Silly Swift Screen Saver Sample Source

ScreenSaver.swift

import SwiftUI

struct Point {
    var position: CGPoint
    var velocity: CGPoint
}

struct ContentView: View {
    @State
    var lines: [[Point]] = []

    var body: some View {
        GeometryReader { geometry in
            TimelineView(.animation(paused: false)) { timeline in
                Canvas(rendersAsynchronously: true) { context, size in
                    for (index, line) in lines.enumerated() {
                        let path = Path { path in
                            path.move(to: line.first!.position)
                            for i in 1..<line.count {
                                let cp2 = line[i].position
                                let cp1 = line[(i + 1) % line.count].position
                                let end = line[(i + 2) % line.count].position
                                path.addCurve(to: end, control1: cp1, control2: cp2)
                            }
                        }
                        let color = Color(hue: 1 - Double(index) / Double(lines.count), saturation: 0.8, brightness: 0.8, opacity: 1 - Double(index) / Double(lines.count))
                        context.stroke(path, with: .color(color))
                    }
                }
                .onAppear {
                    let lineVelocity = CGPoint(x: .random(in: -1 ... 1), y: .random(in: -1 ... 1))
                    return lines = [
                        (0...10).map { _ in
                            let position = CGPoint(x: .random(in: 0..<geometry.size.width), y: .random(in: 0..<geometry.size.height))
                            let velocity = CGPoint(x: lineVelocity.x + .random(in: -0.5 ... 0.5), y: lineVelocity.y + .random(in: -0.5 ... 0.5))
                            return .init(position: position, velocity: velocity)
                        }
                    ]
                }
                .onChange(of: timeline.date) {
                    let old = lines
                    lines = lines.map { line in
                        line.map { point in
                            var point = point
                            point.position.x += point.velocity.x
                            point.position.y += point.velocity.y
                            if point.position.x < 0 {
                                point.position.x = 0 - point.position.x
                                point.velocity.x *= -1
                            }
                            else if point.position.x > geometry.size.width {
                                point.position.x = geometry.size.width - (geometry.size.width - geometry.size.width)
                                point.velocity.x *= -1
                            }
                            if point.position.y < 0 {
                                point.position.y = 0 - point.position.y
                                point.velocity.y *= -1
                            }
                            else if point.position.y > geometry.size.height {
                                point.position.y = geometry.size.height - (geometry.size.height - geometry.size.height)
                                point.velocity.y *= -1
                            }

                            return point
                        }
                    }
                    if lines.count < 50, let last = old.last {
                        lines.append(last)
                    }
                }
            }
        }
        .background(.black)
    }
}

#Preview {
    ContentView()
}