Heatmap

heatmap · Charts · interactive

Charts: a scale, its ticks, and a line or area drawn from data.

Import

#include "gbui/widgets/chart.hpp"

Example

Nothing is downloaded until you press it.

HeatmapResult heatmap(Ui& ui, const Interaction& input, std::string_view id, const std::vector<std::vector<double>>& values, const HeatmapOptions& options = {});

A grid of cells shaded by value. values is row-major and may be ragged — a short row simply has fewer cells, which is what a calendar's last week is. The colour is one token at varying strength rather than a rainbow. A multi-hue scale looks richer and reads worse: hue carries no order, so a reader has to consult the legend for every cell, while "more of the same colour" needs no legend at all.

API

HeatmapOptions

Option	Type	Default	What it does
rows	std::vector<std::string>		Names down the side and along the top. Fewer than there are rows or columns leaves the rest unlabelled rather than renumbering them.
columns	std::vector<std::string>		As above, along the top.
scale	Scale	0.0, 0.0
autoScale	bool	true
steps	int	5	Quantise the colour into this many steps; zero is a continuous ramp. Five by default, and steps rather than a ramp because a reader compares cells by matching them, not by judging absolute lightness. Two cells one step apart are visibly different; two cells 3% apart on a continuous ramp are the same colour to anyone reading a grid at a glance.
color optional	std::optional<Token>		The hue the scale runs to. Unset takes the design's first chart colour, so the grid re-themes with everything else.
cellSize	float	0.0f	Zero lets the cells share out the width.
gap	float	3.0f
radius	float	2.0f
rowLabels	float	34.0f	Room for the labels. Zero draws none.
columnLabels	float	16.0f	The same, along the top.
hover	bool	true
valueFormat	std::string_view	"%.0f"
tooltip	ChartTooltip
name	std::string_view		What the chart is of — "Revenue by month". A chart is the one thing on a screen a reader gets nothing from: the shapes carry all of it, and the numbers behind them are the caller's. A name and a Figure role are the least that makes it navigable, and they are not the whole answer — see the note in docs/reference/accessibility.