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