Contour Plot

Contour Plot is a TypeScript library designed for efficient plotting of functions that map (x, y) points to a limited set of discrete values. The library evaluates the function at grid points with configurable density, refines boundaries where neighboring grid points produce different values, and generates a list of squares or runs (unit-height rectangles). Within each square or run, the function's value is treated as constant. The coordinates of the building blocks are selected so that they can be precisely and efficiently rendered as SVG.

Example usage

SVG output

The following TypeScript code snippet will create an SVG and draw a filled hyperbola:

import {Plot, runsToSvg} from 'contour-plot-svg';

document.body.innerHTML =
    '<svg style="width: 100%; height: calc(100vh - 20px)" />';
const svg = document.querySelector('svg')!;

const hyperbola = (x: number, y: number) => x * y > 10000;

const [width, height] = [svg.clientWidth, svg.clientHeight];
const domain = {x: -width / 2, y: -height / 2, width, height};
const domainToViewTransform =
    new DOMMatrix().translate(width / 2, height / 2).flipY();

svg.append(...runsToSvg(
    new Plot<boolean>(hyperbola)
        .compute(domain, /* sampleSpacing= */ 128, /* pixelSize= */ 1)
        .runs(),
    /* addStyles= */ (el, isInside) => {
      el.style.stroke = isInside ? 'olive' : 'lightgreen';
    }, {transform: domainToViewTransform}));

Demo on CodePen

Text output

The library can also visualize boolean-valued functions using Unicode block drawing characters, exposing the plot's underlying structure:

import {Plot, squaresToText} from 'contour-plot-svg';

const domain = {x: -8, y: -8, width: 16, height: 8};
const plot = new Plot((x, y) => x * x + y * y < 45)
    .compute(domain, /* sampleSpacing= */ 4, /* pixelSize= */ 1);

const pre = document.createElement('pre');
pre.style.lineHeight = '1';
pre.textContent = squaresToText(plot.squares());
document.body.append(pre);

Result

┌─┐ ┌─┐ ┌─┐ □ □ □ □ ┌─┐ ┌─┐ ┌─┐ 
└─┘ └─┘ └─┘ ■ ■ ■ ■ └─┘ └─┘ └─┘ 
┌─┐ □ □ ▗▄▖ ▗▄▖ ▗▄▖ ▗▄▖ □ □ ┌─┐ 
└─┘ □ ■ ▝▀▘ ▝▀▘ ▝▀▘ ▝▀▘ ■ □ └─┘ 
┌─┐ ▗▄▖ ▗▄▄▄▄▄▖ ▗▄▄▄▄▄▖ ▗▄▖ ┌─┐ 
└─┘ ▝▀▘ ▐█████▌ ▐█████▌ ▝▀▘ └─┘ 
□ ■ ▗▄▖ ▐█████▌ ▐█████▌ ▗▄▖ ■ □ 
□ ■ ▝▀▘ ▝▀▀▀▀▀▘ ▝▀▀▀▀▀▘ ▝▀▘ ■ □ 

Demo on CodePen

Interactive demo

To start a demo showcasing all features, run the following commands then open http://localhost:4173. There you can select a function to plot, specify the resolution, and optionally highlight the edges of the building blocks.

git clone https://github.com/pallosp/contour_plot.git
cd contour_plot
npm install
npm run build
npm run preview

Screenshot