getScrollToTrack method
Implementation
double getScrollToTrack(ScrollMetrics metrics) {
final double scrollableExtent =
metrics.maxScrollExtent - metrics.minScrollExtent;
final double fractionPast = (scrollableExtent > 0)
? clampDouble(
(metrics.pixels - metrics.minScrollExtent) / scrollableExtent,
0.0,
1.0)
: 0;
return (_isReversed ? 1 - fractionPast : fractionPast) *
(_traversableTrackExtent - _thumbExtent);
}