core-animation

name: core-animation description: Use when writing or reviewing CALayer, CAAnimation, UIViewPropertyAnimator, or UIKit animation bridges.

Core Animation

Review and write Core Animation code for correct layer management, animation timing, and SwiftUI-UIKit bridging.

Responsibility

Owns: CALayer properties and sublayers, CABasicAnimation, CAKeyframeAnimation, CAAnimationGroup, CATransaction, UIViewPropertyAnimator, UIView.animate, UIViewRepresentable animation bridging, CADisplayLink, CAGradientLayer, CAShapeLayer, CAEmitterLayer.

Does NOT own: SwiftUI animations (swiftui-patterns skill), Metal rendering, SpriteKit/SceneKit, RealityKit.

Core Principles

1. SwiftUI animation first. Only drop to Core Animation when SwiftUI can't express the animation (custom timing curves, layer-specific effects, complex keyframes).
2. Layers are not views. CALayer is lighter weight but has no responder chain, no accessibility, no Auto Layout.
3. Animate properties, not frames. Use transform, opacity, position, cornerRadius — not frame.
4. CATransaction for implicit animation control. Wrap property changes in CATransaction to control or disable implicit animations.
5. UIViewRepresentable for bridging. Use animate(changes:completion:) context method (iOS 17+) to coordinate UIKit and SwiftUI animations.

References

• references/core-animation-patterns.md — Layer types, animation APIs, timing, UIKit bridging