charts.color

import { type Rgb } from "./charts_color_types.ts";

const HEX = "0123456789abcdef";

function nibble(ch: string, hex: string): number {
  const n = HEX.indexOf(ch.toLowerCase());
  if (n < 0) throw new RangeError(`"${hex}" is not a hex colour (#rgb or #rrggbb)`);
  return n;
}

/**
 * "#rrggbb" or the short "#rgb" (each digit doubled, as CSS does), in either
 * case. Anything else, including a missing "#", names or rgb() syntax, is an
 * error rather than a guess.
 */
export function parseHex(hex: string): Rgb {
  if (typeof hex !== "string" || hex[0] !== "#" || (hex.length !== 4 && hex.length !== 7)) {
    throw new RangeError(`"${hex}" is not a hex colour (#rgb or #rrggbb)`);
  }
  if (hex.length === 4) {
    const r = nibble(hex[1], hex);
    const g = nibble(hex[2], hex);
    const b = nibble(hex[3], hex);
    return { r: r * 17, g: g * 17, b: b * 17 };
  }
  return {
    r: nibble(hex[1], hex) * 16 + nibble(hex[2], hex),
    g: nibble(hex[3], hex) * 16 + nibble(hex[4], hex),
    b: nibble(hex[5], hex) * 16 + nibble(hex[6], hex),
  };
}

import { type Rgb } from "./charts_color_types.ts";

const HEX = "0123456789abcdef";

function pair(value: number): string {
  if (!Number.isInteger(value) || value < 0 || value > 255) {
    throw new RangeError(`rgb channels must be whole numbers from 0 to 255, received ${value}`);
  }
  return HEX[Math.floor(value / 16)] + HEX[value % 16];
}

/** Lowercase "#rrggbb", the form every renderer accepts. */
export function toHex(rgb: Rgb): string {
  return "#" + pair(rgb.r) + pair(rgb.g) + pair(rgb.b);
}

Imports name this capability’s declared dependencies, which fune builds next to it in your project; each one links to its page.

import { pow } from "./math_pow.ts";  ← from math.pow ^1.0.0 · built alongside by fune
import { roundFloat } from "./math_round_float.ts";  ← from math.round-float ^1.0.0 · built alongside by fune

/**
 * The sRGB transfer function (IEC 61966-2-1) undone: an 8-bit channel as
 * linear light from 0 to 1. Colour arithmetic (mixing, luminance) is only
 * meaningful on these values, not on the stored channel numbers.
 */
export function srgbToLinear(channel: number): number {
  if (!Number.isInteger(channel) || channel < 0 || channel > 255) {
    throw new RangeError(`channel must be a whole number from 0 to 255, received ${channel}`);
  }
  const c = channel / 255;
  const linear = c <= 0.04045 ? c / 12.92 : pow((c + 0.055) / 1.055, 2.4);
  return roundFloat(linear, 12);
}

Imports name this capability’s declared dependencies, which fune builds next to it in your project; each one links to its page.

import { pow } from "./math_pow.ts";  ← from math.pow ^1.0.0 · built alongside by fune
import { roundFloat } from "./math_round_float.ts";  ← from math.round-float ^1.0.0 · built alongside by fune

/**
 * Linear light back to an 8-bit sRGB channel. Values outside 0..1 (a mix in
 * another colour space can land slightly out of gamut) are clipped first.
 */
export function linearToSrgb(value: number): number {
  if (typeof value !== "number" || !Number.isFinite(value)) {
    throw new RangeError(`value must be a finite number, received ${value}`);
  }
  const v = value < 0 ? 0 : value > 1 ? 1 : value;
  const encoded = v <= 0.0031308 ? 12.92 * v : 1.055 * pow(v, 1 / 2.4) - 0.055;
  return roundFloat(encoded * 255, 0);
}