William F Pokorny <ano### [at] anonymousorg> wrote:

> The prism and lathe bezier spline can represent curved portions,
> discontinuities in slope between curved portions and linear segments in
> a single spline.

Always back to Bezier.   I will have to do some more thinking on this and see
what I come up with.

> My belief is your particular proposal for supporting different stand
> alone spline segment types to represent an overall prism shape won't
> fly. In the POV-Ray code there would be too much context switching and
> fuzziness as to what segments together constitute an enclosed region /
> loop for it to be practical.

I'm sure there are certain things that are probably too complex to do, esp if
they're hand-coded SDL rather than prism/spline definitions guided and
restricted to valid configurations by a GUI, but I have the gut feeling that
exploration in this area would yield dividends.
Perhaps the result would not be exactly what I proposed, but that's never really
the case, is it?
I just have a sense that with all of the modelers out there, and the papers I've
seen published on somewhat esoteric work, that maybe a method / code must exist
already and it's just a matter of discovering and implementing it.


Now, having said that, Leroy just chimed in right after you, and so I gave his
site a quick look.  One of the things I noticed, given some work that I still
need to finish on the first part, is the pulley file.   I think that if
something was put together to create a pulley/belt system - that would address
quite a lot of what I was after.
And it would serve double duty actually describing a pulley/belt system.
Throw in a twist to allow using 3+ sided "pulleys" and there's our linear bends.
And I have a nice little equation that allows making any N-sided shape.  I can't
recall if I've posted that or not.
(I haven't tracked down the same in 3D --- yet)

Maybe I'll have a chance to work on this soon and make some progress.

It would be interesting to also address making other specific curves with Bezier
splines - sin, parabola, spiral - etc.



> (1) I saw your suggestions for point lists and point list manipulation.
> Good ideas I think which would help with 'trace() based jig methods'
> among other things.

Yes, and just to add to that, when I was working on the vortex scene, I needed
to do something along those lines and thought that maybe I could do something
clever with functions, splines, and transform, but I got errors.  I'll have to
see if there's any vestiges of that in the scrap pile, or maybe I can just take
a crack at it again with new eyes.

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2.2.1.6.4 Declaring User-Defined Vector Functions
Right now you may only declare vector functions using one of the special
function types. Supported types are transform and spline functions. For example:

 #declare foo = function {
   transform {
     rotate <90, 0, 0>
     scale 4
   }
 }

 #declare myvector = foo(4, 3, 7);

 #declare foo2 = function {
   spline {
     linear_spline
     0.0, <0,0,0>
     0.5, <1,0,0>
     1.0, <0,0,0>
   }
 }


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