
        wc.hInstance      = moduleHandle;
        wc.lpszClassName  = className.toWideCharPointer();

        atom = RegisterClassEx (&wc);
        jassert (atom != 0);

        hwnd = CreateWindow (getClassNameFromAtom(), messageWindowName,
                             0, 0, 0, 0, 0, 0, 0, moduleHandle, 0);
        jassert (hwnd != 0);
    }

    ~HiddenMessageWindow()
    {
        DestroyWindow (hwnd);
        UnregisterClass (getClassNameFromAtom(), 0);
    }

    inline HWND getHWND() const noexcept     { return hwnd; }

private:
    ATOM atom;
    HWND hwnd;

    LPCTSTR getClassNameFromAtom() noexcept  { return (LPCTSTR) (pointer_sized_uint) atom; }
};

//==============================================================================
class JuceWindowIdentifier
{
public:
    static bool isJUCEWindow (HWND hwnd) noexcept
    {
        return GetWindowLongPtr (hwnd, GWLP_USERDATA) == getImprobableWindowNumber();
    }

    static void setAsJUCEWindow (HWND hwnd, bool isJuceWindow) noexcept
    {
        SetWindowLongPtr (hwnd, GWLP_USERDATA, isJuceWindow ? getImprobableWindowNumber() : 0);
    }

private:
    static LONG_PTR getImprobableWindowNumber() noexcept
    {
        static auto number = (LONG_PTR) Random().nextInt64();
        return number;
    }
};

//==============================================================================
class DeviceChangeDetector  : private Timer
{
public:
    DeviceChangeDetector (const wchar_t* const name)
        : messageWindow (name, (WNDPROC) deviceChangeEventCallback)
    {
        SetWindowLongPtr (messageWindow.getHWND(), GWLP_USERDATA, (LONG_PTR) this);
    }

    virtual ~DeviceChangeDetector() {}

    virtual void systemDeviceChanged() = 0;

    void triggerAsyncDeviceChangeCallback()
    {
        // We'll pause before sending a message, because on device removal, the OS hasn't always updated
        // its device lists correctly at this point. This also helps avoid repeated callbacks.
        startTimer (500);
    }

private:
    HiddenMessageWindow messageWindow;

    static LRESULT CALLBACK deviceChangeEventCallback (HWND h, const UINT message,
                                                       const WPARAM wParam, const LPARAM lParam)
    {
        if (message == WM_DEVICECHANGE
             && (wParam == 0x8000 /*DBT_DEVICEARRIVAL*/
                  || wParam == 0x8004 /*DBT_DEVICEREMOVECOMPLETE*/
                  || wParam == 0x0007 /*DBT_DEVNODES_CHANGED*/))
        {
            ((DeviceChangeDetector*) GetWindowLongPtr (h, GWLP_USERDATA))
                ->triggerAsyncDeviceChangeCallback();
        }

        return DefWindowProc (h, message, wParam, lParam);
    }

    void timerCallback() override
    {
        stopTimer();
        systemDeviceChanged();
    }
};

} // namespace juce