progress.swift

//

import SwiftUI

struct ContentView: View {
    @State var progress: Double = 0
    var body: some View {
        VStack {
            Slider(value: $progress, in: 0...1)
            Text("Hello, world")
                .foregroundStyle(.white)
                .padding()
                .frame(maxWidth: .infinity)
                .background(Color.black)
                .overlay {
                    GeometryReader { proxy in
                        Color.green
                            .overlay {
                                Text("Hello, world")
                                    .foregroundStyle(.black)
                            }
                            .frame(width: proxy.size.width)
                            .frame(width: proxy.size.width*progress, alignment: .leading)
                            .clipped()
                    }
                }
        }
    }
}

#Preview {
    ContentView()
}