POV-Ray : Newsgroups : povray.bugreports : Intersection causes quadric to disappear : Re: Intersection causes quadric to disappear Server Time
23 Oct 2021 04:43:37 EDT (-0400)
  Re: Intersection causes quadric to disappear  
From: Le Forgeron
Date: 1 Aug 2015 08:58:27
Message: <55bcc273$1@news.povray.org>
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Le 31/07/2015 19:31, clipka a écrit :
> Am 29.07.2015 um 22:22 schrieb Le_Forgeron:
> 
>> I have it... you of course had to choose the sole kind of quadric
>> that get "optimized" bounding box in 3.7 : paraboloid. (the 3
>> axes are impacted)
> 
> ...
> 
>> The object has been translated to the origin, the 3.6 version
>> only reduced the "diameter" of the paraboloid. 3.7 is more
>> ambitious... and fails with a bounding box that has a null
>> dimension.
>> 
>> When used alone, the paraboloid bounding box is ok in 3.7
>> (because the evaluation of radius is above critical length, the
>> bounding box is reset to infinity, so tracing is fine.
>> 
>> But used in an intersection, the null bounding box is kept, due
>> to the other objects bounding box being smaller than infinity,
>> and nothing is traced.
> 
> Not sure I understand exactly what's happening there, but if you
> do, that's fine with me :). Are you already working on a fix?
> 

Yes, I'm working on a fix... and understanding the various
transformations of the equation to get a translation and adjusted
coefficients.

Not as obvious as it might seems. Previously I was asserting the
translation was in the wrong direction, but "not always". Seems there
is a few sign errors deep in some branches of code for that translation.

I have some testing scenes (rather kind of animation) with many
quadrics (nobody uses "coefficients translated quadrics", and that
what I need to use to trigger the bug). Once I'm happy with the
solution, I will post it (here and in flyspray)
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