Hello,
this e-mail is addressed to anyone, who belongs to the POVRAY-TEAM!
First of all, I would like to express my deep respect to this guys,
who wrote their famous and powerful POVRAY-program. I have never tried
any other raytracing-program, but I use POVRAY mainly to create
animations for some years now. I inspected a part of the source-code of
POVRAY 3.1g for WINDOWS95, which belongs to the "smooth_triangle"
objects.

There I found a BUG, because the normal vectors of the smooth_triangle
objects are not treated correctly during transformations which changes
the aspect ratios. Therefore this bug won't occur very often, but it
can be quite annoying in special situations. I wrote a scenefile,
which demonstrates this behaviour, and attached it to this e-mail
together with a suggestion for a source code patch. The last
attachment will only be included in the posting to 'povray.programming'.
To conclude, the BUG will

NOT    occur in TRANSLATE-transformations,
NOT    occur in ROTATE-transformations,
NOT    occur in SCALE-transformations with equal scale factors,
ALWAYS occur in SCALE-transformations with different scale factors,
ALWAYS occur in shear transformations and so
MIGHT  occur in general transformations.

The reason for this lies in the wrong treatment of the normal vectors
at the three edges of the smooth_triangle object. They are
NOT transformed in the special scale transformation subroutine and
WRONGLY transformed like points in the general transformation subroutine.
In the scene file you can see this BUG, if you are playing with the
flags "Triangle" and "Scaled". A "sphere {0,1}" object is compared to
a sphere, buildt completely from smooth_triangles. If they are scaled
You can see the difference.
Note, that I first believed to see another bug if the "Nu" and "Nv"
values, which compute the number of smooth_triangles in each of the
earth coordinates are too low. The construction will look edged, if
I use normal triangles, which is clearly quite normal. But the construction
will look really damaged, if I use smooth_triangles. And this occurs
at the parts of the sphere, whose normal vectors are perpendicular to the
camera ray. But I came to the conclusion, that this is a
general lack in objects, which have other RAW normal vectors than the
pure geometry would produce. At the damaged parts of the scene, the rays
are reflected through the surface and this cannot be catched like in the
case of disturbed normal vectors in the REFLECTION subroutine.
Maybe You find a way to solve this problem, but one can still live with it,
if the number of triangles in the problematic regions are increased.

With the best wishes for Your team and the development of POVRAY,
Michael Rose.

P.S.: The code of POVRAY is written in C, but the object orientated
      formulation seems to be adopted from C++ (could be wrong :-)).
      Why don't You change to C++? I don't think this would be a
      speed problem, if You avoid some critical copy constructions.
      Or do You think the language is still to buggy or to incompatible
      on different platforms?
      [Probably the amount of work to convert the program is also too big]

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Attachments:
Download 'test.pov.txt' (3 KB) Download 'us-ascii' (29 KB)

Hi Michael!

I fear this is the wrong group to report a bug. There's a group called
povray.bugreports that suits your needs. It would also be nice if you
wouldn't attach the files to your post because real newsreaders
interpret them as binary which is very annoying for their users.
If you want to make a proper bug report you should consider to use the
way described in the manuals because the povray team doesn`t guarantee
that they have a look into these group (although some individual have
been seen here). :-)

It's good if you find a bug and report is really welcomed. If you think
this post of mine is rude so please excuse me and write it off to my bad
english.

All the Best,

Marc

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On Mon, 25 Oct 1999 21:17:24 +0200, Marc Schimmler wrote:
>Hi Michael!
>
>I fear this is the wrong group to report a bug. There's a group called
>povray.bugreports that suits your needs. It would also be nice if you
>wouldn't attach the files to your post because real newsreaders
>interpret them as binary which is very annoying for their users.
>If you want to make a proper bug report you should consider to use the
>way described in the manuals because the povray team doesn`t guarantee
>that they have a look into these group (although some individual have
>been seen here). :-)

.bugreports is a fairly good way to make bug reports these days, 
especially now that it's moderated.  But please, please post a diff
of your changes instead of just posting the whole file.  Makes it a
little easier to see what you're trying to show.  Also, as Marc said,
don't post attachments if you can avoid it - paste the actual code
into the message if you can.  If not, post it in a binaries group 
and tell us where to find it in the bug report message.

