"Mike Williams" <nos### [at] econymdemoncouk> wrote in message
news:aDeV$GAGakgCFwx2@econym.demon.co.uk...

[...snip...]

> // tetrahedron function
> // a is 'radius' of outcube
> // b is 'blob' strength
> #declare fn_blobbed_tetra = function(x, y, z, a, b) {
>         - ( x+y+z -a)
>         * (-x+y-z -a)
>         * ( x-y-z -a)
>         * (-x-y+z -a)
>         + b
> }

Interesting approach.  If I calculate correctly we need
0 <= b <= a^4 and now the object (without crack and agate)
is contained by box {-c,c} where c = sqrt(a*a - sqrt(b)).
Note that this approaches 0 (i.e. a single point, the
origin) as b approaches a^4.

I have not yet used isosurfaces but I was surprized that
you set it up so that the function is negative inside
the surface and positive outside the surface.  When
I tried your code with the negative of your function I
got the bounding box, not your surface.  That really
surprised me.  Is that a bug or am I missing something?
--
Jim Buddenhagen

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