Merge branch 'perf/label-scan' into feat/drawn-set-follows-view

The label fix turns the brightness order into an index with positions and ids
laid out beside it. The star field only needs the order, so it is handed
`.order`. Both sides added scene tests in the same place; both are kept.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_016jxMkwA2rbicdGxHosecYi

src/app/shared/astro/brightest.spec.ts

@@ -1,6 +1,6 @@
 import { describe, expect, it } from 'vitest';
 
-import { brightestWithin, brightnessOrder } from './brightest';
+import { brightestWithin, brightnessIndex, brightnessOrder } from './brightest';
 
 interface TestStar {
   id: number;
@@ -46,11 +46,11 @@ describe('brightestWithin', () => {
 
   it('yields exactly what filtering and then sorting the catalogue did, in the same order', () => {
     const stars = cloud(3000);
-    const order = brightnessOrder(stars);
+    const index = brightnessIndex(stars);
     const centre = { x: 12, y: -30, z: 5 };
 
     for (const [radius, alwaysId] of [[40, null], [15, 7 * 2999], [0, 7 * 11], [500, null]] as const) {
-      const lazy = Array.from(brightestWithin(stars, order, centre, radius, alwaysId), (star) => star.id);
+      const lazy = Array.from(brightestWithin(stars, index, centre, radius, alwaysId), (star) => star.id);
       expect(lazy).toEqual(filterThenSort(stars, centre, radius, alwaysId));
     }
   });
@@ -61,7 +61,7 @@ describe('brightestWithin', () => {
       { id: 2, x: 3, y: 4.001, z: 0, magnitude: 0 }
     ];
 
-    expect(Array.from(brightestWithin(stars, brightnessOrder(stars), { x: 0, y: 0, z: 0 }, 5, null), (star) => star.id)).toEqual([1]);
+    expect(Array.from(brightestWithin(stars, brightnessIndex(stars), { x: 0, y: 0, z: 0 }, 5, null), (star) => star.id)).toEqual([1]);
   });
 
   it('reads no further than the caller takes', () => {
@@ -77,7 +77,7 @@ describe('brightestWithin', () => {
     });
 
     const taken: number[] = [];
-    for (const star of brightestWithin(counted, brightnessOrder(stars), { x: 0, y: 0, z: 0 }, 1000, null)) {
+    for (const star of brightestWithin(counted, brightnessIndex(stars), { x: 0, y: 0, z: 0 }, 1000, null)) {
       taken.push(star.id);
       if (taken.length === 15) {
         break;

src/app/shared/astro/brightest.ts

@@ -30,6 +30,38 @@ export function brightnessOrder(stars: readonly BrightnessRanked[]): Uint32Array
   return Uint32Array.from(stars.keys()).sort((a, b) => magnitudes[a] - magnitudes[b]);
 }
 
+/**
+ * The brightness order, with each star's position and id laid out beside it in that order.
+ *
+ * A walk has to test every star it passes, and near the Sun it passes nearly all of them: a 4 pc
+ * label radius holds a few dozen stars, faint dwarfs deep in the order, so the walk rarely finds
+ * fifteen to name before the end. Reading the stars themselves in brightness order jumps all over
+ * the catalogue, and a full walk took 19-23 ms — slower than the scan and sort it replaced. Read
+ * from these arrays, laid out in the order they are walked, the same walk touches memory in
+ * sequence and reads a star only when it yields one.
+ */
+export interface BrightnessIndex {
+  /** Indices into the catalogue, brightest first. */
+  readonly order: Uint32Array;
+  /** Positions in the same order, three to a star, at full precision so a star on a radius stays on it. */
+  readonly positions: Float64Array;
+  readonly ids: Float64Array;
+}
+
+export function brightnessIndex<T extends BrightnessRanked & Positioned & { readonly id: number }>(stars: readonly T[]): BrightnessIndex {
+  const order = brightnessOrder(stars);
+  const positions = new Float64Array(order.length * 3);
+  const ids = new Float64Array(order.length);
+  order.forEach((index, at) => {
+    const star = stars[index];
+    positions[at * 3] = star.x;
+    positions[at * 3 + 1] = star.y;
+    positions[at * 3 + 2] = star.z;
+    ids[at] = star.id;
+  });
+  return { order, positions, ids };
+}
+
 /**
  * The stars within `radiusPc` of `centre`, brightest first, plus the one star `alwaysId` names
  * wherever it is — handed over lazily, so a caller that stops after the first few pays for no
@@ -37,19 +69,19 @@ export function brightnessOrder(stars: readonly BrightnessRanked[]): Uint32Array
  */
 export function* brightestWithin<T extends BrightnessRanked & Positioned & { readonly id: number }>(
   stars: readonly T[],
-  order: Uint32Array,
+  index: BrightnessIndex,
   centre: Positioned,
   radiusPc: number,
   alwaysId: number | null
 ): Generator<T> {
+  const { order, positions, ids } = index;
   const radiusSq = radiusPc * radiusPc;
-  for (const index of order) {
-    const star = stars[index];
-    const dx = star.x - centre.x;
-    const dy = star.y - centre.y;
-    const dz = star.z - centre.z;
-    if (dx * dx + dy * dy + dz * dz <= radiusSq || star.id === alwaysId) {
-      yield star;
+  for (let at = 0; at < order.length; at++) {
+    const dx = positions[at * 3] - centre.x;
+    const dy = positions[at * 3 + 1] - centre.y;
+    const dz = positions[at * 3 + 2] - centre.z;
+    if (dx * dx + dy * dy + dz * dz <= radiusSq || ids[at] === alwaysId) {
+      yield stars[order[at]];
     }
   }
 }