e0716a3a38
* feat: author behaviours on main components
A main component or component set can behave as a Switch, Checkbox,
Slider, or Tabs, after Reka UI's primitives. The behaviour lives in
OpenPencil plugin data: boolean values bind to variant or boolean
properties with the values meaning on and off, a number keeps its own
range since Figma has no number property, and the control's
subcomponents bind to the component's slots. A Behaviour section in the
properties panel adds, binds, and removes it, each as one undo step,
and flags required bindings that are missing. The canvas-only layout's
pill becomes a component that preview will reuse.
* feat: preview instances with behaviours on the canvas
View > Preview (Cmd+Alt+Enter) puts the canvas in preview: a lone canvas
switches to the canvas-only layout with a Previewing pill, and a split
canvas previews on its own side. Clicking a Switch or Checkbox flips it,
dragging a Slider moves its thumb and range, and clicking a Tabs trigger
shows its panel. Preview keeps its state on copies of the instances it
touched, in a private graph with the document's ids, and the canvas
draws those copies in place of the originals, so the document, undo,
autosave, and collaborators never see it. Escape or the pill leaves
preview, Reset restores every control, and editing shortcuts, labels,
and outlines stay off while previewing.
* feat: translate behaviour and preview strings; cover preview with an e2e flow
* refactor(vue): reuse VariantDefinitionControl for behaviour property options
* refactor: split variant actions and preview interactions by domain
Variant authoring was one 706-line closure; it is now graph queries
(model), undo snapshots (history), property definition edits
(definitions), and the editor facade (index). Preview interactions move
into play/kinds, one module per control, registered by behaviour kind so
a new kind cannot ship without its contract and interaction. Behaviour
contracts are keyed by kind. In the Vue SDK, slot and variant authoring
controls get their own folders beside component-props and behaviour,
and the app's variant section joins slot/ and behaviour/.
* refactor: keep the behaviour model in scene-graph's plugin-data registry
Master now defines every OpenPencil plugin-data key in one typed registry
in scene-graph. The behaviour schema registers there as a field, and the
model and contracts move beside slots, exported from the package root;
the @open-pencil/core/behaviours subpath is gone.
* feat: interaction states and keyboard focus in preview
A behaviour can bind a variant property to the default, hover, pressed,
focus, and disabled states; binding it maps values named like those
states. Preview switches the instance's copy to the matching variant as
the pointer hovers, presses, and releases, keeps other values when the
set draws the combination and falls back to rest otherwise, and skips
disabled instances. Tab moves visible keyboard focus between controls,
Space, Enter, arrows, Home, and End use the focused one, and Escape
takes visible focus off before leaving preview. A Button kind covers
controls that only have states.
* feat: toggle, radio, group, progress, collapsible, and accordion behaviours
Radio group, toggle group, and accordion hold their items in a slot;
each item is an instance with its own behaviour, so a press inside the
slot goes to the group, which turns the pressed item on and the others
off through the item's own interaction. Progress shares the slider's
number handling through rangeControl, and a collapsible shows and hides
its content slot from its trigger, remembering its open state even
when no property draws it. Tabs and groups share arrow-key navigation.
* feat: text field, textarea, and number field behaviours
A behaviour value can now be text, bound to a text property, so
preview types into a copy of the field through the same property path
the editor uses. A bound Filled value switches to the placeholder
variant when the field empties. A number field keeps its own range,
shows its value through a text property, and steps from its increment
and decrement slots and the arrow keys. Text fields show focus from a
click, and the focused control receives every key; Option still types,
and only Cmd or Ctrl combinations stay shortcuts.
* fix: keep behaviour bindings when saving as .fig
Saving as .fig gives component properties new GUIDs, but behaviours
kept the old ids in their plugin data, so every binding read as missing
after reopening. The export now renames the ids behaviours bind with
the same GUIDs, on its own copy of the document.
* fix: let previewed controls resize layout imported from .fig
Layers from a .fig keep the sizes Figma computed, and auto layout
prefers them, so an opened collapsible or accordion item kept its
closed height in preview. When preview shows, hides, or retypes a
layer in a copy, it drops those sizes from the layer's copied ancestors
so auto layout sizes them again; untouched layers keep Figma's sizes.
* fix: publish behaviours and other plugin content with library assets
Every OpenPencil plugin-data field now declares its role: content that
exists only as plugin data (behaviours, OkHCL picks), format copies of
node fields written for files, or bookkeeping about where a document
or node came from. Library snapshots keep a node's content plugin data,
including other plugins' entries, and drop the rest; the asset hash
counts the same entries, so a behaviour-only change is offered as an
update while a .fig round trip still changes nothing.
* feat: name behaviour rows by meaning and create what they need
The Behaviour section named every main value "Value" under a "Values"
heading, and a component without matching properties left an empty
picker with no way forward. Rows are now named for the control (On,
Checked, Pressed, Text), rows the control needs or already uses come
first, and the optional rest folds under More options; a button keeps
its states in view. An empty row creates what it needs in one undo
step: a text layer and text property, Off and On variants on a set, or
a slot frame for a part. The missing chip names the row it means and
takes you there.
* fix(dom-css): position free layers, hug content, and round ellipses
HTML and Tailwind export stacked the layers of frames without auto
layout in block flow, wrote fixed pixel sizes for auto layout frames
set to Hug and for auto-sizing text, and drew ellipses as boxes. Layers
a parent does not lay out are now absolutely positioned at their
coordinates inside a relative frame, hugging axes are left to the
content, and ellipses get a 50% radius.
* feat: run preview as live Reka UI islands over the canvas
Preview simulated controls on the canvas: copies of instances, a
handler per kind, its own key routing, and append-only text. It now
runs them as real components. Each top-level layer that holds an
instance with a behaviour becomes an island: its layers are projected
to DOM through dom-css into a shadow root laid over the pane at its pan
and zoom, and each behaviour mounts its Reka UI primitives on its
layers, so text fields are real inputs and focus, keys, and layout are
the browser's. Core's resolvePlayState shows instances in a state on a
private graph, so the component's variants draw it, and controls are
keyed by layer path so a variant switch keeps their DOM. The canvas
leaves island layers to the islands, and the canvas play runtime and
its key routing are gone.
* fix: derive variant properties from Property=Value component names
figma.combineAsVariants and Combine as variants only derived variant
properties from slash-separated names, so components named as Figma
names variants, such as State=On, Size=Large, became a set with no
properties. Both now derive each named property and its values, after
the slash form.
* feat: script and tool access to behaviours by name
Behaviour contracts follow Reka UI's anatomy: tabs keep their triggers
in the list slot and their content panels in a panels slot, and a slot
of repeated parts names the Reka part of its children. A behaviour
spec names component properties and slots instead of ids and resolves
to the stored behaviour and back, with errors that list what the
component has.
Scripts get an `openpencil` global next to `figma`, in the Figma API's
style: setBehaviour, getBehaviour with bindValue, bindPart, states,
and missing, behaviourKinds, and createSlot. The eval tool, the CLI,
and app automation compile scripts through one compileScript, so the
CLI now returns the last expression as the others do. MCP and AI chat
get set_behaviour, get_behaviour, and create_slot.
* feat: write controls in design JSX with Reka UI's element names
`<Switch.Root modelValue="State">` renders a main component, or a set
when its children are variants, that behaves as a switch, and
`<Switch.Thumb>` the slot that draws its thumb, one slot across the
set's variants. Inputs become the text property of a field, tab
triggers and panels go in their List and Panels slots, and a group's
items are `<RadioGroup.Item of={…} />` instances in its Items slot.
JSX export writes components with behaviours the same way, so they
render back unchanged. The authoring reference documents controls, and
the codegen and chat prompts now include it verbatim instead of
dedenting its code examples.
* chore: format the CLI export test
* docs: document slots, behaviours, preview, and the openpencil API
The components guide covers slots, behaviours, and preview with its
shortcut; scripting covers the openpencil global and eval's last-
expression result; the MCP and AI chat pages list the new tools; the
features overview, README, and roadmap mention working controls. The
chat prompt says how to build a control, and the codegen prompt builds
components with behaviours on their Reka UI primitives.
* chore: format the eval CLI test
* docs: explain behaviours and preview islands, and guide the openpencil API
A development page explains the behaviour model, the four authoring
surfaces, how preview islands turn a control's state into live Reka UI
components, and how to add a kind; the architecture page links it. The
Core guide sets the rules for OpenPencilAPI: Figma-only `figma`,
OpenPencil features on `openpencil` in the same style, one
compileScript, names over ids, and docs with every member. Package
READMEs mention the openpencil global, PlayIslands, Reka-named JSX, and
the behaviour model. Design JSX's behaviour modules move into a
behaviours folder instead of a suffixed sibling.
* refactor: center pasted layers through translate
centerNodesAt repeated translate's loop, which test:dupes reports on
master too.
* fix: validate behaviour ranges and guess on and off by name
A number value now needs max above min and a positive step: the schema,
specs, and the panel reject a range a slider cannot step through. Binding
a variant property guesses on and off by value name, as specs do, and a
boolean property gets no on/off pair. Part bindings are read through
partBinding, a replaced document restarts preview from its designed
state, and the e2e preview shortcut uses ControlOrMeta.
* feat: make the Behaviour section say what to do next
A slider's range fields now carry inline Min, Max, Step, and Start labels.
States offers Add state variants, which adds a Default, Hover, Pressed,
Focus, and Disabled variant and binds them; Add Off and On variants and
Add state variants turn a lone main component into a component set first,
and a part's slot can be added to a set, in every variant under one slot
id. Rows that could do nothing are gone: no empty pickers and no hints to
combine variants by hand, and an unbound Disabled is left to the states.
A warning line names what is still needed and replaces the missing chip,
and the Switch's main value is called Checked.
* fix: keep each slot to one part and keep creating slots at hand
A slot draws one part, so the Behaviour section no longer offers a slot
another part uses, and specs (the openpencil API, tools, and JSX) reject
binding one slot to two parts. A part's picker keeps an action to add a
new slot in its footer, so adding the first slot no longer hides it for
the other parts.
6.5 KiB
Architecture
System Overview
For source identity, override evaluation, page sessions, and export contracts, see .fig Reader Architecture.
graph TB
subgraph Tauri["Tauri v2 Shell"]
subgraph Editor["Editor (Web)"]
UI["Vue 3 UI<br/>Toolbar · Panels · Properties<br/>Layers · Color Picker"]
Skia["Skia CanvasKit (WASM, 7MB)<br/>Vector rendering · Text shaping<br/>Effects · Export"]
subgraph Core["Core Engine (TS)"]
SG[SceneGraph] --- Layout[Layout - Yoga]
SG --- Selection
Undo[Undo/Redo] --- Constraints
Constraints --- HitTest[Hit Testing]
end
subgraph FileFormat["File Format Layer"]
FigIO[".fig import/export"] --- Kiwi[Kiwi codec]
Kiwi --- SVG[SVG export]
end
end
MCP["MCP Server (90 tools, stdio+HTTP)"]
Collab["P2P Collab (Trystero + Yjs)"]
end
Editor Layout
The UI follows Figma's UI3 layout — toolbar at the bottom, navigation on the left, properties on the right:
- Navigation panel (left) — Layers tree, pages panel
- Canvas (center) — Infinite canvas with CanvasKit rendering, zoom/pan
- Properties panel (right) — Context-sensitive sections: Appearance, Fill, Stroke, Typography, Layout, Position
- Toolbar (bottom) — Tool selection: Select, Frame, Section, Rectangle, Ellipse, Line, Text, Pen, Hand
Components
Rendering (CanvasKit WASM)
The same rendering engine as Figma. CanvasKit provides GPU-accelerated 2D drawing with vector shapes, text shaping via Paragraph API, effects (shadows, blurs, blend modes), and export (PNG, SVG). The 7MB WASM binary loads at startup and creates a GPU surface on the HTML canvas.
The renderer is split into focused modules in packages/core/src/renderer/: scene traversal, overlays, fills, strokes, shapes, effects, rulers, labels, and remote cursors.
