SwiftUI CRT effect using metal shaders.

ContentView.swift

import SwiftUI

struct ContentView: View {
    @State private var startDate = Date()
    
    var body: some View {
        VStack {
            GeometryReader { geo in
                ZStack {
                    TimelineView(.animation) { _ in
                        Image("someImage")
                            .resizable()
                            .scaledToFill()
                            .blur(radius: 1.2)
                            .layerEffect(
                                ShaderLibrary.crtEffect(
                                    .float(-startDate.timeIntervalSinceNow),
                                    .float2(geo.size)
                                ),
                                maxSampleOffset: .zero
                            )
                            .opacity(0.4)
                    }
                }
                .overlay(
                    Text("Some content")
                        .fontWidth(.expanded)
                        .fontWeight(.heavy)
                        .minimumScaleFactor(0.5)
                        .foregroundStyle(.white)
                        .frame(maxWidth: .infinity, maxHeight: .infinity, alignment: .leading)
                        .padding(24)
                        .layerEffect(
                            ShaderLibrary.crtEffect(
                                .float(-startDate.timeIntervalSinceNow),
                                .float2(geo.size)
                            ),
                            maxSampleOffset: .zero
                        )
                )
            }
            .aspectRatio(1, contentMode: .fit)

            Spacer()
        }
        .background(
            RadialGradient(stops: [
                .init(color: .white.opacity(0.2), location: 0),
                .init(color: .black, location: 1)
            ], center: .center, startRadius: 10, endRadius: 1000)
        )
    }
}

CRTEffect.metal

#include <metal_stdlib>
#include <SwiftUI/SwiftUI.h>
using namespace metal;

float2 distort(float2 uv, float strength) {
    float2 dist = 0.5 - uv;
    uv.x = (uv.x - dist.y * dist.y * dist.x * strength);
    uv.y = (uv.y - dist.x * dist.x * dist.y * strength);
    return uv;
}

[[stitchable]]
half4 crtEffect(float2 position, SwiftUI::Layer layer, float time, float2 size) {
    float2 uv = position / size;

    uv = distort(uv, 0.3);
    
    // render color
    half4 col;
    col.r = layer.sample(float2(uv.x, uv.y) * size).r;
    col.g = layer.sample(float2(uv.x, uv.y) * size).g;
    col.b = layer.sample(float2(uv.x, uv.y) * size).b;
    col.a = layer.sample(float2(uv.x, uv.y) * size).a;
    
    // brighten image
    col *= half4(0.95, 1.05, 0.95, 1);
    col *= 2.8;

    // add scan lines
    float scans = clamp(0.35 + 0.35 * sin(3.5 * time + uv.y * size.y * 1.5), 0.0, 1.0);
    float s = pow(scans, 1.7);
    float sn = 0.4 + 0.7 * s;
    col = col * half4(sn, sn, sn, 1);

    // normalise color
    col *= 1.0 + 0.01 * sin(110.0 * time);
    float c = clamp((fmod(position.x, 2.0) - 1.0) * 2.0, 0.0, 1.0);
    col *= 1.0 - 0.65 * half4(c, c, c, 1);

    return col;
}