

"Kenneth" <kdw### [at] gmailcom> wrote:
> "Bald Eagle" <cre### [at] netscapenet> wrote:
>
> > Use Mike Williams' "shell" trick for isosurfaces to give an infinitely
> > thin line a visible thickness
>
>
> Do you have a link to this trick, or a short explanation? (keeping my fingers
> crossed)
I just took a look at the Mike Williams 'isosurface tutorial' that you packaged
and sent to me as a .pdf file some years ago. Is the technique you refer to here
the same as Mike's 'thickening' trick using 2 parallel surfaces (page 18 of
149)? Or is it something different?
Thickening
If we have a function F(x,y,z) we can turn it into two parallel surfaces by
using abs(F(x,y,z))C where C is some small value. The original function should
be one that works with zero threshold. The two resulting surfaces are what you
would get by rendering the original function with threshold +C and C, but
combined into a single image. The space between the two surfaces becomes the
"inside" of the object. In this way we can construct things like glasses and
cups that have walls of nonzero thickness.
[example:]
#declare F = function {y + f_noise3d (x*2, 0, z*2)}
isosurface {
function {abs (F(x, y, z))0.1}
......
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