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31 Jul 2024 18:27:22 EDT (-0400)
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From: Inquisitor
Subject: Having trouble with tranparent textures and fog...
Date: 21 Jul 2009 09:35:00
Message: <web.4a65c344db4b35ab182abe670@news.povray.org>

set incorrectly.  Here are the things (I believe) have something to do with the

(1) an island in the distant background
(2) a sailboat in the foreground.
(3) the sails use a png file for the texture.  The png file has some totally
transparent areas along with some totally opaque areas.

#declare SailCloth = texture { uv_mapping pigment {
    image_map {png "SailCloth.png"
interpolate 2 map_type 0  transmit all 0 filter all 0 } } }

(4) I am using a fog effect

fog{C_SkyBottom fog_type 2 distance 1000 fog_alt 50 rotate <90, 0, 0> }

Looking through the sails at near objects (the boat say) or the sail casting
shadows on the boat appear to be correct.  However looking through the sails at
the distant background (where the fog effect comes into play) seems to nullify
the fog.  The two attached renderings show my problem.  In the circled area of
the fogged version, the left side is looking through two layers of the cloth.
This looks pretty much as I would expect it.  The right side is looking through
one layer.  I would expect it to be about the same brightness as the portion of
the beach that is un-blocked.  However, it is far brighter.  Its almost like a
polarizing filter effect on a real camera.

I hope you can point me to the error of my ways.

Thanks.


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Attachments:
Download 'fog.zip' (131 KB)

From: Roman Reiner
Subject: Re: Having trouble with tranparent textures and fog...
Date: 21 Jul 2009 10:40:00
Message: <web.4a65d2a316e4c383e16915000@news.povray.org>
You might want to look up 'hollow' in the docs.


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From: Inquisitor
Subject: Re: Having trouble with tranparent textures and fog...
Date: 21 Jul 2009 11:45:01
Message: <web.4a65e1d916e4c383182abe670@news.povray.org>
"Roman Reiner" <lim### [at] gmxde> wrote:
> You might want to look up 'hollow' in the docs.


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Attachments:
Download 'fog.jpg' (62 KB)

Preview of image 'fog.jpg'
fog.jpg


 

From: Inquisitor
Subject: Re: Having trouble with tranparent textures and fog...
Date: 21 Jul 2009 11:55:01
Message: <web.4a65e3fd16e4c383182abe670@news.povray.org>
"Roman Reiner" <lim### [at] gmxde> wrote:
> You might want to look up 'hollow' in the docs.

I read the section on hollow and was sure you were on to it.  Unfortunately, it
didn't show any improvement.  The previous image is with hollow set for the
sails.  Assuming the mountain/beach was "inside" the sails.


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From: Tim Attwood
Subject: Re: Having trouble with tranparent textures and fog...
Date: 21 Jul 2009 14:27:38
Message: <4a66089a$1@news.povray.org>
"Inquisitor" <dec### [at] sybasecom> wrote in message 
news:web.4a65e3fd16e4c383182abe670@news.povray.org...
> "Roman Reiner" <lim### [at] gmxde> wrote:
>> You might want to look up 'hollow' in the docs.
>
> I read the section on hollow and was sure you were on to it. 
> Unfortunately, it
> didn't show any improvement.  The previous image is with hollow set for 
> the
> sails.  Assuming the mountain/beach was "inside" the sails.

You might need to put your fog (media) in a container, and
remove (difference) a small area so the sails aren't inside the fog.


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From: Tim Attwood
Subject: Re: Having trouble with tranparent textures and fog...
Date: 21 Jul 2009 14:28:37
Message: <4a6608d5$1@news.povray.org>
> You might need to put your fog (media) in a container, and
> remove (difference) a small area so the sails aren't inside the fog.

Oh, and you should make sure max_trace_level is high enough.


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From: Thomas de Groot
Subject: Re: Having trouble with tranparent textures and fog...
Date: 22 Jul 2009 04:34:17
Message: <4a66cf09$1@news.povray.org>
As far as I know, this is a bug within POV-Ray. I have had this problem 
several times. Fog (not media I believe) has a problem with 
textures/image_maps containing transparent sections. Hollow does not help in 
this case. The best you can do is use media within a container instead of 
fog.

Thomas


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From: gonzo
Subject: Re: Having trouble with tranparent textures and fog...
Date: 22 Jul 2009 15:00:00
Message: <web.4a67616216e4c383a0c272b50@news.povray.org>
"Thomas de Groot" <tDOTdegroot@interDOTnlANOTHERDOTnet> wrote:
> As far as I know, this is a bug within POV-Ray. I have had this problem
> several times. Fog (not media I believe) has a problem with
> textures/image_maps containing transparent sections. Hollow does not help in
> this case. The best you can do is use media within a container instead of
> fog.
>
> Thomas

Actually, transparent (transmit) works with fog, it's filter that has the
problem.

Try removing the filter statement from your sail & see how that works.

RG


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From: Christian Froeschlin
Subject: Re: Having trouble with tranparent textures and fog...
Date: 27 Jul 2009 14:57:34
Message: <4a6df89e$1@news.povray.org>
gonzo wrote:
> "Thomas de Groot" <tDOTdegroot@interDOTnlANOTHERDOTnet> wrote:
>> As far as I know, this is a bug within POV-Ray. 

> Actually, transparent (transmit) works with fog, it's filter that has the
> problem.

If this bug is still present in 3.7, it would be useful
to create a problem report at http://bugs.povray.org/, as
far as I can see no fog-related issue is listed there.


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From: Thomas de Groot
Subject: Re: Having trouble with tranparent textures and fog...
Date: 28 Jul 2009 08:16:06
Message: <4a6eec06@news.povray.org>
"Christian Froeschlin" <chr### [at] chrfrde> schreef in bericht 
news:4a6df89e$1@news.povray.org...
> If this bug is still present in 3.7, it would be useful
> to create a problem report at http://bugs.povray.org/, as
> far as I can see no fog-related issue is listed there.

Good idea. As soon as I have a little time, I shall re-visit an old scene of 
mine where the problem was apparent, with transmit in the texture by the 
way, not filter.

Thomas


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