CustomLayout for CollectionViewLayout

CustomLayout.swift

class CustomLayout : UICollectionViewFlowLayout {
    
    
    required init?(coder aDecoder: NSCoder) {
        super.init(coder: aDecoder)
        self.itemSize = CGSize(width: itemWidth, height: itemWidth)
        self.scrollDirection = .horizontal
        self.minimumLineSpacing = 0
        
    }
    
    override func layoutAttributesForElements(in rect: CGRect) -> [UICollectionViewLayoutAttributes]? {
        
        let attributes = super.layoutAttributesForElements(in: rect)!
        let offsetX = self.collectionView!.contentOffset.x

        for anAttribute in attributes {
           
            let x = anAttribute.frame.origin.x - offsetX + halfItemWidth
            var factor = (1 - abs(x - self.collectionView!.frame.size.width/2)/self.collectionView!.frame.size.width)
            factor = pow(factor,2)
            anAttribute.alpha = factor
            
            let isLeft : CGFloat = (x - self.collectionView!.frame.size.width/2 ) > 0 ? -1 : 1
            let newLayerX = anAttribute.frame.size.width * ( 1 - factor ) / 2
            
            let zoom = CATransform3DMakeScale(factor, factor, 1)
            let offset = CATransform3DMakeTranslation(newLayerX * isLeft , 0, 0)
            let transform = CATransform3DConcat(zoom, offset)
            anAttribute.transform3D = transform
        }
        return attributes
        
    }
    
    
    
    
    override func shouldInvalidateLayout(forBoundsChange newBounds: CGRect) -> Bool {
        return true
    }
}