111 lines
5.8 KiB
Plaintext
111 lines
5.8 KiB
Plaintext
---
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id: zooming
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title: Zooming
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sidebar_label: Zooming
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---
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import useBaseUrl from '@docusaurus/useBaseUrl'
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<div class="image-container">
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<svg xmlns="http://www.w3.org/2000/svg" width="283" height="535">
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<image href={useBaseUrl("img/demo.gif")} x="18" y="33" width="247" height="469" />
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<image href={useBaseUrl("img/frame.png")} width="283" height="535" />
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</svg>
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</div>
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## Native Zoom Gesture
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The `<Camera>` component already provides a natively implemented zoom gesture which you can enable with the [`enableZoomGesture`](/docs/api/interfaces/CameraProps#enablezoomgesture) prop. If you don't need any additional logic in your zoom gesture, you can skip to the next section.
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**🚀 Next section: [Focusing](focusing)**
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If you want to setup a custom gesture, such as the one in Snapchat or Instagram where you move up your finger while recording, first understand how zoom is expressed.
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## Min, Max and Neutral Zoom
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A Camera device has different minimum, maximum and neutral zoom values. Those values are expressed through the `CameraDevice`'s [`minZoom`](/docs/api/interfaces/CameraDevice#minzoom), [`maxZoom`](/docs/api/interfaces/CameraDevice#maxzoom) and [`neutralZoom`](/docs/api/interfaces/CameraDevice#neutralzoom) props, and are represented in "scale". So if the `maxZoom` property of a device is `2`, that means the view can be enlarged by twice it's zoom, aka the viewport halves.
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* The `minZoom` value is always `1`.
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* The `maxZoom` value can have very high values (such as `128`), but often you want to clamp this value to something realistic like `16`.
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* The `neutralZoom` value is often `1`, but can be larger than `1` for devices with "fish-eye" (ultra-wide-angle) cameras. In those cases, the user expects to be at whatever zoom value `neutralZoom` is (e.g. `2`) per default, and if he tries to zoom out even more, he goes to `minZoom` (`1`), which switches over to the "fish-eye" (ultra-wide-angle) camera as seen in this GIF:
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<div align="center">
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<img class="doc-image" src="/img/multi-camera.gif" />
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</div>
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The Camera's `zoom` property expects values to be in the same "factor" scale as the `minZoom`, `neutralZoom` and `maxZoom` values - so if you pass `zoom={device.minZoom}` it is at the minimum available zoom, where as if you pass `zoom={device.maxZoom}` the maximum zoom value possible is zoomed in. It is recommended that you start at `device.neutralZoom` and let the user manually zoom out to the fish-eye camera on demand (if available).
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## Logarithmic scale
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A Camera's `zoom` property is represented in a **logarithmic scale**. That means, increasing from `1` to `2` will appear to be a much larger offset than increasing from `127` to `128`. If you want to implement a zoom gesture (`<PinchGestureHandler>`, `<PanGestureHandler>`), try to flatten the `zoom` property to a **linear scale** by raising it **exponentially**. (`zoom.value ** 2`)
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## Pinch-to-zoom
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The above example only demonstrates how to animate the `zoom` property. To actually implement pinch-to-zoom or pan-to-zoom, take a look at the [VisionCamera example app](https://github.com/mrousavy/react-native-vision-camera/tree/main/package/example), the pinch-to-zoom gesture can be found [here](https://github.com/mrousavy/react-native-vision-camera/blob/main/package/example/src/views/CaptureButton.tsx#L189-L208), and the pan-to-zoom gesture can be found [here](https://github.com/mrousavy/react-native-vision-camera/blob/d8551792e97eaa6fa768f54059ffce054bf748d9/example/src/views/CaptureButton.tsx#L185-L205). They implement a real world use-case, where the maximum zoom value is clamped to a realistic value, and the zoom responds very gracefully by using a logarithmic scale.
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## Implementation (Reanimated)
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While you can use any animation library to animate the `zoom` property (or use no animation library at all) it is recommended to use [react-native-reanimated](https://github.com/software-mansion/react-native-reanimated) to achieve best performance. Head over to their [Installation guide](https://docs.swmansion.com/react-native-reanimated/docs/installation) to install Reanimated if you haven't already.
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### Overview
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1. Make the Camera View animatable using `createAnimatedComponent`
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2. Make the Camera's `zoom` property animatable using `addWhitelistedNativeProps`
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3. Create a SharedValue using [`useSharedValue`](https://docs.swmansion.com/react-native-reanimated/docs/api/useSharedValue) which represents the zoom state (from `0` to `1`)
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4. Use [`useAnimatedProps`](https://docs.swmansion.com/react-native-reanimated/docs/api/useAnimatedProps) to map the zoom SharedValue to the zoom property.
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5. We apply the animated props to the `ReanimatedCamera` component's `animatedProps` property.
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### Code
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The following example implements a button which smoothly zooms to a random value using [react-native-reanimated](https://github.com/software-mansion/react-native-reanimated):
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```tsx
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import Reanimated, {
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useAnimatedProps,
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useSharedValue,
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withSpring,
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addWhitelistedNativeProps
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} from "react-native-reanimated"
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const ReanimatedCamera = Reanimated.createAnimatedComponent(Camera)
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addWhitelistedNativeProps({
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zoom: true,
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})
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export function App() {
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const device = useCameraDevice('back')
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const zoom = useSharedValue(0)
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const onRandomZoomPress = useCallback(() => {
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zoom.value = withSpring(Math.random())
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}, [zoom])
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const animatedProps = useAnimatedProps<Partial<CameraProps>>(
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() => ({ zoom: zoom.value }),
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[zoom]
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)
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if (device == null) return <NoCameraDeviceError />
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return (
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<>
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<ReanimatedCamera
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style={StyleSheet.absoluteFill}
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device={device}
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isActive={true}
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animatedProps={animatedProps}
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/>
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<TouchableOpacity
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style={styles.zoomButton}
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onPress={onRandomZoomPress}>
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<Text>Zoom randomly!</Text>
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</TouchableOpacity>
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</>
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)
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}
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```
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<br />
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#### 🚀 Next section: [Focusing](focusing)
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