lamp/.agents/skills/building-native-ui/references/animations.md

# Animations

Use Reanimated v4. Avoid React Native's built-in Animated API.

## Entering and Exiting Animations

Use Animated.View with entering and exiting animations. Layout animations can animate state changes.

```tsx
import Animated, {
  FadeIn,
  FadeOut,
  LinearTransition,
} from "react-native-reanimated";

function App() {
  return (
    <Animated.View
      entering={FadeIn}
      exiting={FadeOut}
      layout={LinearTransition}
    />
  );
}
```

## On-Scroll Animations

Create high-performance scroll animations using Reanimated's hooks:

```tsx
import Animated, {
  useAnimatedRef,
  useScrollViewOffset,
  useAnimatedStyle,
  interpolate,
} from "react-native-reanimated";

function Page() {
  const ref = useAnimatedRef();
  const scroll = useScrollViewOffset(ref);

  const style = useAnimatedStyle(() => ({
    opacity: interpolate(scroll.value, [0, 30], [0, 1], "clamp"),
  }));

  return (
    <Animated.ScrollView ref={ref}>
      <Animated.View style={style} />
    </Animated.ScrollView>
  );
}
```

## Common Animation Presets

### Entering Animations

- `FadeIn`, `FadeInUp`, `FadeInDown`, `FadeInLeft`, `FadeInRight`
- `SlideInUp`, `SlideInDown`, `SlideInLeft`, `SlideInRight`
- `ZoomIn`, `ZoomInUp`, `ZoomInDown`
- `BounceIn`, `BounceInUp`, `BounceInDown`

### Exiting Animations

- `FadeOut`, `FadeOutUp`, `FadeOutDown`, `FadeOutLeft`, `FadeOutRight`
- `SlideOutUp`, `SlideOutDown`, `SlideOutLeft`, `SlideOutRight`
- `ZoomOut`, `ZoomOutUp`, `ZoomOutDown`
- `BounceOut`, `BounceOutUp`, `BounceOutDown`

### Layout Animations

- `LinearTransition` — Smooth linear interpolation
- `SequencedTransition` — Sequenced property changes
- `FadingTransition` — Fade between states

## Customizing Animations

```tsx
<Animated.View
  entering={FadeInDown.duration(500).delay(200)}
  exiting={FadeOut.duration(300)}
/>
```

### Modifiers

```tsx
// Duration in milliseconds
FadeIn.duration(300);

// Delay before starting
FadeIn.delay(100);

// Spring physics
FadeIn.springify();
FadeIn.springify().damping(15).stiffness(100);

// Easing curves
FadeIn.easing(Easing.bezier(0.25, 0.1, 0.25, 1));

// Chaining
FadeInDown.duration(400).delay(200).springify();
```

## Shared Value Animations

For imperative control over animations:

```tsx
import {
  useSharedValue,
  withSpring,
  withTiming,
} from "react-native-reanimated";

const offset = useSharedValue(0);

// Spring animation
offset.value = withSpring(100);

// Timing animation
offset.value = withTiming(100, { duration: 300 });

// Use in styles
const style = useAnimatedStyle(() => ({
  transform: [{ translateX: offset.value }],
}));
```

## Gesture Animations

Combine with React Native Gesture Handler:

```tsx
import { Gesture, GestureDetector } from "react-native-gesture-handler";
import Animated, {
  useSharedValue,
  useAnimatedStyle,
  withSpring,
} from "react-native-reanimated";

function DraggableBox() {
  const translateX = useSharedValue(0);
  const translateY = useSharedValue(0);

  const gesture = Gesture.Pan()
    .onUpdate((e) => {
      translateX.value = e.translationX;
      translateY.value = e.translationY;
    })
    .onEnd(() => {
      translateX.value = withSpring(0);
      translateY.value = withSpring(0);
    });

  const style = useAnimatedStyle(() => ({
    transform: [
      { translateX: translateX.value },
      { translateY: translateY.value },
    ],
  }));

  return (
    <GestureDetector gesture={gesture}>
      <Animated.View style={[styles.box, style]} />
    </GestureDetector>
  );
}
```

## Keyboard Animations

Animate with keyboard height changes:

```tsx
import Animated, {
  useAnimatedKeyboard,
  useAnimatedStyle,
} from "react-native-reanimated";

function KeyboardAwareView() {
  const keyboard = useAnimatedKeyboard();

  const style = useAnimatedStyle(() => ({
    paddingBottom: keyboard.height.value,
  }));

  return <Animated.View style={style}>{/* content */}</Animated.View>;
}
```

## Staggered List Animations

Animate list items with delays:

```tsx
{
  items.map((item, index) => (
    <Animated.View
      key={item.id}
      entering={FadeInUp.delay(index * 50)}
      exiting={FadeOutUp}
    >
      <ListItem item={item} />
    </Animated.View>
  ));
}
```

## Best Practices

- Add entering and exiting animations for state changes
- Use layout animations when items are added/removed from lists
- Use `useAnimatedStyle` for scroll-driven animations
- Prefer `interpolate` with "clamp" for bounded values
- You can't pass PlatformColors to reanimated views or styles; use static colors instead
- Keep animations under 300ms for responsive feel
- Use spring animations for natural movement
- Avoid animating layout properties (width, height) when possible — prefer transforms