HorizontalAxis: No way to display labels at first and last x-values with edge-aligned text

[github-actions[bot]]

Moved from #1472 (opened by @dmitry-stakhov).

---

Problem

There is currently no way to display x-axis labels at the first and last data points with proper edge alignment (left-aligned at start, right-aligned at end).

Two separate limitations combine to make this impossible:

1. First and last x-values are excluded from label positions

In HorizontalAxisItemPlacers.kt, the private getLabelValues helper explicitly skips the range boundaries:

if (potentialValue < ranges.minX || potentialValue == fullXRange.start) continue
if (potentialValue > ranges.maxX || potentialValue == fullXRange.endInclusive) break

Both ItemPlacer.aligned() and ItemPlacer.segmented() use this helper, so neither built-in placer can produce labels at the first or last x-value.

A custom ItemPlacer implementation can return these values from getLabelValues(), but then hits the second issue:

2. All labels are center-aligned on their x-position

In HorizontalAxis.drawUnderLayers(), labels are always drawn centered on canvasX:

label?.draw(
    context = this,
    text = ...,
    x = canvasX,
    y = textY,
    verticalPosition = position.textVerticalPosition,
    maxWidth = maxWidth,
    ...
)

For labels at the plot boundaries, center-alignment causes half of the label to extend outside the plot area and get clipped. The addExtremeLabelPadding flag on ItemPlacer.aligned() addresses this by adding unscalableStartPadding/unscalableEndPadding, but this shrinks the plot area rather than adjusting label alignment.

Expected behavior

It should be possible to configure the horizontal axis to:

• Place labels at the first and last x-values
• Left-align the first label and right-align the last label at the plot edges
• Do so without shrinking the plot area

Use case

This is a common pattern in financial/asset charts where the x-axis shows a date range and only the start and end dates should be labeled, flush with the plot edges.

Workaround

We currently disable the bottom axis labels entirely (label = null) and place Compose Text components manually below the chart, measuring the y-axis label width to align them with the plot area.

Version

Vico 3.1.0 (Compose Multiplatform)

[nagatsuka-shuuya]

@Gowsky I've raised the PR that implements this feature. Could you check please?

[github-actions[bot]]

Thanks for the detailed write-up! Closing this as a duplicate, as the underlying needs are already tracked across a few existing ideas:

• Axes labels should be able to clip, rather than require padding #1003 — letting axis labels overflow/clip instead of forcing plot-area padding
• `HorizontalAxis`: Add label-alignment customization #1313 — adding label-alignment customization to HorizontalAxis
• `HorizontalAxis`: Let extreme labels overlap y-axes #1317 — letting extreme labels overlap the y-axes

Together these cover both halves of what you describe (label placement at the extremes and avoiding plot-area shrinkage). Please follow / upvote those so interest stays consolidated.