VisionCamera Patterns

Quick Guide: Use VisionCamera for high-performance camera features in React Native. Control the camera lifecycle with isActive (never unmount/remount). Use useCameraDevice to select back/front cameras, useCameraPermission for permissions. Capture photos with takePhoto(), record video with startRecording()/stopRecording(), scan codes with useCodeScanner, and process frames in real time with useFrameProcessor worklets. Frame processors run on a parallel JS thread via JSI -- keep them fast or use runAsync/runAtTargetFps to avoid blocking the pipeline.

---

<critical_requirements>

CRITICAL: Before Using This Skill

All code must follow project conventions in CLAUDE.md (kebab-case, named exports, import ordering, import type, named constants)

(You MUST set isActive based on screen focus AND app state -- camera must pause when backgrounded or navigated away)

(You MUST request permissions before rendering the Camera -- useCameraPermission returns hasPermission and requestPermission)

(You MUST include the 'worklet' directive as the first line of every frame processor function body)

(You MUST enable only the pipelines you need (photo, video, codeScanner, frameProcessor) -- unused pipelines waste resources)

(You MUST use useSharedValue (not useState) for data shared between frame processors and the React thread)

</critical_requirements>

---

Auto-detection: VisionCamera, react-native-vision-camera, useCameraDevice, useCameraDevices, useCameraPermission, useMicrophonePermission, useCodeScanner, useFrameProcessor, useSkiaFrameProcessor, useCameraFormat, takePhoto, takeSnapshot, startRecording, stopRecording, Camera component, frame processor, worklet, codeScanner, photoQualityBalance, enableLocation, videoHdr, photoHdr

When to use:

• Capturing photos or recording video in a React Native app
• Scanning QR codes or barcodes (EAN-13, Code-128, etc.)
• Real-time frame processing for ML, object detection, or image analysis
• Implementing zoom, focus, exposure, or HDR controls
• Embedding GPS location metadata in captured media
• Selecting specific camera devices (ultra-wide, telephoto, front/back)

When NOT to use:

• Picking images from the device gallery (use an image picker)
• Simple static image display (use standard Image component)
• Web-only camera access (use browser MediaDevices API)

Key patterns covered:

• Camera lifecycle management with isActive and screen/app state
• Permission handling with hooks (useCameraPermission, useMicrophonePermission)
• Photo capture (takePhoto, takeSnapshot) and video recording
• QR/barcode scanning with useCodeScanner
• Frame processors with worklets, runAsync, and runAtTargetFps
• Device selection, format selection, zoom, focus, exposure, HDR
• Location metadata embedding
• Performance optimization (pipeline selection, buffer compression, pixel format)

Detailed Resources:

• examples/core.md - Camera setup, permissions, lifecycle, photo capture, video recording
• examples/scanning-and-processing.md - Code scanning, frame processors, worklet patterns
• reference.md - Decision frameworks, device/format selection, performance checklist

---

Philosophy

VisionCamera provides direct, high-performance camera access in React Native via JSI (JavaScript Interface). It bypasses the legacy bridge entirely, giving synchronous control over native camera hardware from JavaScript.

Core principles:

1. Lifecycle-driven -- the isActive prop controls the camera session. Toggle it instead of mounting/unmounting. Resuming is much faster than re-mounting.
2. Pipeline-based -- enable only what you need (photo, video, codeScanner, frame processor). Each pipeline allocates resources.
3. Worklet-powered -- frame processors run on a parallel JS thread via react-native-worklets-core. They execute synchronously in the video pipeline, so they must be fast.
4. Device/format-aware -- different physical cameras and formats have different capabilities. Always check device and format properties before enabling features like HDR or high FPS.

When to use VisionCamera:

• You need camera preview with capture, scanning, or real-time processing
• You need fine-grained control over device, format, zoom, focus, exposure
• You need frame-level access for ML inference or custom image processing

When NOT to use:

• Gallery/file picking (different concern entirely)
• Screenshot or screen recording (not camera-related)

---

Core Patterns

Pattern 1: Camera Lifecycle and Permissions

The camera must be activated only when the screen is focused AND the app is in the foreground. Always check permissions before rendering.

import { useCameraDevice, useCameraPermission, Camera } from "react-native-vision-camera";
import { StyleSheet } from "react-native";

export function CameraScreen() {
  const device = useCameraDevice("back");
  const { hasPermission, requestPermission } = useCameraPermission();

  // Request permission on mount if not granted
  // Render permission UI or Camera based on hasPermission

  if (!hasPermission) return <PermissionRequest onRequest={requestPermission} />;
  if (device == null) return <NoCameraDeviceError />;

  return <Camera style={StyleSheet.absoluteFill} device={device} isActive={isActive} />;
}

Why good: permission checked before render, device null-checked, isActive controls lifecycle without unmounting

The isActive prop should combine screen focus and app state:

const isFocused = useIsFocused(); // from navigation
const appState = useAppState(); // from community hooks
const isActive = isFocused && appState === "active";

See examples/core.md for the complete lifecycle pattern with permissions, device selection, and app state handling.

