Does the convexity argument need to be exact (i.e. exact maximum number
front/back faces a ray might intersect) or just large enough? I've
a file that I can't get to display right in preview mode (it comes out
of inside-out), that looks fine when rendered. I'm guess I have the
convexity argument or have supplied it in the wrong place.
The file it kind of long but it is mostly just a profile that gets
in for a rotational extrusion, in form it is like this: