Add support for rendering drop shadows (airbnb#2142)

Sources/Private/CoreAnimation/Animations/DropShadowAnimation.swift

@@ -0,0 +1,183 @@
+// Created by Cal Stephens on 8/15/23.
+// Copyright © 2023 Airbnb Inc. All rights reserved.
+
+import QuartzCore
+
+// MARK: - DropShadowModel
+
+protocol DropShadowModel {
+  /// The opacity of the drop shadow, from 0 to 100.
+  var _opacity: KeyframeGroup<LottieVector1D>? { get }
+
+  /// The shadow radius of the blur
+  var _radius: KeyframeGroup<LottieVector1D>? { get }
+
+  /// The color of the drop shadow
+  var _color: KeyframeGroup<LottieColor>? { get }
+
+  /// The angle of the drop shadow, in degrees,
+  /// with "90" resulting in a shadow directly beneath the layer.
+  /// Combines with the `distance` to form the `shadowOffset`.
+  var _angle: KeyframeGroup<LottieVector1D>? { get }
+
+  /// The distance of the drop shadow offset.
+  /// Combines with the `angle` to form the `shadowOffset`.
+  var _distance: KeyframeGroup<LottieVector1D>? { get }
+}
+
+// MARK: - DropShadowStyle + DropShadowModel
+
+extension DropShadowStyle: DropShadowModel {
+  var _opacity: KeyframeGroup<LottieVector1D>? { opacity }
+  var _color: KeyframeGroup<LottieColor>? { color }
+  var _angle: KeyframeGroup<LottieVector1D>? { angle }
+  var _distance: KeyframeGroup<LottieVector1D>? { distance }
+
+  var _radius: KeyframeGroup<LottieVector1D>? {
+    size.map { sizeValue in
+      // `DropShadowStyle.size` is approximately double as large
+      // as the visually-equivalent `cornerRadius` value
+      LottieVector1D(sizeValue.cgFloatValue / 2)
+    }
+  }
+}
+
+// MARK: - DropShadowEffect + DropShadowModel
+
+extension DropShadowEffect: DropShadowModel {
+  var _color: KeyframeGroup<LottieColor>? { color?.value }
+
+  var _distance: KeyframeGroup<LottieVector1D>? {
+    distance?.value?.map { distanceValue in
+      // `DropShadowEffect.distance` doesn't seem to map cleanly to
+      // `CALayer.shadowOffset` (e.g. with a simple multiplier).
+      // Instead, this uses a custom quadratic regression eyeballed
+      // to match the expected appearance of the start / end of the
+      // `issue_1169_shadow_effect_animated.json` sample animation:
+      //  - `distance=5` roughly corresponds to an offset value of 4
+      //  - `distance=10` roughly corresponds to an offset value of 5
+      // This could probably be improved with more examples.
+      let x = distanceValue.cgFloatValue
+      let cornerRadiusMapping = (-0.06 * pow(x, 2)) + (1.1 * x)
+
+      return LottieVector1D(cornerRadiusMapping)
+    }
+  }
+
+  var _radius: KeyframeGroup<LottieVector1D>? {
+    softness?.value?.map { softnessValue in
+      // `DropShadowEffect.softness` doesn't seem to map cleanly to
+      // `CALayer.cornerRadius` (e.g. with a simple multiplier).
+      // Instead, this uses a custom quadratic regression eyeballed
+      // to match the expected appearance of the start / end of the
+      // `issue_1169_shadow_effect_animated.json` sample animation:
+      //  - `softness=10` roughly corresponds to `cornerRadius=2.5`
+      //  - `softness=50` roughly corresponds to `cornerRadius=6.25`
+      // This could probably be improved with more examples.
+      let x = softnessValue.cgFloatValue
+      let cornerRadiusMapping = (-0.003 * pow(x, 2)) + (0.281 * x)
+
+      return LottieVector1D(cornerRadiusMapping)
+    }
+  }
+
+  var _opacity: KeyframeGroup<LottieVector1D>? {
+    opacity?.value?.map { originalOpacityValue in
