Add gesture recognition and collaborative sync to folk-drawfast

Implements $1 Unistroke Recognizer for detecting circles, rectangles,
triangles, lines, arrows, and checkmarks from freehand strokes. Detected
gestures are converted to clean geometric shapes with a confidence badge.

Fixes applyData() to restore strokes, prompt text, and generated images
from Automerge sync data, enabling collaborative drawing across clients.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

lib/folk-drawfast.ts

@@ -309,6 +309,28 @@ const styles = css`
 	.export-btn:hover {
 		opacity: 0.9;
 	}
+
+	.gesture-badge {
+		position: absolute;
+		top: 8px;
+		left: 50%;
+		transform: translateX(-50%);
+		background: rgba(249, 115, 22, 0.9);
+		color: white;
+		padding: 4px 12px;
+		border-radius: 12px;
+		font-size: 11px;
+		font-weight: 600;
+		z-index: 3;
+		pointer-events: none;
+		animation: badge-fade 1.5s ease-out forwards;
+	}
+
+	@keyframes badge-fade {
+		0% { opacity: 1; transform: translateX(-50%) translateY(0); }
+		70% { opacity: 1; }
+		100% { opacity: 0; transform: translateX(-50%) translateY(-10px); }
+	}
 `;
 
 const COLORS = ["#0f172a", "#ef4444", "#f97316", "#eab308", "#22c55e", "#3b82f6", "#8b5cf6", "#ec4899", "#ffffff"];
@@ -320,6 +342,213 @@ interface Stroke {
 	tool: string;
 }
 
