Native source code for CodeSlicing episode on advanced activity indicators - Part 1

CircularActivityIndicatorAdvancedDemoNative.swift

//
//  CircularActivityIndicatorAdvancedDemoNative.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 CircularActivityIndicatorAdvancedDemoNative: View {

    @State private var animating = false

    var body: some View {
        let numSegments = 8
        let duration: Double = 1
        let rotationPerSegment: Angle = .degrees(360 / Double(numSegments) )
        let delayPerSegment = duration / Double(numSegments)
        GeometryReader { (geo: GeometryProxy) in
            ZStack {
                Color.clear
                ForEach(0..<numSegments) { index in
                    let delay = delayPerSegment * Double(index)
                    Capsule()
                        .fill(Color.black)
                        .frame(width: geo.size.width * 0.15, height: geo.size.height * 0.3)
                        .offset(y: -geo.size.height * 0.35)
                        .rotationEffect(rotationPerSegment * Double(index))
                        .opacity(animating ? 1 : 0)
                        .animation(Animation.linear(duration: 0.001).delay(delay))
                        .modifier(OpacityFadingModifier(fadeFactor: 1.4, animating: animating))
                        .animation(Animation.linear(duration: duration).repeatForever(autoreverses: false).delay(delay))
                }
            }
        }
        .onAppear {
            animating = true
        }
    }
}

private struct OpacityFadingModifier: AnimatableModifier {
    
    private let fadeFactor: Double
    
    var animatableData: Double
    
    init(fadeFactor: Double = 1, animating: Bool) {
        self.fadeFactor = fadeFactor
        animatableData = animating ? 1 : 0
    }
    
    private var animatedOpacity: Double {
        (fadeFactor - animatableData) / fadeFactor
    }
    
    func body(content: Content) -> some View {
        content
            .opacity(animatedOpacity)
            .animation(nil)
    }
}

struct CircularActivityIndicatorAdvancedDemoNative_Previews: PreviewProvider {
    struct CircularActivityIndicatorAdvancedDemoNative_Harness: View {

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

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