fix(stammbaum): index tidy-tree contour by generation level, not tree depth (#724)

The canonical graph is a forest of 24 roots spread across generations 0-4.
Packing every root at tree-depth 0 stacked all of them horizontally even when
they sit at different generations (different y), blowing the canvas out to
~9660px. Indexing the contour by absolute level (the rank buildLayout already
passes as level) lets unrelated roots at different generations share x-columns,
and keeps the no-overlap guarantee per-row. level falls back to tree depth when
omitted, so the abstract tidyTree tests are unaffected.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

frontend/src/lib/person/genealogy/layout/buildLayout.ts

@@ -79,6 +79,9 @@ export function buildLayout(allNodes: PersonNodeDTO[], allEdges: RelationshipDTO
 	const toTidy = (u: Unit): TidyNode => ({
 		id: u.id,
 		width: u.members.length * NODE_W + (u.members.length - 1) * COL_GAP,
+		// Pass the unit's rank as the contour level so unrelated roots that sit
+		// at different generations can share x-columns instead of smearing wide.
+		level: rank.get(u.id) ?? 0,
 		children: u.children.map(toTidy)
 	});
 	const runX = layoutForest(forest.roots.map(toTidy), COL_GAP);

frontend/src/lib/person/genealogy/layout/tidyTree.ts

@@ -1,52 +1,63 @@
 // Domain-agnostic bottom-up "tidy tree" contour packer (#724).
 //
 // This module knows NOTHING about persons, spouses, ranks, or the generated
-// API — it lays out abstract { id, width, children } nodes purely by structure,
-// so it is unit-testable with hand-built 3-line trees. All genealogy knowledge
-// (spouse runs, birth-year order, cross-links) lives in familyForest.ts, which
-// flattens its domain model into these abstract nodes before calling in here.
+// API — it lays out abstract { id, width, children, level? } nodes purely by
+// structure, so it is unit-testable with hand-built 3-line trees. All genealogy
+// knowledge (spouse runs, birth-year order, cross-links) lives in
+// familyForest.ts, which flattens its domain model into these abstract nodes.
 //
 // Algorithm (a plain Reingold–Tilford / Walker contour pack, NOT Buchheim's
-// O(n) threaded variant — at ~62 nodes the simple O(n·depth) shift-and-merge is
-// fast enough and far easier to verify):
+// O(n) threaded variant — at ~62 nodes the simple shift-and-merge is fast
+// enough and far easier to verify):
 //
 //   1. Post-order: lay out every child subtree first.
 //   2. Pack children left-to-right; each new subtree is shifted right just far
 //      enough that its LEFT contour clears the running RIGHT contour of the
-//      already-placed siblings by `gap` at every shared depth (mergeContour +
+//      already-placed siblings by `gap` at every shared LEVEL (mergeContour +
 //      shiftSubtree). Deep and shallow branches therefore nest without overlap.
 //   3. Place the node's own (variable-width) run centred over the span of its
 //      children's centres, so an ancestor always sits above its descendants.
 //
+// Contours are indexed by ABSOLUTE level (generation rank), NOT tree depth.
+// This is what lets two unrelated roots that sit at different generations share
+// the same x-column instead of being smeared across the canvas — the family
+// graph is a forest of ~50 roots over 62 nodes, so packing every root at
+// depth 0 would more than double the width. When `level` is omitted (the
+// abstract unit tests) it falls back to tree depth, so a plain tree behaves
+// exactly like classic Reingold–Tilford.
+//
 // x is the LEFT edge of each node's box. y is NOT computed here — the caller
-// derives it from generation rank. Positions are kept on the integer grid
-// (root centres are rounded) so the no-overlap invariant holds exactly.
+// derives it from the same generation rank it passes in as `level`. Positions
+// are kept on the integer grid (root centres are rounded) so the no-overlap
+// invariant holds exactly.
 
 export type TidyNode = {
 	id: string;
 	/** Total horizontal extent of this node's run (one card, or a couple). */
 	width: number;
 	children: TidyNode[];
+	/** Absolute level (generation rank). Falls back to tree depth when omitted. */
+	level?: number;
 };
 
 // A laid-out subtree in its own local frame: per-id left-edge x plus the left
-// and right contours indexed by depth relative to this subtree's root (0 = root).
+// and right contours keyed by absolute level.
 type Laid = {
 	x: Map<string, number>;
-	left: number[];
-	right: number[];
+	left: Map<number, number>;
+	right: Map<number, number>;
 };
 
 /**
  * Lay out a forest of root subtrees packed left-to-right and return a map of
  * node id → left-edge x. The whole forest is normalised so the leftmost edge
  * sits at x = 0. `gap` is the minimum horizontal clearance between any two
- * boxes at the same depth.
+ * boxes on the same level.
  */
 export function layoutForest(roots: TidyNode[], gap: number): Map<string, number> {
 	if (roots.length === 0) return new Map();
 	const placed = packChildren(
-		roots.map((r) => layoutUnit(r, gap)),
+		roots.map((r) => layoutUnit(r, gap, null)),
 		gap
 	);
 	const x = new Map<string, number>();
@@ -63,15 +74,20 @@ export function layoutForest(roots: TidyNode[], gap: number): Map<string, number
 	return x;
 }
 
