[Spinner] a simple loading spinner for SwiftUI

Spinner.swift

struct Spinner: View {

    var outerColor = Color.blue
    var innerColor = Color.red

    @State private var isAnimating = false

    var body: some View {

        GeometryReader { proxy in
            ZStack {
                self.trimmedCircle(color: self.outerColor, clockwise: true, scale: 1.0, proxy: proxy)
                self.trimmedCircle(color: self.innerColor, clockwise: false, scale: 0.75, proxy: proxy)
            }
        }
        .frame(idealWidth: 100, idealHeight: 100)
        .onAppear { self.isAnimating = true }

    }

    private func trimmedCircle(color: Color, clockwise: Bool, scale: CGFloat, proxy: GeometryProxy) -> some View {

        let start: Double = clockwise ? 360 : 0
        let end: Double = clockwise ? 0 : 360
        let borderWidth = min(proxy.size.width, proxy.size.height) / 14

        return Circle()
            .inset(by: borderWidth / 2)
            .scale(scale)
            .trim(from: 0.1, to: 0.9)
            .stroke(color, lineWidth: borderWidth)
            .rotationEffect(.degrees(isAnimating ? start : end))
            .animation(repeatingAnimation)

    }

    private let repeatingAnimation = Animation
        .linear(duration: 1.0)
        .repeatForever(autoreverses: false)
}
```

Usage.swift

struct ContentView: View {
    var body: some View {
        Spinner().fixedSize()
    }
}