SwiftUI ViewModifier to create a parallax and stretchy background header based on ScrollView offset

BackgroundParallaxHeaderModifier.swift

// Assumes usage of:
//  - https://gist.github.com/LePips/3640ad0cd9b6e2ceb407e9d0e9e32b5c
//  - https://gist.github.com/LePips/5c6b4546e9bd8f91c029f705347be974
//
// Last gist not required, but nice to have for headers.

struct BackgroundParallaxHeaderModifier<Header: View>: ViewModifier {

    @Binding
    var scrollViewOffset: CGFloat
    
    let height: CGFloat

    let multiplier: CGFloat
    let header: () -> Header
    
    init(_ scrollViewOffset: Binding<CGFloat>,
         height: CGFloat,
         multiplier: CGFloat = 1,
         @ViewBuilder header: @escaping () -> Header) {
        self._scrollViewOffset = scrollViewOffset
        self.height = height
        self.multiplier = multiplier
        self.header = header
    }

    func body(content: Content) -> some View {
        content.background(alignment: .top, content: {
            header()
                .offset(y: scrollViewOffset > 0 ? -scrollViewOffset * multiplier : 0)
                .scaleEffect(scrollViewOffset < 0 ? (height - scrollViewOffset) / height : 1, anchor: .top)
                .mask(alignment: .top) {
                    Color.black
                        .frame(height: max(0, height - scrollViewOffset))
                }
                .ignoresSafeArea()
        })
    }
}

extension View {
    func backgroundParallaxHeader<Header: View>(_ scrollViewOffset: Binding<CGFloat>,
                                                height: CGFloat,
                                                multiplier: CGFloat = 1,
                                                @ViewBuilder header: @escaping () -> Header) -> some View {
        self.modifier(BackgroundParallaxHeaderModifier(scrollViewOffset,
                                                       height: height,
                                                       multiplier: multiplier,
                                                       header: header))
    }
}

// Example

struct ContentView: View {
    
    @State
    private var scrollViewOffset: CGFloat = 0

    var body: some View {
        NavigationView {
                ScrollView {
                    VStack {
                        
                        // Show background parallax header
                        Color.clear
                            .frame(height: 300)
                        
                        VStack {
                            ForEach(0..<100) { _ in
                                Text("Hello There")
                            }
                        }
                        .background(Color.black)
                    }
                    .frame(maxWidth: .infinity)
                }
                .navigationTitle("Test")
                .navigationBarTitleDisplayMode(.inline)
                .ignoresSafeArea()
                .scrollViewOffset($scrollViewOffset)
                .navBarOffset($scrollViewOffset, start: 270, end: 320)
                .backgroundParallaxHeader($scrollViewOffset, height: 300, multiplier: 0.5) { // Will offset slower than scroll speed
                    Color.red
                        .frame(height: 300)
                }
        }
    }
}