directionStateForX function

DragDirectionState directionStateForX({ required double delta, required Rect currentRect, required Rect baseRect, required Rect displayRect, })

Four-value X-axis direction state: combines the motion direction (extending vs retracting, decided by delta's sign relative to boundForX) with whether the rect's relevant edge is past the display edge.

Implementation

DragDirectionState directionStateForX({
  required double delta,
  required Rect currentRect,
  required Rect baseRect,
  required Rect displayRect,
}) {
  final isRight = boundForX(delta: delta, currentRect: currentRect, baseRect: baseRect) == .right;
  // Past-display semantic depends on rect size: small rect ⇒ far edge off
  // display; zoomed rect ⇒ near edge past display edge (uncovers display).
  final pastDisplay = currentRect.width <= displayRect.width
      ? (isRight
          ? currentRect.right > displayRect.right
          : currentRect.left < displayRect.left)
      : (isRight
          ? currentRect.left > displayRect.left
          : currentRect.right < displayRect.right);
  final extending = isRight ? delta > 0 : delta < 0;
  if (extending) return pastDisplay ? .extendingPast : .extending;
  return pastDisplay ? .retractingPast : .retracting;
}