docs(performance): slowdown audit of main, with the cause and fix for each finding

Co-Authored-By: Claude Fable 5.2 <[email protected]>

docs/PERFORMANCE-AUDIT-2026-11.md

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+# Slowdown audit, November 2026
+
+A sweep of `main` (`c02ede3bb`, 13 November 2026) for bugs that freeze the page
+or hold the frame rate down. This page lists what was found, why it happens and
+how to fix it, and names the pull request that carries each fix.
+
+[PERFORMANCE.md](PERFORMANCE.md) is the measured baseline of a healthy build;
+this page is the list of things that fall outside it.
+
+## How it was measured
+
+- Keyless dev server, headless Chrome at 1440 x 900 on Apple silicon (Metal
+  through ANGLE), default globe map.
+- Per scenario: load, a spell at rest, scripted drags and wheel zooms, then a
+  settle. Long tasks were counted with a `PerformanceObserver`, the hot function
+  named from a CPU profile, and `globe.getHeight`, `scene.sampleHeight`,
+  `scene.pick` and friends wrapped to count calls and time.
+- A long task is one main-thread task over 50 ms. With no layers on, the
+  baseline is two at load (longest about 240 ms) and none afterwards, with zero
+  frames rendered while the camera is still.
+- Four profiling sessions ran on one machine at the same time, so absolute
+  timings carry some noise. Ratios against the baseline are what to read.
+
+Nothing here was measured on Google Photorealistic 3D Tiles, on a discrete or
+integrated PC GPU, or with keyed feeds (AISStream, FIRMS, TomTom). Those rows
+are marked "read in code".
+
+## Findings and fixes
+
+Worst first. "Fix" names the pull request; a dash means none is open yet.
+
+### Measured
+
+| # | Where | What happens | Fix |
+| ---: | --- | --- | --- |
+| 1 | Bike Share, local data layers, Transit, Rail | 18 s freeze switching Bike Share on over New York (2,519 stations); 2.7 s on Data Centers; multi-second freezes with Transit while zooming | #1688, #1689 |
+| 2 | Shipwrecks | 4.6 to 5.1 s freeze when the markers are first built; a share link with the layer on holds the loading screen for 22.9 s | — |
+| 3 | Camera | Rendering stops until reload: at a whole-globe view looking straight down, pan a few times, then scroll one notch | — |
+| 4 | Street Traffic | Zooming at 250 m over Manhattan: 25 long tasks in 24 s, longest 746 ms, 6.6 s in total | — |
+| 5 | ALPR cameras | Up to a 1.9 s long task on load; eight off/on toggles cost 512 depth samples and 6.3 s | — |
+| 6 | Wind | 14 long tasks while zooming (longest 414 ms), 3.2 s of long tasks on load, about 32 renders a second for as long as it is on | — |
+| 7 | Submarine cables | About 2 s of long tasks on load, heap briefly at 1 GB, about 0.5 s again on each re-enable | — |
+| 8 | Live Flights at whole-globe view with detection labels | Fine on the test machine; at 4x CPU throttle, 8 fps with 143 long tasks in 15 s | — |
+| 9 | Radio | 7 to 10 long tasks when the directory loads, longest 447 ms | — |
+| 10 | Pointer pick | One pick on a pointer gesture takes 207 to 342 ms with an entity-heavy layer on, against about 4 ms with none | — |
+| 11 | CCTV | A still-image camera holds continuous rendering at 60 frames a second although its picture changes about every 10 s | — |
+
+### Read in code
+
+| # | Where | What happens | Fix |
+| ---: | --- | --- | --- |
+| 12 | `/api/firms` | The whole fire set is filtered, serialised and sent uncompressed on every request; 15 to 55 MB estimated in a heavy season | — |
+| 13 | AIS store | Both vessel maps are walked on every position message, and sorted whole once past the cap | — |
+| 14 | Satellite clouds on the 3D Tiles map | A CPU pass over a 4096 x 2048 image, 90 to 180 ms measured on a synthetic canvas, twice in a row | — |
+| 15 | NVG and FLIR styles | Over 100 texture reads per pixel on every frame | — |
+| 16 | Wind server | Full 0.25 degree GRIB fields decoded on the event loop, 200 to 600 ms estimated per refresh | — |
+| 17 | Imported geo files and other per-feature ground clamps | The Shipwrecks pattern (finding 2) at whatever size the data has | — |
+
+## Cause and fix, per finding
+
+### 1. Terrain height reads
+
+`globe.getHeight` casts a ray against the mesh of the tile under the point, and
+`scene.sampleHeight` renders a depth pass. Transit asked for every trail fix of
+every vehicle several times per poll; Bike Share sampled every station in one
+go. The fix keeps heights per point in one shared reader with a read budget
+(`src/services/terrainSurface.js`) and spreads the depth samples across frames.
