axiom-swiftui-animation-ref

# SwiftUI Animation

## Overview

Comprehensive guide to SwiftUI's animation system, from foundational concepts to advanced techniques. This skill covers the Animatable protocol, the iOS 26 @Animatable macro, animation types, and the Transaction system.

**Core principle** Animation in SwiftUI is mathematical interpolation over time, powered by the VectorArithmetic protocol. Understanding this foundation unlocks the full power of SwiftUI's declarative animation system.

## When to Use This Skill

- Implementing custom animated views or shapes
- Understanding why a property doesn't animate (Int vs Float/Double)
- Choosing between spring and timing curve animations
- Using the @Animatable macro (iOS 26+)
- Conforming views to the Animatable protocol
- Debugging animation merging behavior
- Optimizing animation performance
- Creating multi-step or complex animations
- Understanding model vs presentation values
- Implementing custom animation algorithms
- Adding zoom transitions for navigation/presentation (iOS 18+)
- Animating UIKit/AppKit views with SwiftUI animations (iOS 18+)
- Bridging animations through UIViewRepresentable (iOS 18+)
- Building gesture-driven animations with velocity preservation

## System Requirements

#### iOS 13+ for Animatable protocol
#### iOS 17+ for default spring animations, scoped animations
#### iOS 18+ for zoom transitions, UIKit/AppKit animation bridging
#### iOS 26+ for @Animatable macro

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## Part 1: Understanding Animation

### What Is Interpolation

Animation is the process of generating intermediate values between a start and end state.

#### Example: Opacity animation

```swift
.opacity(0) → .opacity(1)
```

While this animation runs, SwiftUI computes intermediate values:

```
0.0 → 0.02 → 0.05 → 0.1 → 0.25 → 0.4 → 0.6 → 0.8 → 1.0
```

**How values are distributed**
- Determined by the animation's timing curve or velocity function
- Spring animations use physics simulation
- Timing curves use bezier curves
- Each animation typ