Help needed calculating vertex normals...

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big10p

Hi

Hope it's OK posting here as I'm not sure my problem can be considered 'advanced 3D' but here goes...

Basically, I've written a function to do tri sub-division by placing a new vertex at the centre of each side of a tri. The problem I'm having is calculating the normals of the new vertices. The calculation I'm using at the moment to do this is as follows:

norm_x_of_centre_vert# = norm_x_of_vert_0 + ((norm_x_of_vert_1-norm_x_of_vert_0)/2)
norm_y_of_centre_vert# = norm_y_of_vert_0 + ((norm_y_of_vert_1-norm_y_of_vert_0)/2)
norm_z_of_centre_vert# = norm_z_of_vert_0 + ((norm_z_of_vert_1-norm_z_of_vert_0)/2)

I think this gives the new normals the right direction but it also 'crops' them so that they don't have a length of 1. I'm pretty new to 3D concepts so don't really understand why normals have to have a unit length.

Any help sorting this problem out would be much appreciated!

Thanks in advance.