Shader fun

ContentView.swift

import SwiftUI

struct ContentView: View {
    @State private var start = Date.now
    
    var body: some View {
        VStack {
            TimelineView(.animation) { timeline in
                let time = start.distance(to: timeline.date)
                Rectangle()
                    .frame(width: 300, height: 500)
                    .visualEffect { content, proxy in
                        content
                            .colorEffect(
                                ShaderLibrary.colorEffect(
                                    .float2(proxy.size),
                                    .float(time)
                                )
                            )
                    }
                    .colorEffect(ShaderLibrary.colorEffect())
                    .clipShape(RoundedRectangle(cornerRadius: 20))
            }
        }
        .padding()
        .frame(maxWidth: .infinity, maxHeight: .infinity)
        .background(.gray)
    }
}

Shader.metal

#include <metal_stdlib>
using namespace metal;

[[ stitchable ]] half4 colorEffect(float2 position, half4 color, float2 size, float time) {
    float2 uv = (position / size) * 2 - 1;
    half3 luma = half3(0.0);
    for (int i = 0; i < 3; i++) {
        float wave = cos(uv.x * 3.0 + time * 2.0) * sin(time * 3 + i * 2.0) * 5;
        luma[i] = abs(1 / (50 * uv.y + 10 + wave)) + abs(1 / (50 * uv.y - 10 - wave));
    }
    
    return half4(luma * smoothstep(0, 1, (1 - abs(uv.x))) * smoothstep(0, 1, (1 - abs(uv.y))), 1.0);
}