Record a mouse movement
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An immediate solution that comes into mind is to push points into a QPolygon in the mouseMoveEvent(). You can then use containsPoint() or get the boundingRect() to determine which object has been selected.
QRubberBand might be another alternative if you are not bound to the circling gesture.
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I am not quite sure if this only works with touch screens or if they will be recognised from mouse movement as well but if so you should have a look at "QGesture":http://qt-project.org/doc/qt-4.8/qgesture.html
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You can have a look on "this":http://qt-project.org/forums/viewthread/18613/ thread.
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QpanGestureˊs delta property maybe helpful."Click here":http://qt-project.org/doc/qt-5/qpangesture.html