シェーダー関数で螺旋

SpiralShader.metal

#include <metal_stdlib>
using namespace metal;

[[ stitchable ]] half4 spiral(
    float2 position,
    half4 color,
    float4 box,
    float scale
) {
    position = position - box.zw/2;
    position = position / (10 * scale);

    float r = length(position);
    float t = atan2(position.y, position.x);
    float offset = int(10 * t) % 2 ? 0 : M_PI_F;
    half3 value = int((sin((r + t + offset)) + 1)) % 2;
    return half4(value * color.xyz, 1.0);
}

SpiralShader.swift

import SwiftUI

struct ContentView: View {
    @State private var start = Date()

    var body: some View {
        TimelineView(.animation) { context in
            let time = context.date
                .timeIntervalSince(start)
            let scale = 0.3 + 6 * (sin(time) + 1) / 2
            Rectangle()
                .colorEffect(shader(scale: scale))
                .foregroundStyle(.white)
                .ignoresSafeArea()
        }
    }

    func shader(scale: Double) -> Shader {
        ShaderLibrary
            .spiral(.boundingRect, .float(scale))
    }
}

#Preview {
    ContentView()
}