+// --- $1 Unistroke Recognizer (lightweight, self-contained) ---
+// Based on Wobbrock et al. 2007, adapted from canvas-website gesture templates
+
+interface Point2D { x: number; y: number; }
+interface RecognizeResult { name: string; score: number; }
+
+const NUM_POINTS = 64;
+const SQUARE_SIZE = 250;
+const HALF_DIAGONAL = 0.5 * Math.sqrt(SQUARE_SIZE * SQUARE_SIZE + SQUARE_SIZE * SQUARE_SIZE);
+const ANGLE_RANGE = Math.PI * 2;
+const ANGLE_PRECISION = Math.PI / 90; // 2 degrees
+const PHI = 0.5 * (-1 + Math.sqrt(5)); // golden ratio
+
+function resample(pts: Point2D[], n: number): Point2D[] {
+	const totalLen = pathLength(pts);
+	const interval = totalLen / (n - 1);
+	const newPts: Point2D[] = [pts[0]];
+	let D = 0;
+	for (let i = 1; i < pts.length; i++) {
+		const d = distance(pts[i - 1], pts[i]);
+		if (D + d >= interval) {
+			const t = (interval - D) / d;
+			const qx = pts[i - 1].x + t * (pts[i].x - pts[i - 1].x);
+			const qy = pts[i - 1].y + t * (pts[i].y - pts[i - 1].y);
+			const q: Point2D = { x: qx, y: qy };
+			newPts.push(q);
+			pts.splice(i, 0, q);
+			D = 0;
+		} else {
+			D += d;
+		}
+	}
+	while (newPts.length < n) newPts.push(pts[pts.length - 1]);
+	return newPts;
+}
+
+function rotateToZero(pts: Point2D[]): Point2D[] {
+	const c = centroid(pts);
+	const angle = Math.atan2(c.y - pts[0].y, c.x - pts[0].x);
+	return rotateBy(pts, -angle);
+}
+
+function scaleToSquare(pts: Point2D[]): Point2D[] {
+	let minX = Infinity, maxX = -Infinity, minY = Infinity, maxY = -Infinity;
+	for (const p of pts) {
+		minX = Math.min(minX, p.x); maxX = Math.max(maxX, p.x);
+		minY = Math.min(minY, p.y); maxY = Math.max(maxY, p.y);
+	}
+	const w = maxX - minX || 1;
+	const h = maxY - minY || 1;
+	return pts.map(p => ({ x: p.x * (SQUARE_SIZE / w), y: p.y * (SQUARE_SIZE / h) }));
+}
+
+function translateToOrigin(pts: Point2D[]): Point2D[] {
+	const c = centroid(pts);
+	return pts.map(p => ({ x: p.x - c.x, y: p.y - c.y }));
+}
+
+function recognize(pts: Point2D[], templates: { name: string; points: Point2D[] }[]): RecognizeResult {
+	let best = Infinity;
+	let bestName = "none";
+	for (const t of templates) {
+		const d = distanceAtBestAngle(pts, t.points, -ANGLE_RANGE, ANGLE_RANGE, ANGLE_PRECISION);
+		if (d < best) {
+			best = d;
+			bestName = t.name;
+		}
+	}
+	const score = 1 - best / HALF_DIAGONAL;
+	return { name: bestName, score };
+}
+
+function distanceAtBestAngle(pts: Point2D[], template: Point2D[], a: number, b: number, threshold: number): number {
+	let x1 = PHI * a + (1 - PHI) * b;
+	let f1 = distanceAtAngle(pts, template, x1);
+	let x2 = (1 - PHI) * a + PHI * b;
+	let f2 = distanceAtAngle(pts, template, x2);
+	while (Math.abs(b - a) > threshold) {
+		if (f1 < f2) {
+			b = x2; x2 = x1; f2 = f1;
+			x1 = PHI * a + (1 - PHI) * b;
+			f1 = distanceAtAngle(pts, template, x1);
+		} else {
+			a = x1; x1 = x2; f1 = f2;
+			x2 = (1 - PHI) * a + PHI * b;
+			f2 = distanceAtAngle(pts, template, x2);
+		}
+	}
+	return Math.min(f1, f2);
+}
+
+function distanceAtAngle(pts: Point2D[], template: Point2D[], angle: number): number {
+	const rotated = rotateBy(pts, angle);
+	return pathDistance(rotated, template);
+}
+
+function centroid(pts: Point2D[]): Point2D {
+	let x = 0, y = 0;
+	for (const p of pts) { x += p.x; y += p.y; }
+	return { x: x / pts.length, y: y / pts.length };
+}
+
+function rotateBy(pts: Point2D[], angle: number): Point2D[] {
+	const c = centroid(pts);
+	const cos = Math.cos(angle), sin = Math.sin(angle);
+	return pts.map(p => ({
+		x: (p.x - c.x) * cos - (p.y - c.y) * sin + c.x,
+		y: (p.x - c.x) * sin + (p.y - c.y) * cos + c.y,
+	}));
+}
+
+function pathDistance(a: Point2D[], b: Point2D[]): number {
+	let d = 0;
+	const n = Math.min(a.length, b.length);
+	for (let i = 0; i < n; i++) d += distance(a[i], b[i]);
+	return d / n;
+}
+
