I want to grab screen of my QML application. But my root QML object is `ApplicationWindow`, so I can't use `QQuickView` to show it. Instead I have to use `QQmlApplicationEngine`.
I know how to take screenshot with `QQuickView` (`QQuickWindow::grabWindow`), but don't know how to take it with `QQmlApplicationEngine`.

My `main` file:

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

    ApplicationData appData;
    QQmlApplicationEngine engine;
    engine.load(QUrl("qrc:///main.qml"));
    return app.exec();
}

```

`main.qml` :

```
import QtQuick 2.1
import QtQuick.Controls 1.1
import QtQuick.Window 2.1

ApplicationWindow {
    id: mainWindow
    width: appData.screenWidth
    height: appData.screenHeight
    visible: true

    Rectangle {
        id: mainWindowBackground
        color: "red"
        anchors.fill: parent
    } 

    //...
}

```