LightTip

Tip calculator and AI receipt splitter for the Light Phone III. Shows up on the phone as Tip Calculator, package com.gios.lighttip. Current released version: v1.0.13.

Why this exists

LightOS has no calculator built for splitting a bill, and every figure here is money — which is the whole design constraint. All amounts are held in cents as Long, never Double. Floating point can't represent most cent amounts exactly, and repeated allocation (tax and tip spread across N diners) compounds that error into totals that don't add back up to the bill. Tax and tip are instead allocated by largest-remainder apportionment, verified against the invariant "per-person totals sum to the bill exactly" across 20,000 randomised trials. This is not a detail to refactor away later.

Quick start

Every push to main publishes one signed APK as a GitHub Release — a push is a release trigger, not a cosmetic action.

1. Grab the newest APK from Releases:

   adb install -r LightTip-v<version>.apk
   

   or track https://github.com/gi-os/LightTip in Obtainium (the repo URL, not the GitHub Pages URL below).
2. Only the Split tab needs a key. Open gi-os.github.io/LightTip, paste an Anthropic API key, and a QR appears — the page is entirely client-side, the key never leaves the browser. On the phone: gear → Scan QR (or type the key by hand).
3. Tip tab works offline immediately: punch the bill into the keypad, pick a preset (10/15/18/20/22%) or type your own, read tip and total.

Tip: keypad, presets, tip and total

Split: line items read off the receipt, initials for who is on each

Totals: tax and tip shared in proportion

Taken on a Light Phone III.

Configuration and usage

Splitting a bill

1. SPLIT tab → + → photograph the bill.
2. Wait a second or two while Claude Haiku reads the line items off the photo. Vision runs on your own Anthropic key, stored on the phone; nothing else leaves the device, and quantities are expanded (2x Beer becomes two rows) so two people can each claim one.
3. Person icon → add everyone at the table. Names are remembered between bills.
4. Tap an item, tick everyone sharing it — a shared item divides evenly among whoever is ticked. Items nobody claims are excluded from every share and reported separately in Totals, rather than silently absorbed into someone's bill.
5. TOTALS → per-person breakdown of items, tax and tip. Tip defaults to 20% on the pre-tax subtotal and is adjustable per receipt.

The wheel

Turning the phone's wheel scrolls the receipt list, the line items, the people list, the per-person totals and the tick-list in the assign dialog — the reason it's wired up at all: on a 472dp-tall panel a table of six shows about four, and reaching over the list to drag it is the one gesture a bill-splitting app should never need mid-conversation.

LightTip alone is the whole install for this — no service, no permission, no root. The wheel arrives as ordinary key events (LightOS relabels an optical sensor's scancodes as WHEEL_CCW/WHEEL_CW, and nothing in the system intercepts them), and the Activity claims them in dispatchKeyEvent, before the view hierarchy gets a look, so a focused name field can't swallow them. Notches arrive faster than a frame, so each is paid off a fraction per frame; the first notch after a pause is held back, since the wheel sits under a thumb. The assign dialog is its own window and picks the wheel up separately, so the list underneath stands down while it's open.

The wheel click and the camera button do nothing here. Optional, separate install for those: LightControl gives the whole phone brightness (hold wheel + turn), flashlight (tap), and camera (camera button), each rebindable. It passes bare turns straight through to com.gios.*, so it doesn't cost this app the scrolling above.

adb install -r LightControl-v1.0.x.apk

# NOTE: this replaces the accessibility-service list — colon-join if you also run
# LightVoice's push-to-talk.
adb shell settings put secure enabled_accessibility_services \
  com.gios.lightcontrol/com.gios.lightcontrol.keys.ControlService
adb shell settings put secure accessibility_enabled 1

adb shell appops set com.gios.lightcontrol WRITE_SETTINGS allow
adb shell appops set com.gios.lightcontrol SYSTEM_ALERT_WINDOW allow

Notes for the LPIII panel

• The screen is greyscale on matte glass. Selected tip chips invert rather than tint, because hue is discarded and a low-alpha fill disappears.
• Surfaces are true black with no tonal elevation, so 1dp rules separate regions and dialogs get an explicit dark-grey fill — a scrim over black tints nothing.
• The display is roughly 411 × 472 dp, normal width and about half the usual height; the keypad takes the leftover vertical space rather than a fixed fraction of the screen.
• Text uses Akkurat when LightOS provides it, so the app matches the system UI.

Why this isn't a Light SDK tool

The Light SDK sandbox rejects CameraX and blocks LocalContext outright, and READ_MEDIA_IMAGES is not on its permission allowlist — so a sanctioned SDK tool cannot photograph anything. LightTip is a plain sideloaded APK for the same reason LightPass is; it started as a light-sdk fork and had to be rebuilt from scratch as one.