+function pathLength(pts: Point2D[]): number {
+	let d = 0;
+	for (let i = 1; i < pts.length; i++) d += distance(pts[i - 1], pts[i]);
+	return d;
+}
+
+function distance(a: Point2D, b: Point2D): number {
+	const dx = b.x - a.x, dy = b.y - a.y;
+	return Math.sqrt(dx * dx + dy * dy);
+}
+
+function processTemplate(pts: Point2D[]): Point2D[] {
+	return translateToOrigin(scaleToSquare(rotateToZero(resample(pts, NUM_POINTS))));
+}
+
+// Generate templates procedurally (more compact than storing point arrays)
+function makeCircleTemplate(): Point2D[] {
+	const pts: Point2D[] = [];
+	for (let i = 0; i <= 32; i++) {
+		const a = (i / 32) * Math.PI * 2;
+		pts.push({ x: 100 + 80 * Math.cos(a), y: 100 + 80 * Math.sin(a) });
+	}
+	return processTemplate(pts);
+}
+
+function makeRectangleTemplate(): Point2D[] {
+	const pts: Point2D[] = [];
+	// Draw rectangle starting top-left, clockwise
+	const steps = 8;
+	for (let i = 0; i <= steps; i++) pts.push({ x: 20 + (160 * i / steps), y: 20 }); // top
+	for (let i = 0; i <= steps; i++) pts.push({ x: 180, y: 20 + (160 * i / steps) }); // right
+	for (let i = 0; i <= steps; i++) pts.push({ x: 180 - (160 * i / steps), y: 180 }); // bottom
+	for (let i = 0; i <= steps; i++) pts.push({ x: 20, y: 180 - (160 * i / steps) }); // left
+	return processTemplate(pts);
+}
+
+function makeLineTemplate(): Point2D[] {
+	const pts: Point2D[] = [];
+	for (let i = 0; i <= 16; i++) pts.push({ x: 20 + (160 * i / 16), y: 100 });
+	return processTemplate(pts);
+}
+
+function makeArrowTemplate(): Point2D[] {
+	// Horizontal line with arrowhead at the end
+	const pts: Point2D[] = [];
+	for (let i = 0; i <= 12; i++) pts.push({ x: 20 + (140 * i / 12), y: 100 }); // shaft
+	for (let i = 0; i <= 4; i++) pts.push({ x: 160 - (40 * i / 4), y: 100 - (40 * i / 4) }); // upper head
+	pts.push({ x: 160, y: 100 }); // back to tip
+	for (let i = 0; i <= 4; i++) pts.push({ x: 160 - (40 * i / 4), y: 100 + (40 * i / 4) }); // lower head
+	return processTemplate(pts);
+}
+
+function makeTriangleTemplate(): Point2D[] {
+	const pts: Point2D[] = [];
+	const steps = 8;
+	// Top to bottom-right
+	for (let i = 0; i <= steps; i++) pts.push({ x: 100 + (80 * i / steps), y: 20 + (160 * i / steps) });
+	// Bottom-right to bottom-left
+	for (let i = 0; i <= steps; i++) pts.push({ x: 180 - (160 * i / steps), y: 180 });
+	// Bottom-left to top
+	for (let i = 0; i <= steps; i++) pts.push({ x: 20 + (80 * i / steps), y: 180 - (160 * i / steps) });
+	return processTemplate(pts);
+}
+
+function makeCheckTemplate(): Point2D[] {
+	const pts: Point2D[] = [];
+	for (let i = 0; i <= 6; i++) pts.push({ x: 20 + (40 * i / 6), y: 100 + (60 * i / 6) });
+	for (let i = 0; i <= 8; i++) pts.push({ x: 60 + (120 * i / 8), y: 160 - (140 * i / 8) });
+	return processTemplate(pts);
+}
+
+const GESTURE_TEMPLATES = [
+	{ name: "circle", points: makeCircleTemplate() },
+	{ name: "rectangle", points: makeRectangleTemplate() },
+	{ name: "line", points: makeLineTemplate() },
+	{ name: "arrow", points: makeArrowTemplate() },
+	{ name: "triangle", points: makeTriangleTemplate() },
+	{ name: "check", points: makeCheckTemplate() },
+];
+
+function recognizeGesture(rawPoints: Point2D[]): RecognizeResult | null {
+	if (rawPoints.length < 8) return null; // too few points
+	const processed = processTemplate(rawPoints);
+	const result = recognize(processed, GESTURE_TEMPLATES);
+	if (result.score < 0.7) return null; // low confidence
+	return result;
+}
+// --- End $1 Unistroke Recognizer ---
+
 declare global {
 	interface HTMLElementTagNameMap {
 		"folk-drawfast": FolkDrawfast;
@@ -364,6 +593,8 @@ export class FolkDrawfast extends FolkShape {
 	#promptInput: HTMLInputElement | null = null;
 	#generateBtn: HTMLButtonElement | null = null;
 	#resultArea: HTMLElement | null = null;
+	#canvasArea: HTMLElement | null = null;
+	#gestureEnabled = true;
 
