It appears that the superpatch already has a very good implementation of
'direct' rendering of bicubic patches, so I guess my mission (should I chose
to accept it), is to come up with a way to convert a NURBS surface into a
bezier representation.  :)

I think I have some references that cover this.  I would base the syntax for
NURBS on how it's laid out in the renderman interface specification, since
that seems to be a comprehensive approach that includes trimmed surfaces.

I also have some papers that discuss how it's possible to speed up bezier
clipping by about 20% by including some other methods.  I'll see if I can get
anywhere with that too.

I'll be more than happy to dump this project on someone once I fail
miserably. :)

-Mike

Thomas Baier wrote:

> Hi,
>
> would it be possible raytrace NURBS direct without tesslating to
> faces?
> I think i have seen some hints for a ray NURBS intersection in
> comp.graphics algorithms.
> If it possible rendering NURBS would be image size independent.
>
> I have some code to convert NURBS (Rhino) to triangles with dynamic
> subdivision. If you are interessted please mail me: thb### [at] ibmnet
>
> But the key feature would be "trimmed NURBS". It means that a NURBS
> curve cuts a hole into the NURBS surface.
> The NURBS curve is usally given in uv coordinates.
>
> If there is a NURBS ray hit test, it would be possible to test for a
> trimming curve.
> Usally all CSG operations with NURBS are done with trimmed NURBS.
>
> >A long time ago someone mentioned that they had written a preliminary
> >patch for NURBS.  I think it was Nathan but the messages I have don't
> >seem to go back far enough.
> >
> >Anyway, the person offered to share it with anyone interested.  If I can
> >find the time, I plan on writing a patch to do direct rendering of
> >bicubic patches, and it seems it should be possible to include NURBS.  I
> >could use any help I could get, so it would be great if whoever has that
> >code could forward it to me.  :)
> >
> >I hear that the direct approach causes rendering artifacts, but I'd like
> >to try it just the same.
> >
> >-Mike
>
> -tb

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