The Persistence of Vision Raytracer (POV-Ray).

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Attached to Project: POV-Ray
Opened by Benedikt Adelmann - 2013-03-12
Last edited by Christoph Lipka - 2013-03-12

FS#276 - SDL Access to Spline Derivatives

I would like to suggest an additional feature regarding splines. POV-Ray’s spline objects (spline {}) are very useful to create animation paths as a function of time from reference points; however, in many cases you do not only need a position to place an object correctly, but also its velocity etc., e.g. if you are animating a car moving along a spline you do not only need to know where the car is at a given clock value but also in which direction it is going. If you want to rotate the wheels correctly you even need to know how this direction is currently changing.

In a nutshell, if you are using splines to create an animation path, you might not only need the spline value itself, but also the value of its first and second derivative. So I suggest adding an SDL capability to access these values like it is possible to access the spline value for a given parameter.

I do not think it would be too difficult to add a feature like this as far as the backend is concerned, since for computing a (cubic) spline you need the first and second derivatives anyway. (They are probably not being stored separately, but a polynomial is not that hard to differentiate.)

Indeed I do not know how an SDL language construct for it should look like (i.e. whether to use ' and ‘’ like in mathematics or a second spline function parameter).

Closed by  Christoph Lipka
Tuesday, 12 March 2013, 18:18 GMT
Reason for closing:  Duplicate report
Additional comments about closing:  

duplicate of FS#248

Benedikt Adelmann commented on Tuesday, 12 March 2013, 16:23 GMT

Oh, I just see this is similar to #248.


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