ImageViewer to Display UIImage with SwiftUI (Zoomable)

ImageViewer.swift

/*
 * FILE:	ImageViewer.swift
 * DESCRIPTION:	AppDevKitSwiftUI: Image Viewer
 * DATE:	Thu, May 19 2022
 * UPDATED:	Thu, May 19 2022
 * AUTHOR:	Kouichi ABE (WALL) / 阿部康一
 * E-MAIL:	kouichi@MagickWorX.COM
 * URL:		https://www.MagickWorX.COM/
 * COPYRIGHT:	(c) 2022 阿部康一／Kouichi ABE (WALL)
 * LICENSE:	The 2-Clause BSD License (See LICENSE.txt)
 */

import SwiftUI

public struct ImageViewer: View
{
  private let image: Image

  private let imageWidth: CGFloat
  private let imageHeight: CGFloat

  public init(uiImage: UIImage) {
    self.image = Image(uiImage: uiImage)
    self.imageWidth = uiImage.size.width
    self.imageHeight = uiImage.size.height

    UIScrollView.appearance().bounces = false
  }


  @State private var currentScale: CGFloat = 1.0
  @State private var previousScale: CGFloat = 1.0

  private var magnificationGesture: some Gesture {
    MagnificationGesture()
      .onChanged {
        (scale) in
        let delta = scale / self.previousScale
        self.previousScale = scale
        self.currentScale = max(0.5, self.currentScale * delta)
      }
      .onEnded { _ in
        self.previousScale = 1.0
      }
  }

  private var doubleTapGesture: some Gesture {
    TapGesture(count: 2)
      .onEnded { _ in
        self.currentScale = 1.0
        self.previousScale = 1.0
      }
  }

  @ViewBuilder
  public var body: some View {
    GeometryReader {
      (geometry) in
      let  viewWidth = geometry.size.width
      let viewHeight = geometry.size.height
      let  widthFactor = viewWidth / imageWidth
      let heightFactor = viewHeight / imageHeight
      let  scaleFactor = min(widthFactor, heightFactor) * self.currentScale
      let  width = floor(imageWidth * scaleFactor)
      let height = floor(imageHeight * scaleFactor)
      ZStack {
        Color.black.ignoresSafeArea()
        ScrollView([ .horizontal, .vertical ], showsIndicators: false) {
          image
            .resizable()
            .edgesIgnoringSafeArea(.all)
            .frame(width: width, height: height)
        }
        .gesture(magnificationGesture)
        .gesture(doubleTapGesture)
      }
    }
  }
}

struct ImageViewer_Previews: PreviewProvider
{
  static var previews: some View {
    ImageViewer(uiImage: UIImage(named: "azakura")!)
  }
}