main.cpp

LRESULT CALLBACK WndProc(HWND hWnd, UINT message, WPARAM wParam, LPARAM lParam)
{
    switch (message)
    {
        case WM_NCHITTEST: {
            return 0;
        }
        default:
        {
            return DefWindowProc(hWnd, message, wParam, lParam);
        }
    }
}

class MyEventFilter : public QAbstractNativeEventFilter
{
public:
    MyEventFilter(){}
    bool nativeEventFilter(const QByteArray &eventType, void *message, long* res) override
    {
        if (eventType == "windows_generic_MSG") {
            res = (long*)WndProc(((MSG*)message)->hwnd, ((MSG*)message)->message, ((MSG*)message)->wParam, ((MSG*)message)->lParam);
        }
        return true;
    }
};

int main(int argc, char *argv[])
{
    QGuiApplication app(argc, argv);

    QQmlApplicationEngine engine;
    const QUrl url(QStringLiteral("qrc:/main.qml"));
    QObject::connect(&engine, &QQmlApplicationEngine::objectCreated,
                     &app, [url](QObject *obj, const QUrl &objUrl) {
        if (!obj && url == objUrl)
            QCoreApplication::exit(-1);
    }, Qt::QueuedConnection);
    engine.load(url);
    app.installNativeEventFilter(new MyEventFilter());
    return app.exec();
}