Haris Haris - 24 days ago 7
C++ Question

Save QML image inside c++

I am trying to display network image using qml and then save this image using c++ code,

Here is the qml code,

import QtQuick 2.3
import QtQuick.Window 2.2
import com.login 1.0
Window {
visible: true
width : 500
height: 500

Login{id: login}

MouseArea {
anchors.fill: parent
onClicked: {
// Qt.quit();
login.save(image);
}
}



Image {
id: image
source: "http://www.test.com/webp/gallery/4.jpg"
}


}


And inside my login class saving image like,

void Login::save( QQuickItem *item)
{
qDebug()<<"width: "<<item->width();
qDebug()<<"height: "<<item->height();

QQuickWindow *window = item->window();
QImage image = window->grabWindow();

QPixmap pix = QPixmap::fromImage(image);
pix.save("C:/Users/haris/Desktop/output.png");
}


I am getting the correct width and height of the image inside c++ class, but the problem is I cannot find a way to save the image item from
QQuickItem
.

Right now I am saving the image by grabing the window, which actually not giving the actual image size on output file, instead giving output file with current qml window size.

Basically I am following the code here saving QML image but it seems
QDeclarativeItem
is deprecated in Qt5, so I choose
QQuickItem
where as there is no paint option in
QQuickItem
.

Answer

Fortunately QQuickItem has a convenient grabToImage function which does that.

void Login::save( QQuickItem *item)
{
    auto grabResult = item->grabToImage();

    connect(grabResult.data(), &QQuickItemGrabResult::ready, [=]() {
        grabResult->saveToFile("C:/Users/haris/Desktop/output.png");
        //grabResult->image() gives the QImage associated if you want to use it directly in the program
    });
}

Alternate solution without using lambdas:

void Login::save( QQuickItem *item)
{
    auto grabResult = item->grabToImage();

    /* Need to store grabResult somewhere persistent to avoid the SharedPointer mechanism from deleting it */
    ...

    connect(grabResult.data(), SIGNAL(ready()), this, SLOT(onAsynchroneousImageLoaded()));
}

void Login::onAsynchroneousImageLoaded() {
    auto grabResult = qobject_cast<QQuickItemGrabResult*>(sender());
    if (grabResult) {
        grabResult->saveToFile("C:/Users/haris/Desktop/output.png");
    } else {
        //something went wrong
    }
});