ActivityRing.swift

//
//  ContentView.swift
//  Ring
//
//  Created by Ray Fix on 6/20/20.
//  Copyright © 2020 Ray Fix. All rights reserved.
//

import SwiftUI

struct ActivityRing: View {
  
  @Binding var progress: Double
  var lineWidth: CGFloat = 40
  var gradient = Gradient(colors: [Color.blue, Color.green])
  
  var body: some View {
    Circle()
      .trim(from: 0, to: CGFloat(progress))
      .stroke(
        AngularGradient(gradient: gradient,
                        center: .center,
                        endAngle: .degrees(360*progress)),
        style: .init(lineWidth: lineWidth, lineCap: .round))
      .overlay(
        GeometryReader { proxy in
        Circle()
          .fill(self.gradient.stops.last!.color)
          .offset(x: proxy.size.width/2)
          .rotationEffect(.degrees(360*self.progress))
          .frame(width: self.lineWidth)
        }
      )
      .rotationEffect(.degrees(-90))
      .scaledToFit()
      .padding(lineWidth/2)
  }
}

struct ContentView: View {
  
  @State private var progress: Double = 0.3
  
  var body: some View {
    VStack {
      ActivityRing(progress: $progress)
      Slider(value: $progress, in: 0...10)
    }.padding()
  }
}
  
  struct ContentView_Previews: PreviewProvider {
    static var previews: some View {
      ContentView()
    }
}