+
+### 2. Shipwrecks
+
+`rebuild()` in `src/layers/shipwrecks/index.js` adds 7,958 billboards with
+`heightReference: CLAMP_TO_GROUND`. Each constructor runs
+`Billboard._updateClamping`, which intersects a ray with the terrain mesh,
+synchronously: 4.8 of the 4.9 s.
+
+Fix: do not clamp. Wrecks are at sea and the markers already ignore the depth
+test, so place them on the ellipsoid with `HeightReference.NONE`.
+
+### 3. Camera: rendering stops after pan then zoom
+
+Cesium's zoom-to-cursor path (`ScreenSpaceCameraController` `zoom3D` →
+`handleZoom` → `Camera.rotate`) builds a rotation from a zero or NaN axis when
+the camera looks straight down at a whole-globe view, throws
+`DeveloperError: normalized result is not a number`, and Cesium stops its render
+loop for good.
+
+Fix: keep the wheel zoom off the degenerate case (no zoom-to-cursor at near
+−90° pitch above a set altitude, or a pitch nudged off exactly −90°), and handle
+`scene.renderError` by restoring a sane camera and restarting the loop, so one
+bad frame does not need a reload.
+
+### 4. Street Traffic road loading
+
+Three costs in one task after the detail tiles arrive, in
+`src/layers/traffic/source.js`:
+
+- `outsideDetailTiles` clips every coarse z12 road against every loaded detail
+  tile (up to 16) for four regions.
+- The composed set is then handed on with `replace: true`, so
+  `ingestion.js` parses every road again although each tile was parsed as it
+  streamed.
+- `parseRoads` (`model.js`) asks `cachedGroundFloor` once per coordinate, and
+  each call builds several string keys.
+
+Fix: clip once per coarse tile against the detail tiles' union box and slice the
+work across frames (or do it in the vector-tile worker); reuse the roads parsed
+while streaming and parse only the clipped coarse remainder; look the floor up
+once per floor cell within a parse.
+
+This is separate from the one-viewport-tile-at-a-time loading recorded in
+[KNOWN-ISSUES.md](KNOWN-ISSUES.md).
+
+### 5. ALPR cameras
+
+`refineAnchors` and `anchorFor` in `src/layers/alpr/overlay.js` call
+`scene.sampleHeight` from the overlay's paint, four per paint. Each is a depth
+render and a `readPixels`; the first one also compiles the pick shader. Results
+are kept on the entity, so a rebuild or a re-enable samples everything again.
+
+Fix: on a terrain globe read `globe.getHeight` through the shared terrain reader
+instead of sampling; keep the answers in a map keyed by camera that outlives the
+entities; move what sampling remains out of the paint into a queue of one per
+frame.
+
+### 6. Wind
+
+The layer draws 7,184 paths as 916,476 vertices in 73 primitives. Cesium's
+zoom-to-cursor reads the depth buffer back, which has to flush that draw: 1.9 s
+of `readPixels` in a zoom against 0.2 s without Wind. A frame loop in
+`src/layers/wind/rendering.js` requests a render about 32 times a second to
+advance one uniform, and `disable()` throws the baked geometry away.
+
+Fix: fewer vertices (merged typed-array geometry, shorter or fewer paths), keep
+the bake across disable and enable, register the animation with the render
+governor at a lower rate, and keep wind out of the depth and pick passes.
+
+### 7. Submarine cables
+
+`src/layers/submarineCables/ingestion.js` loads both collections through
+`Cesium.GeoJsonDataSource` with `clampToGround`. That is one entity per cable
+part, and the entity visualisers walk all of them on every update.
+
+Fix: build one batched `GroundPolylinePrimitive` and one
+`PointPrimitiveCollection` directly, and keep them across disable and enable.
+
+### 8. Live Flights at whole-globe view
+
+Two costs that scale with the 7,500 aircraft of a full poll:
+
+- The fleet pass (`src/layers/flights/rendering.js`, every 80 ms) dead-reckons
+  each visible aircraft and asks `cachedGroundFloor` for it, including aircraft
+  at cruise altitude that can never touch the floor. Each lookup formats numbers
+  to strings several times and rewrites a cache entry: 40% of the busy time.
+- The detection overlay (`src/data/detection.js` `_drawOverlay`) collects every
+  detectable object and strokes every bracket on every frame.
+
+Fix: skip the floor path for a contact clearly above any terrain, keep the floor
+per aircraft per fix, make the floor-cell key a number, and stop promoting the
+cache entry on every read. Collect detection candidates when the fleet pass, the
+poll or the camera changes rather than per frame, and stroke the brackets as one
+path per colour.
+
+### 9. Radio
+
