Circle SDF2

Shader.metal

#include <metal_stdlib>
using namespace metal;

float smoothMin(float x1, float x2, float k) {
    float h = clamp(0.5 - 0.5 * (x2 - x1) / k, 0.0, 1.0);
    return mix(x1, x2, h) - k * h * (1.0 - h);
}

float circleSDF(float2 point, float2 center, float radius) {
    return length(point - center) - radius;
}

namespace SDF {
    [[ stitchable ]] half4 main(float2 position, half4 color, float4 box, float sec, float k) {
        float2 pos = -1.0 + 2.0 * position / min(box.w, box.z);
        float tx = 0.5 * (1.0 + sin(2.0 * sec)) / 2.0;
        float ty = sin(sec);

        float sdf1 = circleSDF(pos, float2(tx, 1.0 + ty), k);
        float sdf2 = circleSDF(pos, float2(-tx, 1.0 - ty), k);
        float sdf3 = smoothMin(sdf1, sdf2, k);
        if (sdf3 < 0) {
            float value = 20 * abs(sdf3);
            if (abs(value - floor(value)) < 0.2) {
                return half4(1, 1, 1, 1);
            } else {
                return half4(0, 0.5, 1, 1);
            }
        }
        return half4(1, 1, 1, 1);
    }
}

ShaderView.swift

import SwiftUI

struct ShaderView: View {
    let name: String
    @State var k: Double = 0.36
    @State var time: Double = .pi

    var body: some View {
        ZStack {
            Rectangle()
                .colorEffect(shader)
            VStack {
                Button("Reset", action: reset)
                    .frame(maxWidth: .infinity, alignment: .leading)
                    .font(.title)
                    .fontWeight(.bold)
                Slider(value: $time, in: 0...(2.0 * .pi))
                Slider(value: $k, in: 0...0.72)
            }
            .frame(maxHeight: .infinity, alignment: .bottom)
            .padding()
        }
        .animation(.default, value: k)
        .animation(.default, value: time)
    }

    private var shader: Shader {
        let function = ShaderFunction(library: .default, name: name)
        return function(.boundingRect, .float(time), .float(k))
    }

    private func reset() {
        k = 0.36
        time = .pi
    }
}

#Preview("SDF") {
    ShaderView(name: "SDF::main")
}