/**
 * Select which direction vector to use for dynamic atmosphere lighting based on an enum value
 *
 * @name czm_getDynamicAtmosphereLightDirection
 * @glslfunction
 * @see DynamicAtmosphereLightingType.js
 *
 * @param {vec3} positionWC the position of the vertex/fragment in world coordinates. This is normalized and returned when dynamic lighting is turned off.
 * @param {float} lightEnum The enum value for selecting between light sources.
 * @return {vec3} The normalized light direction vector. Depending on the enum value, it is either positionWC, czm_lightDirectionWC or czm_sunDirectionWC
 */
vec3 czm_getDynamicAtmosphereLightDirection(vec3 positionWC, float lightEnum) {
    const float NONE = 0.0;
    const float SCENE_LIGHT = 1.0;
    const float SUNLIGHT = 2.0;

    vec3 lightDirection =
        positionWC * float(lightEnum == NONE) +
        czm_lightDirectionWC * float(lightEnum == SCENE_LIGHT) +
        czm_sunDirectionWC * float(lightEnum == SUNLIGHT);
    return normalize(lightDirection);
}