color-welcome.js

#! /usr/bin/env node

// * ================================================================================ lolcat

/**
 * hsl color space
 * https://stackoverflow.com/questions/36721830/convert-hsl-to-rgb-and-hex#answer-54014428
 */
const hsl2rgb = (h, s = 1, l = 0.5) => {
  const a = s * Math.min(l, 1 - l);
  const f = (n, k = (n + h / 30) % 12) => Math.round((l - a * Math.max(Math.min(k - 3, 9 - k, 1), -1)) * 255);
  return [f(0), f(8), f(4)];
};

// * ----------------

/**
 * smoother color space
 * https://github.com/jaseg/lolcat/blob/main/lolcat.c
 */
const circle2rgb = (hue) => {
  /**
   * saturation
   * 0: white
   * 1: colorful
   */
  const s = 1;
  const r = Math.round((1 - s + s * (0.5 + 0.5 * Math.sin(((hue + 0) / 180) * Math.PI))) * 255);
  const g = Math.round((1 - s + s * (0.5 + 0.5 * Math.sin(((hue + 120) / 180) * Math.PI))) * 255);
  const b = Math.round((1 - s + s * (0.5 + 0.5 * Math.sin(((hue + 240) / 180) * Math.PI))) * 255);

  return [r, g, b];
};

// * ---------------- ansi escape color

// * https://en.wikipedia.org/wiki/ANSI_escape_code#Colors
const ansicolor = (hue, [r, g, b] = circle2rgb(hue)) => `\x1b[38;2;${r};${g};${b}m`;

const resetcolor = "\x1b[0m";

// * ---------------- lolcat

const lolcat = (str, h = 0.2, v = 0.1) => {
  const offset = 0 + Math.random() * 360;
  const direction = Math.random() < 0.5 ? -1 : 1;

  str.split("\n").forEach((line, l) => {
    line.split("").forEach((char, i) => {
      const hue = ((i * h) / 5.0 + l * v) * 60 * direction + offset;
      process.stdout.write(ansicolor(hue) + char + "");
    });
    process.stdout.write("\n");
  });

  process.stdout.write(resetcolor);
};

// * ================================================================================

const theWelcome = String.raw`
 _____  _    _         _      _____
|  __ \| |  | |  /\   | |    / ____|
| |__) | |  | | /  \  | |   | |
|  _  /| |  | |/ /\ \ | |   | |
| | \ \| |__| / ____ \| |___| |____
|_|  \_\\____/_/    \_\______\_____|
`;

// * ----------------------------------------------------------------

const height = theWelcome.split("\n").length;
const width = Math.max(...theWelcome.split("\n").map((e) => e.length));
const len = Math.sqrt(height ** 2 * 4 + width ** 2);
const ratio = height / width;

lolcat(theWelcome, 2 / len, 0.2 * ratio);