react-native-vision-camera/docs/DEVICES.md

<table>
<tr>
<th><a href="../README.md">README</a></th>
<th>DEVICES</th>
<th><a href="./FORMATS.md">FORMATS</a></th>
<th><a href="./FRAME_PROCESSORS.md">FRAME_PROCESSORS</a></th>
<th><a href="./ANIMATED.md">ANIMATED</a></th>
<th><a href="./ERRORS.md">ERRORS</a></th>
</tr>
</table>

<br/>

<h1 align="center">Devices</h1>

<div>
  <img align="right" width="35%" src="../img/ultra-wide-demo.gif">
</div>

### What are camera devices?

Camera devices are the physical (or "virtual") devices that can be used to record videos or capture photos.

* **Physical**: A physical camera device is a **camera lens on your phone**. Different physical camera devices have different specifications, such as different capture formats, field of views, focal lengths, and more. Some phones have multiple physical camera devices.

  > Examples: _"Backside Wide-Angle Camera"_, _"Frontside Wide-Angle Camera (FaceTime HD)"_, _"Ultra-Wide-Angle back camera"_.

* **Virtual**: A virtual camera device is a **combination of one or more physical camera devices**, and provides features such as _virtual-device-switchover_ while zooming or _combined photo delivery_ from all physiscal cameras to produce higher quality images.

  > Examples: _"Triple-Camera"_, _"Dual-Wide-Angle Camera"_

### Get available camera devices

To get a list of all available camera devices, use the `getAvailableCameraDevices` function:

```ts
const devices = await Camera.getAvailableCameraDevices()
```

> [🔗 See the `CameraDevice` type](./../src/CameraDevice.ts)

A camera device (`CameraDevice`) contains a list of physical device types this camera device consists of.

Example:
* For a single Wide-Angle camera, this would be `["wide-angle-camera"]`
* For a Triple-Camera, this would be `["wide-angle-camera", "ultra-wide-angle-camera", "telephoto-camera"]`

You can use the helper function `parsePhysicalDeviceTypes` to convert a list of physical devices to a single device descriptor type which can also describe virtual devices:

```ts
console.log(device.devices)
//  --> ["wide-angle-camera", "ultra-wide-angle-camera", "telephoto-camera"]

const deviceType = parsePhysicalDeviceTypes(device.devices)
console.log(deviceType)
//  --> "triple-camera"
```

The `CameraDevice` type also contains other useful information describing a camera device, such as `position` ("front", "back", ...), `hasFlash`, it's `formats` (See [FORMATS.md](./FORMATS.md)), and more.

Make sure to carefully filter out unneeded camera devices, since not every phone supports all camera device types. Some phones don't even have front-cameras.

<div>
  <img align="right" width="35%" src="../img/11_back.png">
</div>

### `useCameraDevices` hook

The react-native-vision-camera library provides a hook to make camera device selection a lot easier.

You can specify a device type to only find devices with the given type:

```tsx
function App() {
  const devices = useCameraDevices('wide-angle-camera')
  const device = devices.back

  return (
    <Camera
      style={StyleSheet.absoluteFill}
      device={device}
    />
  )
}
```

Or just return the "best matching camera device". This function prefers camera devices with more physical cameras, and always ranks "wide-angle" physical camera devices first.

> Example: `triple-camera` > `dual-wide-camera` > `dual-camera` > `wide-angle-camera` > `ultra-wide-angle-camera` > `telephoto-camera` > ...

```tsx
function App() {
  const devices = useCameraDevices()
  const device = devices.back

  return (
    <Camera
      style={StyleSheet.absoluteFill}
      device={device}
    />
  )
}
```

### The `isActive` prop

The Camera's `isActive` property can be used to _pause_ the session (`isActive={false}`) while still keeping the session "warm". This is more desirable than completely unmounting the camera, since _resuming_ the session (`isActive={true}`) will be **much faster** than re-mounting the camera view.

For example, you want to **pause the camera** when the user **navigates to another page** or **minimizes the app** since otherwise the camera continues to run in the background without the user seeing it, causing **siginificant battery drain**. Also, on iOS a green dot indicates the user that the camera is still active, possibly causing the user to raise privacy concerns. (🔗 See ["About the orange and green indicators in your iPhone status bar"](https://support.apple.com/en-us/HT211876))

This example demonstrates how you could pause the camera stream once the app goes into background using a custom `useIsAppForeground` hook:

```tsx
function App() {
  const devices = useCameraDevices()
  const device = devices.back
  const isAppForeground = useIsAppForeground()

  return (
    <Camera
      style={StyleSheet.absoluteFill}
      device={device}
      isActive={isAppForeground}
    />
  )
}
```

> Note: If you don't care about fast resume times you can also fully unmount the `<Camera>` view instead, which will use a lot less memory (RAM).