ContentView.swift

import SwiftUI

struct ContentView: View 
{
    @State var angle: CGFloat = 0

    let animation = Animation.linear(duration: 10).repeatForever(autoreverses: false)

    var body: some View 
    {
        ZStack 
        {
            Color(white: 0.9).edgesIgnoringSafeArea(.all)
            
            RoundedRectangle(cornerRadius: 25.0, style: .continuous)
                .fill(Color.white)
                .overlay(VStack(spacing: 15)
                {
                    Text("Hello World!").font(.system(.largeTitle))
                    Text("Foo").font(.system(.headline))
                    Text("Bar").font(.system(.caption))
                })
                .frame(width: 200, height: 200, alignment: .center)
                .panYawEffect(angle: angle)
                .angleShadow(angle: angle)
                .onAppear 
                {
                    withAnimation(animation)
                    {
                        angle = CGFloat.pi * 2
                    }
            }
        }
    }
}

struct PanYawEffect: GeometryEffect 
{
    var animatableData: CGFloat 
    {
        get { angle }
        set { angle = newValue }
    }
    
    var angle: CGFloat
    
    func effectValue(size: CGSize) -> ProjectionTransform 
    {
        var transform3d = CATransform3DIdentity;
        transform3d.m34 = -1 / max(size.width, size.height)
        
        transform3d = CATransform3DTranslate(transform3d, 0.5 * size.width, 0.5 * size.height, 0)
        transform3d = CATransform3DRotate(transform3d, sin(angle) * 0.1, 1, 0, 0)
        transform3d = CATransform3DRotate(transform3d, -cos(angle) * 0.1, 0, 1, 0)
        transform3d = CATransform3DTranslate(transform3d, -0.5 * size.width, -0.5 * size.height, 0)
                
        return ProjectionTransform(transform3d)
    }
}

struct AngleShadow : AnimatableModifier
{
    var angle: CGFloat = 0
    
    var animatableData: CGFloat
    {
        get { angle }
        set { angle = newValue }
    }
    
    func body(content: Content) -> some View 
    {
        content.shadow(radius: 30, x: cos(angle) * 30, y: sin(angle) * 30)
    }
}

public extension View
{
    func angleShadow(angle: CGFloat) -> some View
    {
        return modifier(AngleShadow(angle: angle))
    }
    
    func panYawEffect(angle: CGFloat) -> some View
    {
        return modifier(PanYawEffect(angle: angle))
    }
}

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