preview

# /preview — see and shape what the panel shows The display is **rendered server-side in HelmLog**, so you preview and change it without touching this firmware or the device. The device just blits whatever HelmLog returns. ## See the current frame (no device needed) If your Mac and the Pi are both on Tailscale (or you're on the boat LAN): ```bash KEY=<device-api-key> # from include/config.h, or a HelmLog device key HOST=<pi-host>:3002 # Tailscale name or LAN IP; HelmLog WEB_PORT=3002 curl -s -H "Authorization: Bearer $KEY" \ "http://$HOST/api/display.png" -o preview.png && open preview.png ``` - `/api/display.png` — human-viewable render (open in a browser you're logged into HelmLog and the session cookie authenticates — no key needed). - `/api/display.raw` — the byte-identical 4-bit frame the device blits. - Append `?invert=1` to preview inverted polarity. ## Change the layout The renderer lives in HelmLog, not here: - `helmlog/src/helmlog/display_render.py` — the 960×540 Pillow layout (cells, fonts, values, VMG = `STW·cos(TWA)`, LIVE/NO DATA badge). Iterate by editing it and re-running the PNG preview above; there are tests in `helmlog/tests/test_display.py`. - `helmlog/src/helmlog/routes/display.py` — the `.png` / `.raw` endpoints and the `X-Refresh-Seconds` / `X-Full-Refresh-Seconds` headers. Follow HelmLog's own `AGENTS.md` (worktree + PR + `Closes #N`) when editing it. A render change only reaches the device after HelmLog is **redeployed to the Pi**; the device then picks it up automatically on the next poll — no reflash. ## e-paper legibility notes - Mid-grey renders faint on this panel — keep text black (labels were darkened for exactly this reason). - The render is landscape 960×540; the device is mounted landscape to match. - Each update flashes the panel, so prefer a calm refresh (`DISPLAY_REFRESH_SECONDS` ~20–30 in HelmLog settings) over 5 s.