Final code for "Implementing the Apple Watch activity rings in SwiftUI - Part 1"

ActivityRing.swift

struct ActivityRing: View {
    var progress: Double
    var lineWidth: CGFloat
    var gradient: Gradient

    var body: some View {
        // Main ring
        Circle()
            .rotation(.degrees(-90))
            .trim(from: 0, to: CGFloat(progress))
            .stroke(
                AngularGradient(gradient: gradient,
                                center: .center,
                                startAngle: .degrees(-90),
                                endAngle: .degrees(progress * 360 - 90)),
                style: .init(lineWidth: lineWidth, lineCap: .round)
            )
            .overlay(
                GeometryReader { geometry in
                    // End round butt and shadow
                    Circle()
                        .fill(self.gradient.stops[1].color)
                        .frame(width: self.lineWidth, height: self.lineWidth)
                        .position(x: geometry.size.width / 2, y: geometry.size.height / 2)
                        .offset(x: min(geometry.size.width, geometry.size.height)/2)
                        .rotationEffect(.degrees(self.progress * 360 - 90))
                        .shadow(color: .black, radius: self.lineWidth/2, x: 0, y: 0)
                }
                .clipShape(
                    // Clip end round line cap and shadow to front
                    Circle()
                        .rotation(.degrees(-90 + self.progress * 360 - 0.5))
                        .trim(from: 0, to: 0.25)
                        .stroke(style: .init(lineWidth: self.lineWidth))
                )
            )
            .scaledToFit()
            .padding(lineWidth/2)
    }
}