Three changes that shrink first-paint and make layer toggles instant:
1. Server: /weather/cells now supports ?format=bin and ?layers=a,b,c. The
binary "WCEL" pack is ~3× smaller than JSON (Float32 columns, no key
overhead) and parses with DataView + typed-array views — essentially
memcpy on the client.
2. Client: replaced JSON parse + per-cell SVG <rect> with a custom
Leaflet canvas layer. The pack is columnar (lats/lons + Float32Array
per layer) and each draw is one fillRect per cell against a
precomputed 256-step color LUT. At low zoom (CONUS, ~80k cells) SVG
paint cost dominated; canvas keeps it under one frame.
3. Lazy prefetch: the initial fetch only requests the *current* layer
(~1/19 the bytes). Right after paint, a single background fetch
pulls every other layer into the same pack. Layer switches that land
after the prefetch finishes are pure recolor — no network, no
server CPU.
The /weather/tiles endpoint stays for backward compat. The JSON path of
/weather/cells stays too — the binary path is opt-in via ?format=bin.
Previously every layer toggle triggered 21 fresh tile requests with the
new layer in the URL — ~21 server-side SVG renders, plus the round-trip
overhead. Even with the GridCache fix the server still spent real CPU
generating thousands of <rect>s per tile, and the user felt it.
Add /weather/cells: a single JSON endpoint returning every layer field
for every cell in the requested viewport. The hook fetches once on
mount, time change, or pan/zoom, caches the cells in memory, and paints
them via L.svgOverlay. Layer switches now re-color the same cached
cells locally — zero network, zero server CPU.
The single SVG uses lat/lon coords with preserveAspectRatio="none";
Leaflet stretches it linearly to the bbox. There is mild equirect→
mercator distortion at low zoom over CONUS but it's imperceptible at
typical use (z6+) and the layer-toggle UX win is large.
Tile endpoint kept for back-compat. svgOverlay opacity matches the
prior tile renderer's 0.55 fill-opacity.
Move the /weather render path off raw HRRR profile decoding + per-cell
SoundingParams + WeatherLayers derivation. The dominant cost was
re-deriving the same scalar fields on every viewport pan and timeline
scrub.
Server side:
- New Microwaveprop.Weather.ScalarFile persists pre-derived scalar
rows on NFS, bucketed into 5°×5° chunk files under
<base>/weather_scalars/<iso>/<lat_band>_<lon_band>.etf.gz. Viewport
reads only decode the chunks that overlap the requested bounds;
point-detail clicks read exactly one chunk.
- weather_grid_at/2 and weather_point_detail/3 prefer ScalarFile;
ProfilesFile is now the cold-start fallback only.
- warm_grid_cache_and_broadcast/1 and warm_grid_cache_from_latest_profile/0
also persist the scalar artifact, and the cold-derive path kicks
off a per-valid_time-locked async materialization so the next
reader gets the cheap path.
- NotifyListener.handle_propagation_ready/1 fires
Weather.materialize_scalar_file/1 in a detached Task on the Rust
pipeline's NOTIFY propagation_ready, so steady-state forecast hours
arrive with their scalar artifact already on disk.
- available_weather_valid_times/0 unions ScalarFile + ProfilesFile so
the timeline survives an aggressive retention sweep on either side.
Browser side (finding #8):
- Mount the legend Leaflet control once and patch its inner content
on layer changes instead of remove + re-add on every renderLayer.
- renderTimeline now keys off the rendered button set: selection-only
updates take an applyTimelineSelection patch path that restyles
existing buttons in place. Full innerHTML rebuild only fires when
timelineData itself changes.
Also fixes a credo nesting-depth flag in tile_renderer.ex by extracting
interpolate_pair/2 from the inner anonymous function.
