Source-code for CodeSlicing Episode on inner-shadows

InnerShadowsDemo.swift

//
//  InnerShadowsDemo.swift
//
//  Permission is hereby granted, free of charge, to any person obtaining a copy
//  of this software and associated documentation files (the "Software"), to deal
//  in the Software without restriction, including without limitation the rights
//  to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies
//  of the Software, and to permit persons to whom the Software is furnished to do so,
//  subject to the following conditions:
//
//  THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED,
//  INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A
//  PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR
//  COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN
//  AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
//  WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
//
//  Created by Adam Fordyce on 12/02/2021.
//  Copyright © 2021 Adam Fordyce. All rights reserved.
//

import SwiftUI
import PureSwiftUI

private let niceBackground = LinearGradient([.red, .orange], to: .trailing)

struct InnerShadowsDemo: View {
    var body: some View {
        Image("claw-marks")
            .innerShadow(Color.rgb8(200, 0, 0), radius: 10, opacity: 0.8, offset: .x(5))
            .shadowColor(Color(white: 0.8), 5, x: -6, y: -2)
            .shadowColor(Color(white: 0.2), 5, x: 6, y: 2)
            .shadowColor(Color(white: 0.4), 10, x: 10, y: 5)
            .shadowColor(Color(white: 0.75), 10, x: -10, y: -5)
            .rotate(10.degrees)
    }
}

private extension Image {
    
    func innerShadow<V: View>(_ background: V, radius: CGFloat = 5, opacity: Double = 0.7, offset: CGPoint = .zero) -> some View {
        
        Color.clear
            .background(background)
            .blendMode(.multiply)
            .background(
                ZStack {
                    Color(white: 1 - opacity)
                    self.renderingMode(.template).foregroundColor(.white).blur(radius).offset(offset)
                }
            )
            .mask(self)
    }
}

private extension Shape {
    
    func innerShadow<V: View>(_ background: V, radius: CGFloat = 5, opacity: Double = 0.7, offset: CGPoint = .zero) -> some View {
        self.fill(Color.clear).innerShadow(background, self, radius: radius, opacity: opacity, offset: offset)
    }
}

private extension View {
    
    func innerShadow<V: View, S: Shape>(_ background: V, _ shape: S, radius: CGFloat = 5, opacity: Double = 0.7, offset: CGPoint = .zero) -> some View {
        self
            .background(background)
            .blendMode(.multiply)
            .background(
                ZStack {
                    shape.fill(Color(white: 1 - opacity))
                    shape.fill(Color.white).blur(radius).offset(offset)
                }
            )
            .mask(self.overlay(shape))
    }
}

private extension Text {
    
    func innerShadow<V: View>(_ background: V, radius: CGFloat = 5, opacity: Double = 0.7, offset: CGPoint = .zero) -> some View {
        self
            .foregroundColor(.clear)
            .overlay(background.mask(self))
            .overlay(
                ZStack {
                    self.foregroundColor(Color(white: 1 - opacity))
                    self.foregroundColor(.white).blur(radius).offset(offset)
                }
                .mask(self)
                .blendMode(.multiply)
            )
    }
}

struct InnerShadowsDemo_Previews: PreviewProvider {
    struct InnerShadowsDemo_Harness: View {

        var body: some View {
            InnerShadowsDemo()
                .greedyFrame()
                .background(LinearGradient([Color(white: 0.7), Color(white: 0.4)], to: .bottomTrailing))
                .ignoresSafeArea()
        }
    }

    static var previews: some View {
        InnerShadowsDemo_Harness()
            .previewDevice(.iPhone_12_Pro_Max)
    }
}