67 lines
2.2 KiB
JavaScript
67 lines
2.2 KiB
JavaScript
// In our case, there's only one dependency
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var toRgb = require('hsl-to-rgb-for-reals')
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var debug = require('debug')('hsl-to-hex')
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// Typically all dependencies should be declared at the top of the file.
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// Now let's define an API for our module, we're taking hue, saturation and luminosity values and outputting a CSS compatible hex string.
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// Hue is in degrees, between 0 and 359. Since degrees a cyclical in nature, we'll support numbers greater than 359 or less than 0 by "spinning" them around until they fall within the 0 to 359 range.
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// Saturation and luminosity are both percentages, we'll represent these percentages with whole numbers between 0 and 100. For these numbers we'll need to enforce a maximum and a minimum, anything below 0 will become 0, anything above 100 will become 100.
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// Let's write some utility functions to handle this logic:
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function max (val, n) {
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debug('ensuring ' + val + ' is no more than ' + n)
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return (val > n) ? n : val
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}
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function min (val, n) {
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debug('ensuring ' + val + ' is no less than ' + n)
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return (val < n) ? n : val
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}
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function cycle (val) {
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debug('resolving ' + val + ' within the 0-359 range')
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// for safety:
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val = max(val, 1e7)
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val = min(val, -1e7)
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// cycle value:
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while (val < 0) { val += 360 }
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while (val > 359) { val -= 360 }
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return val
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}
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// Now for the main piece, the `hsl` function:
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function hsl (hue, saturation, luminosity) {
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debug('calculating hex for hue: ' + hue + ' saturation: ' + saturation + ' luminosity: ' + luminosity)
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// resolve degrees to 0 - 359 range
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hue = cycle(hue)
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// enforce constraints
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saturation = min(max(saturation, 100), 0)
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luminosity = min(max(luminosity, 100), 0)
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// convert to 0 to 1 range used by hsl-to-rgb-for-reals
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saturation /= 100
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luminosity /= 100
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// let hsl-to-rgb-for-reals do the hard work
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var rgb = toRgb(hue, saturation, luminosity)
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// convert each value in the returned RGB array
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// to a 2 character hex value, join the array into
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// a string, prefixed with a hash
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return '#' + rgb
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.map(function (n) {
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return (256 + n).toString(16).substr(-2)
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})
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.join('')
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}
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// In order to make our code into a bona fide module we have to export it:
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module.exports = hsl
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