RaindropView

RaindropView.swift

class RaindropView: UIView {

    var images: [CGImage] {
        return [UIImage(named: "rain"),
                UIImage(named: "rain"),
                UIImage(named: "rain"),
                UIImage(named: "rain"),
                UIImage(named: "rain")].map({ $0?.cgImage }).compactMap({ $0 })
    }

    var birthRate: Float = 2.0 {
        didSet {
            confettiViewEmitterLayer.birthRate = birthRate
        }
    }

    private let confettiViewEmitterLayer = CAEmitterLayer()
    private let confettiViewEmitterCell = CAEmitterCell()

    override init(frame: CGRect) {
        super.init(frame: frame)
        setup()
    }

    required init?(coder aDecoder: NSCoder) {
        super.init(coder: aDecoder)
        setup()
    }

    func setup() {
        backgroundColor = UIColor.clear
        setupConfettiEmitterLayer()
        confettiViewEmitterLayer.birthRate = 0.0
        confettiViewEmitterLayer.emitterCells = generateConfettiEmitterCells()
        layer.addSublayer(confettiViewEmitterLayer)
    }

    func setupConfettiEmitterLayer() {
        confettiViewEmitterLayer.emitterSize = CGSize(width: bounds.width, height: 2)
        confettiViewEmitterLayer.emitterShape = CAEmitterLayerEmitterShape.line
        confettiViewEmitterLayer.emitterPosition = CGPoint(x: bounds.width / 2, y: 0)
    }

    func generateConfettiEmitterCells() -> [CAEmitterCell] {
        let velocities: [CGFloat] = [500, 550, 600, 650, 700]

        var cells = [CAEmitterCell]()
        for image in images {
            let cell = CAEmitterCell()
            cell.contents = image
            cell.birthRate = 5.0
            cell.lifetime = 30.0
            cell.lifetimeRange = 0
            cell.scale = 0.3
            cell.scaleRange = 0.35
            cell.velocity = velocities[Int.random(in: 0..<velocities.count)]
            cell.velocityRange = 0
            cell.emissionLongitude = CGFloat.pi - 0.05
            cells.append(cell)
        }

        return cells
    }
}

extension String {
    var cgImage: CGImage? {
        let size = CGSize(width: 40, height: 40)
        UIGraphicsBeginImageContextWithOptions(size, false, 0)
        UIColor.clear.set()
        let rect = CGRect(origin: .zero, size: size)
        UIRectFill(CGRect(origin: .zero, size: size))
        (self as AnyObject).draw(in: rect, withAttributes: [.font: UIFont.systemFont(ofSize: 40)])
        let image = UIGraphicsGetImageFromCurrentImageContext()
        UIGraphicsEndImageContext()
        return image?.cgImage
    }
}