SliderThumbView.swift

import SwiftUI

struct SliderThumbView: View {
  static let thumbHeight = CGFloat(28)
  @Environment(\.colorScheme) var colorScheme
  @Binding var value: Double
  let bounds: ClosedRange<Double>
  
  var shadowColour: Color {
    colorScheme == .light ? Color(white: 0.85) : .clear
  }
  
  var body: some View {
    GeometryReader { proxy in
      let maxOffset = proxy.frame(in: .global).width - Self.thumbHeight
      Circle()
        .foregroundColor(.white)
        .frame(maxWidth: .infinity, alignment: .leading)
        .offset(x: (value / bounds.upperBound) * maxOffset)
        .shadow(color: shadowColour, radius: 3, x: 1, y: 3)
        .gesture(
          DragGesture()
            .onChanged { gesture in
              if gesture.location.x < 1 {
                value = bounds.lowerBound
              } else if gesture.location.x > maxOffset {
                value = bounds.upperBound
              } else {
                let amount = gesture.location.x / maxOffset
                value = amount * bounds.upperBound
              }
            }
        )
    }
    .frame(height: Self.thumbHeight)
  }
}