[SOLVED] How to create QML Image Element from a QImage Object (C++)?

fcrochik

How can I convert a QImage into a QML Element? I can't use the Image QML Element because the source property requires an URL and I only have the actual QImage in memory.

The only way I could come up with so far is to extend the QDeclarativeItem and render the image. It is far from ideal because then I can't make use of the capabilities of the QML Image element.

Thanks,
Felipe

mbrasser

Hi,

You can use "QDeclarativeImageProvider":http://doc.qt.nokia.com/4.7/qdeclarativeimageprovider.html to load a QImage into an Image element.

Regards,
Michael

fcrochik

Michael,
Thanks, it worked. It is not as straight forward as I would expect for something that looks like a very common scenario (e.g. a model view with QImage returned for the DecorationRole) but will do.
Felipe

mbrasser

Yes, it's less than ideal. Originally we allowed setting a QPixmap directly on the Image element, but there were memory management issues with that approach. QDeclarativeImageProvider was the solution we came up with to those issues for 4.7 -- it may be that a better solution is possible in future releases.

Please let us know if you have any suggestions.

fcrochik

Michael,
Unfortunately I don't know the details about how Qt manage memory so can't even guess the best way to implement but I can think of two user case scenarios:

When you have a "legacy" model with images, you would want to initialize the Image Element with the QImage doing something hopefully as simple as this:

@Image {
sourceX: modelData.decorationRole;
}
@

On a little more sophisticated user case you could have a c++ class like:
@class A : public QObject {
Q_OBJECT
Q_PROPERTY(QImage image READ image NOTIFY imageChanged)
...
}@

set the context property:

@ui->view->rootContext()->setContextProperty("myA", new A());@

and then you could bind the QImage on QML:

@Image {
sourceWithBinding: myA.image;
}@

so the QML Image element could be notified of changes on the property (for example as result of the C++ app generating a new graph as result of the user input)

fdelgado

It's maybe too late but I wrote an article about this and it can maybe help someone.

"http://www.fdelgado.fr/QtQuick/2011/08/30/72/":http://www.fdelgado.fr/QtQuick/2011/08/30/72/

It's in french but easily too translate with tools, and the code can be usefull.