Animation Patterns

Correct API shapes and patterns for SwiftUI animations. Prevents the most common mistakes: mixed spring parameter generations, wrong PhaseAnimator/KeyframeAnimator closure signatures, and using matchedGeometryEffect where matchedTransitionSource is needed.

When This Skill Activates

Use this skill when the user:

• Asks to add, fix, or review animation code
• Mentions spring, bounce, or snappy animations
• Wants view transitions (insertion/removal, hero, zoom)
• Asks about PhaseAnimator or KeyframeAnimator
• Wants SF Symbol effects (bounce, pulse, wiggle, breathe)
• Mentions matchedGeometryEffect or matchedTransitionSource
• Asks about reduce motion / animation accessibility
• Wants to sequence or chain animations
• Mentions withAnimation, animation completions, or Transaction
• Wants scroll-driven effects (parallax, carousels, scrollTransition, visualEffect)
• Mentions MeshGradient, TextRenderer, or Metal shader effects (colorEffect, distortionEffect, layerEffect)

Decision Tree

Choose the right reference file based on what the user needs:

What are you animating?
│
├─ A state change (opacity, position, color)
│  └─ → core-animations.md
│     ├─ withAnimation { } — explicit animation
│     ├─ .animation(_:value:) — implicit animation
│     └─ Spring configuration — .spring, .bouncy, .snappy, .smooth
│
├─ A multi-step / sequenced animation
│  └─ → phase-keyframe-animators.md (PhaseAnimator)
│     └─ Cycles through discrete phases automatically or on trigger
│
├─ A complex multi-property animation (scale + rotation + offset)
│  └─ → phase-keyframe-animators.md (KeyframeAnimator)
│     └─ Timeline-based keyframes with per-property tracks
│
├─ A view appearing / disappearing
│  └─ → transitions.md
│     ├─ .transition() — insertion/removal
│     ├─ .contentTransition() — text/symbol changes
│     └─ .asymmetric() — different in/out
│
├─ A hero / zoom navigation transition
│  └─ → transitions.md (matchedTransitionSource section)
│     ├─ iOS 18+: matchedTransitionSource + .navigationTransition(.zoom)
│     ├─ UIKit: preferredTransition = .zoom (capture stable IDs, never views)
│     └─ iOS 14+: matchedGeometryEffect (NOT for NavigationStack)
│
├─ A UIKit view driven by SwiftUI state or gestures
│  └─ → transitions.md (Bridging UIKit and SwiftUI Animations)
│     └─ UIView.animate(.spring(...)) / context.animate in updateUIView
│
├─ An SF Symbol animation
│  └─ → symbol-effects.md
│     └─ .symbolEffect(.bounce), .pulse, .wiggle, .breathe, .rotate
│
├─ A scroll-driven, geometry-driven, or shader effect
│  └─ → visual-effects.md
│     ├─ .scrollTransition — carousel scale/parallax/caption fades
│     ├─ .visualEffect — position-based effects without GeometryReader
│     ├─ MeshGradient — animatable multi-point gradients
│     ├─ TextRenderer — per-line / per-glyph text animation
│     └─ ShaderLibrary + .colorEffect / .distortionEffect / .layerEffect
│
└─ Spring physics / timing configuration
   └─ → core-animations.md (Spring Configurations section)

