ShadowPerfBench.swift

import SwiftUI

struct ContentView: View {
  @State var selected = 0
  @State var count: Int = 100
  @State var position: CGPoint = .zero
  var body: some View {
    VStack {
      Picker(selection: $selected) {
        Text("Mask").tag(0)
        Text("ClipShape").tag(1)
        Text("Background").tag(2)
        Text("Background Style").tag(3)
      } label: {
        Text("Type")
      }.pickerStyle(.segmented)
      Stepper("Count: \(count)") {
        count += 100
      } onDecrement: {
        count -= 100
        count = max(0, count)
      }

      let content = Text("Hello")
      let shadowShape = Ellipse()

      ZStack {
        Color.clear
        ForEach(Array(0..<count), id: \.self) { _ in
          switch selected {
          case 0:
            MaskView {
              shadowShape
            } content: {
              content
            }
          case 1:
            ClipView {
              shadowShape
            } content: {
              content
            }
          case 2:
            BackgroundView {
              shadowShape
            } content: {
              content
            }
          case 3:
            BackgroundView2 {
              shadowShape
            } content: {
              content
            }
          default:
            fatalError()
          }
        }
        .offset(
          x: position.x,
          y: position.y
        )
      }
      .task {
        while true {
          try? await Task.sleep(for: .milliseconds(50))
          self.position = CGPoint(
            x: CGFloat.random(in: 0...150),
            y: CGFloat.random(in: 0...150)
          )
        }
      }
    }
  }
}

struct MaskView<Content: View, ShadowShape: Shape>: View {
  let content: Content
  let shadowShape: ShadowShape
  init(
    shadowShape: () -> ShadowShape,
    @ViewBuilder content: () -> Content
  ) {
    self.shadowShape = shadowShape()
    self.content = content()
  }

  var body: some View {
    content
      .mask(shadowShape)
      .shadow(radius: 10)
  }
}

struct ClipView<Content: View, ShadowShape: Shape>: View {
  let content: Content
  let shadowShape: ShadowShape
  init(
    shadowShape: () -> ShadowShape,
    @ViewBuilder content: () -> Content
  ) {
    self.shadowShape = shadowShape()
    self.content = content()
  }

  var body: some View {
    content
      .clipShape(shadowShape)
      .shadow(radius: 10)
  }
}

struct BackgroundView<Content: View, ShadowShape: Shape>: View {
  let content: Content
  let shadowShape: ShadowShape
  init(
    shadowShape: () -> ShadowShape,
    @ViewBuilder content: () -> Content
  ) {
    self.shadowShape = shadowShape()
    self.content = content()
  }

  var body: some View {
    content
      .background(
        shadowShape.shadow(radius: 10)
      )
  }
}

struct BackgroundView2<Content: View, ShadowShape: Shape>: View {
  let content: Content
  let shadowShape: ShadowShape
  init(
    shadowShape: () -> ShadowShape,
    @ViewBuilder content: () -> Content
  ) {
    self.shadowShape = shadowShape()
    self.content = content()
  }

  var body: some View {
    content
      .background(
        shadowShape.fill(.black.shadow(.drop(radius: 10)))
      )
  }
}

struct ContentView_Previews: PreviewProvider {
  static var previews: some View {
    ContentView()
  }
}