"LibraryMan" <mrm### [at] attnet> wrote in message
news:web.3ed4d89fa160507a738e706a0@news.povray.org...
>
> Well, if it had been specified from the outset that the example spline
> identifier was to be used in an animation, that may have helped clarify
> matters a bit.

That's only one way to think of it though, was what I was saying. The first
example is using #while loop, second is animation, third is macro. So
splines are very versatile, many ways to use it.

> I suppose I *am* being dense about what the -0.25 and 1.25 values have to
do
> with control points of a cubic_spline; I mean, the 3-D vectors are already
> specified, and the spline type could be changed to something else and
> POVRay should know what to do in whichever case...

Having reread that section of the doc myself I can see how it could confuse
people. Lots of things can, in fact. Not always easy to understand until
applying what you learn and practicing, to truly know it.

The Note paragraph is a good thing to see there in section 6.1.9 since that
sums up the reasons for the "t" value (-0.25 to 1.25, for example) and how
it relates to spline type or out of range values for "t". You might ask what
would be out of range... If you had a while loop carrying the t value
from -10 to +10 and your spline contains just 0 to 1 then obviously it will
still only use the 0 through 1 points (vectors). Not expanding it to -10 to
+10 but instead awaiting the valid numbers to be introduced before getting a
change in the spline. It repeats point 0 until reached, doing same for 1
after that is surpassed.

That said, it sure might be a nice feature addition if that could be
switched on and off. That way invalid points could be skipped and not
repeated uselessly if unneeded.

Bob H.

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