POV-Ray : Newsgroups : povray.bugreports : Intersection causes quadric to disappear : Re: Intersection causes quadric to disappear Server Time
23 Oct 2021 03:19:50 EDT (-0400)
  Re: Intersection causes quadric to disappear  
From: Le Forgeron
Date: 27 Jul 2015 14:33:44
Message: <55b67988$1@news.povray.org>
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Le 27/07/2015 20:10, Le_Forgeron a écrit :
> Le 26/07/2015 18:30, Cousin Ricky a écrit :
>> On 07/25/2015 10:25 AM, Cousin Ricky wrote:
>>> The following paraboloid renders correctly:
>>> 
>>> [snip]
>>> 
>>> the object disappears completely in POV-Ray 3.7 and 3.7.1.  In 
>>> POV-Ray 3.6.1, it renders as expected.
>>> 
>>> POV-Ray 3.7.0.unofficial POV-Ray 3.7.1-alpha.8150025.unofficial
>>>  openSUSE 13.2 GNU/Linux
> 
> 
> Confirmed on Ubuntu 15.04 too.
> 

Looking at the bounding box, with -0.999*y :


Min : -10000000000.0000,-10000000000.0000,-10000000000.0000
Max : 10000000000.0000,10000000000.0000,10000000000.0000

whereas with -y :

Min : 1.2500,0.0000,0.0000
Max : 1.2500,0.0000,0.0000

Compared to 3.6.1 with -y :

Min : 0.2500,0.0000,-1.0000
Max : 2.2500,2.0000,1.0000

and 3.6.1 with -y*0.999 :

Min : 0.2500,0.0010,-1.0000
Max : 2.2500,2.0000,1.0000


Raw conclusion so far: the bounding box computation in 3.7 get
something wrong. It might be in intersection/csg or cylinder. (as
quadric is kind of infinite, it is unlikely to be involved... but a
look does not cost that much either).
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