Fill circle with wave animation in SwiftUI

Question

I have created a circle in swiftUI, and I want to fill it with sine wave animation for the water wave effect/animation. I wanted to fill it with a similar look:

Below is my code:

import SwiftUI

struct CircleWaveView: View {
    var body: some View {
        Circle()
            .stroke(Color.blue, lineWidth: 10)
            .frame(width: 300, height: 300)
    }
}

struct CircleWaveView_Previews: PreviewProvider {
    static var previews: some View {
        CircleWaveView()
    }
}

I want to mostly implement it on SwiftUI so that I can support dark mode! Thanks for the help!

Answer 1

Here's a complete standalone example. It features a slider which allows you to change the percentage:

import SwiftUI

struct ContentView: View {
    
    @State private var percent = 50.0
    
    var body: some View {
        VStack {
            CircleWaveView(percent: Int(self.percent))
            Slider(value: self.$percent, in: 0...100)
        }
        .padding(.all)
    }
}

struct Wave: Shape {

    var offset: Angle
    var percent: Double
    
    var animatableData: Double {
        get { offset.degrees }
        set { offset = Angle(degrees: newValue) }
    }
    
    func path(in rect: CGRect) -> Path {
        var p = Path()

        // empirically determined values for wave to be seen
        // at 0 and 100 percent
        let lowfudge = 0.02
        let highfudge = 0.98
        
        let newpercent = lowfudge + (highfudge - lowfudge) * percent
        let waveHeight = 0.015 * rect.height
        let yoffset = CGFloat(1 - newpercent) * (rect.height - 4 * waveHeight) + 2 * waveHeight
        let startAngle = offset
        let endAngle = offset + Angle(degrees: 360)
        
        p.move(to: CGPoint(x: 0, y: yoffset + waveHeight * CGFloat(sin(offset.radians))))
        
        for angle in stride(from: startAngle.degrees, through: endAngle.degrees, by: 5) {
            let x = CGFloat((angle - startAngle.degrees) / 360) * rect.width
            p.addLine(to: CGPoint(x: x, y: yoffset + waveHeight * CGFloat(sin(Angle(degrees: angle).radians))))
        }
        
        p.addLine(to: CGPoint(x: rect.width, y: rect.height))
        p.addLine(to: CGPoint(x: 0, y: rect.height))
        p.closeSubpath()
        
        return p
    }
}

struct CircleWaveView: View {
    
    @State private var waveOffset = Angle(degrees: 0)
    let percent: Int
    
    var body: some View {

        GeometryReader { geo in
            ZStack {
                Text("\(self.percent)%")
                    .foregroundColor(.black)
                    .font(Font.system(size: 0.25 * min(geo.size.width, geo.size.height) ))
                Circle()
                    .stroke(Color.blue, lineWidth: 0.025 * min(geo.size.width, geo.size.height))
                    .overlay(
                        Wave(offset: Angle(degrees: self.waveOffset.degrees), percent: Double(percent)/100)
                            .fill(Color(red: 0, green: 0.5, blue: 0.75, opacity: 0.5))
                            .clipShape(Circle().scale(0.92))
                    )
            }
        }
        .aspectRatio(1, contentMode: .fit)
        .onAppear {
            withAnimation(Animation.linear(duration: 2).repeatForever(autoreverses: false)) {
            self.waveOffset = Angle(degrees: 360)
            }
        }
    }
}

struct ContentView_Previews: PreviewProvider {
    static var previews: some View {
        CircleWaveView(percent: 58)
    }
}