131 lines
3.4 KiB
JavaScript
131 lines
3.4 KiB
JavaScript
import { map } from 'lodash'
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const rgb2hex = (r, g, b) => {
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if (r === null || typeof r === 'undefined') {
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return undefined
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}
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if (r[0] === '#') {
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return r
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}
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if (typeof r === 'object') {
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({ r, g, b } = r)
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}
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[r, g, b] = map([r, g, b], (val) => {
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val = Math.ceil(val)
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val = val < 0 ? 0 : val
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val = val > 255 ? 255 : val
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return val
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})
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return `#${((1 << 24) + (r << 16) + (g << 8) + b).toString(16).slice(1)}`
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}
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/**
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* Converts 8-bit RGB component into linear component
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* https://www.w3.org/TR/2008/REC-WCAG20-20081211/#relativeluminancedef
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* https://www.w3.org/TR/2008/REC-WCAG20-20081211/relative-luminance.xml
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* https://en.wikipedia.org/wiki/SRGB#The_reverse_transformation
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*
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* @param {Number} bit - color component [0..255]
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* @returns {Number} linear component [0..1]
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*/
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const c2linear = (bit) => {
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// W3C gives 0.03928 while wikipedia states 0.04045
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// what those magical numbers mean - I don't know.
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// something about gamma-correction, i suppose.
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// Sticking with W3C example.
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const c = bit / 255
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if (c < 0.03928) {
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return c / 12.92
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} else {
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return Math.pow((c + 0.055) / 1.055, 2.4)
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}
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}
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/**
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* Converts sRGB into linear RGB
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* @param {Object} srgb - sRGB color
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* @returns {Object} linear rgb color
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*/
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const srgbToLinear = (srgb) => {
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return 'rgb'.split('').reduce((acc, c) => { acc[c] = c2linear(srgb[c]); return acc }, {})
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}
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/**
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* Calculates relative luminance for given color
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* https://www.w3.org/TR/2008/REC-WCAG20-20081211/#relativeluminancedef
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* https://www.w3.org/TR/2008/REC-WCAG20-20081211/relative-luminance.xml
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*
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* @param {Object} srgb - sRGB color
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* @returns {Number} relative luminance
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*/
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const relativeLuminance = (srgb) => {
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const { r, g, b } = srgbToLinear(srgb)
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return 0.2126 * r + 0.7152 * g + 0.0722 * b
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}
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/**
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* Generates color ratio between two colors. Order is unimporant
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* https://www.w3.org/TR/2008/REC-WCAG20-20081211/#contrast-ratiodef
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*
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* @param {Object} a - sRGB color
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* @param {Object} b - sRGB color
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* @returns {Number} color ratio
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*/
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const getContrastRatio = (a, b) => {
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const la = relativeLuminance(a)
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const lb = relativeLuminance(b)
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const [l1, l2] = la > lb ? [la, lb] : [lb, la]
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return (l1 + 0.05) / (l2 + 0.05)
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}
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/**
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* This performs alpha blending between solid background and semi-transparent foreground
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*
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* @param {Object} fg - top layer color
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* @param {Number} fga - top layer's alpha
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* @param {Object} bg - bottom layer color
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* @returns {Object} sRGB of resulting color
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*/
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const alphaBlend = (fg, fga, bg) => {
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if (fga === 1 || typeof fga === 'undefined') return fg
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return 'rgb'.split('').reduce((acc, c) => {
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// Simplified https://en.wikipedia.org/wiki/Alpha_compositing#Alpha_blending
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// for opaque bg and transparent fg
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acc[c] = (fg[c] * fga + bg[c] * (1 - fga))
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return acc
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}, {})
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}
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const invert = (rgb) => {
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return 'rgb'.split('').reduce((acc, c) => {
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acc[c] = 255 - rgb[c]
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return acc
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}, {})
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}
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const hex2rgb = (hex) => {
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const result = /^#?([a-f\d]{2})([a-f\d]{2})([a-f\d]{2})$/i.exec(hex)
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return result ? {
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r: parseInt(result[1], 16),
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g: parseInt(result[2], 16),
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b: parseInt(result[3], 16)
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} : null
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}
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const mixrgb = (a, b) => {
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return Object.keys(a).reduce((acc, k) => {
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acc[k] = (a[k] + b[k]) / 2
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return acc
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}, {})
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}
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export {
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rgb2hex,
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hex2rgb,
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mixrgb,
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invert,
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getContrastRatio,
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alphaBlend
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}
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