Hi,

I think Figure 13 is confusing when compared to Code Listing 45.

and

inline vec3 random_on_hemisphere(const vec3& normal) {
 vec3 on_unit_sphere = random_unit_vector();
 if (dot(on_unit_sphere, normal) > 0.0) // In the same hemisphere as the normal
 return on_unit_sphere;
 else
 return -on_unit_sphere;
}

The drawing suggests a symmetry over the plane, whereas the code returns the inverse vector (which is also what the text explains). While both approaches preserve the probabilistic distribution, a new drawing could help avoid this confusion.

It could also be possible to apply the symmetry using:

return on_unit_sphere-2*dot(on_unit_sphere, normal)*normal;