Architecture & Performance

    expo-document-scanner is designed for maximum performance and minimal latency.

    The Nitro Modules Advantage

    Traditional React Native modules use the "Bridge" to communicate between JavaScript and native code. The bridge serializes data into JSON, sends it asynchronously across a message queue, and deserializes it on the other side. This process is slow, especially when dealing with large arrays or image data.

    Nitro Modules revolutionizes this by using JSI (JavaScript Interface):

    1. Direct Invocation: JavaScript calls C++ functions directly, which in turn call Swift/Kotlin methods synchronously. There is no message queue.
    2. Zero Serialization: Complex objects, arrays, and strings are shared directly between environments.
    3. Type Safety: The API surface is generated from TypeScript definitions, creating highly optimized C++ bindings that ensure types are respected natively.

    Why it Matters for Scanning

    Document scanning generates large amounts of data (high-resolution images). In older libraries, returning a base64 string or an array of image paths across the React Native bridge would cause UI stuttering and high CPU usage.

    With Nitro Modules in expo-document-scanner:

    • The UI thread remains completely unblocked while processing images.
    • Passing file URIs back to JS happens instantly.
    • Memory consumption is strictly controlled on the native side.

    Native APIs Used

    We don't build custom camera views. We use the best tools provided by the OS platforms:

    • iOS: VisionKit (VNDocumentCameraViewController) The same technology that powers the Notes app on iOS. It provides unparalleled edge detection, automatic capture, and perspective correction.
    • Android: ML Kit Document Scanner Google's state-of-the-art document scanning API. It includes a beautiful Material UI, automatic cropping, and shadow removal.