[fluxus] sphere triangles

[dave]

this is very akward isn't it. I think we possibly need indexed polyprims
after all. I think what's going on in this case is that there is a
rounding error causing the edge points to be not quite equal, throwing
your hashing off. try adding a small tolerance in your key matching?

the nurbs primitive would be easer for this sort of thing, but
ironically you'd still get the tearing along the seams.

On Mon, 2006-02-20 at 21:55 -0800, Alex wrote:
> I've been doing deformations of the sphere and one thing that i've
> found that is annoying is that (i'm pretty sure) there is an arc on
> the sphere where vertices of the triangles don't match up [i assume
> the first and last triangles computed at each level in y].
> 
> My explanation isn't very good, so see this example:
> 
> (define ob (build-sphere 10 10))
> (grab ob)
> (define deform
>   (let ((pt 0)
>         (myhash (make-vector (inexact->exact (pdata-size))))
>         )
>     (lambda (n)
>       (set! pt (hash-ref myhash (pdata-get "p" n)))
>       (if (not pt)
>         (begin
>           (set! pt (vmul (pdata-get "p" n) (+ 0.7 (* (flxrnd) 0.3))))
>           (hash-set! myhash (pdata-get "p" n) pt)
>           )
>         )
>       (pdata-set "p" n pt)
>       (if (> n 0)
>         (deform (1- n))
>         )
>       )
>     )
>   )
> 
> (deform (pdata-size))
> (ungrab)
> 
> You can see that the sphere is no longer "solid".  I figure this could
> probably be fixed by doing a check when computing the sphere, storing
> the first vertices computed and comparing them to the last ones [if i
> am correct], then setting the two to be equal.  while i could do this
> myself it would take me a while to figure out what exactly is
> happening, it seems like it would be a really quick fix for someone
> who knows the code really well.
> 
> -Alex
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