POV-Ray : Newsgroups : povray.documentation.inbuilt : Lathe and Prism updates requested by Christoph. : Re: Lathe and Prism updates requested by Christoph. Server Time
20 May 2022 16:36:00 EDT (-0400)
  Re: Lathe and Prism updates requested by Christoph.  
From: clipka
Date: 3 Jun 2016 14:24:56
Message: <5751cb78$1@news.povray.org>
Am 27.05.2016 um 02:11 schrieb William F Pokorny:

> POV-Ray today follows the above clockwise vs counter-clockwise 2D
> conventions for determining inside vs outside everywhere except for the
> bezier spline in the prism, where, the inside and outside conventions
> are reversed for the prism sides. Further, all prism ends point outward
> no matter the loop order.

It might be worth actually testing how the clockwise/counter-clockwise
thing works out depending on the handedness of the coordinate system,
rather than just speculating or relying on unconfirmed assumptions.


> So, I guess the question is do we:
> 
> - add some or all the text above about 2d clockwise / counter-clockwise
> conventions?
> 
> - add some figures explicitly showing the two example point lists or
> others showing what would be clockwise and counter-clockwise point lists
> with respect to inside/outside determination?
> 
> - change to more generic wording like 'orientation' and 'reverse
> orientation' without any suggestions about normal, normal directions but
> noting they flip.
> 
> - simply note that point list order matters to surface normal
> determination in lathes and prisms and leave it at that? Starting to
> feel like I have wandered off into the weeds... :-)
> 
> Thoughts?

- Keep the "clockwise" and "counter-clockwise" wording, and add a note
saying that these apply to POV-Ray's left-handed coordinate system,
whereas with a right-handed coordinate system the direction is reverse?

(Of course such a note should only be added if tests show that it is
indeed the case ;))


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