Comment 6 for bug 1656225

some thoughts on the widget implementation:

1) traditional knob with free pointer position
* scale has either highlightable notches or separated arc segments for clear GUI feedback
= controller & GUI knobs are always in the same position

2) new knob widget that snaps to notches
* for clear GUI feedback it doesn't allow positions in between notches
= continuos controller knobs might not match the GUI knob position
* for use with mouse wheel, mouse drag or touch screen drag we should install a scroll distance that must be overcome to make a step with the knob, and reset accumulated scroll ticks after mouse/finger release when the next step wasn' reached

For both versions, both notches and arc segments could accept clicks for easy adjustment.