---

Pattern 2: Photo Capture

Use a Camera ref to call takePhoto(). Enable the photo pipeline on the Camera component. Use takeSnapshot() for fast preview-quality captures.

const camera = useRef<Camera>(null);

const handleCapture = async () => {
  const photo = await camera.current?.takePhoto({
    flash: "auto",
    enableShutterSound: true,
  });
  // photo.path contains the temporary file path
};

<Camera ref={camera} device={device} isActive={isActive} photo={true} />

Why good: photo pipeline explicitly enabled, ref used for imperative capture, options typed

• takePhoto() -- full-quality capture with AE/AF/AWB, supports flash
• takeSnapshot() -- ~16ms capture from preview buffer, requires video enabled on iOS
• photoQualityBalance prop: "speed" | "balanced" | "quality"

See examples/core.md for full photo capture with error handling and format selection.

---

Pattern 3: Video Recording

Use startRecording() with callbacks for completion and errors. stopRecording() triggers onRecordingFinished.

camera.current?.startRecording({
  onRecordingFinished: (video) => {
    // video.path contains the temporary file path
    // video.duration contains the duration in seconds
  },
  onRecordingError: (error) => console.error(error),
});

// Later:
await camera.current?.stopRecording();

Why good: callback-based API handles async completion, error callback prevents silent failures

• Enable video={true} and audio={true} on the Camera component
• pauseRecording() / resumeRecording() for pause support
• cancelRecording() deletes the temp file and fires onRecordingError
• videoBitRate: "low" | "normal" | "high" or custom Mbps number
• videoCodec: "h264" (default, wider compatibility) or "h265" (better compression)

See examples/core.md for complete video recording with pause/resume.

---

Pattern 4: QR/Barcode Scanning

Use the useCodeScanner hook. Runs on the native thread for instant scanning without UI freezing.

const codeScanner = useCodeScanner({
  codeTypes: ["qr", "ean-13"],
  onCodeScanned: (codes) => {
    // codes[0].value contains the decoded string
    // Fires many times per second -- debounce if updating state
  },
});

<Camera device={device} isActive={isActive} codeScanner={codeScanner} />

Why good: native-thread scanning, specific code types listed (not all), callback provides decoded values

Android setup: Requires MLKit. Enable via VisionCamera_enableCodeScanner=true in gradle.properties (or Expo plugin config).

Gotcha: onCodeScanned fires many times per second. Debounce or guard with a ref to avoid processing the same code repeatedly.

See examples/scanning-and-processing.md for debounced scanning and supported code types.

---

Pattern 5: Frame Processors

Frame processors run JavaScript worklets on a parallel camera thread for real-time frame analysis. Requires react-native-worklets-core.

const frameProcessor = useFrameProcessor((frame) => {
  "worklet";
  // frame.width, frame.height, frame.pixelFormat
  // frame.toArrayBuffer() for raw pixel data
  const results = detectObjects(frame); // native plugin call
}, []);

<Camera device={device} isActive={isActive} frameProcessor={frameProcessor} />

Why good: worklet directive present, runs on parallel thread, native plugin for heavy work

• Synchronous by default -- must complete before next frame (~33ms at 30 FPS)
• runAsync(() => { ... }) -- offload heavy processing without blocking
• runAtTargetFps(5, () => { ... }) -- process at lower FPS to save resources
• useSharedValue -- share data between frame processor and React thread
• createRunOnJS(fn) -- call React functions from within a worklet

See examples/scanning-and-processing.md for async processing, shared values, and performance patterns.

---

Pattern 6: Device and Format Selection

Choose camera devices by position and physical lenses. Select formats for resolution, FPS, and HDR support.

// Basic device selection
const device = useCameraDevice("back");

// Multi-camera with specific lenses
const device = useCameraDevice("back", {
  physicalDevices: [
    "ultra-wide-angle-camera",
    "wide-angle-camera",
    "telephoto-camera",
  ],
});

// Format selection (filters ordered by descending priority)
const format = useCameraFormat(device, [
  { videoAspectRatio: 16 / 9 },
  { videoResolution: { width: 1920, height: 1080 } },
  { fps: 30 },
]);

Why good: multi-camera support with fallback, format priorities explicitly ordered, resolution matched to actual need

See reference.md for the device and format decision framework.

---

Pattern 7: Zoom, Focus, and Exposure

Control camera optics via props and ref methods.

// Zoom: use device.minZoom, device.maxZoom, device.neutralZoom
<Camera zoom={device.neutralZoom} />

// Focus: tap-to-focus via ref
await camera.current?.focus({ x: tapX, y: tapY });

// Exposure: offset from auto-exposure (-2 to +2 typical range)
<Camera exposure={exposureOffset} />

• Zoom operates on a logarithmic scale -- use interpolate() for linear gesture mapping
• Built-in pinch-to-zoom: enableZoomGesture={true} (no custom gesture needed)
• Focus adjusts both AF and AE at the tap point
• Check device.supportsFocus before calling focus()
• Exposure range: device.minExposure to device.maxExposure

See reference.md for animated zoom with Reanimated.