+      // `DropShadowEffect.opacity` is a value between 0 and 255,
+      // but `DropShadowModel._opacity` expects a value between 0 and 100.
+      LottieVector1D((originalOpacityValue.value / 255.0) * 100)
+    }
+  }
+
+  var _angle: KeyframeGroup<LottieVector1D>? {
+    direction?.value?.map { originalAngleValue in
+      // `DropShadowEffect.distance` is rotated 90º from the
+      // angle value representation expected by `DropShadowModel._angle`
+      LottieVector1D(originalAngleValue.value - 90)
+    }
+  }
+}
+
+// MARK: - CALayer + DropShadowModel
+
+extension CALayer {
+
+  // MARK: Internal
+
+  /// Adds drop shadow animations from the given `DropShadowModel` to this layer
+  @nonobjc
+  func addDropShadowAnimations(
+    for dropShadowModel: DropShadowModel,
+    context: LayerAnimationContext)
+    throws
+  {
+    try addShadowOpacityAnimation(from: dropShadowModel, context: context)
+    try addShadowColorAnimation(from: dropShadowModel, context: context)
+    try addShadowRadiusAnimation(from: dropShadowModel, context: context)
+    try addShadowOffsetAnimation(from: dropShadowModel, context: context)
+  }
+
+  // MARK: Private
+
+  private func addShadowOpacityAnimation(from model: DropShadowModel, context: LayerAnimationContext) throws {
+    guard let opacityKeyframes = model._opacity else { return }
+
+    try addAnimation(
+      for: .shadowOpacity,
+      keyframes: opacityKeyframes,
+      value: {
+        // Lottie animation files express opacity as a numerical percentage value
+        // (e.g. 0%, 50%, 100%) so we divide by 100 to get the decimal values
+        // expected by Core Animation (e.g. 0.0, 0.5, 1.0).
+        $0.cgFloatValue / 100
+      },
+      context: context)
+  }
+
+  private func addShadowColorAnimation(from model: DropShadowModel, context: LayerAnimationContext) throws {
+    guard let shadowColorKeyframes = model._color else { return }
+
+    try addAnimation(
+      for: .shadowColor,
+      keyframes: shadowColorKeyframes,
+      value: \.cgColorValue,
+      context: context)
+  }
+
+  private func addShadowRadiusAnimation(from model: DropShadowModel, context: LayerAnimationContext) throws {
+    guard let shadowSizeKeyframes = model._radius else { return }
+
+    try addAnimation(
+      for: .shadowRadius,
+      keyframes: shadowSizeKeyframes,
+      value: \.cgFloatValue,
+      context: context)
+  }
+
+  private func addShadowOffsetAnimation(from model: DropShadowModel, context: LayerAnimationContext) throws {
+    guard
+      let angleKeyframes = model._angle,
+      let distanceKeyframes = model._distance
+    else { return }
+
+    let offsetKeyframes = Keyframes.combined(angleKeyframes, distanceKeyframes) { angleDegrees, distance -> CGSize in
+      // Lottie animation files express rotation in degrees
+      // (e.g. 90º, 180º, 360º) so we convert to radians to get the
+      // values expected by Core Animation (e.g. π/2, π, 2π)
+      let angleRadians = (angleDegrees.cgFloatValue * .pi) / 180
+
+      // Lottie animation files express the `shadowOffset` as (angle, distance) pair,
+      // which we convert to the expected x / y offset values:
+      let offsetX = distance.cgFloatValue * cos(angleRadians)
+      let offsetY = distance.cgFloatValue * sin(angleRadians)
+      return CGSize(width: offsetX, height: offsetY)
+    }
+
+    try addAnimation(
+      for: .shadowOffset,
+      keyframes: offsetKeyframes,
+      value: { $0 },
+      context: context)
+  }
+
+}

