/**
 * Adjusts the hue of a color.
 * 
 * @name czm_hue
 * @glslFunction
 * 
 * @param {vec3} rgb The color.
 * @param {float} adjustment The amount to adjust the hue of the color in radians.
 *
 * @returns {float} The color with the hue adjusted.
 *
 * @example
 * vec3 adjustHue = czm_hue(color, czm_pi); // The same as czm_hue(color, -czm_pi)
 */
vec3 czm_hue(vec3 rgb, float adjustment)
{
    const mat3 toYIQ = mat3(0.299,     0.587,     0.114,
                            0.595716, -0.274453, -0.321263,
                            0.211456, -0.522591,  0.311135);
    const mat3 toRGB = mat3(1.0,  0.9563,  0.6210,
                            1.0, -0.2721, -0.6474,
                            1.0, -1.107,   1.7046);
    
    vec3 yiq = toYIQ * rgb;
    float hue = atan(yiq.z, yiq.y) + adjustment;
    float chroma = sqrt(yiq.z * yiq.z + yiq.y * yiq.y);
    
    vec3 color = vec3(yiq.x, chroma * cos(hue), chroma * sin(hue));
    return toRGB * color;
}