On 11/05/2017 07:00 AM, Warren wrote:
> Hi,
> I have the following scene :
> 
>...
> 
> After a quick research, I found this post:
> http://news.povray.org/povray.beta-test/thread/%3C3cd1c5ac%40news.povray.org%3E/
> 
> I have a hard time understanding why this is not a bug (the explanation of "
> Thorsten Froehlich" especially); my camera isn't 'in' the conic_sweep object.
> 
> So , why must I add a small offset in the camera setting to get the expected
> result instead of dark slopes for the pyramid ?
> 
> 

As shown too with an equivalent 'orthographic' user_defined camera in 
the attached version of your scene, the prism issue both in the post you 
referenced, and in your case, has really to do with there being no 
ray/angle offset (x or z) with respect to the sweep sides. Where there 
is no offset the sweep portion of the prism disappears - no roots are 
found - and I do think this a bug(1).

In my experience, orthographic camera rays do start at the 
location/direction plane specified and from that plane in the direction 
given and this is confirmed by the user_defined equivalent camera. I'll 
wait a while to see if others chime in with a clarification to my 
understanding. Otherwise, I'll open up a github issue for this.

Notes to self: 1) Test runs done with Early July 2017 3.8 code. Thinking 
there was a somewhat recent code update related to prism normals by 
Christoph... If so, should verify bug against that update. 2) Wonder if 
some ray/surface orthogonal filtering between the caps is getting in the 
way...

Aside: Your prism is actually inside-out due the clockwise point order. 
I've updated your scene to show both orders with an added 
interior_texture. Oh, and I added the open keyword to eliminate the 
prism caps as these look to me to render correctly with no offset.

Bill P.

(1) - If not, then prism behavior not documented.

Post a reply to this message

Attachments:
Download 'warrennov042017prismissue.pov.txt' (3 KB)