colorizr/src/converters/hsl2rgb.ts

Manipulate colors like a boss

import { addAlpha, extractAlpha } from '~/modules/alpha';
import hue2rgb from '~/modules/hue2rgb';
import { parseInput } from '~/modules/utils';

import { ConverterParameters, HSL, RGB } from '~/types';

/**
 * Convert HSL to RGB.
 *
 * @param input - The HSL color object or tuple.
 * @returns The RGB color object.
 */
export default function hsl2rgb(input: ConverterParameters<HSL>): RGB {
  const value = parseInput(input, 'hsl');
  const alpha = extractAlpha(input);

  const h = value.h / 360;
  const s = value.s / 100;
  const l = value.l / 100;

  let r;
  let g;
  let b;

  let point;
  let chroma;

  if (s < 0.0001) {
    r = l;
    g = l;
    b = l;
  } else {
    chroma = l < 0.5 ? l * (1 + s) : l + s - l * s;
    point = 2 * l - chroma;

    r = hue2rgb(point, chroma, h + 1 / 3);
    g = hue2rgb(point, chroma, h);
    b = hue2rgb(point, chroma, h - 1 / 3);
  }

  return addAlpha(
    {
      r: Math.round(r * 255),
      g: Math.round(g * 255),
      b: Math.round(b * 255),
    },
    alpha,
  );
}