POV-Ray : Newsgroups : irtc.stills : Weird behaviour Server Time: 19 Dec 2018 14:20:51 GMT
  Weird behaviour (Message 1 to 7 of 7)  
From: John Coppens
Subject: Weird behaviour
Date: 15 Aug 2008 00:52:23
Message: <20080814215221.53031872.john@johncoppens.com>
Hello people.

I have a scene with some transparent image_maps, which cast shadows.
Works fine (after adjusting max_trace_level). But if I add a new object
to the scene, suddenly these image_maps case _white_ shadows.

The new object is complicated, but not _that_ much, so I raised max_trace
a bit more (tried up to 100), tried to play with other things, to no
avail. I've changed the order of the objects (I know, it shouldn't
matter). I also tried to add a simple sphere as extra object, but that
doesn't have any effect.

I've put up an image, which show the difference. When the new object is
added, the stained glass (including the non-transparent 'lead') suddenly
seems to become transparent for the shadow cast, but the glass still
shows as colored.

http://jcoppens.com/misc/errors.png

The right image is as it should be, the left one is with the extra object
added. The bright white border is as if the stone were given 'ambient 1',
(or more).

Can anyone suggest a cause for this? I'm not very experienced at povray,
and these is by far the most complicated scene I did...

Thanks in advance.

John


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From: St 
Subject: Re: Weird behaviour
Date: 15 Aug 2008 01:36:54
Message: <48a4ddb6@news.povray.org>
Hi John, any chance you could post larger images? It's difficult to tell 
what's going on there.

  And I think povray.binaries.images would be the right place to post them 
other than here.

      ~Steve~


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From: Mike Williams
Subject: Re: Weird behaviour
Date: 15 Aug 2008 04:54:29
Message: <FTiqm4ApoQpIFwSM@econym.demon.co.uk>
Wasn't it St. who wrote:
>Hi John, any chance you could post larger images? It's difficult to tell
>what's going on there.
>
>  And I think povray.binaries.images would be the right place to post them
>other than here.

I suspect that seeing the images probably won't help. Can you create a 
small scene file that shows the effect and post it to an appropriate 
povray. group?

-- 
Mike Williams
Gentleman of Leisure


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From: John Coppens
Subject: Re: Weird behaviour
Date: 15 Aug 2008 14:28:53
Message: <20080815112852.a771ff10.john@johncoppens.com>
On Fri, 15 Aug 2008 05:46:33 +0100
Mike Williams <nos### [at] econymdemoncouk> wrote:

> >Hi John, any chance you could post larger images? It's difficult to
> >tell what's going on there.
> >
> >  And I think povray.binaries.images would be the right place to post
> > them
> >other than here.
> 
> I suspect that seeing the images probably won't help. Can you create a 
> small scene file that shows the effect and post it to an appropriate 
> povray. group?

Hi Mike, Steve.

No, I haven't been able to find a way to simplify it. I'll post a larger
image later. The weird thing is:

The entire scene is contained in a 2 by 2 by 2 area. If I add the new
object far away (at more than 20 units), it _still_ causes the
transparency problem, so I guess I'm hitting some limit in PovRay. I went
through all the global_settings, tried extreme values, compared the
povray outputs with and without the object, no luck.

I've now tried to install the beta 3.7 version, but the binary won't run
because of a known timing problem, and I can't compile the source,
because the shared version of the boost libraries wasn't installed when I
installed _those_...

John


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From: Mike Williams
Subject: Re: Weird behaviour
Date: 15 Aug 2008 15:37:55
Message: <35LG8yBPIapIFw3i@econym.demon.co.uk>
Wasn't it John Coppens who wrote:

>The entire scene is contained in a 2 by 2 by 2 area. If I add the new
>object far away (at more than 20 units), it _still_ causes the
>transparency problem, so I guess I'm hitting some limit in PovRay. I went
>through all the global_settings, tried extreme values, compared the
>povray outputs with and without the object, no luck.

That sounds like it might be an automatic bounding slab problem of some 
sort.

Try using the -MB switch with the object present and +MB1 with the 
object absent and see if the behaviour changes.

-- 
Mike Williams
Gentleman of Leisure


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From: John Coppens
Subject: Re: Weird behaviour
Date: 15 Aug 2008 17:54:02
Message: <20080815145401.eb0a7b2a.john@johncoppens.com>
On Fri, 15 Aug 2008 16:34:39 +0100
Mike Williams <nos### [at] econymdemoncouk> wrote:

> Try using the -MB switch with the object present and +MB1 with the 
> object absent and see if the behaviour changes.
> 

Hello Mike.

Sorry for the delay - I'm multitasking, installing the boost libraries,
compiling the povray 3.7 beta (with problems), trying out ideas,
presenting the image on TC-IRTC, entering scores, reading mail, etc...

Anyway, -MB is horribly slow (I think - nothing appeared on the screen
after a minute or so, though the CPU is at 100%) with the object present.
In fact, I doubt if anything will come out of that.

I tried with the normal +MB25, but also with +MB1 and several other
values. It shouldn't matter, there are 40800 items in the scene, way over
any minimum number.

Ok. after 2'20", the first line appeared. 5'04" second line. This is
probably take too long to be of use, but I'll leave it a couple of hours
to see if the problem is solved.

Cheers,
John


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From: John Coppens
Subject: Re: Weird behaviour
Date: 15 Aug 2008 19:05:59
Message: <20080815160557.cee59ffe.john@johncoppens.com>
On Fri, 15 Aug 2008 14:54:01 -0300
John Coppens <joh### [at] johncoppenscom> wrote:

> Ok. after 2'20", the first line appeared. 5'04" second line. This is
> probably take too long to be of use, but I'll leave it a couple of hours
> to see if the problem is solved.

Well, after 50 minutes and 15 lines, I confirm that the -MB solved the
problem! I didn't have the patience to wait for another 20 hours
though ;-)

Reading up on MB and friends, I thought that the Bounding box problem
wasn't likely to be the culprit, but I thought it was more likely a
problem with the light_buffer (which is switched off with the -MB switch
automatically).

And behold, +MB25 (the default) and -UL did solve the problem too, but the
rendering was still immensely faster (2 minutes for the entire image)!

Thanks for pointing me in the right direction, Mike!

John


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