fix: drop glare holes before the margin and never auto-pick specks

Filtering holes after the margin let -2 mm grow 1 mm specks past the
3 mm cutoff, and could drop real holes shrunk by a positive margin.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

src/lib/app-state.svelte.ts

@@ -9,6 +9,7 @@ import type { Point, RasterImage, Shape } from './types';
 export type Tool = 'none' | 'scale' | 'seed' | 'draw';
 
 const DEFAULT_THRESHOLD = 128;
+const MIN_HOLE_MM = 3;
 
 export class AppState {
   // Raw: the cv module and pixel buffers must never be wrapped in reactive proxies.
@@ -43,7 +44,10 @@ export class AppState {
     if (this.mode === 'manual') {
       return shapeFromPolygons(cv, image.width, image.height, { outer: this.manualOuter, holes: this.manualHoles }, this.marginPx);
     }
-    return detect(cv, image, { threshold: this.threshold, invert: this.invert, seed: this.seed, marginPx: this.marginPx });
+    return detect(cv, image, {
+      threshold: this.threshold, invert: this.invert, seed: this.seed, marginPx: this.marginPx,
+      minHolePx: this.pxPerMm ? MIN_HOLE_MM * this.pxPerMm : 0,
+    });
   });
 
   exportShape = $derived(this.shapePx && this.pxPerMm ? prepareForExport(this.shapePx, this.pxPerMm) : null);

src/lib/detect.ts

@@ -100,6 +100,7 @@ export function detect(cv: CV, image: RasterImage, params: DetectParams): Shape
     const lab = labels.data32S;
     const m = mask.data;
     for (let i = 0; i < lab.length; i++) m[i] = lab[i] === label ? 255 : 0;
+    fillSmallHoles(cv, mask, params.minHolePx);
     return traceMask(cv, mask, params.marginPx);
   } finally {
     gray.delete();
@@ -134,16 +135,41 @@ function pickComponent(
     }
   }
 
+  // Without a click, specks (dust, grain) must never pass as the piece.
+  const minArea = 0.01 * width * height;
   let best: number | null = null;
   let bestArea = 0;
   for (let label = 1; label < count; label++) {
     const b = box(label);
     if (b.left === 0 || b.top === 0 || b.right === width || b.bottom === height) continue;
     const area = stat(label, cv.CC_STAT_AREA);
-    if (area > bestArea) {
+    if (area >= minArea && area > bestArea) {
       bestArea = area;
       best = label;
     }
   }
   return best;
 }
+
+/** Fill holes under minHolePx in both directions, before the margin can grow them. */
+function fillSmallHoles(cv: CV, mask: Mat, minHolePx: number) {
+  if (minHolePx <= 0) return;
+  const contours = new cv.MatVector();
+  const hierarchy = new cv.Mat();
+  try {
+    cv.findContours(mask, contours, hierarchy, cv.RETR_CCOMP, cv.CHAIN_APPROX_SIMPLE);
+    const h = hierarchy.data32S;
+    for (let i = 0; i < contours.size(); i++) {
+      if (h[i * 4 + 3] === -1) continue;
+      const c = contours.get(i);
+      const rect = cv.boundingRect(c);
+      c.delete();
+      if (rect.width < minHolePx && rect.height < minHolePx) {
+        cv.drawContours(mask, contours, i, new cv.Scalar(255), cv.FILLED);
+      }
+    }
+  } finally {
+    contours.delete();
+    hierarchy.delete();
+  }
+}

src/lib/geometry.ts

@@ -2,8 +2,6 @@ import type { Point, Shape } from './types';
 
 export type Bounds = { minX: number; minY: number; maxX: number; maxY: number };
 
-const MIN_HOLE_MM = 3;
-
 export function bounds(points: Point[]): Bounds {
   let minX = Infinity, minY = Infinity, maxX = -Infinity, maxY = -Infinity;
   for (const p of points) {
@@ -70,11 +68,7 @@ export function prepareForExport(shapePx: Shape, pxPerMm: number, toleranceMm =
     simplifyRing(ring.map((p) => ({ x: p.x / pxPerMm, y: p.y / pxPerMm })), toleranceMm);
   const outer = toMm(shapePx.outer);
   if (outer.length < 3) return null;
-  const holes = shapePx.holes.map(toMm).filter((hole) => {
-    if (hole.length < 3) return false;
-    const { width, height } = shapeSize({ outer: hole, holes: [] });
-    return width >= MIN_HOLE_MM || height >= MIN_HOLE_MM;
-  });
+  const holes = shapePx.holes.map(toMm).filter((hole) => hole.length >= 3);
   const { minX, minY } = bounds(outer);
   const shift = (ring: Point[]) => ring.map((p) => ({ x: p.x - minX, y: p.y - minY }));
   return { outer: shift(outer), holes: holes.map(shift) };

src/lib/types.ts

@@ -12,4 +12,6 @@ export type DetectParams = {
   seed: Point | null;
   /** Negative shrinks the piece (and grows holes). */
   marginPx: number;
+  /** Holes smaller than this in both directions are treated as glare and filled. */
+  minHolePx: number;
 };