Function pbrt::core::geometry::vec3_dot_nrm

pub fn vec3_dot_nrm<T>(v1: &Vector3<T>, n2: &Normal3<T>) -> T where
    T: Copy + Add<T, Output = T> + Mul<T, Output = T>, 

Product of the Euclidean magnitudes of a vector (and a normal) and the cosine of the angle between them. A return value of zero means both are orthogonal, a value if one means they are codirectional.