 	get strokes() {
 		return this.#strokes;
@@ -443,6 +674,7 @@ export class FolkDrawfast extends FolkShape {
 		const sizeSlider = wrapper.querySelector(".size-slider") as HTMLInputElement;
 		const sizeLabel = wrapper.querySelector(".size-label") as HTMLElement;
 		const canvasArea = wrapper.querySelector(".canvas-area") as HTMLElement;
+		this.#canvasArea = canvasArea;
 		const autoCheckbox = wrapper.querySelector(".auto-checkbox") as HTMLInputElement;
 		const providerSelect = wrapper.querySelector(".provider-select") as HTMLSelectElement;
 		const strengthSlider = wrapper.querySelector(".strength-slider") as HTMLInputElement;
@@ -533,10 +765,29 @@ export class FolkDrawfast extends FolkShape {
 			if (!this.#isDrawing) return;
 			this.#isDrawing = false;
 			if (this.#currentStroke && this.#currentStroke.points.length > 0) {
-				this.#strokes.push(this.#currentStroke);
+				// Try gesture recognition before adding stroke
-				this.dispatchEvent(new CustomEvent("stroke-complete", {
+				let gestureResult: RecognizeResult | null = null;
-					detail: { stroke: this.#currentStroke },
+				if (this.#gestureEnabled && this.#currentStroke.tool === "pen") {
-				}));
+					const rawPts = this.#currentStroke.points.map(p => ({ x: p.x, y: p.y }));
+					gestureResult = recognizeGesture(rawPts);
+				}
+
+				if (gestureResult) {
+					// Replace freehand stroke with clean geometric shape
+					const cleanStroke = this.#makeCleanShape(gestureResult.name, this.#currentStroke);
+					this.#strokes.push(cleanStroke);
+					this.#redraw();
+					this.#showGestureBadge(gestureResult.name, gestureResult.score);
+					this.dispatchEvent(new CustomEvent("stroke-complete", {
+						detail: { stroke: cleanStroke, gesture: gestureResult.name },
+					}));
+				} else {
+					this.#strokes.push(this.#currentStroke);
+					this.dispatchEvent(new CustomEvent("stroke-complete", {
+						detail: { stroke: this.#currentStroke },
+					}));
+				}
+
 				// Auto-generate on stroke complete if enabled
 				if (this.#autoGenerate && this.#promptInput?.value.trim()) {
 					this.#scheduleAutoGenerate();
@@ -774,6 +1025,95 @@ export class FolkDrawfast extends FolkShape {
 		ctx.globalCompositeOperation = "source-over";
 	}
 
