Native source code for CodeSlicing episode on simple circular activity indicators

CircularActivityIndicatorDemoNative.swift

//
//  CircularActivityIndicatorDemoNative.swift
//
//  Permission is hereby granted, free of charge, to any person obtaining a copy
//  of this software and associated documentation files (the "Software"), to deal
//  in the Software without restriction, including without limitation the rights
//  to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies
//  of the Software, and to permit persons to whom the Software is furnished to do so,
//  subject to the following conditions:
//
//  THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED,
//  INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A
//  PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR
//  COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN
//  AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
//  WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
//
//  Copyright © 2021 Adam Fordyce. All rights reserved.
//

import SwiftUI

struct CircularActivityIndicatorDemoNative: View {
    var body: some View {
        GeometryReader { (geo: GeometryProxy) in
            let numSegments = 12
            
            let degreesPerSegment = 360 / Double(numSegments)
            ZStack {
                Color.clear
                ForEach(0..<numSegments) { index in
                    Capsule()
                        .frame(width: geo.size.width * 0.25, height: geo.size.height * 0.06)
                        .offset(x: geo.size.width * 0.37)
                        .rotationEffect(.degrees(degreesPerSegment * Double(index)))
                }
            }
//            .background(
            .mask(
                CircularActivityMask()
                    .scaleEffect(1.2)
                    .blur(radius: geo.size.width * 0.05)
            )
        }
    }
}

private extension Color {
    
    static let clearRed = Color.red.opacity(0)
}

private struct CircularActivityMask: View {
    
    @State private var animating = false

    var body: some View {
        
        AngularGradient(gradient: Gradient(stops: [
            Gradient.Stop(color: .clearRed, location: 0.4),
            Gradient.Stop(color: .red, location: 1)
        ]), center: .center, angle: animating ? .degrees(270) : .degrees(-90))
        
        .onAppear {
            withAnimation(Animation.linear(duration: 1).repeatForever(autoreverses: false)) {
                animating = true
            }
        }
    }
}

struct CircularActivityIndicatorDemoNative_Previews: PreviewProvider {
    struct CircularActivityIndicatorDemoNative_Harness: View {

        var body: some View {
            CircularActivityIndicatorDemoNative()
                .frame(width: 300, height: 300)
                .frame(maxWidth: .infinity, maxHeight: .infinity)
                .ignoresSafeArea()
        }
    }

    static var previews: some View {
        CircularActivityIndicatorDemoNative_Harness()
            .previewDevice("iPhone 12 Pro Max")
            .previewDisplayName("iPhone 12 Pro Max")
    }
}