Masks any cells behind the section header of a .Plain UITableView

MyTableViewController.swift

override func scrollViewDidScroll(scrollView: UIScrollView) {
    super.scrollViewDidScroll(scrollView)

    for cell in self.tableView.visibleCells {
        let hiddenFrameHeight = scrollView.contentOffset.y + self.tableView(tableView, heightForHeaderInSection: 0) - cell.frame.origin.y

        if hiddenFrameHeight >= 0 || hiddenFrameHeight <= cell.frame.size.height {
            self.maskCell(cell, fromTopWithMargin: hiddenFrameHeight)
        }
    }
}

func maskCell(cell: UITableViewCell, fromTopWithMargin margin: CGFloat) {
    cell.layer.mask = visibilityMaskForCell(cell, withLocation: margin/cell.frame.size.height)
    cell.layer.masksToBounds = true
}

func visibilityMaskForCell(cell: UITableViewCell, withLocation location: CGFloat) -> CAGradientLayer {
    let mask = CAGradientLayer()
    mask.frame = cell.bounds
    mask.colors = [RGB(255, a: 0.0).CGColor, RGB(255, a: 1.0).CGColor]
    mask.locations = [NSNumber(float: Float(location)), NSNumber(float: Float(location))]
    return mask
}