Calendar / annual heatmap
GitHub-style contribution graph or year-in-review heatmap — one cell per day, 7 rows × 53 columns, colour intensity reflects daily value.
The demo plots weekly excess-mortality from influenza + pneumonia in NYC across 1918 — the year the Spanish flu killed more Americans than World War I, World War II, the Korean War, and the Vietnam War combined. The lighter March / April band is the "first wave"; the saturated October cluster is the catastrophic autumn second wave that peaked at ~13 weekly deaths per 10 k population.
Source: 1918 flu pandemic in the United States — Wikipedia
Public surface
use wisp_chart::heatmap::{CalendarHeatmap, CalendarValue, SequentialPalette};
use jiff::civil::date;
let cal = CalendarHeatmap::new(2025, vec![
CalendarValue::new(date(2025, 1, 15), 5.0),
CalendarValue::new(date(2025, 6, 1), 12.0),
/* ... */
])
.palette(SequentialPalette::github());
let g = cal.emit_graphics(&theme, Vec2::new(720.0, 120.0));Layout
Columns are ISO weeks (1..52, occasionally 53 for leap years).
Rows are weekdays — Monday at row 0, Sunday at row 6. Days with
no entry render at the palette's 0.0 stop. Values from other
years are silently ignored so reusing a multi-year dataset
across multiple heatmaps is safe.
Date math via jiff
wisp-chart depends on jiff for date /
weekday / ISO-week math. jiff is scoped to this crate's
Cargo.toml so wisp itself stays date-free.