Hi Momso, n-gon means a polygon with more than 3 or 4 sides.
This option allows you to control whether n-gons will be allowed to be created in the exported file, or whether n-gons will be broken down into smaller polygons.
Some programs are not able to work on polygons that have more than 4 sides in them.
So this option allows you to restrict the polygon shape if your other program requires it.
When you have it set to n-gons, mesh output will look like this:
Here's a close up of one of the n-gons, a 6-sided polygon in this case (I have labeled the 6 different edges):
If your program cannot process n-gons, then you can choose "Quad & Triangles" - this will only create polygons with a maximum of 4 sides in them. 4-sided polygons (Quads) will be used where possible, and otherwise if a quad did not naturally occur in a spot, triangles will be used instead. Here is an example:
You can see that there are some 4-sided polygons on the internal portions, but areas like that 6-sided n-gon are now broken down into triangles instead.
Finally some programs may not even deal with 4-sided polygons, so there is an option to subdivide everything into only triangles:
As you can see from these examples, the cleanest wireframe comes from using the n-gon output, so that is generally preferred if your program can handle it. But support varies quite a bit between different applications, some programs may not allow them at all, and some may allow them but have difficulty processing more complex shapes. In those cases you will have to switch to one of the other methods.
The Quads & Triangles option keeps the wireframe cleaner than going to triangles only so usually you would use that option if you can't use n-gons.
re: question #2 - there isn't really any difference at all between these methods for rendering speed, your renderer will automatically break n-gons into triangles and internal to the renderer everything is processed as triangles.
I hope this helps explain it, please let me know if you have any other questions about it.
- Michael
