Implement selection of multiple points on QwtPlotCurve

[Sergey <po...@il...>]

Hello readers!

For my qwt-based application I need to implement selection of points. I
would like to implement most common used way of selection.
1) single LMB (Left mouse button) click drops selection of all
previously selected points and selects nearest point (like in
event_filter example

2) Ctrl+LMB click adds nearest point of the currently selected curve to
the selection or removes selection of point was selected previously. If
no points were selected previously then it should act as LMB without
Ctrl

3) Shift+LMB click selects interval of points on the current selected
curve. If no current curve selected then act in 1)

Can anyone suggest best way to do it?
Now I think that I should implement my QwtPickerMachine subclass and
make signal-slot communications inside QwtPlot subclass that will
handle selections. Probably there's easier ways, I don't know.

-- 
Sergey Popov
B. Verkin Institute for Low Temperature Physics and Engineering
Kharkov, Ukraine