FireworkView.swift

import UIKit

class FireworkView: UIView {

    private let emitterLayer = CAEmitterLayer()
    private let emitterCell = CAEmitterCell()
    private let trailCell = CAEmitterCell()
    private let fireworkCell = CAEmitterCell()

    // MARK: - Initializers
    override init(frame frameRect: CGRect) {
        super.init(frame: frameRect)
        commonInit()
    }

    required init?(coder decoder: NSCoder) {
        super.init(coder: decoder)
        commonInit()
    }

    private func commonInit() {
        setupEmitterLayer()
        setupEmitterCell()
        setupTrailCell()
        setupFireworkCell()

        emitterCell.emitterCells = [trailCell, fireworkCell]
        emitterLayer.emitterCells = [emitterCell]
        layer.addSublayer(emitterLayer)
    }

    private func setupEmitterLayer() {
        emitterLayer.emitterSize = bounds.size
        emitterLayer.emitterPosition = CGPoint(x: bounds.width / 2, y: bounds.height)
        emitterLayer.renderMode = CAEmitterLayerRenderMode.additive
    }

    private func setupEmitterCell() {
        emitterCell.color = UIColor(red: 0.5, green: 0.5, blue: 0.5, alpha: 0.5).cgColor
        emitterCell.redRange = 0.9
        emitterCell.greenRange = 0.9
        emitterCell.blueRange = 0.9
        emitterCell.lifetime = 2.5
        emitterCell.birthRate = 5
        emitterCell.velocity = 300
        emitterCell.velocityRange = 100
        emitterCell.emissionRange = CGFloat.pi / 8
        emitterCell.emissionLongitude = CGFloat.pi + CGFloat.pi / 2
        emitterCell.yAcceleration = -100
    }

    private func setupTrailCell() {
        trailCell.contents = UIImage(named: "particle")?.cgImage
        trailCell.lifetime = 0.5
        trailCell.birthRate = 30
        trailCell.velocity = 80
        trailCell.scale = 0.4
        trailCell.alphaSpeed = -0.7
        trailCell.scaleSpeed = -0.1
        trailCell.scaleRange = 0.1
        trailCell.beginTime = 0.01
        trailCell.duration = 1.7
        trailCell.emissionRange = CGFloat.pi / 8
        trailCell.emissionLongitude = CGFloat.pi * 2
        trailCell.yAcceleration = 350
    }

    private func setupFireworkCell() {
        fireworkCell.contents = UIImage(named: "particle")?.cgImage
        fireworkCell.lifetime = 100
        fireworkCell.birthRate = 10000
        fireworkCell.velocity = 130
        fireworkCell.scale = 0.6
        fireworkCell.spin = 2
        fireworkCell.alphaSpeed = -0.2
        fireworkCell.scaleSpeed = -0.1
        fireworkCell.beginTime = 1.2
        fireworkCell.duration = 0.1
        fireworkCell.emissionRange = CGFloat.pi * 2
        fireworkCell.yAcceleration = 80
    }
}