SwiftUI confetti effect.

ConfettiView.swift

//
//  ConfettiView.swift
//  Glosify
//
//  Created by Mikael Deurell on 2023-07-21.
//

import Foundation
import SwiftUI

struct ConfettiView: View {
    
    var body: some View {
        GeometryReader { geometry in
            ConfettiUIViewRepresentable(rect: geometry.frame(in: .local))
        }
    }
}

struct ConfettiUIViewRepresentable: UIViewRepresentable {
    let rect: CGRect
    
    func makeUIView(context: Context) -> ConfettiUIView {
        let view = ConfettiUIView(frame: .zero)
        view.isUserInteractionEnabled = false
        return view
    }
    
    func updateUIView(_ uiView: ConfettiUIView, context: Context) {
        uiView.frame = rect
    }
}

class ConfettiUIView: UIView {
    
    private var particleEmitter: CAEmitterLayer?
    
    override func layoutSubviews() {
        super.layoutSubviews()
        
        if particleEmitter == nil {
            DispatchQueue.main.asyncAfter(deadline: .now() + 0.2) { [weak self] in
                self?.setupEmitter()
            }
        }
    }
    
    private func setupEmitter() {
        let particleEmitter = CAEmitterLayer()
        particleEmitter.emitterPosition = CGPoint(x: frame.size.width / 2.0, y: frame.size.height / 4.0)
        particleEmitter.emitterShape = .point
        particleEmitter.emitterCells = generateEmitterCells()
        
        layer.addSublayer(particleEmitter)
        self.particleEmitter = particleEmitter
        
        // After the explosion, stop emitting particles.
        DispatchQueue.main.asyncAfter(deadline: .now() + 0.1) {
            particleEmitter.birthRate = 0
        }
    }
    
    private func generateEmitterCells() -> [CAEmitterCell] {
        var cells:[CAEmitterCell] = [CAEmitterCell]()
        
        for _ in 0..<6 {
            let cell = CAEmitterCell()
            
            cell.birthRate = 16.0
            cell.lifetime = 16.0
            cell.velocity = CGFloat(350.0)
            cell.velocityRange = CGFloat(100.0)
            cell.emissionLongitude = CGFloat(0)
            cell.emissionRange = CGFloat(2 * Double.pi)
            cell.spin = 3.5
            cell.spinRange = 1.0
            cell.yAcceleration = 256
            cell.scale = 1.0
            cell.scaleRange = 0.1
            cell.color = randomColor().cgColor
            cell.contents = UIImage(named: "confetti")?.cgImage
            cells.append(cell)
        }
        
        return cells
    }
    
    private func randomColor() -> UIColor {
        let colors: [UIColor] = [.red, .blue, .green, .yellow]
        return colors[Int.random(in: 0..<colors.count)]
    }
}