Helper for rendering metrics of SwiftUI views in debugging

DebugMetrics.swift

//  Created by Marc Palmer on 13/02/2020.
//
//  Usage: Add .debugMetrics(.yellow) or similar to any view

import Foundation
import SwiftUI

/// Renders the width and height of a view
struct DebugMetricsModifier: ViewModifier {
    let colour: Color

    fileprivate func capsuleText(_ text: LocalizedStringKey) -> some View {
        return Text(text)
            .foregroundColor(.white)
            .font(.caption)
            .padding(EdgeInsets(top: 2, leading: 10, bottom: 2, trailing: 10))
            .background(Capsule().foregroundColor(colour))
    }
    
    func body(content: Content) -> some View {
        return content.overlay(
            GeometryReader { proxy in
                ZStack {
                    ZStack {
                        self.capsuleText("\(proxy.size.height, specifier: "%.f")")
                        .background(Rectangle()
                            .foregroundColor(self.colour)
                            .frame(width: 2, height: proxy.size.height))
                    }
                    .frame(width: proxy.size.width, height: proxy.size.height, alignment: .trailing)

                    ZStack {
                        self.capsuleText("\(proxy.size.width, specifier: "%.f")")
                        .background(Rectangle()
                            .foregroundColor(self.colour)
                            .frame(width: proxy.size.width, height: 2))
                    }
                    .frame(width: proxy.size.width, height: proxy.size.height, alignment: .bottom)
                }.overlay(Rectangle()
                    .stroke(self.colour,
                            style: StrokeStyle(lineWidth: 1,
                                               lineCap: .round,
                                               lineJoin: .miter,
                                               miterLimit: 0,
                                               dash: [2, 2],
                                               dashPhase: 0)))
            }
        )
    }
}

extension View {
    func debugMetrics(_ colour: Color = .red) -> some View {
        self.modifier(DebugMetricsModifier(colour: colour))
    }
}