Tract

An infinite-canvas handwriting app for iPad, built for maths homework.

You write with the Apple Pencil on a dotted paper canvas; fingers only pan and zoom. A problem wheel in the top bar tags each stroke with a problem number (1.b.ii), so a whole page of scratch work can be exported as a PDF laid out as a clean problem table — or as PNG/SVG. Every stroke keeps its full pencil telemetry (position, pressure, tilt, timing) for future local ML features.

Three tools, nothing else: pen, eraser, lasso. iPadOS 26+, SwiftUI, Swift 6.2.

Setup

brew install xcodegen
cp Local.xcconfig.example Local.xcconfig   # fill in DEVELOPMENT_TEAM

Signing needs an Apple ID with a paid Developer Program membership added in Xcode → Settings → Accounts. xcode-select -p must point at your Xcode install.

Develop

Xcode never needs to be opened — everything runs from the shell.

./scripts/build.sh                        # compile / type-check (unsigned) — the inner loop
./scripts/test.sh                         # unit + UI tests on an iPad simulator
./scripts/screenshot.sh both              # → build/screenshots/*.png, to actually see a UI change
./scripts/deploy-device.sh                # signed build onto a connected, unlocked iPad
xcodegen generate                         # only after editing project.yml

Tract.xcodeproj is generated and gitignored — never edit it. Sources are collected by folder, so a new .swift file in an existing folder needs no config change; a new top-level folder goes in project.yml.

Because the canvas takes pencil input only, a simulator can't draw on it — hand-test on a real iPad, and use screenshot.sh (canvas / library / exportpicker / problempicker) to look at chrome changes. Xcode runs are slow, so bundle build + tests + screenshots into one invocation rather than running them one at a time.

Where things live

Canvas/ drawing engine and CanvasViewModel (the single source of truth) · Stroke/ pure data types · Document/ model, persistence and the home screen · ToolDock/ the floating tool bar · Toolbar/ the top glass pill · ProblemPicker/ the tagging wheel · Export/ PDF/PNG/SVG · Tests/, UITests/.

project_context.md is the full map — every file, the architectural rules, and a "where to make common changes" table. Read it before changing anything; keep it current after.