jQuery color test

by Arnaud Buchholz

HTML

<div class="source">
  <div class="square red"></div>
  <div class="square green"></div>
  <div class="square blue"></div>
  <div class="square custom"></div>
  Initial color
</div>
<hr>
<div class="transparency">
  <div class="square red"></div>
  <div class="square green"></div>
  <div class="square blue"></div>
  <div class="square custom"></div>
  Using transparency
</div>
<hr>
<div class="maths">
  <div class="square red"></div>
  <div class="square green"></div>
  <div class="square blue"></div>
  <div class="square custom"></div>
  Adding value to each RGB component
</div>
<hr>
<div class="hsl">
  <div class="square red"></div>
  <div class="square green"></div>
  <div class="square blue"></div>
  <div class="square custom"></div>
  Using HSL and increasing luminance
</div>
<hr>
<input type="color" id="color">
<button id="go">go</button>

CSS

.square {
  display: inline-block;
  width: 32px;
  height: 32px;
  margin: 2px;
  border: 1px solid black;
  z-index: 1;
}

.transparency {
  position: relative;
}

.transparency::before {
  z-index: -1;
  position: absolute;
  content: "";
  left: 0;
  top: 0;
  width: 256px;
  height: 18px;
  background-color: #FFFFFF;
}

.transparency::after {
  z-index: -1;
  position: absolute;
  content: "";
  left: 0;
  top: 18px;
  width: 256px;
  height: 18px;
  background-color: #404040;
}

JavaScript

// http://stackoverflow.com/questions/2353211/hsl-to-rgb-color-conversion

/**
 * Converts an HSL color value to RGB. Conversion formula
 * adapted from http://en.wikipedia.org/wiki/HSL_color_space.
 * Assumes h, s, and l are contained in the set [0, 1] and
 * returns r, g, and b in the set [0, 255].
 *
 * @param   {number}  h       The hue
 * @param   {number}  s       The saturation
 * @param   {number}  l       The lightness
 * @return  {Array}           The RGB representation
 */
function hslToRgb(h, s, l){
    var r, g, b;

    if(s == 0){
        r = g = b = l; // achromatic
    }else{
        var hue2rgb = function hue2rgb(p, q, t){
            if(t < 0) t += 1;
            if(t > 1) t -= 1;
            if(t < 1/6) return p + (q - p) * 6 * t;
            if(t < 1/2) return q;
            if(t < 2/3) return p + (q - p) * (2/3 - t) * 6;
            return p;
        }

        var q = l < 0.5 ? l * (1 + s) : l + s - l * s;
        var p = 2 * l - q;
        r = hue2rgb(p, q, h + 1/3);
        g = hue2rgb(p, q, h);
        b = hue2rgb(p, q, h - 1/3);
    }

    return [Math.round(r * 255), Math.round(g * 255), Math.round(b * 255)];
}

/**
 * Converts an RGB color value to HSL. Conversion formula
 * adapted from http://en.wikipedia.org/wiki/HSL_color_space.
 * Assumes r, g, and b are contained in the set [0, 255] and
 * returns h, s, and l in the set [0, 1].
 *
 * @param   {number}  r       The red color value
 * @param   {number}  g       The green color value
 * @param   {number}  b       The blue color value
 * @return  {Array}           The HSL representation
 */
function rgbToHsl(r, g, b){
    r /= 255, g /= 255, b /= 255;
    var max = Math.max(r, g, b), min = Math.min(r, g, b);
    var h, s, l = (max + min) / 2;

    if(max == min){
        h = s = 0; // achromatic
    }else{
        var d = max - min;
        s = l > 0.5 ? d / (2 - max - min) : d / (max + min);
        switch(max){
            case r: h = (g - b) / d + (g < b ? 6 : 0); break;
         ...