117 lines
4.0 KiB
Swift
117 lines
4.0 KiB
Swift
//
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// FlipView.swift
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// Tusker
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//
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// Created by Shadowfacts on 12/21/22.
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// Copyright © 2022 Shadowfacts. All rights reserved.
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//
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import SwiftUI
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// Based on https://stackoverflow.com/a/60807269
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struct FlipView<Front: View, Back: View> : View {
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private let front: Front
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private let back: Back
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@State private var flipped = false
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@State private var angle: Angle = .zero
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@State private var width: CGFloat = 0
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@State private var initialFlipped: Bool!
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init(@ViewBuilder front: () -> Front, @ViewBuilder back: () -> Back) {
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self.front = front()
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self.back = back()
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}
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var body: some View {
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ZStack {
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front
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.opacity(flipped ? 0.0 : 1.0)
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back
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.rotation3DEffect(.degrees(180), axis: (0, 1, 0))
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.opacity(flipped ? 1.0 : 0.0)
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}
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.modifier(FlipEffect(flipped: $flipped, angle: angle.degrees, axis: (x: 0, y: 1)))
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.background(GeometryReader { proxy in
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Color.clear
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.preference(key: WidthPrefKey.self, value: proxy.size.width)
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.onPreferenceChange(WidthPrefKey.self) { newValue in
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width = newValue
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}
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})
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.gesture(
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DragGesture()
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.onChanged({ value in
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if initialFlipped == nil {
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initialFlipped = flipped
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}
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let adj = (width / 2) - value.location.x
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let hyp = abs((width / 2) - value.startLocation.x)
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let clamped: Double = min(max(adj / hyp, -1), 1)
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let startedOnRight = value.startLocation.x > width / 2
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angle = .radians(acos(clamped) + (startedOnRight != initialFlipped ? .pi : 0))
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})
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.onEnded({ value in
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initialFlipped = nil
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let deg = angle.degrees.truncatingRemainder(dividingBy: 360)
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if deg == 0 {
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angle = .zero
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} else if deg == 180 {
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angle = .degrees(180)
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} else {
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withAnimation(.easeInOut(duration: 0.25)) {
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angle = deg > 90 && deg < 270 ? .degrees(180) : .zero
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}
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}
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})
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)
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.onTapGesture {
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withAnimation(.easeInOut(duration: 0.5)) {
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angle = angle == .zero ? .degrees(180) : .zero
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}
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}
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}
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}
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// Based on https://swiftui-lab.com/swiftui-animations-part2/
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struct FlipEffect: GeometryEffect {
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var animatableData: Double {
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get { angle }
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set { angle = newValue }
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}
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@Binding var flipped: Bool
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var angle: Double
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let axis: (x: CGFloat, y: CGFloat)
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func effectValue(size: CGSize) -> ProjectionTransform {
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// We schedule the change to be done after the view has finished drawing,
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// otherwise, we would receive a runtime error, indicating we are changing
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// the state while the view is being drawn.
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DispatchQueue.main.async {
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self.flipped = self.angle >= 90 && self.angle < 270
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}
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let a = CGFloat(Angle.degrees(angle).radians)
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var transform3d = CATransform3DIdentity
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transform3d.m34 = -1/max(size.width, size.height)
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transform3d = CATransform3DRotate(transform3d, a, axis.x, axis.y, 0)
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transform3d = CATransform3DTranslate(transform3d, -size.width/2.0, -size.height/2.0, 0)
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let affineTransform = ProjectionTransform(CGAffineTransform(translationX: size.width/2.0, y: size.height / 2.0))
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return ProjectionTransform(transform3d).concatenating(affineTransform)
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}
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}
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private struct WidthPrefKey: PreferenceKey {
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static var defaultValue: CGFloat = 0
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static func reduce(value: inout CGFloat, nextValue: () -> CGFloat) {
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value = nextValue()
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}
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}
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