+`stationTags()` in `src/layers/radio/categories.js` splits and normalises a
+station's tags on every `hasTag` call, and `buildRadioCategories` runs that for
+every station against every category, twice.
+
+Fix: normalise once per station at ingest and count categories from that.
+
+### 10. Pointer pick
+
+`pickPointer` in `src/voice/pointerPick.js` calls `scene.pick` on pointer
+gestures. A pick renders the scene's pickable primitives, so its cost follows
+the entity count of whatever layers are on.
+
+Fix: do not pick while a gesture is in progress; pick once when the pointer
+rests, or only when something consumes the answer.
+
+### 11. CCTV still-image cameras
+
+`src/layers/cctv/projection.js` holds continuous rendering for as long as any
+projected camera is active and redraws the projection every frame.
+
+Fix: hold only for video. For a still image, request one render when a new image
+lands or while a focus fade runs.
+
+### 12. `/api/firms`
+
+`server/providers/firms.js` builds the payload and calls `JSON.stringify` per
+request, with no kept body and no compression, and the client refetches every
+ten minutes.
+
+Fix: build the body and its gzip once per refresh and serve those bytes, as the
+OpenSky provider does.
+
+### 13. AIS store
+
+`server/providers/vessels/ais-store.js` calls `pruneAisStreamCache()` for every
+message; the static-data map is never pruned.
+
+Fix: prune on a timer, evict in insertion order, and drop a vessel's static
+entry with the vessel.
+
+### 14. Satellite clouds on the 3D Tiles map
+
+`src/layers/weather/infraredImage.js` runs `getImageData`, a per-pixel power
+curve and `putImageData` over the whole canvas.
+
+Fix: a 256-entry lookup table applied in place for the canvas path; for the
+shell, do the transfer in its fragment shader.
+
+### 15. NVG and FLIR styles
+
+`src/styles/surveillance.js` loops 11 x 11 texture reads per pixel and
+`src/styles/thermal.js` totals 106.
+
+Fix: a separable or half-resolution blur, and noise ticked at about 15 Hz.
+
+### 16. Wind server
+
+`server/providers/wind/decode.js` decodes about a million doubles per message
+synchronously, hourly, for six keys.
+
+Fix: decode in a worker thread and keep the decoded U and V fields per cycle.
+
+### 17. Per-feature ground clamps
+
+`heightReference: CLAMP_TO_GROUND` per feature is also set in
+`installations/rendering.js`, `alpr/presentation.js`, `ghostMaps/index.js`,
+`earthquakes/index.js`, `airQuality/index.js`, `news/index.js`,
+`osmPlaces/index.js` and `src/data/geoFileImport.js`. Their counts were small in
+these runs (30 to 1,500), but an imported file sets its own size.
+
+Fix: where the count is not bounded, place through the shared terrain reader or
+add in slices across frames.
+
+## Checked and fine
+
+- Start-up of a production build: viewer ready in about 0.5 s, loading screen
+  gone at 1.6 s, three long tasks totalling about 300 ms.
+- Idle: no frames rendered with no layers on; every render hold was released
+  when its layer went off.
+- Leaks: all 41 layers toggled three times and ten of them eight times; no
+  timer, scene listener, primitive or data source grew per cycle. The heap
+  levelled off near 320 MB over 7.5 minutes of toggling eleven layers.
+- At most one long task after load: Military, Satellites (including 11,903
+  Starlink points), Earthquakes, News, Wildlife, GNSS, Drone Airspace, Military
+  Installations, Fire Perimeters, rain radar, lightning, and satellite clouds on
+  the globe map.
+- Live Flights at city scale with the same 7,500 aircraft loaded: 60 fps, no
+  long tasks.
+
+## Not covered
+
+- Google Photorealistic 3D Tiles: nothing was run there. Depth sampling is the
+  only height source on that map, so findings 4, 5 and 17 may be worse.
+- Live Vessels, FIRMS with data, TomTom traffic, Local ADS-B.
+- Frame rate on anything but one Apple silicon machine.
+- One all-layers run over Manhattan grew the heap from 346 to 638 MB in 60 s;
+  whether that is retained was not established.
+- One Satellites load showed a 5.2 s long task once and never again in four more
+  loads.

docs/PERFORMANCE.md

@@ -6,6 +6,9 @@ specification and should not be used to predict performance on untested systems.
 The original capture artifacts are not included here, so this page records
 results rather than defining a runnable benchmark.
 
+For slowdowns found since, with their causes and fixes, see
+[PERFORMANCE-AUDIT-2026-11.md](PERFORMANCE-AUDIT-2026-11.md).
+
 ## Test context
 
 The baseline was captured on 22 August 2026 with these conditions: