Scene Graph

In-Memory Representation

Nodes live in a flat Map<string, Node> keyed by GUID string. The tree structure is maintained via parentIndex references. This gives O(1) lookup by ID and efficient traversal.

interface SceneGraph {
  nodes: Map<string, Node>
  root: string

  getNode(id: string): Node
  getChildren(id: string): Node[]
  getParent(id: string): Node | null

  createNode(type: NodeType, parent: string, props: Partial<NodeChange>): Node
  updateNode(id: string, changes: Partial<NodeChange>): void
  deleteNode(id: string): void
  moveNode(id: string, newParent: string, position: string): void

  findByType(type: NodeType): Node[]
  findByName(pattern: string): Node[]
  hitTest(point: Vector, canvas: string): Node | null
  getNodesInRect(rect: Rect, canvas: string): Node[]
}

Undo/Redo

The system uses Figma's inverse command pattern. Each undo entry contains the forward changes and their automatically-computed inverse:

Operation	Forward	Inverse
Create node	`{guid, phase: CREATED, ...props}`	`{guid, phase: REMOVED}`
Delete node	`{guid, phase: REMOVED}`	`{guid, phase: CREATED, ...allProps}`
Change prop	`{guid, fill: "#F00"}`	`{guid, fill: "#00F"}`
Move node	`{guid, parentIndex: newParent}`	`{guid, parentIndex: oldParent}`

Before applying any change, affected fields are snapshotted. The snapshot becomes the inverse.

Batching — operations like drag-to-move produce hundreds of position changes per second. These are debounced into a single undo entry. beginBatch/commitBatch wraps multi-step operations.

Layout Engine (Yoga)

Figma's auto-layout properties map to Yoga flexbox:

Figma Property	Yoga Equivalent
`stackMode: HORIZONTAL`	`flexDirection: row`
`stackMode: VERTICAL`	`flexDirection: column`
`stackSpacing`	`gap`
`stackPadding`	`padding`
`stackJustify: MIN/CENTER/MAX/SPACE_BETWEEN`	`justifyContent`
`stackCounterAlign`	`alignItems`
`stackPrimarySizing: FIXED/HUG/FILL`	width/height + flex-grow
`stackChildPrimaryGrow`	`flexGrow`
`stackChildAlignSelf`	`alignSelf`
`stackPositioning: ABSOLUTE`	`position: absolute`

Hit Testing

Given a point in canvas coordinates, the scene graph returns the topmost visible node at that position. The algorithm:

Traverse visible nodes in reverse z-order (top to bottom)
Transform the test point into each node's local coordinate system
Check if the point is within the node's bounds (including rotation)
Return the first match

For marquee selection, getNodesInRect returns all nodes whose bounds intersect the given rectangle.

Coordinate System

Nodes store position and size relative to their parent. To get absolute (canvas) coordinates, walk up the parent chain applying transforms. The renderer uses this to draw nested frames with correct positioning.

Rotation is stored in degrees and applied as part of the 2×3 transform matrix. Snap guides and hit testing account for rotation when computing visual bounds.

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