evaluateMove method

Implementation

bool evaluateMove(
  double y,
  double x,
  GlassSheetState currentState,
  GlassSheetState maxState,
  double threshold, {
  required bool canScrollListUp,
  required bool hasScrollClients,
}) {
  if (phase == GesturePhase.contentDrag) return true;
  if (phase == GesturePhase.scrolling) return false;
  if (phase == GesturePhase.handleDrag) return true;

  final dy = (y - dragStartY).abs();
  final dx = (x - dragStartX).abs();

  // Decide the axis ONCE per touch, on the first movement past the
  // threshold, and hold that decision for the rest of the gesture.
  //
  // The comparison is still cumulative from the touch origin, but it is now
  // only ever read at the moment of decision, which fixes two things:
  //
  //  * A gesture that started horizontal stays horizontal. Previously the
  //    test was re-run on every move, so a sideways swipe would grab the
  //    sheet the instant total vertical travel happened to exceed total
  //    horizontal — and conversely, after a long sideways scroll the sheet
  //    could not be dragged at all without out-travelling that distance
  //    vertically, which on a wide swipe is most of the screen.
  //  * The reverse latch is gone. `contentDrag` was only ever set from a
  //    vertical-looking move and then never re-evaluated, so a horizontal
  //    swipe that began with a slight vertical wobble dragged the sheet for
  //    its whole duration.
  //
  // Below the threshold on both axes the gesture is still undecided; return
  // false and wait rather than guessing from a few pixels of noise.
  if (dy <= threshold && dx <= threshold) return false;

  if (dx >= dy) {
    // Horizontal. An inner scrollable owns this touch; the sheet stays out
    // of it until the finger lifts and `reset()` clears the phase.
    phase = GesturePhase.scrolling;
    return false;
  }

  if (dy > threshold) {
    // At the topmost detent the sheet can't expand further, so an inner
    // scroll view (if any) owns the gesture. maxState is `full` for a
    // normal sheet but `half` for a half-only sheet (enableFull: false),
    // which is why this compares against maxState rather than hardcoding
    // full — otherwise a half-only sheet would never scroll its content.
    if (currentState == maxState) {
      if ((y - dragStartY) < 0) {
        // Swiping UP
        if (hasScrollClients) {
          phase = GesturePhase.scrolling;
          return false;
        } else {
          phase = GesturePhase.contentDrag;
          isVerticalGesture = true;
          return true;
        }
      } else {
        // Swiping DOWN
        if (canScrollListUp) {
          phase = GesturePhase.scrolling;
          return false;
        } else {
          phase = GesturePhase.contentDrag;
          isVerticalGesture = true;
          return true;
        }
      }
    } else {
      phase = GesturePhase.contentDrag;
      isVerticalGesture = true;
      return true;
    }
  }
  return false;
}