type: task id: GRAPH_LIBRARY-ADD_ORIENTATION_AWARE_BAR_DIRECTION_AND_GRID_DEFAULTS title: Add orientation-aware bar direction and grid defaults description: Capture follow-on work to make bar direction semantics and grid defaults follow actual bar direction. Document that Vega-Lite treats vertical bars as default and horizontal bars as rotated, which is the opposite of the desired design perspective. milestone: m1-ft-analytics-analyst-pilot owner: data-viz-designer-engineer status: not_started priority: p2

Add orientation-aware bar direction and grid defaults

Superseded (2026-03-27). This narrowly scoped follow-on was consolidated into Consolidate semantic chart defaults and rendering control-surface follow-ons so the active backlog carries one M2 umbrella task instead of many M1 leaf items. Keep the notes below as reference detail, not as a separately scheduled task.

Problem

Capture follow-on work to make bar direction semantics and grid defaults follow actual bar direction. Document that Vega-Lite treats vertical bars as default and horizontal bars as rotated, which is the opposite of the desired design perspective.

Context

During M1 structure-lab work, we wanted bar charts to keep only the dependent-axis grid lines:

horizontal bars should keep only the vertical grid lines running across the quantitative x-axis
vertical bars should keep only the horizontal grid lines running across the quantitative y-axis

Today this can be hacked at the authored-chart level with per-chart settings.x_axis and settings.y_axis overrides, but it is not expressible as a clean shared structure default because structure files only provide global Vega-Lite config defaults such as axisX.grid and axisY.grid.

Relevant files:

examples/playground/faces/labs/m1-structure-bars-lines-lab.yml
dataface/core/compile/chart_structures/m1-candidate.yml
dataface/core/render/chart/standard_renderer.py
dataface/core/render/chart/DESIGN.md

Note: - m1-structure-bars-lines-lab.yml and chart_structures/m1-candidate.yml were captured from the parallel codex/m1-structure-lab branch during the March 26, 2026 design session. If they have not landed on main yet, treat them as historical repro artifacts rather than required files for taking this task.

Important nuance:

Vega-Lite treats vertical bars as the default bar orientation and horizontal bars as a rotated/special case.
From the design perspective, that is backwards from the mental model we want: the system should reason from the actual bar direction and the dependent axis, not from Vega-Lite's default encoding arrangement.
We also want vertical-bar y-axis behavior to depend on the x-axis semantic type:
if the x-axis is temporal, keep the quantitative y-axis on the right
if the x-axis is not temporal (for example, a quantitative age axis), move the quantitative y-axis to the left
Today the shared structure only provides a global axisY.orient default, so this kind of type-aware axis-side logic cannot be expressed cleanly in theme/structure alone.

Possible Solutions

Keep using per-chart authored overrides for bar grids. This is workable for labs and one-off examples, but it does not scale and does not solve the platform-level semantic problem.
Add a structure-level switch for bar grid behavior. This sounds attractive, but structure files today do not know enough about chart orientation to express different defaults for horizontal vs vertical bars.
Recommended: add orientation-aware renderer defaults for bar charts. Teach the standard chart renderer to reason from actual bar direction after orientation is resolved, then apply bar-specific axis/grid defaults and axis-side defaults accordingly. That keeps authored charts simple and makes the behavior consistent across the system.

Plan

Recommended implementation:

Trace where bar orientation is finalized in the standard renderer.
Define the intended defaults in design terms: - vertical bars: x_axis.grid = false, y_axis.grid = true - horizontal bars: x_axis.grid = true, y_axis.grid = false - vertical bars with temporal x-axis: y_axis.orient = right - vertical bars with non-temporal x-axis: y_axis.orient = left
Apply those defaults after orientation swapping so they follow actual bar direction, not Vega-Lite's default assumption.
Preserve authored chart overrides when users explicitly set axis-grid behavior.
Add regression coverage for both bar directions.

Implementation Progress

Not started.

March 26, 2026 notes:

Confirmed that shared structure files are too global for this behavior.
Confirmed that the lab can use per-chart settings.x_axis.grid / settings.y_axis.grid overrides as a temporary workaround.
Confirmed that the real solution belongs in renderer logic, likely near the existing horizontal-bar orientation handling in standard_renderer.py.

QA Exploration

N/A for now. This task has not been implemented yet.

[ ] QA exploration completed (or N/A for non-UI tasks)

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