2D histogram (binned heatmap)

Bin a 2D point cloud into a fixed grid and emit one filled cell per bin, coloured by count. Useful when a scatterplot over-plots so heavily that individual points stop being legible.

The demo plots the Hertzsprung–Russell diagram — stellar effective temperature (log K, X) against absolute magnitude (M_V, Y, brighter up) for ~640 synthesised stars. The dense diagonal running top-right → bottom-left is the main sequence; the cluster top-left is white dwarfs; the upper-right scatter is red giants + supergiants. The chart was published independently by Hertzsprung (1911) and Russell (1913) and is the single most important diagram in stellar astrophysics.

Source: Hertzsprung–Russell diagram — Wikipedia

Public surface

use wisp_chart::heatmap::Histogram2D;

let points: Vec<(f32, f32)> = collect_xy_observations();
let h2 = Histogram2D::from_points(
    &points,
    /* cols */ 24,
    /* rows */ 24,
    Some(((-5.0, 5.0), (-5.0, 5.0))),  // optional clipping extent
);
let g = h2.emit_graphics(&theme, viewport);