Option to make x-axis calendar-scaled

[ankurjuneja]

Rationale

The platform vis library (TrendingLinePlot) only supported an ordinal/discrete X-axis, so equal time gaps and long gaps between dates looked identical. These changes add an opt-in timeBasedXTick mode that renders a continuous, day-offset–based time scale (with same-day jitter on the continuous axis and a shared LABKEY.vis.dateToDayNumber helper), enabling the targetedms calendar grouping without affecting existing discrete-axis callers.

https://github.com/LabKey/internal-issues/issues/1209

Related Pull Requests

• Option to make x-axis calendar-scaled targetedms#1229

Changes

• Added opt-in timeBasedXTick continuous time X-axis.
• Added shared LABKEY.vis.dateToDayNumber helper.

Tasks 📍

• Claude Code Review
• Manual Testing
• Test Automation
• Verify Fix

[labkey-jeckels]

A too-verbose but still relevant finding from my own Claude review:

Issue: The jitter/sequential branch was broadened from discrete-only to also include scaleType.continuous. This is a shared library used well beyond this feature. The CDS Connector chart (server/modules/clientModules/cds/webapp/Connector/src/view/Chart.js, getPointLayer) sets position: 'jitter' whenever plotNullPoints is true, and its x-scale is continuous for continuous/numeric/timestamp x measures. Before this change, that combination fell into the else branch and received no horizontal jitter; after it, points are jittered by xBinWidth = |scale(1) - scale(0)| / 2. That width assumes "1 x-unit = one slot ≈ one day," which is only meaningful for the calendar day-offset axis — for an arbitrary continuous measure (e.g. a concentration or an integer time index), scale(1)-scale(0) is an essentially arbitrary jitter magnitude.
Why it matters: A visual regression in CDS/Connector scatter plots (and any other continuous-x + jitter caller) that is unrelated to this story, with a jitter amount that has no defined meaning for non-day axes. It will not crash, which is why it's easy to miss, but it changes existing plot output.
Suggestion: Gate the new continuous behavior on explicit intent rather than on scaleType === continuous broadly — e.g. have the calendar feature set a geom flag (geom.timeBasedXTick/geom.continuousJitterUnit) and only take the continuous-jitter path when that flag is present. At minimum, confirm with manual testing that CDS plots with null points on a continuous axis are visually unchanged, and note the result on the PR.

[labkey-jeckels]

Consider a constant with a helpful name for this hard-coded value.