getTrackToScroll method
Convert between a thumb track position and the corresponding scroll position.
The thumbOffsetLocal
argument is a position in the thumb track.
Implementation
double getTrackToScroll(double thumbOffsetLocal) {
final double scrollableExtent =
_lastMetrics!.maxScrollExtent - _lastMetrics!.minScrollExtent;
final double thumbMovableExtent = _traversableTrackExtent - _thumbExtent;
return scrollableExtent * thumbOffsetLocal / thumbMovableExtent;
}