Deneb Visuals

Skill: Deneb Visuals in Power BI (PBIR)

Purpose

Create custom Vega and Vega-Lite visualizations using the Deneb certified custom visual for Power BI. Author specs, inject them into PBIR visual.json files, and configure interactivity.

Provider Policy

Prefer Vega-Lite for new Deneb visuals unless specific Vega-only features are required (signals, event streams, custom projections, force/voronoi layouts). Vega-Lite is more concise, easier to maintain, and covers most chart types.

Visual Identity

• visualType: deneb7E15AEF80B9E4D4F8E12924291ECE89A
• Bundled runtime: Vega 6.2.0 / Vega-Lite 6.4.1 (since Deneb 1.8; use v6.json schema URLs)
• Data role: Single dataset role (all fields go into one "Values" well)
• Default row limit: 10,000 rows (override via dataLimit.override)
• Provider: vegaLite (default) or vega (when Vega-specific features needed)
• Render modes: svg (default, sharp text) or canvas (better for large datasets)

Custom Visual Registration (Required)

Register deneb7E15AEF80B9E4D4F8E12924291ECE89A in report.json publicCustomVisuals array. Without this, the visual shows "Can't display this visual."

{
  "publicCustomVisuals": ["deneb7E15AEF80B9E4D4F8E12924291ECE89A"]
}

Workflow: Creating a Deneb Visual

Step 1: Add the Visual

Create the visual.json file with visualType: deneb7E15AEF80B9E4D4F8E12924291ECE89A, field bindings for the columns and measures you need, and position/size as required.

All fields bind to the single dataset role. Use Table.Column for columns and Table.Measure for measures. Field names in bindings must match those used in the Vega/Vega-Lite spec.

See references/pbir-structure.md for the complete visual.json structure.

Step 2: Write the Spec

Create a Vega-Lite (or Vega) JSON spec. Key difference:

• Vega-Lite: "data": {"name": "dataset"} (object)
• Vega: "data": [{"name": "dataset"}] (array)

{
  "$schema": "https://vega.github.io/schema/vega-lite/v6.json",
  "data": {"name": "dataset"},
  "mark": {"type": "bar", "tooltip": true},
  "encoding": {
    "y": {"field": "Category", "type": "nominal"},
    "x": {"field": "Value", "type": "quantitative"}
  }
}

See references/vega-lite-patterns.md for common chart patterns and references/vega-patterns.md for advanced Vega specs. Field names in the spec must match the nativeQueryRef from the field bindings.

Step 3: Inject the Spec into PBIR

Set the spec and config in objects.vega[0].properties as single-quoted DAX literal strings.

Escaping rules for visual.json injection:

• The entire JSON spec is flattened to one line
• All inner double quotes (") become \" (standard JSON string escaping)
• The stringified JSON is wrapped in single quotes: '...'
• Field names with spaces inside Vega expressions use doubled single quotes: datum[''Sales Amount'']

"jsonSpec": {"expr": {"Literal": {"Value": "'{\"$schema\":\"...\",\"data\":{\"name\":\"dataset\"},\"mark\":\"bar\"}'" }}}

See references/pbir-structure.md for the full encoding pattern and examples.

Step 4: Validate

Validate JSON syntax and inspect the visual.json to confirm spec content and field bindings.

Spec Authoring Rules

Data Binding

• Vega: "data": [{"name": "dataset"}] (array form)
• Vega-Lite: "data": {"name": "dataset"} (object form)
• Fields reference display names. Special characters (., [, ], \, ") become _
• Spaces are NOT replaced — field names keep their spaces

Responsive Sizing (Vega)

Use Deneb's built-in signals for responsive container sizing:

"width": {"signal": "pbiContainerWidth - 25"},
"height": {"signal": "pbiContainerHeight - 27"}

Config (Separate from Spec)

Always provide a config for consistent styling. Use examples/standard-config.json as a baseline. Key settings: autosize: fit, view.stroke: transparent, font: Segoe UI.

Theme Integration

Use Power BI theme colors instead of hardcoded hex values:

Interactivity

Enable interactivity via the vega objects in visual.json:

Cross-Filtering

When enableSelection is true, handle __selected__ ("on", "off", "neutral") in encode blocks:

"fillOpacity": [
  {"test": "datum.__selected__ == 'off'", "value": 0.3},
  {"value": 1}
]

Cross-Highlighting

Use layered marks — background at reduced opacity, foreground shows <field>__highlight values.

Special Runtime Fields

Key fields: __row__ (zero-based row index), __selected__ (selection state), <field>__highlight + <field>__highlightStatus (cross-highlighting), <field>__formatted (pre-formatted string), <field>__format (format string).

Breaking change in Deneb 1.9: __identity__ and __key__ were removed. Use datum.__row__ instead.

Best Practices

1. Use Vega-Lite unless Vega-specific features are needed
2. Always use autosize: fit in config for responsive sizing
3. Use pbiContainerWidth/pbiContainerHeight signals for responsive Vega specs
4. Use theme colors (pbiColor, pbiColorNominal) instead of hex values
5. Enable tooltips with "tooltip": {"signal": "datum"} on marks
6. Mind row limits — 10K default; set dataLimit.override and use renderMode: canvas for large datasets
7. Test field names — verify nativeQueryRef matches spec field references
8. Avoid external data — AppSource certification prevents loading external URLs
9. Escaping depends on context — double quotes in standalone specs, doubled single quotes in PBIR visual.json

When to Use Deneb

Deneb is the preferred choice for advanced custom visuals that need interactivity and go beyond what native Power BI visuals offer:

• Custom chart types not available natively (bullet charts, beeswarms, sankeys, etc.)
• Fine-grained control over visual encoding, animation, and interactivity
• Vector-based rendering (crisp at any size)

For inline micro-charts in table/matrix rows, prefer SVG visuals (see svg-visuals skill).

References

Examples

See examples/ for ready-to-use artifacts:

• standard-config.json — reusable Deneb config
• spec/vega-lite/ — standalone Vega-Lite specs (bullet chart, KPI card)
• spec/vega/ — standalone Vega specs (bar chart, line chart)
• visual/ — complete PBIR visual.json files (bullet chart, KPI card, trend line, YTD comparison, YTD line chart)