Warp <war### [at] tagpovrayorg> wrote:
>   I don't have the motivation to study exactly which mathematical function
> POV-Ray is using for its splines nor calculating its derivatives.

You do have the motivation throwing smart statements about, but you don't have
any motivation to really investigate the issues you are talking about.

Wise guy.

You don't have to calculate any particular spline's derivative to find out what
the problem is. You just have to look at the macros and SDL statements we're
discussing about, to find out that you're overlooking a much more serious
obstacle.


>   I don't see the problem you are having. A derivative function is nothing
> more than a function. In the exact same way as you can create a macro which
> returns values of a function, you can create another macro which returns
> values of its derivative function. Because it's just another function.

BTW, *I* am not having *any* problem. I'm just describing why a problem the OP
has is inevitable.

Anyway, we are talking about macros. SDL statements, you know?

So how do you get the function value of an arbitrary spline out of POV-Ray?

Rrrright - you use an interface built into the SDL, which lets you use the
spline as a function.

Fine. Now how do you get the derivative value of an arbitrary spline out of
POV-Ray?

Um... yes?

Mind you: The spline type and coefficients are buried in the bowels of POV-Ray.
If you want to get at them from SDL, you need an interface to do that. No
interface - no access to the data. No access to the data - no way to insert the
data into your derivative formula (let alone decide on which formula to use,
because we don't even know the type of the spline).


Now, your turn. Stop blurping and show what you *really* know and understand
about the OP's question.

And no excuses: If you're too lazy to really investigate a certain matter,
better hold your breath about it right from the start.

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