gistfile1.txt

//
//  KnobView.swift
//
//  Created by Steve Riggins on 6/30/19.
//  Copyright © 2019 Steve Riggins. All rights reserved.
//

import SwiftUI

struct KnobView : View {
    @State var degrees = 0.0

    var body: some View {
      
        var dragGesture = DragGesture()
        dragGesture.coordinateSpace = .global
        
        return GeometryReader() { proxy in
            ZStack {
                Rectangle()
                .fill(Color.red)
                .gesture(dragGesture
                    .onChanged() { value in
                    // Calculate degrees using proxy.frame(in: .global).....
                  }
                )
                
                Path() { path in
                    let f = proxy.frame(in: .local)
                    let centerX = f.width / 2.0
                    
                    // Vertical line
                    path.move(to: .init(x: centerX, y:f.maxY))
                    path.addLine(to: .init(x: centerX, y:f.minY))
                    
                    // Left arrow arm
                    path.move(to: .init(x: centerX, y:f.minY))
                    path.addLine(to: .init(x: centerX - 30, y:f.minY + 30))
   
                    // Right arrow arm
                    path.move(to: .init(x: centerX, y:f.minY))
                    path.addLine(to: .init(x: centerX + 30, y:f.minY + 30))
                    }
                .stroke()
            }
            .rotationEffect(.degrees(self.degrees))
        }
        .frame(width: 100, height: 100)
    }
}

#if DEBUG
struct KnobView_Previews : PreviewProvider {
    static var previews: some View {
        KnobView()
    }
}
#endif