Deneb Visuals

Deneb Visuals in Power BI (PBIR)

Use pbir for every report mutation. Read PBIR metadata only for diagnosis. If pbir is unavailable or lacks an operation, stop and report the gap; never edit report JSON directly.

Deneb is a certified custom visual for Power BI that enables Vega and Vega-Lite declarative visualization specs directly inside reports. Author specs using this skill.

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. For advanced Vega features, see references/vega-patterns.md and the Vega documentation.

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)

Copying a working Deneb visual with pbir cp carries its registration. For a new visual, inspect publicCustomVisuals with pbir get and update the complete list through pbir set --json, preserving any existing ids. Never edit report.json directly.

Workflow: Creating a Deneb Visual

Step 1: Add the Visual

Create the visual and bindings through pbir:

pbir add visual deneb7E15AEF80B9E4D4F8E12924291ECE89A \
  "Report.Report/Page.Page" --name RevenueByCategoryDeneb
pbir visuals bind "Report.Report/Page.Page/RevenueByCategoryDeneb.Visual" \
  --add "dataset:Sales.Category" --type Column
pbir visuals bind "Report.Report/Page.Page/RevenueByCategoryDeneb.Visual" \
  --add "dataset:Sales.Revenue" --type Measure

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.

Step 2: Write the Spec

Create a Vega-Lite (or Vega) JSON spec file. 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 examples/spec/ for complete spec files (Vega and Vega-Lite) and examples/visual/ for full PBIR visual.json files. Field names in the spec must match the nativeQueryRef (display name) from the field bindings.

Step 3: Inject the Spec

pbir visuals deneb "Report.Report/Page.Page/RevenueByCategoryDeneb.Visual" \
  --spec-file chart.vl.json --provider vegaLite

The CLI handles PBIR encoding. Keep ordinary Vega or Vega-Lite JSON in the spec file.

Step 3b: Review

Before presenting the spec to the user, dispatch the deneb-reviewer agent to validate syntax and provide design feedback.

Step 4: Validate

pbir visuals bind "Report.Report/Page.Page/RevenueByCategoryDeneb.Visual" --show
pbir validate "Report.Report" --all

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 (e.g., "Order Lines")

Field Name Escaping in Expressions (Critical)

Escaping depends on whether the spec is standalone or injected into a PBIR visual.json:

Standalone spec files (in examples/spec/): use double quotes with JSON escaping:

{"calculate": "datum[\"Order Lines\"] - datum[\"Order Lines (PY)\"]", "as": "diff"}

Inside PBIR visual.json (in examples/visual/): the entire spec is a single-quoted DAX literal string. Field names with spaces use doubled single quotes (''):

datum[''Order Lines''] - datum[''Order Lines (PY)'']

Single quotes that are NOT part of field name escaping (e.g., string literals in filter expressions like datum.Series == 'Actuals') work as-is because they don't conflict with the outer single-quote wrapper.

Responsive Sizing (Vega)

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

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

The offsets account for padding. For absolute positioning of text marks, use {"signal": "width"} instead of hardcoded pixel values.

Config (Separate from Spec)

Always provide a config file for consistent styling. See the Standard Config section in references/vega-patterns.md. 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. Selection modes: simple (auto-resolves, up to 250 data points) or advanced (Vega only; required for brush/lasso/region selection, supports up to 2500 via options.limit, exposes pbiCrossFilterApply and pbiCrossFilterClear signals). See references/vega-patterns.md for the simple pattern and references/advanced-patterns.md for the advanced signal API.

Cross-Highlighting

Use layered marks -- background at reduced opacity, foreground shows <field>__highlight values. See references/vega-patterns.md for details.

Special Runtime Fields

Deneb injects runtime fields into each dataset row. See references/capabilities.md for the full table.

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

Breaking change in 1.9: __identity__ and __key__ were removed. Replace any datum.__identity__ with datum.__row__.