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openpencil/AGENTS.md

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OpenPencil

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

Roadmap: plan.md — phases, tech stack, CLI architecture, test strategy, keyboard shortcuts.

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.
  • packages/docs — @open-pencil/docs: VitePress documentation site. Run with cd packages/docs && bun run dev.

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 test:dupes — jscpd copy-paste detection across all TS sources
  • 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 node <file> --id <id> — detailed node properties
  • bun open-pencil pages <file> — list pages
  • bun open-pencil variables <file> — list design variables
  • bun open-pencil export <file> — headless render to PNG/JPG/WEBP
  • bun open-pencil analyze colors <file> — color palette usage
  • bun open-pencil analyze typography <file> — font/size/weight stats
  • bun open-pencil analyze spacing <file> — gap/padding values
  • bun open-pencil analyze clusters <file> — repeated patterns
  • bun open-pencil eval <file> --code '<js>' — execute JS with Figma Plugin API

CLI

  • All CLI output must use agentfmt formatters — fmtList, fmtHistogram, fmtSummary, fmtNode, fmtTree, kv, entity, bold, dim, etc.
  • Don't hand-roll console.log formatting — use the helpers from packages/cli/src/format.ts which re-exports agentfmt with project-specific adapters (nodeToData, nodeDetails, nodeToTreeNode, nodeToListItem)
  • Every command supports --json for machine-readable output

Tools (AI / MCP / CLI)

  • Tool operations are defined once in packages/core/src/tools/schema.ts as framework-agnostic ToolDef objects
  • Each tool has: name, description, typed params, and an execute(figma: FigmaAPI, args) function
  • defineTool() gives type-safe params in the execute body; the array ALL_TOOLS erases the generics for adapters
  • AI adapter (packages/core/src/tools/ai-adapter.ts): toolsToAI() converts ToolDefs → valibot schemas + Vercel AI tool() wrappers
  • src/ai/tools.ts is just a thin wire: creates FigmaAPI from editor store, calls toolsToAI()
  • CLI commands (packages/cli/src/commands/) are not generated from ToolDefs — they have custom agentfmt formatting, tree walking, pagination. The eval command is the CLI's access to all ToolDef operations via FigmaAPI.
  • To add a new tool: add a defineTool() in schema.ts, add to ALL_TOOLS array — it's instantly available in AI chat, and via eval in CLI
  • FigmaAPI (packages/core/src/figma-api.ts) is the execution target for all tools — Figma Plugin API compatible, uses Symbols for hidden internals

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
  • App menu (src/components/AppMenu.vue) — browser-only menu bar using reka-ui Menubar components; Tauri uses native menus, so menu is hidden when IS_TAURI is true
  • 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
  • Safari save: no File System Access API → uses <a> download link with deferred revokeObjectURL. SafariBanner warns users about limitations.
  • 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
  • Test fixtures (tests/fixtures/*.fig) are Git LFS — use git push --no-verify to skip the slow LFS pre-push hook. Use regular git push only when .fig fixtures changed.

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