# CLAUDE.md

This file provides guidance to Claude Code (claude.ai/code) when working with code in this repository.

## Project Overview

eng-pad is an Android note-taking app built around notebooks with an EMR pen as the primary input method. Target devices are the Supernote Manta (Android 11) and Daylight DC-1 (Android 13). Minimum API level is Android 11 (API 30).

## Build Commands

```bash
make all                 # lint → test → build
make build               # Compile debug + release APKs
make test                # Run unit tests
make lint                # Run Android Lint
make clean               # Clean build artifacts
make run                 # Build, install, and launch on emulator (starts emulator if needed)
make devrun              # Build, install, and launch on connected USB device
make run AVD=Medium_Phone_API_36.0  # Use a specific AVD

# Run a single test class:
make test-one CLASS=net.metacircular.engpad.data.StrokeBlobTest
```

## Architecture

- **Kotlin + Jetpack Compose** for UI chrome (screens, toolbar, dialogs)
- **Custom View** (`PadCanvasView`) for the drawing canvas — Compose Canvas lacks `MotionEvent` access needed for stylus input
- **Room** (SQLite) for persistence — notebooks, pages, strokes
- **Single Activity** with Compose Navigation (three screens: notebook list → page list → editor)
- **Coordinate system**: 300 DPI canonical points. Regular page = 2550×3300pt, large = 3300×5100pt. Scaled to 72 DPI (×0.24) for PDF export.
- **Input dispatch**: `TOOL_TYPE_STYLUS` → draw/erase/select, `TOOL_TYPE_FINGER` → zoom/pan

## Project Documents

- **DESIGN.md** — Full technical design (architecture, data model, rendering, source tree)
- **PROJECT_PLAN.md** — All implementation steps with checkboxes. Check off steps as completed.
- **PROGRESS.md** — What's been done, what's in progress, decisions made. Update after every step.

**Keep PROJECT_PLAN.md and PROGRESS.md in sync.** When a step is completed, check it off in PROJECT_PLAN.md and log it in PROGRESS.md. When files are added, update the source tree in both DESIGN.md and this file.

## Source Tree

```
eng-pad/
├── app/
│   ├── build.gradle.kts                              -- Module build config
│   └── src/
│       ├── main/
│       │   ├── AndroidManifest.xml
│       │   ├── kotlin/net/metacircular/engpad/
│       │   │   ├── EngPadApp.kt                      -- Application class
│       │   │   ├── MainActivity.kt                   -- Single activity, Compose NavHost
│       │   │   ├── data/
│       │   │   │   ├── db/                           -- Room database, DAOs, converters
│       │   │   │   ├── model/                        -- Entities: Notebook, Page, Stroke, PageSize
│       │   │   │   └── repository/                   -- NotebookRepository, PageRepository
│       │   │   ├── ui/
│       │   │   │   ├── navigation/NavGraph.kt        -- Route definitions
│       │   │   │   ├── notebooks/                    -- List screen + ViewModel
│       │   │   │   ├── pages/                        -- Page grid screen + ViewModel
│       │   │   │   ├── editor/                       -- PadCanvasView, EditorScreen, ViewModel
│       │   │   │   ├── export/PdfExporter.kt         -- PDF generation + sharing
│       │   │   │   └── theme/Theme.kt                -- Material3 theme
│       │   │   └── undo/                             -- UndoManager, UndoableAction
│       │   └── res/
│       └── test/                                     -- Unit tests
├── build.gradle.kts                                  -- Root build config
├── settings.gradle.kts                               -- Project settings (foojay JDK resolver)
├── gradle.properties
├── gradle/libs.versions.toml                         -- Version catalog
├── Makefile                                          -- Build targets (build, test, lint, run, devrun)
├── CLAUDE.md                                         -- This file
├── README.md
├── DESIGN.md                                         -- Technical design
├── PROJECT_PLAN.md                                   -- Implementation steps
└── PROGRESS.md                                       -- Completion tracking
```

## Key Conventions

- Stroke points are packed as little-endian float BLOBs: `[x0,y0,x1,y1,...]`
- All coordinates are in canonical space (300 DPI). Screen transform via `Matrix`.
- Grid drawn in **screen space** with pixel-snapped positions (not canonical space) for uniform squares.
- Pen widths: 0.38mm = 4.49pt, 0.5mm = 5.91pt (at 300 DPI).
- Anti-aliasing disabled on all paint objects for crisp e-ink rendering.
- No backing bitmap — strokes draw directly as paths.
- Viewport: page always fills screen, pan clamped to edges, dynamic min zoom.
- Line snap: hold pen still 1.5s to snap to straight line (60pt movement threshold).
- Hardware palm rejection only (EMR digitizer).