Custom UIScrollView with fade effect

FadeScrollView.swift

//
//  FadeScrollView.swift
//
//  Created by Jesus Martin Alonso on 24/06/2019.
//  Inspired by https://gist.github.com/luismachado/1423427b4c60021d71a8772e4dabc140
//  Copyright © 2017 Luis Machado. All rights reserved.

import UIKit

/// UIScrollView subclass that fades the top/bottom edges depending of the scroll position
/// How to use it:
/// - Adds FadeScrollView to your view
/// - Set your view as UIScrollViewDelegate
/// - In scrollViewDidScroll delegate method call [updateGradient]
class FadeScrollView: UIScrollView {
    
    let fadePoints: Float = 64.0
    let gradientLayer = CAGradientLayer()
    let transparentColor = UIColor.clear.cgColor
    let opaqueColor = UIColor.black.cgColor
    
    
    var topFadingOpacity: CGColor {
        
        let scrollOffset = contentOffset.y
        let alpha:CGFloat = ( scrollOffset <= 0) ? 1 : 0
        let color = UIColor(white: 0, alpha: alpha)
        return color.cgColor
    }
    
    var bottomFadingOpacity: CGColor {
        let scrollViewHeight = frame.size.height
        let scrollContentSizeHeight = contentSize.height
        let scrollOffset = contentOffset.y
        
        let alpha:CGFloat = (scrollOffset + scrollViewHeight >= scrollContentSizeHeight) ? 1 : 0
        let color = UIColor(white: 0, alpha: alpha)
        return color.cgColor
    }
    
    override func layoutSubviews() {
        super.layoutSubviews()
        
        let maskLayer = CALayer()
        maskLayer.frame = self.bounds
        
        let gradientLocation = fadePoints / Float(contentSize.height)
        gradientLayer.frame = CGRect(x: self.bounds.origin.x, y: 0, width: self.bounds.size.width, height: self.bounds.size.height)
        gradientLayer.colors = [topFadingOpacity, opaqueColor, opaqueColor, bottomFadingOpacity]
        gradientLayer.locations = [0, NSNumber(value: gradientLocation), NSNumber(value: 1 - gradientLocation), 1]
        maskLayer.addSublayer(gradientLayer)
        
        self.layer.mask = maskLayer
    }

    /// Update gradient depending on content offset of the scrollview
    /// Call this function in [scrollViewDidScroll] of UIScrollViewDelegate
    func updateGradient() {
        gradientLayer.colors = [topFadingOpacity, opaqueColor, opaqueColor, bottomFadingOpacity]
    }

}