therwi/sunkkoma
1
0
Fork 0
Code Issues Pull requests Projects Releases Packages Wiki Activity Actions

cleanup, documentation, contrast taking alpha into account.

Browse source
This commit is contained in:
Henry Jameson 2018-10-10 05:39:02 +03:00
parent 87e98772b0
commit 4b7b7d9905
2 changed files with 91 additions and 17 deletions
Download patch file Download diff file Expand all files Collapse all files

70
src/services/color_convert/color_convert.js
View file

@ -19,15 +19,21 @@ const rgb2hex = (r, g, b) => {
return `#${((1 << 24) + (r << 16) + (g << 8) + b).toString(16).slice(1)}`
}
// https://www.w3.org/TR/2008/REC-WCAG20-20081211/#relativeluminancedef
// https://www.w3.org/TR/2008/REC-WCAG20-20081211/relative-luminance.xml
// https://en.wikipedia.org/wiki/SRGB#The_reverse_transformation
const c2linear = (b) => {
/**
* Converts 8-bit RGB component into linear component
* https://www.w3.org/TR/2008/REC-WCAG20-20081211/#relativeluminancedef
* https://www.w3.org/TR/2008/REC-WCAG20-20081211/relative-luminance.xml
* https://en.wikipedia.org/wiki/SRGB#The_reverse_transformation
*
* @param {Number} bit - color component [0..255]
* @returns {Number} linear component [0..1]
*/
const c2linear = (bit) => {
// W3C gives 0.03928 while wikipedia states 0.04045
// what those magical numbers mean - I don't know.
// something about gamma-correction, i suppose.
// Sticking with W3C example.
const c = b / 255
const c = bit / 255
if (c < 0.03928) {
return c / 12.92
} else {
@ -35,18 +41,36 @@ const c2linear = (b) => {
}
}
/**
* Converts sRGB into linear RGB
* @param {Object} srgb - sRGB color
* @returns {Object} linear rgb color
*/
const srgbToLinear = (srgb) => {
return 'rgb'.split('').reduce((acc, c) => { acc[c] = c2linear(srgb[c]); return acc }, {})
}
// https://www.w3.org/TR/2008/REC-WCAG20-20081211/#relativeluminancedef
// https://www.w3.org/TR/2008/REC-WCAG20-20081211/relative-luminance.xml
/**
* Calculates relative luminance for given color
* https://www.w3.org/TR/2008/REC-WCAG20-20081211/#relativeluminancedef
* https://www.w3.org/TR/2008/REC-WCAG20-20081211/relative-luminance.xml
*
* @param {Object} srgb - sRGB color
* @returns {Number} relative luminance
*/
const relativeLuminance = (srgb) => {
const {r, g, b} = srgbToLinear(srgb)
return 0.2126 * r + 0.7152 * g + 0.0722 * b
}
// https://www.w3.org/TR/2008/REC-WCAG20-20081211/#contrast-ratiodef
/**
* Generates color ratio between two colors. Order is unimporant
* https://www.w3.org/TR/2008/REC-WCAG20-20081211/#contrast-ratiodef
*
* @param {Object} a - sRGB color
* @param {Object} b - sRGB color
* @returns {Number} color ratio
*/
const getContrastRatio = (a, b) => {
const la = relativeLuminance(a)
const lb = relativeLuminance(b)
@ -55,6 +79,33 @@ const getContrastRatio = (a, b) => {
return (l1 + 0.05) / (l2 + 0.05)
}
/**
* This generates what "worst case" color would look like for transparent
* segments. I.e. black with .2 alpha and pure-white background image
* could make white text unreadable
*
* @param {Object} srgb - transparent color
* @param {Number} alpha - color's opacity/alpha channel
* @param {Boolean} white - use white "background" if true, black otherwise
* @returns {Object} sRGB of resulting color
*/
const transparentWorstCase = (srgb, alpha, white = false) => {
const bg = 'rgb'.split('').reduce((acc, c) => { acc[c] = Number(white) * 255; return acc }, {})
return 'rgb'.split('').reduce((acc, c) => {
// Simplified https://en.wikipedia.org/wiki/Alpha_compositing#Alpha_blending
// for opaque bg and transparent fg
acc[c] = (srgb[c] * alpha + bg[c] * (1 - alpha))
return acc
}, {})
}
const worstCase = (bg, bga, text) => {
if (bga === 1 || typeof bga === 'undefined') return bg
// taken from https://github.com/toish/chromatism/blob/master/src/operations/contrastRatio.js
const blackWorse = ((text.r * 299) + (text.g * 587) + (text.b * 114)) / 1000 <= 128
return transparentWorstCase(bg, bga, !blackWorse)
}
const hex2rgb = (hex) => {
const result = /^#?([a-f\d]{2})([a-f\d]{2})([a-f\d]{2})$/i.exec(hex)
return result ? {
@ -84,5 +135,6 @@ export {
hex2rgb,
mixrgb,
rgbstr2hex,
getContrastRatio
getContrastRatio,
worstCase
}