Sources/Private/CoreAnimation/Animations/LayerProperty.swift

@@ -26,6 +26,16 @@ struct LayerProperty<ValueRepresentation> {
 }
 
 extension LayerProperty where ValueRepresentation: Equatable {
+  /// Initializes a `LayerProperty` that corresponds to a property on `CALayer`
+  /// or some other `CALayer` subclass like `CAShapeLayer`.
+  /// - Parameters:
+  ///   - caLayerKeypath: The Objective-C `#keyPath` to the `CALayer` property,
+  ///     e.g. `#keyPath(CALayer.opacity)` or `#keyPath(CAShapeLayer.path)`.
+  ///   - defaultValue: The default value of the property (e.g. the value of the
+  ///     property immediately after calling `CALayer.init()`). Knowing this value
+  ///     lets us perform some optimizations in `CALayer+addAnimation`.
+  ///   - customizableProperty: A description of how this property can be customized
+  ///     dynamically at runtime using `AnimationView.setValueProvider(_:keypath:)`.
   init(
     caLayerKeypath: String,
     defaultValue: ValueRepresentation?,
@@ -159,6 +169,34 @@ extension LayerProperty {
       },
       customizableProperty: nil /* currently unsupported */ )
   }
+
+  static var shadowOpacity: LayerProperty<CGFloat> {
+    .init(
+      caLayerKeypath: #keyPath(CALayer.shadowOpacity),
+      defaultValue: 0,
+      customizableProperty: nil /* currently unsupported */ )
+  }
+
+  static var shadowColor: LayerProperty<CGColor> {
+    .init(
+      caLayerKeypath: #keyPath(CALayer.shadowColor),
+      defaultValue: .rgb(0, 0, 0),
+      customizableProperty: nil /* currently unsupported */ )
+  }
+
+  static var shadowRadius: LayerProperty<CGFloat> {
+    .init(
+      caLayerKeypath: #keyPath(CALayer.shadowRadius),
+      defaultValue: 3.0,
+      customizableProperty: nil /* currently unsupported */ )
+  }
+
+  static var shadowOffset: LayerProperty<CGSize> {
+    .init(
+      caLayerKeypath: #keyPath(CALayer.shadowOffset),
+      defaultValue: CGSize(width: 0, height: -3.0),
+      customizableProperty: nil /* currently unsupported */ )
+  }
 }
 
 // MARK: CAShapeLayer properties

Sources/Private/CoreAnimation/Animations/TransformAnimations.swift

@@ -6,7 +6,7 @@ import QuartzCore
 // MARK: - TransformModel
 
 /// This protocol mirrors the interface of `Transform`,
-/// but it also implemented by `ShapeTransform` to allow
+/// but is also implemented by `ShapeTransform` to allow
 /// both transform types to share the same animation implementation.
 protocol TransformModel {
   /// The anchor point of the transform.

Sources/Private/CoreAnimation/Layers/BaseCompositionLayer.swift

@@ -67,6 +67,15 @@ class BaseCompositionLayer: BaseAnimationLayer {
         inFrame: CGFloat(baseLayerModel.inFrame),
         outFrame: CGFloat(baseLayerModel.outFrame),
         context: context)
+
+      // There are two different drop shadow schemas, either using `DropShadowEffect` or `DropShadowStyle`.
+      // If both happen to be present, prefer the `DropShadowEffect` (which is the drop shadow schema
+      // supported on other platforms).
+      let dropShadowEffect = baseLayerModel.effects.first(where: { $0 is DropShadowEffect }) as? DropShadowModel
+      let dropShadowStyle = baseLayerModel.styles.first(where: { $0 is DropShadowStyle }) as? DropShadowModel
+      if let dropShadowModel = dropShadowEffect ?? dropShadowStyle {
+        try contentsLayer.addDropShadowAnimations(for: dropShadowModel, context: context)
+      }
     }
   }
 

