Thanks again for your advice. Of course if the object is simple enough,
it is easy to deduce what's the normal from the knowledge of its position.
However I wanted to deal with more complicated objects like animated blobs
or other  primitives with a normal perturbed by a wild normal noise.

I could as well construct all my object as big mesh and calculate the color
of each triangle using a little C program but it's a bit painfull, and
sillly since povray spends its time (I guess) to acces normal vector in
order to render the pictures.

So I am trying to install Povman now. I managed to install megapov --- easy!
But I don't manage to install Povman on the top, it isn't well documented
and I am not a linux guru... any help?

Thanks,
Yann



"Christopher James Huff" <cja### [at] earthlinknet> wrote in message
news:cja### [at] netplexaussieorg...
> In article <3fa06504$1@news.povray.org>,
>  "Yann" <[antispam]rollin***@mit..edu))> wrote:
>
> > I want to use a pattern defined by a function. I know that it is
possible to
> > access the coordinates from inside the function, however is it possible
to
> > access the normal vector to the object ?
>
> Very unfortunately, this is not possible. Of course, if you know the
> object the pattern is being applied to, you can compute the normal given
> the point being evaluated, but this is only practical in very limited
> and simple cases.
>
> -- 
> Christopher James Huff <cja### [at] earthlinknet>
> http://home.earthlink.net/~cjameshuff/
> POV-Ray TAG: chr### [at] tagpovrayorg
> http://tag.povray.org/

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