openpencil/AGENTS.md

# OpenPencil

Vue 3 + CanvasKit (Skia WASM) + Yoga WASM design editor. Tauri v2 desktop, also runs in browser.

## Monorepo

Bun workspace with two packages:

- `packages/core` — `@open-pencil/core`: scene graph, renderer, layout, codec, kiwi, clipboard, vector, snap, undo. Zero DOM deps, runs headless in Bun.
- `packages/cli` — `@open-pencil/cli`: headless CLI for .fig inspection, export, linting. Uses `citty` + `agentfmt`.

The root app (`src/`) is the Tauri/Vite desktop editor. Its `src/engine/` files are thin re-export shims from `@open-pencil/core`.

## Commands

- `bun run check` — lint + typecheck (run before committing)
- `bun run format` — oxfmt with import sorting
- `bun test ./tests/engine` — unit tests
- `bun run test` — Playwright visual regression
- `bun run tauri dev` — desktop app with hot reload
- `bun open-pencil info <file>` — document stats
- `bun open-pencil tree <file>` — node tree
- `bun open-pencil find <file>` — search nodes
- `bun open-pencil export <file>` — headless render to PNG/JPG/WEBP

## Code conventions

- `@/` import alias for app cross-directory imports, relative imports within core
- No `any` — use proper types, generics, declaration merging
- No `!` non-null assertions — use guards, `?.`, `??`
- Shared types (GUID, Color, Vector, Matrix, Rect) live in `packages/core/src/types.ts`
- Window API extensions (showOpenFilePicker, queryLocalFonts) live in `src/global.d.ts` and `packages/core/src/global.d.ts`
- Use `culori` for color conversions — don't reimplement parseColor/colorToRgba
- Use `@vueuse/core` hooks (useEventListener, etc.) — don't do manual addEventListener/removeEventListener
- `packages/core/src/kiwi/kiwi-schema/` is vendored — don't modify
- Core code must guard browser APIs: `typeof window !== 'undefined'`, `typeof document === 'undefined'`

## Rendering

- Canvas is CanvasKit (Skia WASM) on a WebGL surface, not DOM
- `renderVersion` vs `sceneVersion`: `renderVersion` = canvas repaint (pan/zoom/hover); `sceneVersion` = scene graph mutations. UI panels watch `sceneVersion` only.
- `requestRender()` bumps both counters; `requestRepaint()` bumps only `renderVersion`
- `renderNow()` is only for surface recreation and font loading (need immediate draw)
- Resize observer uses rAF throttle, not debounce — debounce causes canvas skew
- Viewport culling skips off-screen nodes; unclipped parents are NOT culled (children may extend beyond bounds)
- Selection border width must be constant regardless of zoom — divide by scale
- Section/frame title text never scales — render at fixed font size, ellipsize to fit
- Rulers are rendered on the canvas (not DOM), with selection range badges that don't overlap tick numbers

## Scene graph

- Nodes live in flat `Map<string, SceneNode>`, tree via `parentIndex` references
- Frames clip content by default is OFF (unlike what you'd assume)
- When creating auto-layout, sort children by geometric position first
- Dragging a child outside a frame should reparent it, not clip it
- Layer panel tree must react to reparenting — watch for stale children refs
- Groups: creating a group must preserve children's visual positions

## Components & instances

- Purple (#9747ff) for COMPONENT, COMPONENT_SET, INSTANCE — matches Figma
- Instance children map to component children via `componentId` for 1:1 sync
- Override key format: `"childId:propName"` in instance's `overrides` record
- Editing a component must call `syncIfInsideComponent()` to propagate to instances
- `SceneGraph.copyProp<K>()` typed helper — uses `structuredClone` for arrays

## Layout

- `computeAllLayouts()` must be called after demo creation and after opening .fig files
- Yoga WASM handles flexbox; CSS Grid blocked on upstream (facebook/yoga#1893)
- Auto-layout creation (Shift+A) must recompute layout immediately to update selection bounds

## UI

- Use reka-ui for UI components (Splitter, ContextMenu, DropdownMenu, etc.)
- Tailwind 4 for styling — no inline CSS, no component-level `<style>` blocks
- Mac keyboards: use `e.code` not `e.key` for shortcuts with modifiers (Option transforms characters)
- Splitter resize handles need inner div with `pointer-events-none` for sizing (zero-width handle collapses without it)
- Number input spinner hiding is global CSS in `app.css`, not per-component
- ScrubInput (drag-to-change number) — cursor and pointerdown on outer container, not inner spans
- Icons: use unplugin-icons with Iconify/Lucide (`<icon-lucide-*>`) — don't use raw SVG or Unicode symbols
- Sections are draggable by title pill, not by the area to the right of the title
- CSS `contain: paint layout style` on side panels to isolate repaints from WebGL canvas

## File format

- .fig files use Kiwi binary codec — schema in `packages/core/src/kiwi/codec.ts`
- `NodeChange` is the central type for Kiwi encode/decode
- Vector data uses reverse-engineered `vectorNetworkBlob` binary format — encoder/decoder in `packages/core/src/vector.ts`
- showOpenFilePicker/showSaveFilePicker are File System Access API (Chrome/Edge), not Tauri-only — code has fallbacks
- Tauri detection: `IS_TAURI` constant from `packages/core/src/constants.ts` — don't use `'__TAURI_INTERNALS__' in window` inline
- .fig export: compression with fflate (browser) or Tauri Rust commands
- Test .fig round-trip by exporting and reimporting in Figma

## Tauri

- Tauri v2 with plugin-dialog, plugin-fs, plugin-opener
- File system permissions must be configured in `desktop/tauri.conf.json` — "Internal error" on save means missing permissions
- Dev tools: add a menu item to toggle, don't rely on keyboard shortcut

## Publishing

- `bun publish` from package dirs — resolves `workspace:*` → actual versions
- Core: `prepublishOnly` runs `tsc` to build `dist/` for Node.js consumers
- CLI requires Bun runtime (`#!/usr/bin/env bun`)

## Reference

[figma-use](https://github.com/dannote/figma-use) — our Figma toolkit. Use as reference for:
- Kiwi binary format, schema, encode/decode (`packages/shared/src/kiwi/`)
- Figma WebSocket multiplayer protocol (`packages/plugin/src/ws/`)
- Vector network blob format (`packages/shared/src/vector/`)
- Node types, paints, effects, layout fields (`packages/shared/src/types/`)
- MCP tools / design operations (`packages/mcp/`)
- JSX-to-design renderer (`packages/render/`)
- Design linter rules (`packages/linter/`)

## Known issues

- Safari ew-resize/col-resize/ns-resize cursor bug (WebKit #303845) — fixed in Safari 26.3 Beta