ConfettiView.swift

import UIKit
import QuartzCore

class ConfettiView: UIView {
    
    public var colors: [UIColor]!
    public var intensity: Float!
    private(set) var active: Bool!
    
    override public class var layerClass: Swift.AnyClass {
        return CAEmitterLayer.self
    }
    
    required public init?(coder aDecoder: NSCoder) {
        super.init(coder: aDecoder)
        setupEmitter()
    }
    
    init() {
        super.init(frame: .zero)
        setupEmitter()
    }
    
    override func didMoveToSuperview() {
        super.didMoveToSuperview()
        
        guard let superview = superview else {
            return
        }
        
        NSLayoutConstraint.activate([
            topAnchor.constraint(equalTo: superview.topAnchor),
            bottomAnchor.constraint(equalTo: superview.bottomAnchor),
            leadingAnchor.constraint(equalTo: superview.leadingAnchor),
            trailingAnchor.constraint(equalTo: superview.trailingAnchor)
            ])

        layoutIfNeeded()
    }
    
    override func layoutSubviews() {
        super.layoutSubviews()
        guard let emitter = self.layer as? CAEmitterLayer else { return }
        
        emitter.emitterPosition = CGPoint(x: frame.size.width / 2.0, y: -64)
        emitter.emitterSize = CGSize(width: frame.size.width, height: 1)
    }
    
    func setupEmitter() {
        translatesAutoresizingMaskIntoConstraints = false
        
        colors = [UIColor(red:0.93, green:0.30, blue:0.24, alpha:1.00),
                  UIColor(red:0.95, green:0.60, blue:0.22, alpha:1.00),
                  UIColor(red:0.97, green:0.80, blue:0.27, alpha:1.00),
                  UIColor(red:0.47, green:0.84, blue:0.45, alpha:1.00),
                  UIColor(red:0.46, green:0.78, blue:0.96, alpha:1.00),
                  UIColor(red:0.17, green:0.49, blue:0.96, alpha:1.00),
                  UIColor(red:0.33, green:0.36, blue:0.81, alpha:1.00),
                  UIColor(red:0.93, green:0.27, blue:0.35, alpha:1.00)]
        intensity = 0.5
        active = false
        layer.masksToBounds = true
    }
    
    public func startConfetti() {
        guard let emitter = self.layer as? CAEmitterLayer else { return }
        
        emitter.emitterShape = CAEmitterLayerEmitterShape.line
        
        var cells = [CAEmitterCell]()
        for color in colors {
            cells.append(confettiWithColor(color: color, image: #imageLiteral(resourceName: "circle_cut")))
            cells.append(confettiWithColor(color: color, image: #imageLiteral(resourceName: "circle")))
            cells.append(confettiWithColor(color: color, image: #imageLiteral(resourceName: "line")))
            cells.append(confettiWithColor(color: color, image: #imageLiteral(resourceName: "triangle")))
        }
        
        emitter.emitterCells = cells
        
        active = true

    }
    
    public func stopConfetti() {
        guard let emitter = self.layer as? CAEmitterLayer else { return }
        emitter.birthRate = 0
        active = false
    }
    
    private func confettiWithColor(color: UIColor, image: UIImage) -> CAEmitterCell {
        let confetti = CAEmitterCell()
        confetti.birthRate = 2 * intensity
        confetti.lifetime = 14.0 * intensity
        confetti.lifetimeRange = 0
        confetti.color = color.cgColor
        confetti.velocity = CGFloat(350.0 * intensity)
        confetti.velocityRange = CGFloat(80.0 * intensity)
        confetti.emissionLongitude = CGFloat(Double.pi)
        confetti.emissionRange = CGFloat(Double.pi / 2)
        confetti.spin = CGFloat(3.5 * intensity)
        confetti.spinRange = CGFloat(4.0 * intensity)
        confetti.scaleRange = CGFloat(0.5 * intensity)
        confetti.scaleSpeed = CGFloat(-0.1 * intensity)
        confetti.contents = image.cgImage
        return confetti
    }
}