Heatmap

A 2D grid of values, each rendered as a block character whose density represents the cell’s intensity within the visible range.

See also: CalendarHeatmap for values keyed by date.

Import: package:fleury/fleury.dart, or package:fleury/fleury_core.dart in browser code.

Usage

const Heatmap(
  values: <List<num>>[
    <num>[0.1, 0.3, 0.6, 0.9],
    <num>[0.2, 0.5, 0.8, 0.4],
    <num>[0.7, 0.6, 0.3, 0.1],
  ],
  rowLabels: <String>['a', 'b', 'c'],
  colLabels: <String>['w', 'x', 'y', 'z'],
  showLegend: true,
)

Details

Common shapes: GitHub-style activity calendars, time-of-day usage matrices, attention heatmaps. Each value maps to one of four blocks (░▒▓█) by where it falls in the range from min to max (fitted to the data by default); a value at or below the low end leaves its cell blank. Cells draw in the theme’s primary color unless you pass color.

Screen readers and agents get one chart node: semanticLabel plus the row and column counts and the value range the blocks are scaled to, not a node per cell.

Constructors

`Heatmap()`

Parameter	Type	Default	Description
`values:`	`List<List<num>>`	required	`values[row][col]` — outer list is rows top→bottom, inner is cols left→right.
`min:`	`num?`	—	Low end of the color/intensity range. `null` autoscales.
`max:`	`num?`	—	High end. `null` autoscales.
`cellWidth:`	`int`	`2`	Cells per data point (≥ 1). Wider cells make each data point easier to read; 2 is a nice default.
`color:`	`Color?`	—	Foreground for active cells. Defaults to the theme’s primary.
`rowLabels:`	`List<String>?`	—	Optional labels for the rows (drawn to the left).
`colLabels:`	`List<String>?`	—	Optional labels for the columns (drawn above the grid).
`showLegend:`	`bool`	`false`	When true, append a `░▒▓█ min – max` scale strip below the grid so the intensity ladder maps to real values — the encoding is otherwise opaque (and color/glyph-density-only is an accessibility red flag).
`semanticLabel:`	`String`	`'Heatmap'`	Label exposed through the semantic app graph.

Source

Heatmap is defined in packages/fleury/lib/src/catalog/heatmap.dart.

Category: Charts & meters · All widgets