Am 30.09.2017 um 21:10 schrieb Bald Eagle:
> 
> Aaaannd....
> my initial instinct seems to be right.
> 
> Commenting out that equation for a sphere ... gets rid of the sphere.
> 
> No idea why they have that in there - r isn't redefined in any of the other
> sections.
> 
>      #else
>           #declare r2 = max (abs(r2), abs(Y));
>           //#declare r = sqrt(X*X + Y*Y + Z*Z);  <<< comment out
> 
>  #end
> 
> I'd say if someone can recompile their source code with that one line edited
> out, and see if the isosurface for that function works fine without it, then
> 
> "It's a bug".

No, I don't think so.

My guess is that it was added deliberately, but that the person who
added it wasn't aware of all the different spirals that can be created
by the function, and therefore only regarded one special case.

Look again at this spiral:

http://www.econym.demon.co.uk/isotut/std007.jpg

Now imagine this with a circular (rather than diamond-shaped) cross section.

In that case, the sphere would seem to serve as a neat inner end for the
spiral.


I'd say, "It /is/ not a bug - it /has/ a bug." It probably needs to be
modified to fit different cross sections, and it should be suppressed
for non-equidistant spirals because for those the "natural" behaviour at
the center is for the cross-section to approach zero size.

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