/* A basic directional light just has a light color. The light shines in the 
direction of local <0, 0, -1> rotated by the isometry. */
#define dirDATASIZE (3 * sizeof(double))

void dirGetLighting(
        const isoIsometry *isom, const void *data, const double p[3], 
        const double u[3], const rayIntersection *inter, 
        rayLighting *lighting) {
    double *color = (double *)data;
    
}