setPostPixels method

double setPostPixels(double newPixels, double clipedOverscroll, double systemOverscroll)

Implementation

double setPostPixels(
  double newPixels,
  double clipedOverscroll,
  double systemOverscroll,
) {
  final double overscroll =
      overscrollOf(newPixels, minScrollExtent, maxScrollExtent);
  final double oldPixels = pixels;
  final double rawPixels = newPixels - overscroll;
  final double overDelta = systemOverscroll - clipedOverscroll;
  final isBouncing = overDelta.abs() > precisionErrorTolerance;

  // Notifies that the scroll offset has changed.
  void onNotify() {
    if (pixels != oldPixels) {
      notifyListeners();
      didUpdateScrollPositionBy(pixels - oldPixels);
    }
  }

  // First, apply clipped a given new pixels.
  correctPixels(rawPixels);

  final double available = isBouncing ? -overDelta : -clipedOverscroll;
  final double consumed =
      (isBouncing ? overDelta != 0.0 : clipedOverscroll != 0.0)
          ? _postScroll(available)
          : 0.0;

  clipedOverscroll += consumed;

  /// It is also considered nested scrolling when the remaining
  /// scroll amount is fully consumed in the post phase.
  if ((consumed - available).abs() < precisionErrorTolerance) {
    isNestedScrolling = true;
  }

  // When overscrolling is clipped or bouncing.
  if (overDelta.abs() < precisionErrorTolerance) {
    if (clipedOverscroll.abs() > precisionErrorTolerance) {
      didOverscrollBy(clipedOverscroll);
      onNotify();
      return clipedOverscroll;
    }
  } else {
    final double bouncingDelta = overDelta + consumed;
    if (bouncingDelta.abs() > precisionErrorTolerance) {
      final double consumed = _bouncing(bouncingDelta);
      final double restDelta = bouncingDelta - consumed;

      lentPixels += consumed;

      if (restDelta.abs() > precisionErrorTolerance) {
        correctBy(restDelta);
      }

      didOverscroll();
    }
  }

  onNotify();

  return 0.0;
}