ggaction 0.0.5

Rule Marks

Car observations with grouped mean confidence intervals
Observation points layered with fixed-pixel error-bar caps.

Rule marks represent reference lines and intervals. They use concrete line primitives without exposing a renderer-specific path format.

createRuleMark({ id?, data? } = {})

const threshold = chart()
  .createData({ values: [{ limit: 25 }] })
  .createRuleMark()
  .encodeY({ field: "limit" })
  .encodeStroke({ value: "#dc2626" })
  .encodeStrokeWidth({ value: 2 });

The first ID is "rule", data defaults to current data, and creation assigns no position or style. A single x or y encoding creates a full plot-span rule. Add encodeY2 for a bounded vertical interval, encodeX2 for a bounded horizontal interval, or both secondary endpoints for a diagonal rule. Every endpoint may use a field or constant datum.

When a rule is layered without explicit data, it may first inherit a compatible source layer’s x/y positions. A constant datum endpoint takes precedence over the inherited opposite position when no secondary endpoint exists: datum y removes only inherited x and creates a horizontal full-span rule, while datum x symmetrically creates a vertical full-span rule. Field endpoints preserve the orthogonal inherited channel for interval construction. Rules created with explicit data do not apply this provenance-based cleanup.

Rule appearance is edited through encoding actions rather than a separate mark editor:

encodeStrokeWidth({ field, scale? }) maps a non-negative quantitative field to one concrete width per rule item. Use createLegend({ channels: ["strokeWidth"] }) for a sampled quantitative guide. Constant encodeStrokeWidth({ value }) remains available and removes the field binding.

Every complete rule stores concrete x1, y1, x2, and y2 values. An incomplete endpoint combination remains empty until another encoding completes it. Canvas and scale changes recompute all endpoints.

Appearance encodings · Error bars · Advanced axis components