---

Pattern 8: HDR and Location Metadata

Enable HDR for enhanced dynamic range. Enable location for GPS EXIF/MP4 tags.

const format = useCameraFormat(device, [
  { videoHdr: true },
  { photoHdr: true },
]);

<Camera
  format={format}
  videoHdr={format?.supportsVideoHdr}
  photoHdr={format?.supportsPhotoHdr}
  enableLocation={true}
/>

• Video HDR uses 10-bit pixel format (adds processing overhead)
• Photo HDR combines multiple exposures into one image
• Location requires useLocationPermission and platform-specific manifest entries
• Disable location APIs entirely with build flag if not needed (avoids App Store rejection)

See examples/core.md for HDR format selection and location permission flow.

---

<decision_framework>

Decision Framework

Capture Method

What do you need to capture?
|
+-> Still image?
|   +-> High quality (AE/AF/AWB) → takePhoto()
|   +-> Fast preview capture (~16ms) → takeSnapshot() (requires video pipeline)
|
+-> Video?
|   +-> Continuous recording → startRecording() / stopRecording()
|   +-> Need pause/resume → pauseRecording() / resumeRecording()
|   +-> User cancelled → cancelRecording()
|
+-> QR/barcode scanning?
|   +-> useCodeScanner (native thread, no frame processor needed)
|
+-> Real-time frame analysis (ML, detection)?
    +-> useFrameProcessor with native plugins
    +-> Need Skia drawing on frames? → useSkiaFrameProcessor

Frame Processor Scheduling

How fast must your processor run?
|
+-> Every frame (30/60 FPS)?
|   +-> Processing < 33ms? → Default synchronous processor
|   +-> Processing > 33ms? → runAsync (offload to separate thread)
|
+-> Lower rate is fine (5-10 FPS)?
    +-> runAtTargetFps(targetFps, () => { ... })

Device Selection

Which camera?
|
+-> Simple back/front → useCameraDevice("back") or useCameraDevice("front")
+-> Multi-lens (0.5x + 1x + 3x) → useCameraDevice("back", { physicalDevices: [...] })
+-> External USB camera → Filter useCameraDevices() for position === "external"
+-> Custom logic → useCameraDevices() + useMemo with your own filter

</decision_framework>

---

<red_flags>

RED FLAGS

High Priority Issues:

• Mounting/unmounting Camera instead of toggling isActive -- wastes resources, slow resume
• Missing 'worklet' directive in frame processor function -- silently runs on wrong thread, crashes
• Using useState to share data from frame processors -- causes thread context switching, use useSharedValue
• Enabling all pipelines (photo, video, codeScanner, frame processor) when only one is needed -- wastes memory and battery
• Not requesting permissions before rendering Camera -- causes crash or blank preview
• Calling camera.current.takePhoto() before onInitialized fires -- method not ready, throws error

Medium Priority Issues:

• Capturing 4K when 1080p is sufficient -- wastes memory, slower processing
• Not debouncing onCodeScanned -- fires many times per second, causes excessive state updates
• Using useSkiaFrameProcessor when useFrameProcessor suffices -- Skia adds overhead
• Enabling videoHdr without checking format.supportsVideoHdr -- crashes on unsupported formats
• Not checking device.supportsFocus before calling focus() -- fails on devices without AF

Gotchas & Edge Cases:

• Zoom is logarithmic -- 1x to 2x is a much bigger visual change than 127x to 128x. Use interpolate() for linear gesture mapping.
• takeSnapshot() requires video={true} on iOS -- it captures from the video preview buffer
• Frame processors at 4K process ~12MB per frame -- use lower resolution if possible
• device.neutralZoom may not be 1.0 on ultra-wide cameras -- always use it as the starting zoom
• Android code scanner requires MLKit (VisionCamera_enableCodeScanner=true) -- without it, scanning silently does nothing
• UPC-A codes report as EAN-13 on iOS (EAN-13 is a superset)
• cancelRecording() fires onRecordingError with capture/recording-canceled -- handle this error type gracefully
• enableLocation requires platform manifest entries (iOS: NSLocationWhenInUseUsageDescription, Android: ACCESS_FINE_LOCATION)
• Disable location APIs entirely via build flag if unused -- prevents App Store rejection for unnecessary privacy APIs
• exposure prop is an offset from auto-exposure, not an absolute ISO value
• Video HDR uses 10-bit pixel format which adds processing overhead -- disable when not needed

</red_flags>

---

<critical_reminders>

CRITICAL REMINDERS

All code must follow project conventions in CLAUDE.md

(You MUST set isActive based on screen focus AND app state -- camera must pause when backgrounded or navigated away)

(You MUST request permissions before rendering the Camera -- useCameraPermission returns hasPermission and requestPermission)

(You MUST include the 'worklet' directive as the first line of every frame processor function body)

(You MUST enable only the pipelines you need (photo, video, codeScanner, frameProcessor) -- unused pipelines waste resources)

(You MUST use useSharedValue (not useState) for data shared between frame processors and the React thread)

Failure to follow these rules will cause crashes, blank previews, wasted battery, and dropped frames.

</critical_reminders>