Scene Graph
Flat Map<string, Node> keyed by GUID strings. Tree structure via parentIndex references. Provides O(1) lookup, efficient traversal, hit testing, and rectangular area queries for marquee selection.
The graph emits typed events via nanoevents: node:created, node:updated, node:deleted, node:reparented, node:reordered. Subsystems subscribe to these instead of manual call-site wiring — the editor uses them for render invalidation and microtask-batched component instance sync, while the collab system uses them for Yjs propagation.
See Scene Graph Reference for internals.
Layout Engine (Yoga WASM)
Meta's Yoga provides CSS flexbox and grid layout computation via a fork with CSS Grid support. A thin adapter maps Figma property names to Yoga equivalents:
| Figma Property | Yoga Equivalent |
|---|---|
stackMode: HORIZONTAL |
flexDirection: row |
stackMode: VERTICAL |
flexDirection: column |
stackSpacing |
gap |
stackPadding |
padding |
stackJustify |
justifyContent |
stackChildPrimaryGrow |
flexGrow |
File Format (Kiwi Binary)
Reuses Figma's Kiwi binary codec with 194 message/enum/struct definitions. Import: parse header → Zstd decompress → Kiwi decode → NodeChange[] → scene graph. Export reverses the process with thumbnail generation.
See File Format Reference for details.
AI & Tools
Tools are defined once in packages/core/src/tools/, split by domain: read, create, modify, structure, variables, vector, analyze. Each tool has typed params and an execute(figma, args) function. Adapters convert them for:
- AI chat — valibot schemas, multi-provider (Anthropic, OpenAI, Google AI, OpenRouter, compatible endpoints)
- MCP server — zod schemas, stdio + HTTP transports
- CLI — available via the
evalcommand, whose scripts get thefigmaPlugin API and theopenpencilAPI
90+ core tools + 3 MCP file management tools. Includes XPath query (query_nodes), JSX inspection (get_jsx, diff_jsx), semantic description (describe), and vision-based verification (export_image returns images to the model).
Behaviours and Preview
A behaviour stored on a main component makes it work as a Reka UI control. Preview runs top-level layers holding controls as live islands: shadow-DOM projections laid over the canvas, with each control mounted as its Reka UI primitive and drawn by the component's variants. See Behaviours and Preview.
Undo/Redo
Inverse-command pattern. Before applying any change, affected fields are snapshotted. The snapshot becomes the inverse operation. Batching groups rapid changes (like drag) into single undo entries.
Clipboard
Figma-compatible bidirectional clipboard. Encodes/decodes Kiwi binary (same format as .fig files) via native browser copy/paste events. Handles vector path scaling, instance children, component set detection, and override application.
P2P Collaboration
Real-time peer-to-peer collaboration via Trystero (WebRTC) + Yjs CRDT. No server relay — signaling over MQTT public brokers, STUN/TURN for NAT traversal. Awareness protocol provides live cursors, selections, and presence. Local persistence via y-indexeddb.
CLI-to-App RPC Bridge
When the desktop app is running, CLI commands connect to it via WebSocket instead of requiring a .fig file. The automation server runs on 127.0.0.1:7600 (HTTP) and 127.0.0.1:7601 (WebSocket). Commands execute against the live editor state, enabling automation scripts and AI agents to interact with the running app.
What's Next
Full figma-use Tool Set
The MCP server currently exposes 90 tools. The reference implementation in figma-use has 118. The remaining tools cover advanced layout constraints, prototype connections, advanced component property editing, and bulk document operations.
CI Design Tooling
The headless CLI already supports analyze colors/typography/spacing/clusters. Next: GitHub Actions integration for automated design linting and visual regression in PRs.
Prototyping
Preview already runs components with behaviours as live controls. Next: reactions and variables that let controls drive the rest of a design, frame-to-frame transitions, interaction triggers, and overlays.
Windows Code Signing
macOS binaries are signed and notarized since v0.6.0. Windows Authenticode signing via Azure Code Signing is planned to remove the SmartScreen warning.