Qt5. Embed QWidget object in QML

You can embed QWidget to QML by using QQuickPaintedItem class: http://doc.qt.io/qt-5/qquickpainteditem.html

Qt5 has an example: http://doc.qt.io/qt-5/qtquick-customitems-painteditem-example.html

You should implement an inherent of QQuickPaintedItem with private widget attribute, that you want to embed. Provide paint method, that just render the QtWidget and provide mouse and other event transmitting from inherit of QQuickPaintedItem to embed QtWidget.

There's also QSG (Qt scene graph API), but my experience with that thing wasn't smooth. I believe the clue in multithreading (performing rendering in the different thread (not the Qt GUI thread one, however on Windows that's not true and all is done in main GUI thread).

I've implemented embedding of QCustomPlot, here's link: github.com/mosolovsa/qmlplot

Qt Quick 2 uses a scene graph for efficient rendering on the GPU. Unfortunately this makes it impossible to embed classic widgets into the scene. The old approach to embed such widgets with the help of QGraphicsProxyWidget works only with Qt Quick 1, because internally it uses a QGraphicsView for all the heavy lifting and QGraphicsProxyWidget is meant to be used with it.

As of now there are no plans to enable embedding classic QWidgets into the scene graph I know of. I think this is rather unlikely to change, because the concepts of QPainter, the painting framework used for the classic widgets, and the new scene graph doesn't play well with each other.

There some efforts to develop new widgets sets specifically tailored for the needs of QML, but none of them are as powerful and mature as the classic widgets. The most prominent ones are the QML Quick Controls, bundled with Qt since version 5.1.

If you really depend on QWT my advice would be to stick with Qt Quick 1.1 for now. It's still bundled with Qt 5, probably for cases like yours. That way you won't take advantage of the new scene graph, though.

What could be done is to render the widget to an image and upload as texture.For interaction someone needs to forward events like mouseClick or keyPressed from the sceneGraph, translate to widget coordinates, pass on, render and upload texture again. Just an idea :)