Post a reply to this message

On 25 Oct 1999 15:33:25 -0400, par### [at] fwicom (Ron Parker) wrote:

>.bugreports is a fairly good way to make bug reports these days, 
>especially now that it's moderated.

  Hi, Ron and Marc. I did receive the bugreport from Michael Rose, first
posted to p.b. but I thought it best to follow a standard of first posting
in .general. At the time, it didn't occur to me to ask Michael to post only
the diff relevant to his bugfix. That's a good idea.

  Here's a copy of my post to Michael:

>  Hello, Michael. Your comments are greatly appreciated by the
>POV-Team members.
>
>  Thank you for taking the time to investigate this apparent bug in
>the POV-Ray source code. I have a request to make of you. Our normal
>procedure for bug checking and verification is to post first in the
>news server, specifically the povray.general group. Can you also post
>the demo scene file in the body of your message in that group but make
>a reference to and post your proposed source code bugfix in the
>povray.programming group?
>
>  I realize that you have spent time and effort researching this bug
>but our normal way of doing things is to post the problem and possible
>solution for all to see before the POV-Team actually designates it as
>a verifiable bug.
>
>  Thank you much for your understanding in this matter and if you have
>any questions about this POV-Team policy concerning bug reporting
>please e-mail me at:

-- 
Alan - ako### [at] povrayorg - a k o n g <at> p o v r a y <dot> o r g
http://www.povray.org - Home of the Persistence of Vision Ray Tracer

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Alan Kong wrote:
> 
> On 25 Oct 1999 15:33:25 -0400, par### [at] fwicom (Ron Parker) wrote:
> 
> >.bugreports is a fairly good way to make bug reports these days,
> >especially now that it's moderated.
> 
>   Hi, Ron and Marc. I did receive the bugreport from Michael Rose, first
> posted to p.b. but I thought it best to follow a standard of first posting
> in .general. At the time, it didn't occur to me to ask Michael to post only
> the diff relevant to his bugfix. That's a good idea.

Poor Michael has been bounced around quite a bit. He first posted the
bug report on c.g.r.r. and I redirected him to the Pov docs for info
on properly worded bug reports and where to send them. I see that he
followed my advice and is still seeing a little conflict with the
proper methods. Oh well some days you win - some day you lose.


Michael: Don't get too frustrated by this becuase everyone does appreciate
         your efforts and we all want a bug free version of POV-Ray to use.

-- 
Ken Tyler -  1100+ Povray, Graphics, 3D Rendering, and Raytracing Links:
http://home.pacbell.net/tylereng/index.html http://www.povray.org/links/

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Marc Schimmler <mar### [at] icauni-stuttgartde> wrote:
: I fear this is the wrong group to report a bug. There's a group called
: povray.bugreports that suits your needs.

  Actually he did just right.
  The correct way is: 1) Ask in another group (usually p.general or
p.advanced-users) if it really is a bug, and 2) if it is, post a proper
bug report to p.bugreports.

  Of course it's not a good idea to attach binaries to an article in a
non-binaries group.

-- 
main(i,_){for(_?--i,main(i+2,"FhhQHFIJD|FQTITFN]zRFHhhTBFHhhTBFysdB"[i]
):5;i&&_>1;printf("%s",_-70?_&1?"[]":" ":(_=0,"\n")),_/=2);} /*- Warp -*/

Post a reply to this message

(Sorry for the empty followup-to-line again; I destroyed my old conf. file
by accident and restored a backup, which had that setting turned on. I fixed
it again)

-- 
main(i,_){for(_?--i,main(i+2,"FhhQHFIJD|FQTITFN]zRFHhhTBFHhhTBFysdB"[i]
):5;i&&_>1;printf("%s",_-70?_&1?"[]":" ":(_=0,"\n")),_/=2);} /*- Warp -*/

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On 26 Oct 1999 04:09:59 -0400, Nieminen Juha wrote:
>Marc Schimmler <mar### [at] icauni-stuttgartde> wrote:
>: I fear this is the wrong group to report a bug. There's a group called
>: povray.bugreports that suits your needs.
>
>  Actually he did just right.
>  The correct way is: 1) Ask in another group (usually p.general or
>p.advanced-users) if it really is a bug, and 2) if it is, post a proper
>bug report to p.bugreports.

Doh!  Of course!  I thought I had seen this posting here, but I had seen
it in cgrr.  If this is the first time it's been on this server, then this
is the right place for it.  Please excuse my temporary insanity.

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