View showing how to use GeometryReader with a greedy view. A companion file to CodeSlicing: CoreConcepts in SwiftUI - GeometryReader

GeometryReaderGreedyViewDemo.swift

import SwiftUI
import PureSwiftUI

private let size: CGFloat = 200
private let numLayers = 20
private let stepSize = 25

struct GeometryReaderGreedyViewDemo: View {
    @State private var animating = false
    var body: some View {
        ZStack {
            ForEach(0..<numLayers) { index in
                ZStack {
                    PyramidLayer()
                        .rotateIf(self.animating, 90.degrees)
                        .shadow(5)
                        .frame(self.sizeForIndex(index))
                        .animation(Animation
                            .easeInOut(duration: 2)
                            .repeatForever()
                            .delay(self.delayForIndex(index)))
                }
            }
            .onAppear {
                self.animating = true
            }
        }
        .padding(100)
        .drawingGroup()
    }
    
    func delayForIndex(_ index: Int) -> Double {
        Double(numLayers - index) * 0.2
    }
    
    func sizeForIndex(_ index: Int) -> CGFloat {
        CGFloat((numLayers - index) * stepSize)
    }
}

private let gradient = LinearGradient([Color.red, Color.yellow], to: .bottomTrailing)

private struct PyramidLayer: View {
    
    var body: some View {
        GeometryReader { (geo: GeometryProxy) in
            RoundedRectangle(geo.widthScaled(0.2))
                .fill(gradient)
        }
    }
}

struct GeometryReaderDemo_Previews: PreviewProvider {
    struct GeometryReaderDemo_Harness: View {
        
        var body: some View {
            GeometryReaderGreedyViewDemo()
        }
    }
    
    static var previews: some View {
        GeometryReaderDemo_Harness()
            .previewDevice(.iPad_Air_2)
    }
}