A demo to show different blending modes using CGBlendMod

gistfile1.txt

//
//  A demo to show different blending modes using CGBlendMod
//

import UIKit

extension CGBlendMode {
    static func count() -> Int {
        return 16
    }
    
    func toString() -> String {
        switch self {
        case .normal:
            return "normal"
        case .multiply:
            return "multiply"
        case .screen:
            return "screen"
        case .overlay:
            return "overlay"
        case .darken:
            return "darken"
        case .lighten:
            return "lighten"
        case .colorDodge:
            return "colorDodge"
        case .colorBurn:
            return "colorBurn"
        case .softLight:
            return "softLight"
        case .hardLight:
            return "hardLight"
        case .difference:
            return "difference"
        case .exclusion:
            return "exclusion"
        case .hue:
            return "hue"
        case .saturation:
            return "saturation"
        case .color:
            return "color"
        case .luminosity:
            return "luminosity"
        default:
            return "Unknown"
        }
    }
}

class BlendView: UIView {
    
    var blendMode: CGBlendMode = .normal {
        didSet {
            setNeedsDisplay()
        }
    }
    
    override func draw(_ rect: CGRect) {
        
        guard let context = UIGraphicsGetCurrentContext() else {
            return
        }
        
        context.setBlendMode(self.blendMode)
        context.setLineWidth(1.0)
        context.setStrokeColor(UIColor.clear.cgColor)
        context.setFillColor(UIColor.lightGray.cgColor)
        
        // Background
        do {
            let path = UIBezierPath(rect: bounds).cgPath
            context.addPath(path)
            context.fillPath()
            context.strokePath()
        }
        context.setStrokeColor(UIColor.black.cgColor)
        context.setFillColor(UIColor.green.withAlphaComponent(0.2).cgColor)
        
        
        // Draw some colored rects
        do {
            let x: CGFloat = 0
            let y: CGFloat = 0
            let width: CGFloat = 200
            let height: CGFloat = 200
            let frame = CGRect(x: x, y: y, width: width, height: height)
            let path = UIBezierPath(rect: frame).cgPath
            context.addPath(path)
            context.fillPath()
            context.strokePath()
        }
        
        do {
            let x: CGFloat = 100
            let y: CGFloat = 100
            let width: CGFloat = 200
            let height: CGFloat = 200
            let frame = CGRect(x: x, y: y, width: width, height: height)
            let path = UIBezierPath(rect: frame).cgPath
            context.addPath(path)
            context.fillPath()
            context.strokePath()
        }
        
        // Change color and draw more rects
        context.setFillColor(UIColor.red.withAlphaComponent(0.2).cgColor)
        
        do {
            let x: CGFloat = 0
            let y: CGFloat = 150
            let width: CGFloat = 200
            let height: CGFloat = 200
            let frame = CGRect(x: x, y: y, width: width, height: height)
            let path = UIBezierPath(rect: frame).cgPath
            context.addPath(path)
            context.fillPath()
            context.strokePath()
        }
        
        do {
            let x: CGFloat = 0
            let y: CGFloat = 250
            let width: CGFloat = 200
            let height: CGFloat = 200
            let frame = CGRect(x: x, y: y, width: width, height: height)
            let path = UIBezierPath(rect: frame).cgPath
            context.addPath(path)
            context.fillPath()
            context.strokePath()
        }
    }
}


class ViewController: UIViewController {
    
    private var stackView: UIStackView!
    override func viewDidLoad() {
        super.viewDidLoad()
        setupStackView()
    }
    
    private func setupStackView() {
        let width: CGFloat = 128
        let height: CGFloat = view.bounds.height
        let x: CGFloat = view.bounds.width - width
        let y: CGFloat = 0
        let frame = CGRect(x: x, y: y, width: width, height: height)
        stackView = UIStackView(frame: frame)
        stackView.axis = .vertical
        stackView.distribution = .fillEqually
        view.addSubview(stackView)
        
        
        for i in 0..<CGBlendMode.count() {
            let blendMode = CGBlendMode(rawValue: Int32(i))
            let button = UIButton(type: .custom)
            button.tag = i
            button.setTitle(blendMode?.toString(), for: .normal)
            button.setTitleColor(UIColor.black, for: .normal)
            button.addTarget(self, action: #selector(blendFilterButtonTouchUpInside), for: .touchUpInside)
            stackView.addArrangedSubview(button)
        }
    }
    
    @objc private func blendFilterButtonTouchUpInside(sender: UIButton) {
        guard let blendView = self.view as? BlendView else {
            return
        }
        
        let tag = sender.tag
        guard let blendMode = CGBlendMode(rawValue: Int32(tag)) else {
            return
        }
        
        blendView.blendMode = blendMode
    }
}