fadeCollectionView.swift

    func fadeHorizontalEdges(in collectionView: UICollectionView, modifier: CGFloat) {
        
        let visibleCells = collectionView.visibleCells
        guard !visibleCells.isEmpty else { return }
        
        let firstCell = visibleCells.first!
        let lastCell = visibleCells.last!
        
        visibleCells.forEach { $0.alpha = 1 }
        
        let cellWidth = firstCell.frame.width - 1 // 1 needs to change for the minimumline spacing
        let collectionViewLeftEdgePosition = collectionView.frame.origin.x
        let collectionViewRightEdgePosition = collectionView.frame.origin.x + collectionView.frame.size.width
        
        
        let indexPath = collectionView.indexPath(for: firstCell)!
        let theAttributes:UICollectionViewLayoutAttributes! = collectionView.layoutAttributesForItem(at: indexPath)
        let firstCellPositionInCollectionView: CGRect = collectionView.convert(theAttributes.frame, to: collectionView.superview)
        
        
        let indexPathLast = collectionView.indexPath(for: lastCell)!
        let theAttributeLast: UICollectionViewLayoutAttributes! = collectionView.layoutAttributesForItem(at: indexPathLast)
        let lastCellPositionInCollectionView: CGRect = collectionView.convert(theAttributeLast.frame, to: collectionView.superview)
        
        let firstCellPosition: CGFloat = collectionView.convert(firstCellPositionInCollectionView, to: collectionView.superview).origin.x
        let lastCellPosition: CGFloat = collectionView.convert(lastCellPositionInCollectionView, to: collectionView.superview).origin.x + cellWidth
        
        
        let firstCellOpacity = 1.0 - (((collectionViewLeftEdgePosition - firstCellPosition) / cellWidth) * modifier)
        let lastCellOpacity = 1.0 - (((lastCellPosition - collectionViewRightEdgePosition) / cellWidth) * modifier)
        
        firstCell.contentView.alpha = firstCellOpacity
        lastCell.contentView.alpha = lastCellOpacity

    }