"Bald Eagle" <cre### [at] netscapenet> wrote:

Alright kids,
I puzzled out the basic conversion from cpp to SDL, and then had to envision how
POV-Ray computes the isosurface (notice the whole internal function just returns
a single scalar value) and emulate that.

First off, this following bit seems to be related to the culprit:

> I'd say that the very last r defines sqrt of x-squared + y-squared + z-squared -
> which is the implicit / closed form of the surface of a sphere.
> So, I'd start looking there....

If you take a look over at
http://www.econym.demon.co.uk/isotut/builtin1.htm
at
http://www.econym.demon.co.uk/isotut/std007.jpg
you'll see that Mike Williams' render of this function shows the same odd sphere
at the center.

ALSO notice that that last parameter is what is used to determine the
cross-sectional shape of the spiral.

> Maybe rewrite it out in SDL so it's easier to play with.

I did, and I will post the results in p.b.i to show the difference between the
round cross section (0) and the square (1)

Other things to notice to get a basic understanding about how the isosurface
gets plotted, is that the code loops/steps through "all" the points in the box
and evaluates the isosurface function.  If that value is zero (or less than
'epsilon' (STEP) ) then it applies the designated texture, lighting, etc (plots
a sphere)

The bigger the box, the more points have to be looped through to run through the
isosurface formula, and the longer the loop takes.
The more complicated / slower the formula is to evaluate, the longer the loop
takes.

That's the basis of why isosurfaces are so slow to evaluate.

If I have more time, I'll see if I can refine it a bit, and maybe do a Paul
Nylander meshification version, and perhaps a wireframe version or two.

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