fluentColorRailAnchor function
The edge a rail's minimum value sits against.
The bottom when vertical — Fluent's vertical sliders put the smallest
value at the bottom, which upstream gets from writing-mode: vertical-lr
plus direction: rtl on the native input. Otherwise the reading-order start
edge, mirrored by textDirection.
The opposite edge is -fluentColorRailAnchor(...), so one call places a
gradient, a thumb and a pointer alike.
Implementation
Alignment fluentColorRailAnchor({
required bool vertical,
required TextDirection textDirection,
}) => vertical
? Alignment.bottomCenter
: (textDirection == TextDirection.rtl
? Alignment.centerRight
: Alignment.centerLeft);