CustomCollectionViewLayout_Prepare_Item.swift

private func layoutItems(...) {

    ....

    let layoutAttributes = UICollectionViewLayoutAttributes(forCellWith: indexPath)
    layoutAttributes.frame = CGRect(
        x: offsetX,
        y: offsetY,
        width: itemWidth,
        height: itemHeight
    )
    allItemAttributes.append(contentsOf: itemsLayoutAttributes)
}