Function pbrt::core::geometry::vec2_dot

pub fn vec2_dot<T>(v1: &Vector2<T>, v2: &Vector2<T>) -> T where
    T: Copy + Add<T, Output = T> + Mul<T, Output = T>, 

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