In article <397CEDA2.548E2CA1@tiac.net>, Alex Vandiver 
<van### [at] tiacnet> wrote:

> Heya -- two questions have reared their ugly heads as I mess around with
> MegaPOV.  Firstly, there seems to be some portability problems with
> respect to isosurfaces -- namely division by zero.  Rendering the
> following scene produces two completely different results under Linux
> and Windows.  Under the former, the result is pure black.  The latter
> spits out a while circle...
...snip...
> I would hesitantly put forth that the all-black version is the "more
> correct" version, as the isosurface evaluates to +infinity at every
> point -- and +infinity is never equal to 0.5 (the threshold) so there
> should be no "surface" at all.

It isn't a very serious problem(you shouldn't expect a surface there 
anyway), and to catch these cases might take too much overhead...I don't 
know the isosurface code very well though. It might be possible to weed 
out functions resulting in these values.
And are you sure about it evaluating to +infinity? I thought it was 
NaN...


> The other, unrelated, quirk is that of nested macro definitions.  Why
> does MegaPOV specifically complain about them, and refuse to parse
> them?  Is there a workaround?  Because otherwise Chris Colefax's
> wonderful spline macro file is useless in MegaPOV..

It could have something to do with the macro speed enhancements...
I thought nested definitions weren't allowed in the official version 
either, but I couldn't find any mention of this restriction in the 
documentation...
Does that spline include require nested macro definitions? I can't think 
of a good reason to use them...I have never used that include, but maybe 
I will download it and try to get it to work.
Couldn't you just use one of the spline patches included in MegaPOV? Or 
are there specific features in Colfax's spline macros which you need?

-- 
Christopher James Huff - Personal e-mail: chr### [at] maccom
TAG(Technical Assistance Group) e-mail: chr### [at] tagpovrayorg
Personal Web page: http://homepage.mac.com/chrishuff/
TAG Web page: http://tag.povray.org/

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