LTN — Laser Tag Now

iPhone laser tag over Ultra-Wideband. Aim your phone like a camera, fire, and the other player's phone buzzes, flashes red, and loses hearts. No server, no venue Wi-Fi — the phones talk directly to each other.

What's in it

• Aiming — Nearby Interaction streams distance and direction to every peer. A shot lands on the most-centered target inside a 9° half-angle cone off the back of the phone; distance never gates it. The ARKit viewfinder behind the HUD doubles as NI's camera assistance — on U2 phones (15/16) that camera-assisted angle is often the only bearing you get.
• Networking — Bonjour plus direct TCP over peer-to-peer Wi-Fi (Network.framework), no backend. Lobbies are scoped, not blindly meshed: a joiner dials the one host it picked, and lobby-mates dial each other only once the host's roster names them.
• Roles — Light / Regular / Heavy, picked in the lobby, trading hearts against fire rate, damage, magazine and reload. Light is full-auto.
• Teams — optional Alpha / Bravo: no friendly fire, scored on team kill totals.
• Power-ups — Medpack (4 hearts, instant), Overdrive (halves cooldown and reload, 10 s), Cloak (5 s), Reflector (5 s), with countdown rings on the drop and on your active effects.
• Ammo — the ring around FIRE is your magazine. Empty auto-reloads; the button beside it reloads early.
• Training Range — solo drill, no lobby and no UWB: shoot a console orb to pick a difficulty, then clear 30 pop-up drones from a frontal arc, three up at a time. Pure ARKit, so any phone runs it.
• Spectating — a Mac or spare phone joins as game master for standings, kill feed and any player's live viewfinder.
• Killcam — shooters keep a rolling ~4 s of viewfinder at 30 fps and snapshot it on a confirmed kill. Clips move to spectators after the match, to review and publish — HUD baked in, sounds remixed, H.264 — to the killcam-web gallery.

Role	Hearts	Damage	Fire	Magazine	Reload
Light	6	1	0.1 s, full auto	16	3 s
Regular	8	2	0.5 s	10	3 s
Heavy	10	3	1.0 s	5	4.5 s

Hearts are discrete and nothing grants i-frames mid-fight, so fire rate, magazine and reload are the only throttles on damage. Match-wide: 9° cone, 5 s respawn, 1 s spawn protection, 2–8 players, 2/5/10/15 min matches — all in Echo/Models/GameModels.swift.

Build & run

iPhone 11 or later, not SE (every player needs the U1/U2 chip), iOS 17+, Xcode 16+. Real devices only — Nearby Interaction doesn't work in the Simulator, which has no camera either, so it only covers menus and static HUD layout.

open Echo.xcodeproj → target Echo → Signing & Capabilities → pick your team. The project, target and source folder are all still named Echo; the app ships as LTN. On first launch allow Local Network, Nearby Interaction and Camera.

How to play

1. Enter a call sign. A hidden #xxxx suffix keeps duplicates distinct on the wire, but unique names keep the kill feed readable.
2. One player taps Host a Lobby and picks role, mode and match length; everyone else taps Find Lobbies. Training Range needs neither. Host taps Start and phones exchange UWB tokens.
3. Hold the phone in portrait like you're photographing your target — the antenna cone points out the back. The reticle closes and ticks on a lock.
4. FIRE. Hits buzz their phone, flash it red and drop hearts; at zero, a death screen and a 5 s respawn. Bodies block UWB — human shields are canon.
5. K/D sits beside the match clock, which goes red for the last 30 s. Time up sends everyone to the summary; Back to Lobby keeps the mesh up for another round.

Architecture

LTNApp            RootView switches on GameEngine.phase — menu · browsing ·
                  lobby · playing · summary · training
Managers/
  GameEngine      the hub: player table · hit resolution · cooldowns ·
                  respawns · match clock · consumables · clip capture
  NetworkManager  Network.framework mesh · Codable GameMessage protocol
  RangingManager  one NISession per peer · token exchange · reading buffer
  AimCameraMgr    the single shared ARSession — viewfinder, NI camera
                  assistance, spectator frame tap, killcam ring buffer
  TrainingRange   solo drill state: console orbs, drone arc, local aim test
  ClipEncoder     frames + HUD + sounds → MP4 · ReplayPublisher uploads it
  HapticsManager  Core Haptics patterns · SoundManager plays Echo/Sounds/
Models/           roles · settings · wire protocol · match results
Design/           Theme (color, spacing, opacity tokens) · Typography
Views/            one screen per phase, plus the HUD layers — reticle,
                  minimap, enemy tags, drop markers, training overlay

Three invariants to know before changing anything:

• Hit resolution runs on the shooter's phone — it holds the ranging data. The victim applies damage on receipt and broadcasts its own health, death and respawn. Hackathon scale: trust the network.
• Only the host calls time. Every phone counts down locally off a wall-clock deadline, but the host's .endMatch tallies are what everyone shows, so two phones can't crown different winners. If the host goes dark, each phone ends on its own after 5 s.
• There is no shared world frame. Each phone knows its peers only through its own pairwise UWB readings, so a power-up drop travels as an affine combination of player positions and every phone resolves the same physical spot in its own AR frame.

Echo/Design/Theme.swift is the source of truth for color and spacing; CLAUDE.md carries the UI rules that go with it.

Troubleshooting

• Reticle never locks — aim like a photo, back of the phone toward the target. direction is nil outside the UWB field of view by design, and camera assistance needs a lit, textured scene to converge.
• Sessions drop in crowds — bodies block UWB. Dead NI sessions auto-restart with fresh tokens; if a peer stays dark, both players bounce to the lobby and back.
• Nobody in the lobby — every phone needs Local Network permission and Wi-Fi/Bluetooth on, though not the same network.
• Battery — UWB, an always-on screen and a live ARSession together are heavy drain.

Sounds in Echo/Sounds/ are synthesized originals, not sampled from any game. iphone-laser-tag-plan.md is the original design doc — historical, and stale on networking in particular.