Hi Phil, also here's another way to describe the stuff about smoothing groups.


So in order to make a flat polygon look like it is actually a piece of a smooth surface rather than a totally flat thing, you need to have vertex normals set up.


If an OBJ file has vertex normals in it, then you only need to read in those normals and then you have the normals all set up and fully prepared to render without doing anything else to the vertex normals at all.

If the file did not have any vertex normals in it, or if the vertex normals were invalidated somehow like by editing the points or morphing or something like that, that's when you would need to go through some process to create some vertex normals. When creating the vertex normals, that's when things like smoothing groups, break angles, etc... can come into play to have various effects on how the normals are created, like if there should be a break line between 2 polygons or not.


But if they are in the file, you don't want to be doing anything related to creating vertex normals or manipulating them by smoothing groups or break angles or anything like that at all, you want to just be using the normals that have been provided directly... If things were supposed to be creased, the polygons will already be set up with different normals specified to make the crease happen.


Does that make sense?


So that's why things like smoothing groups support is not significant in the case when you already have vertex normals present in the OBJ file - smoothing groups would only be significant if you need to create normals but if you have them you should not try to create new ones because you don't have enough information to get the true normal from the original NURBS surface at that point.

- Michael