I am using mesh combiner I made. he only problem is, I dont know it shadows are rendered per mesh ,or per verticy rendered.
From this article on Shadows in Unity from Unity manual it states that:
Unity uses so called shadow maps to
display shadows. Shadow mapping is a
texture based approach,
And as per the Wikipedia link for the Shadow mapping from the same link above. It states that:
Shadows are created by testing whether
a pixel is visible from the light
source, by comparing it to a z-buffer
or depth image of the light source’s
view, stored in the form of a texture.
Which means shadows in Unity are calculated based on pixels.