Building

./gradlew :app:assembleDebug
./gradlew :app:assembleRelease

CI (.github/workflows/build.yml) publishes a signed GitHub Release on every push to main: versionCode = workflow run number, versionName = 1.0.<run>, tag v1.0.<run>, exactly one APK named LightTip-v<version>.apk, marked latest — the debug build stays a workflow artifact. The keystore is committed at keystore/lighttip.jks so adb install -r upgrades in place, and CI pins its cert SHA-256 in signing-fingerprint.txt.

Two CI gotchas worth not relitigating:

• AGP shortens resource paths in release builds, so the icon can land in the APK as something like res/o-.png — grepping the zip for ic_launcher finds nothing; verify with aapt2 dump badging instead.
• Parse apksigner verify --print-certs output with sed -E 's/.*[Dd]igest:[[:space:]]*//'.

The launcher icon is generated, not hand-drawn

The mark is a percent sign — the tip on one tab, two parties with a line between them on the other — white line art on black, matching the icon language of the sibling Light Phone III tools. Geometry lives once in scripts/generate_icon.py and is emitted twice: as Android adaptive vector layers and as raster fallbacks for every mipmap density, everything inside the 18–90 safe zone (of a 108×108 canvas) so no launcher mask clips it. Re-running the script reproduces the shipped assets byte for byte, apart from vector formatting:

python3 scripts/generate_icon.py   # needs Pillow; rewrites app/src/main/res/{drawable,mipmap-*}

It shipped without any android:icon at first, which is why Obtainium and the launcher both showed the default Android robot until ic_launcher/ic_launcher_round were wired up — verified afterward through aapt2 dump badging, not by grepping the APK zip (see above).

Companion QR page for the Anthropic key is GitHub Pages from /docs at https://gi-os.github.io/LightTip/; it is client-side only.

Contributing

Issues and PRs welcome.

• Money math changes need to keep the largest-remainder invariant — run the randomised trial suite, don't just eyeball a couple of examples.
• material-icons-extended is banned here — it alone was ~30 MB of the debug APK. Material3's core icon set plus a stock Checkbox covers everything used; abiFilters is arm64 only and the debug APK sits around 28 MB.
• If you touch the launcher icon, edit the geometry in scripts/generate_icon.py, not the generated XML/PNGs directly, and re-run it.
• CI publishes a release on every push to main — verify locally before pushing there.

Version history

Version	Change
v1.0.13	Say plainly that the wheel works with LightTip alone (docs)
v1.0.12	Scroll with the wheel
v1.0.11	docs: add LightNoise and LightPods to the collection table
v1.0.10	Make the icon reproducible from a script
v1.0.9	Check the icon through aapt2 badging, not the zip listing
—	Add a launcher icon
v1.0.7	docs: add screenshots and the collection table
v1.0.6	Publish a signed release APK alongside the debug one
v1.0.5	Drop material-icons-extended
v1.0.4	Ship arm64 only and use the non-deprecated LocalLifecycleOwner
v1.0.3	Rebuild as a plain sideloaded APK
—	Camera-only capture: READ_MEDIA_IMAGES is not on the SDK permission allowlist
—	LightTip 1.0 — tip calculator and AI receipt splitter for the Light Phone III (initial commit)

The gi-os Light App collection

Twelve tools for the Light Phone III, all open source, all built in one run.

Tool	What it does	Built on
LightPass	Photograph a movie ticket, keep the stub	Plain Android
LightQR	QR scanner, plus a browser generator	Plain Android
LightRSS	RSS and Atom reader with images and QR subscribe	light-sdk, fork of zachattack323/LightRSS
LightNYCSubway	Live MTA subway arrivals	light-sdk fork
chat	iMessage over a self-hosted BlueBubbles server	Fork of craigeley/chat
LightFog	Fog of World companion, GPS recorder and fog map	Fork of garado/light-topographic
LightNonogram	Picross, plus a generator that only ships solvable puzzles	Kotlin generator, light-sdk tool
LightSolitaire	Klondike, draw one, unlimited redeals	light-sdk
LightFastread	RSVP speed reader for EPUB and MOBI	Fork of fluffyspace/FastRead
LightTip (this repo)	Tip calculator, plus a receipt splitter that reads the line items	Plain Android
LightNoise	Twelve synthesized sounds, a two-layer mixer and a sleep timer	Plain Android
LightPods	AirPods battery, in-ear and lid status	Plain Android, ports LibrePods

The Light Phone does not sponsor or endorse any of these. Licences vary per repo; this one is MIT.