QQuickWidget: grabToImage: item's window is not visible - qt

Question

I'm having a problem when I try to use Item::grabToImage() qml method.
No matter which item I point to, it always says the following error:
grabToImage: item's window is not visible
I tried using the root/toplevel Item named rect too, but it didnt work.
My goal: I want to capture a rectangle sized image with the map tile and polygon draw on it
Below there's a minimal reproducible example
import QtQml 2.2
import QtLocation 5.9
import QtPositioning 5.9
import QtQuick 2.0
import QtQuick.Controls 2.4
Item {
id: rect
width: 1024
height: 768
visible: true
Plugin {
id: mapPlugin
name: "osm"
}
Map {
id: map
enabled: true
visible: true
parent: rect
gesture.enabled: true
anchors.fill: parent
plugin: mapPlugin
zoomLevel: 14
activeMapType: supportedMapTypes[3]
}
Item {
anchors.bottom: parent.bottom
anchors.left: parent.left
anchors.right: parent.right
anchors.margins: 10
height: 40
Button {
id: saveToDisk
text: qsTr("Pick")
onClicked: {
map.grabToImage(function (result) {
console.log('saving to disk..')
result.saveToFile("pick.png")
})
}
}
}
}
#include <QApplication>
#include <QQmlApplicationEngine>
#include <QtQuickWidgets/QQuickWidget>
int main(int argc, char *argv[])
{
QCoreApplication::setAttribute(Qt::AA_EnableHighDpiScaling);
QApplication app(argc, argv);
QQuickWidget *q = new QQuickWidget;
q->setResizeMode(QQuickWidget::SizeRootObjectToView);
q->setSource(QUrl("main.qml"));
q->show();
return app.exec();
}

Answer 1

The strategy of QQuickWidget for painting is to create an off-screen QQuickWindow that renders the QML from where a screenshot is taken and drawn onto the widget. The above limits the use of grabToImage() since this method requires that the QQuickWindow of the items be visible.
The solution is to use QQuickView + QWidget::createWindowContainer():
#include <QApplication>
#include <QWidget>
#include <QQuickView>
int main(int argc, char *argv[])
{
QCoreApplication::setAttribute(Qt::AA_EnableHighDpiScaling);
QApplication app(argc, argv);
QQuickView *q = new QQuickView;
q->setResizeMode(QQuickView::SizeRootObjectToView);
q->setSource(QUrl("main.qml"));
QWidget * container = QWidget::createWindowContainer(q);
container->show();
return app.exec();
}