boundForX function
Which X-axis bound the rect is currently sitting on. If centered at
base, delta's sign decides (positive → right).
Implementation
DragBound boundForX({
required double delta,
required Rect currentRect,
required Rect baseRect,
}) {
if (currentRect.center.dx > baseRect.center.dx) return .right;
if (currentRect.center.dx < baseRect.center.dx) return .left;
return delta >= 0 ? .right : .left;
}