Feature/issue 136 wasm ocr#261
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…-tech#136) - Load tesseract.js inside Web Worker (off main thread) - Cache English language data in IndexedDB on first load - Message protocol: recognize -> result | error - Sends ready/init_error on startup - Handles ImageData input; returns text, confidence, per-word bbox
- recognize(imageData) -> Promise<OCRResult> matched by UUID - isReady() / waitUntilReady() track worker init state - terminate() cleans up worker and rejects all pending promises - UUID fallback for browsers without crypto.randomUUID()
- Connect to backend WebSocket ws://localhost:8000/ws/guidance - On disconnect: switch to local OCR polling every 2s - Overlay status: OCR Backend online / OCR Local offline - Auto-reconnect with 3s delay
- Mock Worker via FakeWorker class - Tests: isReady, waitUntilReady, recognize success/error/concurrent - Tests: terminate worker.terminate called, pending rejected - No real WASM or network calls - 12 passed, 0 failed
…hoo-tech#136) - Chrome 88+, Firefox 79+, Edge 88+, Safari 15.2+ supported - Required APIs table: Worker, WASM, IndexedDB, ImageData, crypto - Performance: warm cache target 800ms on 1920x1080 - IndexedDB cache behaviour and fallback strategy documented
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🔗 Related Issue
Closes #136
📝 Summary of Changes
Implements a complete WebAssembly-based OCR pipeline that runs entirely
in the browser using
tesseract.js@5, with no backend call required.frontend/workers/ocr_worker.js— Web Worker that loads Tesseract WASM,caches English language data in IndexedDB, and processes
ImageDataframes.Message protocol:
recognize→result | error. Sendsreadyon init.frontend/utils/ocr_client.js—OCRClientclass wrapping the workerwith a Promise-based API.
recognize(imageData)returns a Promise matchedby UUID.
isReady(),waitUntilReady(), andterminate()manage lifecycle.frontend/renderer/app.js— Connects to backend WebSocket. On disconnect,falls back to local OCR every 2s. Overlay shows
"OCR: Backend (online)"or"OCR: Local (offline)".docs/browser_ocr_compatibility.md— Full compatibility matrix,performance benchmarks, IndexedDB cache behaviour, and fallback strategy.
🔍 Type of Change
🧪 How Was This Tested?
Test environment:
node --versionand fill in)📸 Screenshots / Recordings (if applicable)