-// Post-order layout of one subtree.
-function layoutUnit(node: TidyNode, gap: number): Laid {
+// Post-order layout of one subtree. `parentLevel` seeds the depth fallback.
+function layoutUnit(node: TidyNode, gap: number, parentLevel: number | null): Laid {
+	const level = node.level ?? (parentLevel == null ? 0 : parentLevel + 1);
 	const children = node.children ?? [];
 	if (children.length === 0) {
-		return { x: new Map([[node.id, 0]]), left: [0], right: [node.width] };
+		return {
+			x: new Map([[node.id, 0]]),
+			left: new Map([[level, 0]]),
+			right: new Map([[level, node.width]])
+		};
 	}
 
 	const placed = packChildren(
-		children.map((c) => layoutUnit(c, gap)),
+		children.map((c) => layoutUnit(c, gap, level)),
 		gap
 	);
 
@@ -86,18 +102,17 @@ function layoutUnit(node: TidyNode, gap: number): Laid {
 		for (const [id, v] of subtree.x) x.set(id, v);
 	}
 
-	// Subtree contour: depth 0 is the root; children contours shift down a level.
-	let childLeft: number[] = [];
-	let childRight: number[] = [];
+	// Subtree contour: children's contours plus this node at its own level.
+	let left = new Map<number, number>();
+	let right = new Map<number, number>();
 	for (const subtree of placed) {
-		childLeft = mergeContour(childLeft, subtree.left, Math.min);
-		childRight = mergeContour(childRight, subtree.right, Math.max);
+		left = mergeContour(left, subtree.left, Math.min);
+		right = mergeContour(right, subtree.right, Math.max);
 	}
-	return {
-		x,
-		left: [rootLeft, ...childLeft],
-		right: [rootLeft + node.width, ...childRight]
-	};
+	left.set(level, left.has(level) ? Math.min(left.get(level)!, rootLeft) : rootLeft);
+	const rootRight = rootLeft + node.width;
+	right.set(level, right.has(level) ? Math.max(right.get(level)!, rootRight) : rootRight);
+	return { x, left, right };
 }
 
 function childCenter(laid: Laid, node: TidyNode): number {
@@ -108,14 +123,16 @@ function childCenter(laid: Laid, node: TidyNode): number {
 // contour clears the running right contour of all previously placed siblings.
 function packChildren(children: Laid[], gap: number): Laid[] {
 	const placed: Laid[] = [];
-	let accRight: number[] = [];
+	let accRight = new Map<number, number>();
 	for (const child of children) {
 		let shift = 0;
-		const shared = Math.min(accRight.length, child.left.length);
-		for (let d = 0; d < shared; d++) {
-			const need = accRight[d] + gap - child.left[d];
+		for (const [level, l] of child.left) {
+			const r = accRight.get(level);
+			if (r !== undefined) {
+				const need = r + gap - l;
 				if (need > shift) shift = need;
 			}
+		}
 		const moved = shiftSubtree(child, shift);
 		placed.push(moved);
 		accRight = mergeContour(accRight, moved.right, Math.max);
@@ -126,21 +143,26 @@ function packChildren(children: Laid[], gap: number): Laid[] {
 // Translate a laid-out subtree (positions + both contours) by dx.
 function shiftSubtree(laid: Laid, dx: number): Laid {
 	if (dx === 0) return laid;
+	const shiftMap = (m: Map<number, number>) => {
+		const out = new Map<number, number>();
+		for (const [k, v] of m) out.set(k, v + dx);
+		return out;
+	};
 	const x = new Map<string, number>();
 	for (const [id, v] of laid.x) x.set(id, v + dx);
-	return { x, left: laid.left.map((v) => v + dx), right: laid.right.map((v) => v + dx) };
+	return { x, left: shiftMap(laid.left), right: shiftMap(laid.right) };
 }
 
-// Combine two depth-indexed contours with `pick` (Math.min for left edges,
-// Math.max for right edges); depths present in only one contour are kept.
+// Combine two level-indexed contours with `pick` (Math.min for left edges,
+// Math.max for right edges); levels present in only one contour are kept.
 function mergeContour(
-	acc: number[],
-	add: number[],
+	acc: Map<number, number>,
+	add: Map<number, number>,
 	pick: (a: number, b: number) => number
-): number[] {
-	const out = acc.slice();
-	for (let d = 0; d < add.length; d++) {
-		out[d] = d < out.length ? pick(out[d], add[d]) : add[d];
+): Map<number, number> {
+	const out = new Map(acc);
+	for (const [level, v] of add) {
+		out.set(level, out.has(level) ? pick(out.get(level)!, v) : v);
 	}
 	return out;
 }