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.
Graham McIntire
af8b787915