Message Pipeline

Message Pipeline Skill

The MessagePipeline is the central data bus connecting Players to Panels.

Data Flow

Player (emits PlayerState)
    │  playerListener callback
    ▼
MessagePipeline (zustand store + React context)
    │  selector-based notifications
    ▼
PanelExtensionAdapter (per-panel bridge)
    │
    ▼
Panel (receives RenderState)

Core Files

Store Update Flow

1. Player emits state → the playerListener callback fires
2. Store dispatch → the "update" action merges the new PlayerState into internal state
3. Selectors react → zustand subscribers (panels) are notified via selector equality checks
4. Render state built → PanelExtensionAdapter incrementally builds RenderState per panel

Internal Store Actions

• "update" — new PlayerState received from the player listener
• "set-subscriptions" — a panel's subscriptions changed
• "playback-seek" — user seeks to a new time
• "set-playback-speed" — playback rate changed

Subscription System

Panels declare the topics they need:

context.subscribe([{ topic: "/camera/image" }]);

The pipeline:

1. Collects subscriptions from all active panels
2. Merges overlapping subscriptions (deduplicates topics)
3. Forwards the merged set to the Player via player.setSubscriptions()
4. The Player only iterates topics that are actually subscribed

Subscription Memoization

• subscriptions.ts uses reference equality to avoid recomputing the merged subscription set
• A Player update is only triggered when the effective topic set changes

MessagePipelineContext (what panels access)

• playerState — current player status (playing, paused, error)
• activeData — messages, currentTime, startTime, endTime, topics, datatypes
• messagesByTopic — Map<topic, messages> for the current frame
• sortedTopics — alphabetically sorted topic list
• subscriptions — currently active subscriptions
• seekPlayback(time) — seek to a specific time
• setPlaybackSpeed(speed) — change playback rate

Performance Notes

• Zustand selectors enable per-panel, fine-grained updates (no full re-renders)
• messagesByTopic is rebuilt only when new messages arrive (not every frame)
• Subscription merging prevents redundant data iteration in the Player
• Render state is built incrementally — only changed fields are recomputed

Skills Reference

• For the panel-side bridge and RenderState contract: load panel-extension-api skill
• For Player internals upstream of the pipeline: load player-internals skill