Rune wrote in message <3b1ab995@news.povray.org>...
>I wrote:
>> When looking at wireframes made with nurbs I notice that
>> there's almost always a few vital patches with three or
>> five corners. And the surface is still completely smooth.
>> Is that a special ability nurbs have or what...?
>
>This and the others are questions I've had for a long time and I would
>really appreciate if somebody could enlighten me. Do anybody know anything
>about it?
>
>Rune

When you have an odd number of corners like that, there will be one or more
patch edges terminating. At that point you will have a discontinuity and a sharp
edge. My research indicates internally, all renderers convert patches to
polygons prior to rendering (possible exception: Hash Animator claims
otherwise). Knowing this most of them make allowances for these discontinuities
and smooth out the result. PoV also converts to triangles but has no method for
automatically smoothing discontinuities like this, apparently treating each
patch as a discrete object without regard for its neighbors within a union, with
any smoothness between patches being the natural result of the continuity
between patches as modeled.

My usual workaround to your problem, is to model without regard to the sharp
edges and then export my patch objects to smooth_triangle mesh objects, which
usually solves my 'smoothing' problems. I usually do this from sPatch, exporting
to .dxf and then several other conversion/processing steps depending on whether
I'm going to bone it for posing (Anim8or) and/or apply UV mapping (UVMapper)
etc.

Since you prefer to hand code, I suggest you look into the capabilities of Chris
Colefax's PCM macros and Warp's mesh compressor. They both support bicubic
patches as well as triangles. You could create your models with all the
complexity you wanted, and animate them the way you wanted, without concern for
smoothness (or lack thereof) and then shell out to the compressor between
frames.

Of course it won't be quite as simple as I've made it sound here, but it is
certainly do-able.

Hope that helps.

----------------------------------------
Batronyx ^"^
bat### [at] cadronhsacom
http://www.batronyx.com
Bhuddist monk to hotdog vendor:
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