func scrollViewWillEndDragging(_ scrollView: UIScrollView, withVelocity velocity: CGPoint, targetContentOffset: UnsafeMutablePointer<CGPoint>) {

    let cellWidth = CGFloat(155)
    let cellSpacing = CGFloat(6)

    let leftOffset = scrollView.contentOffset.x - scrollView.contentInset.left
    let cellWidth = cellWidth + cellSpacing
    let rawMovement = leftOffset / cellWidth

    // round down, but if scrolling right, round up
    var proposedPage = Int(rawMovement)
    if velocity.x == 0 {
       proposedPage = Int(round(rawMovement))
    } else if velocity.x > 0 {
       proposedPage += 1
    }

    let newOffset = cellWidth * CGFloat(proposedPage)
    targetContentOffset.pointee = CGPoint(x: newOffset, y: targetContentOffset.pointee.y)
}