This is the wrong group for this question.  This question seems to fit into
the povray.advanced-users group rather well.  Cross-posting and follow-up
set to povray.advanced-users .

	Thorsten, POV-Team

wwyang wrote:
> > Le Forgeron <jgr### [at] freefr> wrote:
>> >> you cannot use macro (#if is macro) inside function the way you want
>> >> to do it (different namespace: x in function space is not the same
>> >> as the x in macro/SDL space). See 2.2.1.6.2 in
>> >>
>> >> http://www.povray.org/documentation/view/3.6.1/231/
>> >>
>> >> If you want to limit to x>0, use the contained_by { box {
>> >> <0,-1,-1>,<1,1,1> } in the isosurface object.
>> >>
>> >>
>> >> --
>> >> The superior man understands what is right;
>> >> the inferior man understands what will sell.
>> >> -- Confucius
> >
> >
> >
> > Forgeron,
> > Thanks for your advice. Now i got the difference of function space and SDL
> > space. But i still have problem in implementing function in SDL for my
> > isosurface.
> >
> > In my scene, the isosurface is defined by implicit polynomials in terms of
> > b-spline basis. And the function evaluation needs the branches that depend
> > on coordinates of point in 3D scene space, e.g. the parameters passed to
> > the function. I've read many examples for definition of isosurface
> > functions in SDL, found that they all only the combination of basic
> > operations(e.g. +,-,*,/,power etc) but without the logic operations(Aand,
> > Or..).
> >
> > So can i implement logic operations in function that will take affect in
> > rendering time but not parsing time? If can do it in function space, how
> > should i do?
> >
> >
> >

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> > > So can i implement logic operations in function that will take affect
in
> > > rendering time but not parsing time? If can do it in function space,
how
> > > should i do?

What you're looking for is the select() function. (Check the documentation
for details.)

 - Slime
 [ http://www.slimeland.com/ ]

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