Reanimated + Skia Performance

Defaults

Keep animation state on the UI thread:
```
useSharedValue
```
,
```
useDerivedValue
```
, worklets.
Prefer Reanimated v4 declarative APIs; avoid legacy
```
Animated
```
.
Prefer
```
shared.get()
```
/
```
shared.set()
```
over
```
shared.value
```
in app code (React Compiler friendly).
Minimize JS↔UI crossings: avoid
```
scheduleOnRN
```
/
```
runOnJS
```
except for unavoidable side effects.
For Skia, avoid per-frame React renders: pass
```
SharedValue
```
s directly to Skia props/uniforms.

Workflow

Define the effect: what animates, duration/curve, interrupt rules, and gesture input.
Choose the renderer:
- Use Reanimated styles for transforms/opacity/layout.
- Use Skia for custom drawing, particles, gradients, runtime effects/shaders.
Choose the primitive:
- Use Reanimated CSS transitions/animations for simple declarative style changes.
- Use
```
withTiming
```
  for tweens,
```
withSpring
```
  for physics,
```
withDecay
```
  for momentum.
- Use Layout Animations for mount/unmount or layout changes.
Implement a single data flow on the UI thread (no
```
setState
```
per frame).
Do a perf pass (see
```
references/perf-checklist.md
```
).

Patterns

Shared values (React Compiler safe)

Read:
```
progress.get()
```
Write:
```
progress.set(withTiming(1))
```

import { useEffect } from 'react';
import { useSharedValue, withTiming } from 'react-native-reanimated';

const progress = useSharedValue(0);

useEffect(() => {
  progress.set(withTiming(1, { duration: 400 }));
}, [progress]);

Reanimated v4 CSS transitions

Use for state-driven style changes where you do not need bespoke worklets.

tsx

import Animated from 'react-native-reanimated';

<Animated.View
  style={{
    width: expanded ? 240 : 160,
    opacity: enabled ? 1 : 0.6,
    transitionProperty: ['width', 'opacity'],
    transitionDuration: 220,
    transitionTimingFunction: 'ease-in-out',
  }}
/>

Reanimated v4 CSS animations (keyframes)

Use for keyframe-like sequences (pulses, wiggles, repeated loops) without writing custom worklets.

Supported settings:

```
animationName
```
(keyframes object)
```
animationDuration
```
```
animationDelay
```
```
animationTimingFunction
```
```
animationDirection
```
```
animationIterationCount
```
```
animationFillMode
```
```
animationPlayState
```

tsx

import Animated from 'react-native-reanimated';

const pulse = {
  from: { transform: [{ scale: 1 }], opacity: 0.9 },
  '50%': { transform: [{ scale: 1.06 }], opacity: 1 },
  to: { transform: [{ scale: 1 }], opacity: 0.9 },
};

<Animated.View
  style={{
    animationName: pulse,
    animationDuration: '900ms',
    animationDelay: '80ms',
    animationTimingFunction: 'ease-in-out',
    animationDirection: 'alternate',
    animationIterationCount: 'infinite',
    animationFillMode: 'both',
    animationPlayState: paused ? 'paused' : 'running',
  }}
/>

Dev-mode tuning panel (sliders)

Use sliders to tune animation configs or shader uniforms in

__DEV__

Keep the tuning UI in a separate component to avoid re-rendering the animated scene.
Write slider values into
```
SharedValue
```
s via
```
.set()
```
.
For shader tuning: feed
```
SharedValue
```
s into uniforms via
```
useDerivedValue
```
.
For animation config tuning: store config params in
```
SharedValue
```
s and read them when starting/restarting the animation.

See:

references/dev-tuning.md

Gesture-driven animation (Gesture Builder API)

Update shared values in

onUpdate

and drive visuals via animated styles.

tsx

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

const x = useSharedValue(0);
const gesture = Gesture.Pan()
  .onUpdate((e) => {
    x.set(e.translationX);
  })
  .onEnd(() => {
    x.set(withSpring(0));
  });

const style = useAnimatedStyle(() => ({ transform: [{ translateX: x.get() }] }));

<GestureDetector gesture={gesture}>
  <Animated.View style={style} />
</GestureDetector>;

Skia shader with animated uniforms

Compile the runtime effect once (
```
useMemo
```
).
Pass uniforms as a
```
SharedValue<Uniforms>
```
(Skia detects animated props by
```
{ value: T }
```
).
Do not access
```
.value
```
in your app code; pass the
```
SharedValue
```
object.

tsx

import { useMemo } from 'react';
import { Skia, Canvas, Fill, Paint, Shader, type Uniforms } from '@shopify/react-native-skia';
import { useDerivedValue } from 'react-native-reanimated';
import { useClock } from '@shopify/react-native-skia';

const sksl = `
uniform float2 u_resolution;
uniform float u_time;

half4 main(float2 xy) {
  float2 uv = xy / u_resolution;
  float v = 0.5 + 0.5 * sin(u_time * 0.002 + uv.x * 8.0);
  return half4(v, v * 0.6, 1.0 - v, 1.0);
}
`;

const effect = useMemo(() => Skia.RuntimeEffect.Make(sksl), []);
if (!effect) return null;

const clock = useClock(); // ms since first frame
const uniforms = useDerivedValue<Uniforms>(() => ({
  u_resolution: Skia.Point(width, height),
  u_time: clock.get(),
}));

<Canvas style={{ width, height }}>
  <Fill>
    <Paint>
      <Shader source={effect} uniforms={uniforms} />
    </Paint>
  </Fill>
</Canvas>;

Common pitfalls

Do not read shared values in React render; read them in worklets (
```
useAnimatedStyle
```
,
```
useDerivedValue
```
).
Do not call
```
runOnJS
```
/
```
scheduleOnRN
```
in
```
onUpdate
```
unless you must.
Do not allocate big arrays/paths/images per frame; memoize Skia objects and update via animated props.
For runtime effects, always provide every uniform declared in the shader; missing uniforms throw.

References

Reanimated v4 patterns and repo conventions:
```
references/reanimated-v4.md
```
Skia Canvas + runtime effects/shaders patterns:
```
references/skia-shaders.md
```
Dev-mode tuning panels (sliders):
```
references/dev-tuning.md
```
Performance checklist + debugging:
```
references/perf-checklist.md
```

reanimated-skia-performance

NPX Install

Tags

SKILL.md Content