Overlays and cursors

Overlays annotate signal data without becoming sampled traces. They are owned by the application and replaced through public APIs.

Scatter series and regions

Points belong to named scatter series. Visibility is controlled per series, while hit testing and selection use each point's stable ID:

viewer.setOverlays({
  scatterSeries: [{
    id: 'peaks',
    label: 'Detected peaks',
    color: '#22d3ee',
    points: peaks.map((peak) => ({
      id: peak.id,
      x: peak.time,
      y: peak.value,
      kind: 'peak',
      metadata: { index: peak.index },
    })),
  }],
  regions: [{
    id: 'stimulus-1',
    xStart: 1.0,
    xStop: 1.5,
    kind: 'stimulus',
    label: 'Stimulus',
  }],
  selectedPointId: null,
})

Regions render behind the traces and are not selectable. overlay-select emits a point ID or null. The application uses that stable identity to link selection with tables or other viewers.

setScatterSeries() replaces point series while preserving regions. addScatterSeries() and updateScatterSeries() provide stable-ID updates.

Measurement cursors

A/B are vertical cursors in calibrated X units. C/D are horizontal cursors in left-axis units. Programmatic cursor methods do not emit user events:

viewer.setCursor('a', 1.25)
viewer.setCursorVisible('b', true)
const cursors = viewer.getCursors()

The first time a cursor pair is enabled in the options panel, it is placed at 25% and 75% of the visible range. Hiding a cursor preserves its value.

A completed user drag emits cursor-change with changedId, defensive copies of all four cursors, deltaX (B - A), and deltaY (D - C). A delta is null unless both cursors in its pair are visible and positioned.