Hitrecord
void set_face_normal(const ray&, const vec3&)
Imagine a surface \(S\).
If the dot product1 of incident ray2 and the normal vector1 is negative, the ray2 is outside of the surface \(S\).
If our condition is true then the normal is the outward normal, otherwise it is opposite to outward normal.
void hit_record::set_face_normal(const ray& r, const vec3& outward_normal) {
// Sets the hit record normal vector.
// NOTE: the parameter `outward_normal` is assumed to have unit length.
front_face = dot(r.direction(), outward_normal) < 0;
normal = front_face ? outward_normal : -outward_normal;
}