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How to create 3D effects like Cover Flow using ScrollView and GeometryReader

Paul Hudson    @twostraws   

Updated for Xcode 12.0

If we combine GeometryReader with any view that can change position – such as something that has a drag gestures or is inside a List – we can create 3D effects very easily. GeometryReader allows us to read the coordinates for a view, and feed those values directly into a rotation3DEffect() modifier.

For example, we could create a Cover Flow-style scrolling effect by stacking up many text views horizontally in a scroll view, then applying rotation3DEffect() so that as they move in the scroll view they gently spin, like this:

struct ContentView: View {
    var body: some View {
        ScrollView(.horizontal, showsIndicators: false) {
            HStack(spacing: 0) {
                ForEach(1..<10) { num in
                    VStack {
                        GeometryReader { geo in
                            Text("Number \(num)")
                                .font(.largeTitle)
                            .padding()
                            .background(Color.red)
                            .rotation3DEffect(.degrees(-Double(geo.frame(in: .global).minX) / 8), axis: (x: 0, y: 1, z: 0))
                        }
                    }
                    .frame(width: 180)
                }
            }
            .padding()
        }
    }
}

We could something similar with a DragGesture() – this code creates a card-like rectangle that can be dragged around in both X and Y axes, and uses two rotation3DEffect() modifiers to apply values from GeometryReader:

struct ContentView: View {
    @State var dragAmount = CGSize.zero

    var body: some View {
        VStack {
            GeometryReader { geo in
                Rectangle()
                    .fill(LinearGradient(gradient: Gradient(colors: [.yellow, .red]), startPoint: .topLeading, endPoint: .bottomTrailing))
                    .frame(width: 300, height: 200)
                    .clipShape(RoundedRectangle(cornerRadius: 20))
                    .rotation3DEffect(.degrees(-Double(self.dragAmount.width) / 20), axis: (x: 0, y: 1, z: 0))
                    .rotation3DEffect(.degrees(Double(self.dragAmount.height / 20)), axis: (x: 1, y: 0, z: 0))
                    .offset(self.dragAmount)
                    .gesture(
                        DragGesture()
                            .onChanged { self.dragAmount = $0.translation }
                            .onEnded { _ in
                                withAnimation(.spring()) {
                                    self.dragAmount = .zero
                                }
                            }
                    )
            }
        }
    }
}

As you drag the card around you’ll see it rotates to give a perspective effect.

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