private var layoutCircleFrame = CGRect.zero
private let layoutInsets = UIEdgeInsets(top: 8, left: 8, bottom: 8, right: 8)
private let itemSize = CGSize(width: 100, height: 100)
private var itemLayoutAttributes = [UICollectionViewLayoutAttributes]()

override func prepare() {
    super.prepare()
    guard let collectionView = collectionView else { return }
    itemLayoutAttributes.removeAll()
    layoutCircleFrame = CGRect(origin: .zero, size: collectionViewContentSize)
        .inset(by: layoutInsets)
        .insetBy(dx: itemSize.width / 2.0, dy: itemSize.height / 2.0)
        .offsetBy(dx: collectionView.contentOffset.x, dy: collectionView.contentOffset.y)
        .insetBy(dx: -collectionView.contentOffset.x, dy: -collectionView.contentOffset.y)

    for section in 0..<collectionView.numberOfSections {
        switch section {
        case 0:
            let itemCount = collectionView.numberOfItems(inSection: section)
            itemLayoutAttributes = (0..<itemCount).map({ (index) -> UICollectionViewLayoutAttributes in
                let angleStep: CGFloat = 2.0 * CGFloat.pi / CGFloat(itemCount)
                var position = layoutCircleFrame.center
                position.x += layoutCircleFrame.size.innerRadius * cos(angleStep * CGFloat(index))
                position.y += layoutCircleFrame.size.innerRadius * sin(angleStep * CGFloat(index))
                let indexPath = IndexPath(item: index, section: section)
                let attributes = UICollectionViewLayoutAttributes(forCellWith: indexPath)
                attributes.frame = CGRect(center: position, size: itemSize)
                return attributes
            })
        default:
            fatalError("Unhandled section \(section).")
        }
    }
}