Function pbrt::core::geometry::pnt3_offset_ray_origin

pub fn pnt3_offset_ray_origin(
    p: &Point3f, 
    p_error: &Vector3f, 
    n: &Normal3f, 
    w: &Vector3f
) -> Point3f

When tracing spawned rays leaving the intersection point p, we offset their origins enough to ensure that they are past the boundary of the error box and thus won't incorrectly re-intersect the surface.