mirror of https://github.com/jkjoy/sunpeiwen.git
41 lines
864 B
JavaScript
41 lines
864 B
JavaScript
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var utils = require('../utils')
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, nodes = require('../nodes');
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/**
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* Returns the relative luminance of the given `color`,
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* see http://www.w3.org/TR/WCAG20/#relativeluminancedef
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*
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* Examples:
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*
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* luminosity(white)
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* // => 1
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*
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* luminosity(#000)
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* // => 0
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*
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* luminosity(red)
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* // => 0.2126
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*
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* @param {RGBA|HSLA} color
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* @return {Unit}
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* @api public
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*/
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function luminosity(color){
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utils.assertColor(color);
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color = color.rgba;
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function processChannel(channel) {
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channel = channel / 255;
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return (0.03928 > channel)
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? channel / 12.92
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: Math.pow(((channel + 0.055) / 1.055), 2.4);
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}
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return new nodes.Unit(
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0.2126 * processChannel(color.r)
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+ 0.7152 * processChannel(color.g)
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+ 0.0722 * processChannel(color.b)
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);
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};
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luminosity.params = ['color'];
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module.exports = luminosity;
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