Simple and efficient hue-shift function for a GLSL fragment shader.

hue-shift.frag

/** 
 * @brief Applies a hue-shift in a GLSL fragment shader.
 * 
 * @param color The color of the fragment to shift.
 * @param hue The amount of hue-shift to apply, in radians. Use GLSL radians function to convert from degrees if needed.
 * 
 * @return The hue-shifted fragment color.
*/
vec3 hueShift(vec3 color, float hue) {
    const vec3 k = vec3(0.57735, 0.57735, 0.57735);
    float cosAngle = cos(hue);
    return vec3(col * cosAngle + cross(k, col) * sin(hue) + k * dot(k, col) * (1.0 - cosAngle));
}