SwiftUI variable blur view

VariableBlurView.swift

import Foundation
import SwiftUI
import UIKit

extension UIBlurEffect {
  public static func variableBlurEffect(radius: Double, imageMask: UIImage) -> UIBlurEffect? {
    let methodType = (@convention(c) (AnyClass, Selector, Double, UIImage) -> UIBlurEffect).self
    let selectorName = ["imageMask:", "effectWithVariableBlurRadius:"].reversed().joined()
    let selector = NSSelectorFromString(selectorName)

    guard UIBlurEffect.responds(to: selector) else { return nil }

    let implementation = UIBlurEffect.method(for: selector)
    let method = unsafeBitCast(implementation, to: methodType)

    return method(UIBlurEffect.self, selector, radius, imageMask)
  }
}

struct VariableBlurView: UIViewRepresentable {
  let radius: Double
  let mask: Image

  func makeUIView(context: Context) -> UIVisualEffectView {
    let maskImage = ImageRenderer(content: mask).uiImage
    let effect = maskImage.flatMap {
      UIBlurEffect.variableBlurEffect(radius: radius, imageMask: $0)
    }
    return UIVisualEffectView(effect: effect)
  }

  func updateUIView(_ view: UIVisualEffectView, context: Context) {
    let maskImage = ImageRenderer(content: mask).uiImage
    view.effect = maskImage.flatMap {
      UIBlurEffect.variableBlurEffect(radius: radius, imageMask: $0)
    }
  }
}

#Preview {
  VStack(spacing: 0) {
    Circle()
      .foregroundStyle(.red)
    Circle()
      .foregroundStyle(.green)
    Circle()
      .foregroundStyle(.blue)
  }
  .frame(maxWidth: .infinity, alignment: .center)
  .overlay(
    VariableBlurView(radius: 10, mask: Image(.gradient))
      .ignoresSafeArea()
  )
}

This is how it looks with a simple black(alpha: 0) to black(alpha: 1) gradient: