perf(flights): skip dead-reckoning contacts that stay behind the horizon

The fleet tick dead-reckoned, floored and distance-tested every contact on
every ~80 ms tick, then hid the ones behind the horizon. The worldwide feed
carries ~13k contacts; zoomed in, well under 1% are on screen, so nearly all
of that work produced a hidden billboard.

A contact that is already hidden and still behind the horizon at its last
position now re-reckons only on its turn in a staggered one-in-12-ticks
rotation (about once a second, HIDDEN_CONTACT_DR_TICKS). Anything that
position puts in view, and any contact with a fleet model, takes the full
pass immediately, so on-screen behaviour is unchanged. Hidden-inclusive
proximity queries (getNearby includeHidden, getAllPositions) read positions
at most about a second old, well inside the 30 s poll's uncertainty.

Measured in Chrome on a Radeon 780M, ~12.9k contacts, 56 on screen over
Colombia at 4 km, same view before and after:
  fleet tick   7.66 -> 2.03 ms/frame, longest tick 50.9 -> ~16 ms
  frame        20.6 -> 14.0 ms, 42.9 -> 57.8 FPS
Teleporting the camera to Madrid showed 975 contacts within 100 ms.

Co-Authored-By: Claude Opus 5.5 <[email protected]>

CHANGELOG.md

@@ -1,5 +1,12 @@
 # Changelog
 
+- Stop dead-reckoning every flight hidden behind the horizon on every fleet
+  tick. With the worldwide feed (~13k contacts, ~56 on screen over Colombia at
+  4 km), the fleet pass drops from 7.7 ms to 2.0 ms per frame and its longest
+  tick from 51 ms to about 16 ms; the scene goes from 43 to 58 FPS. Hidden
+  contacts re-reckon about once a second, staggered, and appear as soon as
+  their position is in view.
+
 - Public Overpass instances are no longer used by default. Street Traffic
   roads come from TomTom flow tiles, OpenFreeMap vector tiles, or both, chosen
   on the layer row (TomTom / OSM / Hybrid) or with `?trafficRoads=`. With a

docs/CURRENT-STATE.md

@@ -3469,7 +3469,7 @@ silently demoting every later lookup for the session.
 
 ### Motion & Symbology Correctness (June 10, 2026)
 
-- **Flights (commercial + military)** render one poll interval behind real time (30s/15s) and interpolate between two known feed-stamped fixes (OpenSky `time_position`; adsb.lol `receipt − seen_pos`). The display latency is an intentional product decision — do not "fix" it away. The whole fleet dead-reckons at ~12Hz (1m² write gating); aircraft get a 3-poll grace period (faded icon) before removal. When a position epoch pauses, both layers coast for at least 60 seconds of contact grace with an absolute five-minute ceiling. Source backoff marks each contact and the cockpit `STALE`; the cockpit then holds the exact layer position instead of continuing inertial flight. Repeated-position kinematic changes create a forward-only synthetic fix rather than mutating history, and grounded history is lifted only when no owned 3D model already controls its datum. A nominally successful worldwide OpenSky response whose own snapshot epoch is more than two minutes old prefers the existing 250-nm viewport-scoped adsb.lol fallback and labels the source/coverage accordingly when that upstream is available. If the fallback is also unavailable, the layer's freshness/error fields use the source epoch—never the cache receipt time—so the UI reports an old snapshot rather than “just now.”
+- **Flights (commercial + military)** render one poll interval behind real time (30s/15s) and interpolate between two known feed-stamped fixes (OpenSky `time_position`; adsb.lol `receipt − seen_pos`). The display latency is an intentional product decision — do not "fix" it away. The fleet dead-reckons at ~12Hz (1m² write gating); a contact already hidden behind the horizon whose last position still is re-reckons on a staggered one-in-12-ticks rotation (about once a second) instead, so the worldwide feed's ~13k contacts no longer cost a full pass when well under 1% are on screen. Anything that position puts in view, and any contact with a fleet model, takes the full pass immediately, and hidden-inclusive proximity queries read positions at most about a second old; aircraft get a 3-poll grace period (faded icon) before removal. When a position epoch pauses, both layers coast for at least 60 seconds of contact grace with an absolute five-minute ceiling. Source backoff marks each contact and the cockpit `STALE`; the cockpit then holds the exact layer position instead of continuing inertial flight. Repeated-position kinematic changes create a forward-only synthetic fix rather than mutating history, and grounded history is lifted only when no owned 3D model already controls its datum. A nominally successful worldwide OpenSky response whose own snapshot epoch is more than two minutes old prefers the existing 250-nm viewport-scoped adsb.lol fallback and labels the source/coverage accordingly when that upstream is available. If the fallback is also unavailable, the layer's freshness/error fields use the source epoch—never the cache receipt time—so the UI reports an old snapshot rather than “just now.”
 - **World-space headings at every angle** (`src/data/iconOrientation.js`): aircraft/vessel icon rotation uses the camera right/up basis per tick (alignedAxis always ZERO), which is exact at screen center and for orthographic/nadir views and remains stable through >180° tracked orbits. Perspective rays vary across the viewport, so off-center contacts at oblique pitch can diverge from an exact finite-difference window projection; a regression test pins that known regime, and field evidence decides whether to adopt exact projection with the basis method as fallback. Fleet rotations refresh on camera-pose change; tracked entities per frame. Billboards are horizon-culled via a shared EllipsoidalOccluder.
 - **Military/OpenSky reconciliation** (`src/data/militaryRegistry.js`): known-military ICAOs render amber in the flights layer (60s self-poll of the cached mil endpoint when the military layer is off) and are suppressed there while the military layer renders them.
 - **Satellites**: 838-sat core catalog (stations/visual/GPS/GLONASS/Galileo/GEO), tracking lands ~726km out via `viewFrom` (tracked entity owns a point graphic so the tracking camera engages), rings realign via primitive modelMatrix (no per-second rebuild flicker), optional `setParams({catalog:'dense'})` Starlink mode.

scripts/format-scope.json

@@ -308,6 +308,7 @@
   "src/layers/flights/tracking.js",
   "src/layers/flights/rendering.js",
   "src/layers/flights/testing.js",
+  "src/layers/flights/hiddenContactRotation.test.mjs",
   "src/layers/flights/evidence.js",
   "src/layers/flights/ingestion.js",
   "src/layers/flights/queries.js",

src/layers/flights/hiddenContactRotation.test.mjs

@@ -0,0 +1,42 @@
+import test from 'node:test';
+import assert from 'node:assert/strict';
+import {
+  FLEET_DR_INTERVAL_MS,
+  HIDDEN_CONTACT_DR_INTERVAL_MS,
+  HIDDEN_CONTACT_DR_TICKS,
+  hiddenContactDrPhase,
+} from './policy.js';
+
+// Contacts hidden behind the horizon re-reckon on one fleet tick per rotation
+// instead of every tick. Their positions still feed hidden-inclusive proximity
+// queries, so the rotation must reach every contact about once a second, and
+// it must spread them across ticks so no single tick carries the whole fleet.
+
+const icao = (n) => n.toString(16).padStart(6, '0');
+
+test('the rotation revisits each hidden contact about once a second', () => {
+  const periodMs = HIDDEN_CONTACT_DR_TICKS * FLEET_DR_INTERVAL_MS;
+  assert.ok(HIDDEN_CONTACT_DR_TICKS > 1);
+  assert.ok(
+    Math.abs(periodMs - HIDDEN_CONTACT_DR_INTERVAL_MS) <= FLEET_DR_INTERVAL_MS,
+  );
+});
+
+test('a contact keeps the same slot, inside the rotation', () => {
+  for (let n = 0; n < 500; n++) {
+    const phase = hiddenContactDrPhase(icao(n * 7919));
+    assert.ok(Number.isInteger(phase));
+    assert.ok(phase >= 0 && phase < HIDDEN_CONTACT_DR_TICKS);
+    assert.equal(hiddenContactDrPhase(icao(n * 7919)), phase);
+  }
+});
+
+test('a worldwide fleet is spread evenly enough that no tick carries a burst', () => {
+  const fleet = 13000;
+  const perSlot = new Array(HIDDEN_CONTACT_DR_TICKS).fill(0);
+  // Real ICAO24 addresses cluster by national block; sample several blocks.
+  for (let n = 0; n < fleet; n++)
+    perSlot[hiddenContactDrPhase(icao(0x0a0000 + n * 53))]++;
+  const fair = fleet / HIDDEN_CONTACT_DR_TICKS;
+  for (const count of perSlot) assert.ok(count < fair * 1.5, `${count} > 1.5×`);
+});

src/layers/flights/policy.js

@@ -200,6 +200,37 @@ export const FLEET_DR_INTERVAL_MS = 80;
 
 export const ROTATION_REFRESH_MS = 1000;
 
+/**
+ * @constant {number} Dead-reckoning cadence (ms) for contacts hidden behind the
+ * horizon. The worldwide feed carries ~13k contacts and a zoomed-in view shows
+ * well under 1% of them; the rest still need positions for hidden-inclusive
+ * proximity queries, but ~1 s old (≈250 m for an airliner) is well inside the
+ * 30 s poll's own uncertainty. Each hidden contact is re-reckoned on one tick in
+ * every HIDDEN_CONTACT_DR_TICKS, staggered by id so no tick carries them all.
+ */
+
+export const HIDDEN_CONTACT_DR_INTERVAL_MS = 1000;
+
+export const HIDDEN_CONTACT_DR_TICKS = Math.max(
+  1,
+  Math.round(HIDDEN_CONTACT_DR_INTERVAL_MS / FLEET_DR_INTERVAL_MS),
+);
+
+/**
+ * Stable slot in [0, HIDDEN_CONTACT_DR_TICKS) for a contact id, so each hidden
+ * contact re-reckons on the same tick of every rotation.
+ * @param {string} id Contact id (ICAO24).
+ * @returns {number}
+ */
+
+export function hiddenContactDrPhase(id) {
+  const text = String(id);
+  let hash = 0;
+  for (let i = 0; i < text.length; i++)
+    hash = (hash * 31 + text.charCodeAt(i)) >>> 0;
+  return hash % HIDDEN_CONTACT_DR_TICKS;
+}
+
 /** Max course slew (deg/s) — well above real turns (≤4°/s), hides fix-boundary
  *  steps. Scaled down toward COURSE_MIN_DPS at low speed (courseSlewCapDps). */
 

src/layers/flights/rendering.js

@@ -33,6 +33,8 @@ import {
   COURSE_SLEW_DT_MAX_SEC,
   ROTATION_REFRESH_MS,
   COURSE_MAX_DPS,
+  HIDDEN_CONTACT_DR_TICKS,
+  hiddenContactDrPhase,
 } from './policy.js';
 
 export function createRendering({
@@ -811,6 +813,12 @@ export function createRendering({
     }
   }
 
+  /** The contact's hidden-rotation slot, cached on its billboard. */
+  function _hiddenDrPhase(bb, icao24) {
+    bb._gevHiddenDrPhase ??= hiddenContactDrPhase(icao24);
+    return bb._gevHiddenDrPhase;
+  }
+
   function _fleetTick() {
     if (
       !flightState._viewer ||
@@ -931,9 +939,25 @@ export function createRendering({
       for (const icao of toRelease) _releaseModel(icao);
     }
 
+    const hiddenDrPhase = flightState._fleetTickSeq++ % HIDDEN_CONTACT_DR_TICKS;
+
     for (const [icao24, bb] of flightState._billboards) {
       if (icao24 === flightState._trackedIcao) continue; // tracked entity owns its own motion
 
+      // A contact still behind the horizon at its last position would only be
+      // re-reckoned to be hidden again, so off its turn it keeps that position
+      // (see HIDDEN_CONTACT_DR_TICKS). Anything the stale position puts in view,
+      // and any contact with a fleet model, takes the full pass below at once.
+      if (
+        !bb.show &&
+        _hiddenDrPhase(bb, icao24) !== hiddenDrPhase &&
+        !flightState._models.has(icao24) &&
+        !occluder.isPointVisible(
+          flightState._cullPositions.get(icao24) || bb.position,
+        )
+      )
+        continue;
+
       const info = flightState.records.data.get(icao24);
 
       const dr = parts.motion._deadReckon(icao24, flightState._scratchFleetPos);

src/layers/flights/state.js

@@ -204,6 +204,10 @@ export function createFlightState({ source, services }) {
 
   flightState._lastFleetTickMs = 0;
 
+  /** @type {number} Fleet ticks run; selects which hidden contacts re-reckon */
+
+  flightState._fleetTickSeq = 0;
+
   /** @type {string} Camera pose signature at the last rotation pass */
 
   flightState._lastCamPoseSig = '';