Architecture

This page describes Quagga2's code structure and design decisions.

Project Structure

quagga2/
├── src/
│   ├── quagga.ts           # Main entry point
│   ├── config/             # Configuration handling
│   ├── decoder/            # Barcode decoding
│   │   ├── barcode_decoder.ts
│   │   └── readers/        # Individual barcode readers
│   ├── locator/            # Barcode localization
│   │   ├── barcode_locator.ts
│   │   └── skeletonizer.ts
│   ├── input/              # Input handling
│   │   ├── camera_access.ts
│   │   └── frame_grabber.ts
│   └── common/             # Shared utilities
│       ├── cv_utils.ts     # Computer vision utilities
│       └── image_wrapper.ts
├── dist/                   # Browser builds
├── lib/                    # Node.js build
└── type-definitions/       # TypeScript types

Core Components

Quagga (Main API)

The main entry point (src/quagga.ts) exposes the public API:

init() / start() / stop()
decodeSingle()
onDetected() / onProcessed()
CameraAccess namespace

Barcode Locator

Located in src/locator/, responsible for finding barcode regions in images:

barcode_locator.ts: Main localization logic
skeletonizer.ts: Line structure extraction (asm.js optimized)

Barcode Decoder

Located in src/decoder/, handles barcode decoding:

barcode_decoder.ts: Coordinates decoding process
readers/: Individual reader implementations
- Each reader extends BarcodeReader base class
- Implements format-specific pattern matching

Input Handling

Located in src/input/:

camera_access.ts: Camera enumeration and control
frame_grabber_browser.ts: Browser frame capture
frame_grabber_node.ts: Node.js image loading

Data Flow

Camera/Image
    ↓
FrameGrabber (captures frame)
    ↓
ImageWrapper (grayscale conversion)
    ↓
BarcodeLocator (finds barcode region)
    ↓
BarcodeDecoder (decodes barcode)
    ↓
Result callbacks

Design Decisions

Bundle Everything

All dependencies are bundled into the final build. This means:

Consumers never install dependencies directly
All packages go in devDependencies
Builds are self-contained

Dual Build Targets

Browser: dist/quagga.min.js - UMD bundle
Node.js: lib/quagga.js - CommonJS module

Reader Architecture

Readers are pluggable:

Built-in readers in src/decoder/readers/
External readers via Quagga.registerReader()
All readers extend common BarcodeReader class

Build System

Webpack 4: Module bundling
Babel: ES6+ transpilation
TypeScript: Type checking (but source is mixed JS/TS)

Algorithm Overview - How the algorithms work
Create External Readers - Extend Quagga2
Contributing - Development setup

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