Thanks, so aside from the decorative ones do normal edges always follow triangle and quad sides.

For example could something like this happen in the current library

x~~~~0~~~~~~~~~0~~~~~x
\ /
\ /
\ /
\ /
0

This being a single type 2 line and a single type 3 line (there will be more triangles in real parts off course this is an 'zoom' if you like)

Or will it allay be guaranteed to be like:

x~~~~X~~~~~~~~~X~~~~~x
\ /
\ /
\ /
\ /
0

Being 3 type 2 lines and a single triangle.

The reason I would like to know this is for the smoothing function I'm working on. It would be very helpful to assume any two triangles can be split by a edge line using the same shared points of the triangle.

I need this information to calculate normals for the triangle vertices. If I can not assume this the alternative would be to do line point intersection tests for all triangle and line data. Which will be much much much slower, and as a result I need to seek an alternative approach.

ps: I'm looking into this at the moment completely unhindered by knowledge of how apps like LDView handle this, just to see if I can come up with something on my own. :)