Overhaul web UI and improve ADS-B emitter category support

[m3ftwz]

Summary

Overhaul of the web interface, replacing the monolithic gmap.html with a modular, multi-file architecture served from web/. This PR also includes backend changes to properly decode and expose ADS-B emitter categories, improved --ifile replay timing, and a more correct embedded HTTP server.

Web UI

Modular architecture

The single gmap.html file has been reorganized into a structured web/ directory:

• web/index.html — minimal shell, external CSS/JS
• web/assets/css/style.css — glassmorphism-styled dark theme
• web/assets/js/main.js — app entry point and data fetch loop
• web/assets/js/aircraft.js — marker icon selection by emitter category, rotation logic
• web/assets/js/panel.js — info panel rendering, dragging, copy-to-clipboard
• web/assets/js/trail.js — flight trail drawing with altitude-based color gradient
• web/assets/js/lib/icons.js — inline SVG aircraft silhouettes (jet, heavy, private jet, prop, helicopter, glider, drone, balloon, ground vehicle, obstacle)
• web/assets/js/lib/storage.js — localStorage helpers for map view persistence
• web/assets/js/lib/utils.js — clipboard utility

SVG aircraft silhouettes

Aircraft markers now use distinct top-down SVG silhouettes based on ADS-B emitter category instead of a generic Font Awesome plane icon for all aircraft. Icons include: single-engine prop, twin turboprop, jet, heavy jet, private jet, helicopter, glider, balloon, drone, ground vehicle, and obstacle marker.
Non-directional icons (balloon, obstacle, parachute) do not rotate with track heading.

Flight trail visualization

Selecting an aircraft now draws its flight trail on the map with:

• Altitude-based color gradient (white → yellow → green → cyan → blue → purple)
• Adaptive trail sampling — more points recorded during turns, fewer on straight legs

Other UI improvements

• Replaced interact.js dependency with native Pointer Events for panel dragging
• Replaced Font Awesome dependency with self-contained inline SVGs
• Added clear selection button and Escape key to deselect aircraft
• Added copy-to-clipboard buttons with visual feedback on individual fields
• Emitter category label displayed in the info panel
• Dark map tile layer for better contrast with aircraft markers
• Glassmorphism panel styling with backdrop blur

Backend (dump1090.c)

ADS-B emitter category support

• Introduced emitter_category, using a flat 0–31 encoding that combines the category set (A–D) and code (0–7)
• Added emitter_category_labels lookup table with human-readable labels per FAA AC 20-165B
• emitter_category is now stored on the aircraft struct, decoded from identification messages, and included in the /data.json response

Improved --ifile replay timing

• Replaced the fixed 5 ms usleep() delay with a sample-rate-proportional nanosleep() delay, so file replay matches real-time SDR data rate
• Replay pacing now also applies in --net mode (previously only --interactive)

HTTP server improvements

• Proper 404 and 500 status codes instead of always returning 200
• Fixed content types: application/json (no charset), added text/css, application/javascript, text/plain
• Static file routing for all web/ assets with explicit path allowlist (no directory traversal)

Misc

• Trailing whitespace cleanup
• Added #include <time.h> for nanosleep() / struct timespec

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Note: This work was developed with assistance from GPT 5.4 (Codex) and Claude Opus 4.6 (Claude Code).

[m3ftwz]

Ready and tested with a real RTL-SDR dongle and antenna :D