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 — 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