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/* This Source Code Form is subject to the terms of the Mozilla Public
* License, v. 2.0. If a copy of the MPL was not distributed with this
* file, You can obtain one at http://mozilla.org/MPL/2.0/. */
"use strict";
this.EXPORTED_SYMBOLS = ["Color"];
/**
* Color class, which describes a color.
* In the future, this object may be extended to allow for conversions between
* different color formats and notations, support transparency.
*
* @param {Number} r Red color component
* @param {Number} g Green color component
* @param {Number} b Blue color component
*/
function Color(r, g, b) {
this.r = r;
this.g = g;
this.b = b;
}
Color.prototype = {
/**
* Formula from W3C's WCAG 2.0 spec's relative luminance, section 1.4.1,
* http://www.w3.org/TR/WCAG20/.
*
* @return {Number} Relative luminance, represented as number between 0 and 1.
*/
get relativeLuminance() {
let colorArr = [this.r, this.b, this.g].map(color => {
color = parseInt(color, 10);
if (color <= 10)
return color / 255 / 12.92;
return Math.pow(((color / 255) + 0.055) / 1.055, 2.4);
});
return colorArr[0] * 0.2126 +
colorArr[1] * 0.7152 +
colorArr[2] * 0.0722;
},
/**
* @return {Boolean} TRUE if the color value can be considered bright.
*/
get isBright() {
// Note: this is a high enough value to be considered as 'bright', but was
// decided upon empirically.
return this.relativeLuminance > 0.7;
},
/**
* Get the contrast ratio between the current color and a second other color.
* A common use case is to express the difference between a foreground and a
* background color in numbers.
* Formula from W3C's WCAG 2.0 spec's contrast ratio, section 1.4.1,
* http://www.w3.org/TR/WCAG20/.
*
* @param {Color} otherColor Color instance to calculate the contrast with
* @return {Number} Contrast ratios can range from 1 to 21, commonly written
* as 1:1 to 21:1.
*/
contrastRatio(otherColor) {
if (!(otherColor instanceof Color))
throw new TypeError("The first argument should be an instance of Color");
let luminance = this.relativeLuminance;
let otherLuminance = otherColor.relativeLuminance;
return (Math.max(luminance, otherLuminance) + 0.05) /
(Math.min(luminance, otherLuminance) + 0.05);
},
/**
* Biased method to check if the contrast ratio between two colors is high
* enough to be discernable.
*
* @param {Color} otherColor Color instance to calculate the contrast with
* @return {Boolean}
*/
isContrastRatioAcceptable(otherColor) {
// Note: this is a high enough value to be considered as 'high contrast',
// but was decided upon empirically.
return this.contrastRatio(otherColor) > 3;
}
};
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