How to convert a View (not UIView) to an image?

Question

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I would like to convert a SwiftUI View rather than a UIView to an image.

Answer 1

Following kontiki answer, here is the Preferences way

import SwiftUI

struct ContentView: View {
    @State private var uiImage: UIImage? = nil
    @State private var rect1: CGRect = .zero
    @State private var rect2: CGRect = .zero

    var body: some View {
        VStack {
            HStack {
                VStack {
                    Text("LEFT")
                    Text("VIEW")
                }
                .padding(20)
                .background(Color.green)
                .border(Color.blue, width: 5)
                .getRect($rect1)
                .onTapGesture {
                    self.uiImage =  self.rect1.uiImage
                }

                VStack {
                    Text("RIGHT")
                    Text("VIEW")
                }
                .padding(40)
                .background(Color.yellow)
                .border(Color.green, width: 5)
                .getRect($rect2)
                .onTapGesture {
                    self.uiImage =  self.rect2.uiImage
                }
            }

            if uiImage != nil {
                VStack {
                    Text("Captured Image")
                    Image(uiImage: self.uiImage!).padding(20).border(Color.black)
                }.padding(20)
            }
        }
    }
}

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

extension CGRect {
    var uiImage: UIImage? {
        UIApplication.shared.windows
            .filter{ $0.isKeyWindow }
            .first?.rootViewController?.view
            .asImage(rect: self)
    }
}

extension View {
    func getRect(_ rect: Binding) -> some View {
        self.modifier(GetRect(rect: rect))
    }
}

struct GetRect: ViewModifier {

    @Binding var rect: CGRect

    var measureRect: some View {
        GeometryReader { proxy in
            Rectangle().fill(Color.clear)
                .preference(key: RectPreferenceKey.self, value:  proxy.frame(in: .global))
        }
    }

    func body(content: Content) -> some View {
        content
            .background(measureRect)
            .onPreferenceChange(RectPreferenceKey.self) { (rect) in
                if let rect = rect {
                    self.rect = rect
                }
            }

    }
}

extension GetRect {
    struct RectPreferenceKey: PreferenceKey {
        static func reduce(value: inout CGRect?, nextValue: () -> CGRect?) {
            value = nextValue()
        }

        typealias Value = CGRect?

        static var defaultValue: CGRect? = nil
    }
}

extension UIView {
    func asImage(rect: CGRect) -> UIImage {
        let renderer = UIGraphicsImageRenderer(bounds: rect)
        return renderer.image { rendererContext in
            layer.render(in: rendererContext.cgContext)
        }
    }
}