Rendering, Color, and Layout

Area versus color

value determines rectangle area. metric determines color through HeatmapColorScale; it does not change area. SignedMetricColorScale is a sensible default for positive/negative measures. Provide color on a node to override the scale for that node.

val scale = SignedMetricColorScale(maximumAbsoluteMetric = 10.0)
Heatmap(state = state, colorScale = scale)
HeatmapLegend(entries = scale.legendEntries())

For non-financial semantics, implement HeatmapColorScale and return an ARGB Long. Keep the meaning of color in the host product, and use an accompanying legend whenever colors carry meaning.

Adaptive content

HeatmapDisplayPolicy uses measured text dimensions by default. It progressively removes logo, label, and metric when a rectangle cannot present them cleanly; it does not force text into tiny cells. Small cells also receive proportionally smaller padding up to cellContentPadding.

Fixed fallback thresholds remain useful for a deliberately deterministic visual system:

val policy = HeatmapDisplayPolicy(
  adaptiveContent = true,
  hideContentBelow = 16.dp,
  showMetricAbove = 40.dp,
  showLabelAbove = 48.dp,
  cellContentPadding = 6.dp,
)

Avoid treating a particular device dp width as an application-wide rule. Parent constraints, font scale, localization, and Desktop window size all affect what fits; measured adaptive content is the default for this reason.

Custom cells

Pass cellContent to replace the default content while Volcano still supplies layout, press, hover, and click modifiers. Apply the supplied modifier to the outermost composable. If the custom cell replaces meaningful label or value information, provide equivalent semantics for assistive technology.