Sources/Private/Model/Extensions/KeyedDecodingContainerExtensions.swift

@@ -41,4 +41,30 @@ extension KeyedDecodingContainer {
     }
     return list
   }
+
+  /// Decode a heterogeneous list of objects for a given family if the given key is present.
+  /// - Parameters:
+  ///     - heterogeneousType: The decodable type of the list.
+  ///     - family: The ClassFamily enum for the type family.
+  ///     - key: The CodingKey to look up the list in the current container.
+  /// - Returns: The resulting list of heterogeneousType elements.
+  func decodeIfPresent<T: Decodable, U: ClassFamily>(_: [T].Type, ofFamily family: U.Type, forKey key: K) throws -> [T]? {
+    var container: UnkeyedDecodingContainer
+    do {
+      container = try nestedUnkeyedContainer(forKey: key)
+    } catch {
+      return nil
+    }
+
+    var list = [T]()
+    var tmpContainer = container
+    while !container.isAtEnd {
+      let typeContainer = try container.nestedContainer(keyedBy: Discriminator.self)
+      let family: U = try typeContainer.decode(U.self, forKey: U.discriminator)
+      if let type = family.getType() as? T.Type {
+        list.append(try tmpContainer.decode(type))
+      }
+    }
+    return list
+  }
 }

Sources/Private/Model/Keyframes/KeyframeGroup.swift

@@ -14,7 +14,6 @@ import Foundation
 /// Keyframe data is wrapped in a dictionary { "k" : KeyframeData }.
 /// The keyframe data can either be an array of keyframes or, if no animation is present, the raw value.
 /// This helper object is needed to properly decode the json.
-
 final class KeyframeGroup<T> {
 
   // MARK: Lifecycle

Sources/Private/Model/LayerEffects/DropShadowEffect.swift

@@ -0,0 +1,45 @@
+// Created by Cal Stephens on 8/14/23.
+// Copyright © 2023 Airbnb Inc. All rights reserved.
+
+import Foundation
+
+final class DropShadowEffect: LayerEffect {
+
+  // MARK: Lifecycle
+
+  required init(from decoder: Decoder) throws {
+    try super.init(from: decoder)
+  }
+
+  required init(dictionary: [String: Any]) throws {
+    try super.init(dictionary: dictionary)
+  }
+
+  // MARK: Internal
+
+  /// The color of the drop shadow
+  var color: ColorEffectValue? {
+    value(named: "Shadow Color")
+  }
+
+  /// Opacity between 0 and 255
+  var opacity: Vector1DEffectValue? {
+    value(named: "Opacity")
+  }
+
+  /// The direction / angle of the drop shadow, in degrees
+  var direction: Vector1DEffectValue? {
+    value(named: "Direction")
+  }
+
+  /// The distance of the drop shadow
+  var distance: Vector1DEffectValue? {
+    value(named: "Distance")
+  }
+
+  /// The softness of the drop shadow
+  var softness: Vector1DEffectValue? {
+    value(named: "Softness")
+  }
+
+}

Sources/Private/Model/LayerEffects/EffectValues/ColorEffectValue.swift

@@ -0,0 +1,38 @@
+// Created by Cal Stephens on 8/14/23.
+// Copyright © 2023 Airbnb Inc. All rights reserved.
+
+import Foundation
+
+final class ColorEffectValue: EffectValue {
+
+  // MARK: Lifecycle
+
+  required init(from decoder: Decoder) throws {
+    let container = try decoder.container(keyedBy: CodingKeys.self)
+    value = try? container.decode(KeyframeGroup<LottieColor>.self, forKey: .value)
+    try super.init(from: decoder)
+  }
+
+  required init(dictionary: [String: Any]) throws {
+    let valueDictionary: [String: Any] = try dictionary.value(for: CodingKeys.value)
+    value = try KeyframeGroup<LottieColor>(dictionary: valueDictionary)
+    try super.init(dictionary: dictionary)
+  }
+
+  // MARK: Internal
+
+  /// The value of the color
+  let value: KeyframeGroup<LottieColor>?
+
+  override func encode(to encoder: Encoder) throws {
+    try super.encode(to: encoder)
+    var container = encoder.container(keyedBy: CodingKeys.self)
+    try container.encode(value, forKey: .value)
+  }
+
+  // MARK: Private
+
+  private enum CodingKeys: String, CodingKey {
+    case value = "v"
+  }
+}