panel-state-transitions

Panel State Transitions Skill

A timeline visualization for discrete state changes extracted from messages.

Structure

panels/StateTransitions/
├── index.tsx                       # main panel, TimeBasedChart usage, message-path config
├── messagesToDataset.ts            # message → Chart.js dataset (perf-critical)
└── hooks/
    ├── useDecodedMessageRange.ts   # preloaded-range subscription, 250ms batch flush
    └── useStateTransitionsData.ts  # merges preloaded blocks + current frame

Data Flow

1. User configures message paths (e.g. /robot/state.mode)
2. useDecodedMessageRange subscribes to preloaded blocks for those paths
3. Messages arrive in batches (250ms flush interval)
4. messagesToDataset extracts discrete values and builds chart segments
5. useStateTransitionsData merges block data with live current-frame data
6. TimeBasedChart renders colored segments on a timeline

messagesToDataset (Performance Critical)

function messagesToDataset(messages: MessageEvent[], path: MessagePath): ChartDataset {
  // iterate all messages, extract value at path
  // create segment boundaries at state-change points
  // return { data: [{ x: startTime, x2: endTime, y: stateLabel }] }
}

Runs on every data update — must stay fast for large datasets.

250ms Batch Flush

useDecodedMessageRange debounces:

• Accumulates incoming messages for 250ms
• Triggers a single state update with the full batch
• Prevents a React re-render per message — critical for topics with thousands of preloaded messages

TimeBasedChart

Shared chart component (also used by other panels):

• Time on the X-axis, discrete values on the Y-axis
• Supports multiple series (each path = a row)
• Zoom/pan synchronized with global playback time
• Colored segments represent distinct state values

Performance Notes

• 250ms batch flush prevents render storms from high-frequency messages
• messagesToDataset is O(n) per path — keep n bounded (downsample if needed)
• Avoid re-processing already-processed blocks during the block + currentFrame merge
• Message-path parsing is cached (nearley grammar not re-parsed)

Key Files

• packages/suite-base/src/panels/StateTransitions/index.tsx
• packages/suite-base/src/panels/StateTransitions/messagesToDataset.ts
• packages/suite-base/src/panels/StateTransitions/hooks/useDecodedMessageRange.ts
• packages/suite-base/src/panels/StateTransitions/hooks/useStateTransitionsData.ts

Skills Reference

• For message-path syntax and extraction: load message-path skill