SwiftUI Zoom

Zoom.swift

import SwiftUI

struct Zoom: ViewModifier {
    @Binding var scale: CGFloat
    @Binding var position: CGPoint
    
    @State private var currentZoom: CGFloat = 0
    
    private let scrollCoordinateSpace = "scroll"
    
    func body(content: Content) -> some View {
        GeometryReader { geometry in
            ScrollView([.vertical, .horizontal]) {
                content
                    .frame(
                        width: sideLength(geometry, multiplier: currentZoom + scale),
                        height: sideLength(geometry, multiplier: currentZoom + scale)
                    )
                    .gesture(
                        MagnificationGesture()
                            .onChanged { scale in
                                currentZoom = scale - 1
                            }
                            .onEnded { _ in
                                scale += currentZoom
                                currentZoom = 0.0
                            }
                    )
                    .accessibilityZoomAction { action in
                        switch action.direction {
                        case .zoomIn:
                            scale += 1
                        case .zoomOut:
                            scale -= 1
                        }
                    }
                    .onTapGesture(count: 2) {
                        withAnimation {
                            // Zoom in / out on double tap
                            scale = scale > 1 ? 1 : 1.5
                        }
                    }
                    .onTapGesture {
                        // Empty to prevent dismiss
                    }
                    .background(
                        GeometryReader { geometry -> Color in
                            Task {
                                position = geometry.frame(in: .named(scrollCoordinateSpace)).origin
                            }
                            return Color.clear
                        }
                    )
            }
            .scrollIndicators(.hidden)
            .coordinateSpace(name: scrollCoordinateSpace)
        }
    }
    
    private func sideLength(_ geometry: GeometryProxy, multiplier: CGFloat = 1) -> CGFloat {
        min(geometry.size.width, geometry.size.height) * multiplier
    }
}

extension View {
    func zoom(scale: Binding<CGFloat>, position: Binding<CGPoint>) -> some View {
        modifier(Zoom(scale: scale, position: position))
    }
}