SlabUploader/frontend/src/worker/mask.worker.ts

import { minAreaRect, slabBounds } from '../geometry/rect';
import type { MaskParams, WorkerIn, WorkerOut } from '../capture/capture.types';

let bitmap: ImageBitmap | null = null;
let data: Uint8ClampedArray | null = null;
let w = 0, h = 0;
let current = 0; // highest job id issued by main; older replies are dropped

// Keep slab pixels; remove the sheet. Higher sensitivity widens the sheet match.
const greenKeep = (r: number, g: number, b: number, s: number): boolean => {
  const t = s / 100;
  const isSheet = g - Math.max(r, b) > 10 + 35 * t;
  return !isSheet;
};
const blackKeep = (r: number, g: number, b: number, s: number): boolean => {
  const lum = 0.2126 * r + 0.7152 * g + 0.0722 * b;
  const isSheet = lum < 40 + 140 * (s / 100);
  return !isSheet;
};
const autoPick = (samples: { r: number; g: number; b: number }[]): 'green' | 'black' => {
  let gr = 0, gl = 0;
  for (const p of samples) {
    if (p.g - Math.max(p.r, p.b) > 20) gr++;
    if (0.2126 * p.r + 0.7152 * p.g + 0.0722 * p.b < 70) gl++;
  }
  return gl >= gr ? 'black' : 'green';
};

function runMask(params: MaskParams, id: number): WorkerOut {
  if (!data) return { id, kind: 'failed', reason: 'no source decoded' };
  let sheet = params.sheet;
  if (sheet === 'auto') {
    const samples: { r: number; g: number; b: number }[] = [];
    for (let y = 0; y < h; y += 16)
      for (let x = 0; x < w; x += 16) {
        const i = (y * w + x) * 4;
        samples.push({ r: data[i], g: data[i + 1], b: data[i + 2] });
      }
    sheet = autoPick(samples);
  }
  const keep = sheet === 'green' ? greenKeep : blackKeep;
  const s = Math.max(0, Math.min(100, params.sensitivity));
  const bitset = new Uint8Array(w * h);
  let slabPx = 0;
  for (let i = 0, p = 0; i < data.length; i += 4, p++) {
    if (keep(data[i], data[i + 1], data[i + 2], s)) {
      bitset[p] = 1;
      slabPx++;
    }
  }
  if (slabPx === 0) {
    return { id, kind: 'ready', slabPx: 0, bitset, bbox: { corners: [], longSidePx: 0, angleDeg: 0 }, slabBounds: { x: 0, y: 0, w: 0, h: 0 } };
  }
  const bbox = minAreaRect(bitset, w, h);
  if (!bbox) {
    return { id, kind: 'ready', slabPx: 0, bitset, bbox: { corners: [], longSidePx: 0, angleDeg: 0 }, slabBounds: { x: 0, y: 0, w: 0, h: 0 } };
  }
  return { id, kind: 'ready', slabPx, bitset, bbox, slabBounds: slabBounds(bitset, w, h) };
}

self.onmessage = (e: MessageEvent<WorkerIn>) => {
  const msg = e.data;
  if (msg.id < current) return; // superseded by a newer job
  current = msg.id;
  if (msg.kind === 'init') {
    if (bitmap) {
      bitmap.close();
      bitmap = null;
    }
    data = null;
    w = h = 0;
    createImageBitmap(msg.blob)
      .then((bmp) => {
        w = bmp.width;
        h = bmp.height;
        const canvas = new OffscreenCanvas(w, h);
        const ctx = canvas.getContext('2d')!;
        ctx.drawImage(bmp, 0, 0);
        data = ctx.getImageData(0, 0, w, h).data;
        bitmap = bmp;
        self.postMessage({ id: msg.id, kind: 'decoded', w, h } as WorkerOut);
      })
      .catch((err) => self.postMessage({ id: msg.id, kind: 'failed', reason: String(err) } satisfies WorkerOut));
    return;
  }
  if (msg.kind === 'invalidate') {
    if (bitmap) {
      bitmap.close();
      bitmap = null;
    }
    data = null;
    w = h = 0;
    return;
  }
  try {
    const out = runMask({ sheet: msg.sheet, sensitivity: msg.sensitivity }, msg.id);
    if (out.kind === 'ready') {
      self.postMessage(out, [out.bitset.buffer]);
    } else {
      self.postMessage(out);
    }
  } catch (err) {
    self.postMessage({ id: msg.id, kind: 'failed', reason: String(err) } satisfies WorkerOut);
  }
};

export {};