https://seriot.ch/projects/drawing_with_computers.html

lines.js

const canvas = document.getElementById('lines');
const ctx = canvas.getContext('2d');

const W = canvas.width;
const H = canvas.height;
const G = 4, N = 6;

const rand = (max, step = 1) => Math.floor(Math.random() * max / step) * step;
const next = (line, vel) => line.map((p, i) => (vel[i] *= (p + vel[i] >= 0 && p + vel[i] < (i % 2 ? H : W)) ? 1 : -1, p + vel[i]));
const drawLines = (lines, ctx) => lines.forEach(l => ctx.stroke(new Path2D(`M ${l[0]} ${l[1]} L ${l[2]} ${l[3]}`)));

let V = Array.from({ length: G }, () => Array(4).fill(rand(18, 2) - 9));
let L = Array.from({ length: G }, () => Array(4).fill().map((_, i) => rand(i % 2 ? H : W)));

(async function animate() {
    while (true) {
        L = [...L.slice(0, G).map((l, i) => next(l, V[i])), ...L.slice(0, G * N)];
        ctx.fillStyle = 'black'; ctx.fillRect(0, 0, W, H);
        ctx.strokeStyle = 'white';
        drawLines(L, ctx);
        await new Promise(r => setTimeout(r, 300));
    }
})();