/**
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* Converts an RGB color to HSL (hue, saturation, lightness)
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* HSL <-> RGB conversion: {@link http://www.chilliant.com/rgb2hsv.html}
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*
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* @name czm_RGBToHSL
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* @glslFunction
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*
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* @param {vec3} rgb The color in RGB.
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*
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* @returns {vec3} The color in HSL.
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*
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* @example
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* vec3 hsl = czm_RGBToHSL(rgb);
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* hsl.z *= 0.1;
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* rgb = czm_HSLToRGB(hsl);
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*/
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vec3 RGBtoHCV(vec3 rgb)
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{
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// Based on work by Sam Hocevar and Emil Persson
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vec4 p = (rgb.g < rgb.b) ? vec4(rgb.bg, -1.0, 2.0 / 3.0) : vec4(rgb.gb, 0.0, -1.0 / 3.0);
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vec4 q = (rgb.r < p.x) ? vec4(p.xyw, rgb.r) : vec4(rgb.r, p.yzx);
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float c = q.x - min(q.w, q.y);
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float h = abs((q.w - q.y) / (6.0 * c + czm_epsilon7) + q.z);
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return vec3(h, c, q.x);
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}
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vec3 czm_RGBToHSL(vec3 rgb)
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{
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vec3 hcv = RGBtoHCV(rgb);
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float l = hcv.z - hcv.y * 0.5;
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float s = hcv.y / (1.0 - abs(l * 2.0 - 1.0) + czm_epsilon7);
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return vec3(hcv.x, s, l);
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}
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