hi

I have a question.
I can't get world normal.

"""
vector i = normalize(I);
normal n = normalize(N),
nf = faceforward(n, i);
"""
From this code it doesn't work.
Because it refers to camera not world.

please help me.
thank you.

Look at vtransform in the documentation of your renderer.
You probably need to do something like:

vector Nw = vtransform( "world", N );