I am using a diffuse based toon shader for NPR models and i need to be able to fine tune vertex normals in order to force certain non realistic shadows.
Trying to rotate them manually is very tedious and imprecise where i know i need to point them either towards or away from the light angle by a certain amount but because of the small amounts involved any minute misalignment will result in bad shadows with other light angles.
The normals don't seem to have any indicator of the rotational position and their rotation axis relative to their from-corner facing direction is very unintuitive.
My question is how can i rotate the normal by x amount either towards or away from the angle of my sun light source with precision?
I am capable of using python if need be. I would appreciate any help, thanks.