fix: Deep-compare constraints instead of JSON.stringify-ing them

[mrousavy]

What

useCameraController kept the user's constraints stable by putting JSON.stringify(constraints) into the useMemo dependency array:

// biome-ignore lint/correctness/useExhaustiveDependencies: It's an array of objects, we either have to deep-memo or just stringify.
const stableConstraints = useMemo<Constraint[]>(() => { ... }, [JSON.stringify(constraints), stableOutputs])

That works for plain constraints like { fps: 60 }, but it silently breaks for { resolutionBias: someOutput }.

Nitro HybridObjects are created via Object.create(prototype) and hold every property on their shared prototype, so the JS object itself has no own keys. JSON.stringify(...) therefore serializes every CameraOutput to the same string:

build	JSON.stringify(photoOutput)
release	{}
debug	{"__type":"HybridObject<CameraPhotoOutput>"}

Two different outputs of the same type are indistinguishable. So this, which is the documented way to express capture priority:

constraints={photoFirst
  ? [{ resolutionBias: photoOutput }, { resolutionBias: videoOutput }]
  : [{ resolutionBias: videoOutput }, { resolutionBias: photoOutput }]}

is invisible to the memo in release builds, and the session is never re-configured.

How

Replaces the stringification with an explicit deep comparison (useMemoizedConstraints(...)) that compares object literals and arrays by value, and everything else (i.e. HybridObjects) by identity. It also drops a full JSON serialization from every render, and lets the useMemo dependency array be honest again (the biome-ignore is gone).

Test

Adds two Harness tests in visioncamera.hooks.harness.tsx:

1. re-renders a component with an inline constraints={[{ fps }]} array and asserts onConfigured fired exactly once, then asserts changing the actual fps value re-configures exactly once more.
2. re-points a resolutionBias constraint at a different CameraPhotoOutput while the attached outputs stay identical, and asserts the session re-configures. Both bias outputs are deliberately the same HybridObject type, which is exactly what JSON.stringify(...) could not tell apart - this test is red on main.

Note

Touches the same import block in visioncamera.hooks.harness.tsx as #4166, so whichever lands second will need a trivial rebase.

🤖 Generated with Claude Code

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Project	Deployment	Actions	Updated (UTC)
react-native-vision-camera-docs	Ready	Preview	Aug 21, 2026 1:26pm