Implications of negative dot product of normal to the triangle and light direction about tinyrenderer HOT 3 CLOSED

There is no such thing as a "proper" rendering; all depends on conventions that you use. Given a single triangle, how can you know which side is the "front" and which one is the "back" side? No way to define in general without some sort of a convention. One possibility is to say that if you look at a triangle from the "front" side, the vertices are numbered counter-clockwise. Or the other way round ;)

Footnote: auto orientation of normals can be possible for closed (i.e. without boundary edges) manifold surfaces.

from tinyrenderer.

One possibility is to say that if you look at a triangle from the "front" side, the vertices are numbered counter-clockwise

Does the model used here follow such a convention so that the normals calculated using the provided code come out to be "outwards" or "inwards" ?

from tinyrenderer.

african_head.obj uses clockwise ordering if I am not mistaken

from tinyrenderer.