layout method

@override List<Widget> layout(BuildContext context, { required double progress, required BoxConstraints constraints, required CarouselAlignment alignment, required Axis direction, required CarouselSizeConstraint sizeConstraint, required double progressedIndex, required int? itemCount, required CarouselItemBuilder itemBuilder, required bool wrap, required bool reverse, })

Layouts the carousel items.

• context is the build context.
• progress is the progress of the carousel.
• constraints is the constraints of the carousel.
• alignment is the alignment of the carousel.
• direction is the direction of the carousel.
• sizeConstraint is the size constraint of the carousel.
• progressedIndex is the progressed index of the carousel.
• itemCount is the item count of the carousel.
• itemBuilder is the item builder of the carousel.
• wrap is whether the carousel should wrap.
• reverse is whether the carousel should reverse.

Implementation

@override
List<Widget> layout(
  BuildContext context, {
  required double progress,
  required BoxConstraints constraints,
  required CarouselAlignment alignment,
  required Axis direction,
  required CarouselSizeConstraint sizeConstraint,
  required double progressedIndex,
  required int? itemCount,
  required CarouselItemBuilder itemBuilder,
  required bool wrap,
  required bool reverse,
}) {
  int additionalPreviousItems = 1;
  int additionalNextItems = 1;
  double originalSize = direction == Axis.horizontal
      ? constraints.maxWidth
      : constraints.maxHeight;
  double size;
  if (sizeConstraint is CarouselFixedConstraint) {
    size = sizeConstraint.size;
  } else if (sizeConstraint is CarouselFractionalConstraint) {
    size = originalSize * sizeConstraint.fraction;
  } else {
    size = originalSize;
  }
  double snapOffsetAlignment = (originalSize - size) * alignment.alignment;
  double gapBeforeItem = snapOffsetAlignment;
  double gapAfterItem = originalSize - size - gapBeforeItem;
  additionalPreviousItems += max(0, (gapBeforeItem / size).ceil());
  additionalNextItems += max(0, (gapAfterItem / size).ceil());
  List<_PlacedCarouselItem> items = [];
  // curving the index
  int start = progressedIndex.floor() - additionalPreviousItems;
  int end = progressedIndex.floor() + additionalNextItems;
  if (!wrap && itemCount != null) {
    start = start.clamp(0, itemCount - 1);
    end = end.clamp(0, itemCount - 1);
  }
  double currentIndex = progressedIndex + (gap / size) * progressedIndex;
  for (int i = start; i <= end; i++) {
    double index;
    if (itemCount != null) {
      index = wrapDouble(i.toDouble(), 0.0, itemCount.toDouble());
    } else {
      index = i.toDouble();
    }
    var itemIndex = reverse ? (-index).toInt() : index.toInt();
    final item = itemBuilder(context, itemIndex);
    double position = i.toDouble();
    // offset the gap
    items.add(_PlacedCarouselItem._(
      relativeIndex: i,
      child: item,
      position: position,
    ));
  }
  if (direction == Axis.horizontal) {
    return [
      for (var item in items)
        Positioned(
            left: snapOffsetAlignment +
                (item.position - currentIndex) * size +
                (gap * item.relativeIndex),
            width: size,
            height: constraints.maxHeight,
            child: item.child),
    ];
  } else {
    return [
      for (var item in items)
        Positioned(
            top: snapOffsetAlignment +
                (item.position - currentIndex) * size +
                (gap * item.relativeIndex),
            width: constraints.maxWidth,
            height: size,
            child: item.child),
    ];
  }
}