+	#makeCleanShape(gesture: string, original: Stroke): Stroke {
+		const pts = original.points;
+		const minX = Math.min(...pts.map(p => p.x));
+		const maxX = Math.max(...pts.map(p => p.x));
+		const minY = Math.min(...pts.map(p => p.y));
+		const maxY = Math.max(...pts.map(p => p.y));
+		const cx = (minX + maxX) / 2;
+		const cy = (minY + maxY) / 2;
+		const w = maxX - minX || 1;
+		const h = maxY - minY || 1;
+		const pressure = 0.5;
+
+		const toStroke = (points: { x: number; y: number }[]): Stroke => ({
+			points: points.map(p => ({ ...p, pressure })),
+			color: original.color,
+			size: original.size,
+			tool: "pen",
+		});
+
+		switch (gesture) {
+			case "circle": {
+				const rx = w / 2, ry = h / 2;
+				const circPts: { x: number; y: number }[] = [];
+				for (let i = 0; i <= 48; i++) {
+					const a = (i / 48) * Math.PI * 2;
+					circPts.push({ x: cx + rx * Math.cos(a), y: cy + ry * Math.sin(a) });
+				}
+				return toStroke(circPts);
+			}
+			case "rectangle": {
+				return toStroke([
+					{ x: minX, y: minY }, { x: maxX, y: minY },
+					{ x: maxX, y: maxY }, { x: minX, y: maxY },
+					{ x: minX, y: minY },
+				]);
+			}
+			case "triangle": {
+				return toStroke([
+					{ x: cx, y: minY }, { x: maxX, y: maxY },
+					{ x: minX, y: maxY }, { x: cx, y: minY },
+				]);
+			}
+			case "line": {
+				// Use first and last point for direction
+				const first = pts[0], last = pts[pts.length - 1];
+				return toStroke([
+					{ x: first.x, y: first.y },
+					{ x: last.x, y: last.y },
+				]);
+			}
+			case "arrow": {
+				const first = pts[0], last = pts[pts.length - 1];
+				const dx = last.x - first.x, dy = last.y - first.y;
+				const len = Math.sqrt(dx * dx + dy * dy) || 1;
+				const ux = dx / len, uy = dy / len;
+				const headLen = Math.min(20, len * 0.3);
+				// Arrow shaft + two head lines
+				return toStroke([
+					{ x: first.x, y: first.y }, { x: last.x, y: last.y },
+					{ x: last.x - headLen * (ux + uy * 0.5), y: last.y - headLen * (uy - ux * 0.5) },
+					{ x: last.x, y: last.y },
+					{ x: last.x - headLen * (ux - uy * 0.5), y: last.y - headLen * (uy + ux * 0.5) },
+				]);
+			}
+			case "check": {
+				// V-shape: find the lowest point as the vertex
+				const lowestIdx = pts.reduce((best, p, i) => p.y > pts[best].y ? i : best, 0);
+				return toStroke([
+					{ x: pts[0].x, y: pts[0].y },
+					{ x: pts[lowestIdx].x, y: pts[lowestIdx].y },
+					{ x: pts[pts.length - 1].x, y: pts[pts.length - 1].y },
+				]);
+			}
+			default:
+				return original;
+		}
+	}
+
+	#showGestureBadge(name: string, score: number) {
+		if (!this.#canvasArea) return;
+		// Remove existing badge
+		this.#canvasArea.querySelector(".gesture-badge")?.remove();
+		const badge = document.createElement("div");
+		badge.className = "gesture-badge";
+		badge.textContent = `${name} (${Math.round(score * 100)}%)`;
+		this.#canvasArea.appendChild(badge);
+		setTimeout(() => badge.remove(), 1500);
+	}
+
 	#exportPNG() {
 		if (!this.#canvas) return;
 		const dataUrl = this.#canvas.toDataURL("image/png");
@@ -808,12 +1148,31 @@ export class FolkDrawfast extends FolkShape {
 				size: s.size,
 				tool: s.tool,
 			})),
+			prompt: this.#promptInput?.value || "",
 			lastResultUrl: this.#lastResultUrl,
 		};
 	}
 
 	override applyData(data: Record<string, any>): void {
 		super.applyData(data);
+
+		// Restore strokes from sync data
+		if (data.strokes && Array.isArray(data.strokes)) {
+			this.#strokes = data.strokes.map((s: any) => ({
+				points: Array.isArray(s.points) ? s.points : [],
+				color: s.color || "#0f172a",
+				size: s.size || 4,
+				tool: s.tool || "pen",
+			}));
+			this.#redraw();
+		}
+
+		// Restore prompt text
+		if (data.prompt !== undefined && this.#promptInput) {
+			this.#promptInput.value = data.prompt || "";
+		}
+
+		// Restore last generated image
 		if (data.lastResultUrl && this.#resultArea) {
 			this.#lastResultUrl = data.lastResultUrl;
 			this.#renderResult(data.lastResultUrl, "");