API Availability

API	Minimum Version	Reference
withAnimation	iOS 13	core-animations.md
.animation(_:value:)	iOS 13	core-animations.md
.spring(response:dampingFraction:)	iOS 13	core-animations.md
.matchedGeometryEffect	iOS 14	transitions.md
.transition(.push(from:))	iOS 16	transitions.md
.contentTransition(.numericText())	iOS 16	transitions.md
PhaseAnimator	iOS 17	phase-keyframe-animators.md
KeyframeAnimator	iOS 17	phase-keyframe-animators.md
.spring(duration:bounce:)	iOS 17	core-animations.md
Spring presets (.bouncy, .snappy, .smooth)	iOS 17	core-animations.md
withAnimation(_:completionCriteria:_:completion:)	iOS 17	core-animations.md
.symbolEffect()	iOS 17	symbol-effects.md
.transition(.blurReplace)	iOS 17	transitions.md
.contentTransition(.symbolEffect(.replace))	iOS 17	transitions.md
Transition protocol / TransitionPhase	iOS 17	transitions.md
TransactionKey, scoped .animation / .transaction variants	iOS 17	core-animations.md
KeyframeTimeline, .mapCameraKeyframeAnimator	iOS 17	phase-keyframe-animators.md
.scrollTransition, .visualEffect	iOS 17	visual-effects.md
Shaders: .colorEffect / .distortionEffect / .layerEffect	iOS 17	visual-effects.md
MeshGradient	iOS 18	visual-effects.md
TextRenderer / TextAttribute	iOS 18	visual-effects.md
.matchedTransitionSource	iOS 18	transitions.md
.navigationTransition(.zoom) — push, sheet, fullScreenCover	iOS 18	transitions.md
UIViewController.preferredTransition = .zoom	iOS 18	transitions.md
UIView.animate(_: Animation) / context.animate	iOS 18	transitions.md

Top 5 Mistakes — Quick Reference

#	Mistake	Fix	Details
1	spring(response:bounce:) — mixing parameter generations	Use either spring(response:dampingFraction:) (iOS 13) or spring(duration:bounce:) (iOS 17)	core-animations.md
2	.animation(.spring()) without value: parameter	Always pass value: — the no-value variant is deprecated (iOS 15)	core-animations.md
3	Wrong PhaseAnimator closure signature	PhaseAnimator(phases) { content, phase in } — not { phase in }	phase-keyframe-animators.md
4	Using matchedGeometryEffect for NavigationStack transitions	Use matchedTransitionSource + .navigationTransition(.zoom) on iOS 18+	transitions.md
5	Using withAnimation for SF Symbol effects	Use .symbolEffect() modifier instead	symbol-effects.md

Review Checklist

When reviewing animation code, verify:

• Reduce motion — animations respect AccessibilityMotionEffect or UIAccessibility.isReduceMotionEnabled; provide non-motion alternatives
• Duration limits — no animation exceeds ~0.5s for UI feedback; longer only for decorative/ambient effects
• Spring vs linear — springs for interactive/physical motion; linear/easeInOut only for opacity fades or progress indicators
• No deprecated APIs — .animation(.spring()) without value: is deprecated; .animation(nil) is replaced by withTransaction
• Correct spring generation — parameter names match the same API generation (never mix response with bounce)
• Completion handlers — using withAnimation(_:completionCriteria:_:completion:) (iOS 17+), not inventing .onAnimationCompleted
• Transition scope — .transition() only affects views inside if/switch controlled by state; not for views that are always present
• Per-frame closures stay cheap — KeyframeAnimator content closures, visualEffect closures, TextRenderer.draw, and Animatable view bodies run every frame; no allocation, formatting, or layout math inside

Reference Files

File	Content
core-animations.md	withAnimation, springs, completions, transactions + TransactionKey, timing curves, Animatable mechanics, fluid-interface principles (momentum projection, rubber-banding, hysteresis)
phase-keyframe-animators.md	PhaseAnimator, KeyframeAnimator, KeyframeTimeline, MapKit camera keyframes, custom animations
transitions.md	View transitions, custom Transition protocol, matched geometry, navigation/zoom transitions (SwiftUI + UIKit), interruptibility, UIKit↔SwiftUI bridging, gesture-driven springs
symbol-effects.md	SF Symbol effects, accessibility
visual-effects.md	scrollTransition, visualEffect, MeshGradient, TextRenderer, shader effects (colorEffect/distortionEffect/layerEffect), effect pipelines, semantic alignment guides