Custom plot selection

[Uwe]

You also need to implement:

QRegion XQwtPicker::rubberBandMask() const override;

QRegion XQwtPicker::rubberBandMask() const override;

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The smaller the region the better - but beside of environments like remote X11 you probably won't notice much difference when returning the complete canvas rectangle.
In your case the optimal solution would be the rectangle spanned by the w points. See https://qwt.sourceforge.io/class_qwt...04f237062b75fc

Have a look at the implementation of QwtPicker::rubberBandMask - it will help with how to find the rectangle.

HTH,
Uwe