R3f Animation

# React Three Fiber Animation

## Quick Start

```tsx
import { Canvas, useFrame } from '@react-three/fiber'
import { useRef } from 'react'

function RotatingBox() {
  const meshRef = useRef()

  useFrame((state, delta) => {
    meshRef.current.rotation.x += delta
    meshRef.current.rotation.y += delta * 0.5
  })

  return (
    <mesh ref={meshRef}>
      <boxGeometry />
      <meshStandardMaterial color="hotpink" />
    </mesh>
  )
}

export default function App() {
  return (
    <Canvas>
      <ambientLight />
      <RotatingBox />
    </Canvas>
  )
}
```

## useFrame Hook

The core animation hook in R3F. Runs every frame.

### Basic Usage

```tsx
import { useFrame } from '@react-three/fiber'
import { useRef } from 'react'

function AnimatedMesh() {
  const meshRef = useRef()

  useFrame((state, delta) => {
    // state contains: clock, camera, scene, gl, mouse, etc.
    // delta is time since last frame in seconds

    meshRef.current.rotation.y += delta
  })

  return (
    <mesh ref={meshRef}>
      <boxGeometry />
      <meshStandardMaterial color="orange" />
    </mesh>
  )
}
```

### State Object

```tsx
useFrame((state, delta, xrFrame) => {
  const {
    clock,           // THREE.Clock
    camera,          // Current camera
    scene,           // Scene
    gl,              // WebGLRenderer
    mouse,           // Normalized mouse position (-1 to 1)
    pointer,         // Same as mouse
    viewport,        // Viewport dimensions
    size,            // Canvas size
    raycaster,       // Raycaster
    get,             // Get current state
    set,             // Set state
    invalidate,      // Request re-render (when frameloop="demand")
  } = state

  // Time-based animation
  const t = clock.getElapsedTime()
  meshRef.current.position.y = Math.sin(t) * 2
})
```

### Render Priority

```tsx
// Lower numbers run first. Default is 0.
// Use negative for pre-render, positive for post-render

function PreRender() {
  useFrame(() => {
    // Runs before main render
  }, -1)
}

function PostRender() {
  useFrame(() => {
    // Runs after main render
  }, 1)
}

function DefaultRender() {
  useFrame(() => {
    // Runs at default priority (0)
  })
}
```

### Conditional Animation

```tsx
function ConditionalAnimation({ isAnimating }) {
  const meshRef = useRef()

  useFrame((state, delta) => {
    if (!isAnimating) return
    meshRef.current.rotation.y += delta
  })

  return <mesh ref={meshRef}>...</mesh>
}
```

## GLTF Animations with useAnimations

The recommended way to play animations from GLTF/GLB files.

### Basic Usage

```tsx
import { useGLTF, useAnimations } from '@react-three/drei'
import { useEffect, useRef } from 'react'

function AnimatedModel() {
  const group = useRef()
  const { scene, animations } = useGLTF('/models/character.glb')
  const { actions, names } = useAnimations(animations, group)

  useEffect(() => {
    // Play first animation
    actions[names[0]]?.play()
  }, [actions, names])

  return <primitive ref={group} object={scene} />
}
```

### Animation Control

```tsx
function Character() {
  const group = useRef()
  const { scene, animations } = useGLTF('/models/character.glb')
  const { actions, mixer } = useAnimations(animations, group)

  useEffect(() => {
    const action = actions['Walk']
    if (action) {
      // Playback control
      action.play()
      action.stop()
      action.reset()
      action.paused = true

      // Speed
      action.timeScale = 1.5  // 1.5x speed
      action.timeScale = -1   // Reverse

      // Loop modes
      action.loop = THREE.LoopOnce
      action.loop = THREE.LoopRepeat
      action.loop = THREE.LoopPingPong
      action.repetitions = 3
      action.clampWhenFinished = true

      // Weight (for blending)