[Gambas-user] Need a good idea - a slider with two handles

[Bruce]

A user had a good idea and wants to know if we can build a form with
sliders that control both the maxima and minima of various parameters.

I have attached a mocked up picture of the sort of thing that is
required for a "squeeze" filter i.e. a low bandpass combined with a high
band-limiter.  Similar things could be imagined for a "flange" type of
filter.

There are some controls in Gimp, for example (in second attachment) that
further show what is required.

I have made a couple of preliminary attempts to create a custom control
in Gambas3 to do this but I am not getting very far.  The problems are:
a) being able to detect which handle the user is trying to move and
b) stopping the min handle from exceeding the max handle and v.v. 

Has anyone attempted this type of control (successfully)?
Has anyone got any good ideas?

tia
Bruce

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