在SwiftUI中，如何确定circle ()的大小来绘制与该圆成比例的覆盖图？

import SwiftUI

struct ContentView: View {
    var body: some View {
        GeometryReader { geometry in
            ZStack {
                Circle()
                    .fill(Color.blue)
                    .frame(width: geometry.size.width * 0.5, height: geometry.size.width * 0.5)
                
                Image("coverImage")
                    .resizable()
                    .aspectRatio(contentMode: .fit)
                    .frame(width: geometry.size.width * 0.5, height: geometry.size.width * 0.5)
            }
        }
    }
}

struct ContentView_Previews: PreviewProvider {
    static var previews: some View {
        ContentView()
    }
}