Contour plot
Draw iso-level contours over a 2D scalar field using marching squares. Useful for topology, terrain, response surfaces, and 2D density visualisations where the lines themselves are the feature.
The demo draws the bivariate normal density Sir Francis Galton popularised in his 1885 quincunx + regression-board demonstration — a single radial Gaussian peak with five nested iso-density contours. The same shape underlies modern density estimation and 2D KDEs.
Source: Galton board — Wikipedia
Public surface
use wisp_chart::contour::ContourPlot;
let field: Vec<f32> = sample_function_on_grid(); // rows × cols
let plot = ContourPlot::new(
field,
/* cols */ 48,
/* rows */ 48,
vec![0.15, 0.35, 0.55, 0.75, 0.9], // iso-levels
);
let g = plot.emit_graphics(&theme, viewport);Each grid cell's four corners are compared to the iso-level
threshold; the 16 possible above/below sign-bit combinations map
to 16 line-segment cases. The implementation is a flat match —
no degenerate ambiguities are smoothed (saddle points pick a
fixed orientation), which keeps the output deterministic across
runs and platforms.
- A 2D histogram or table heatmap shows the bulk of the field via colour — easy to read overall shape.
- A contour plot shows specific levels — easy to read "everything above 0.75 is here". Compose both: filled heatmap underneath, contour lines on top.