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From: Gilles Tran
Subject: Possible pair of bugs affecting transparency.
Date: 22 Sep 2002 00:18:03
Message: <3d8d447b@news.povray.org>
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The code below shows 2 potential bugs affecting transparency.
These have been observed on 3.1 (using material_map) and 3.5, at least on a
Windows version, running XP.
The first bug makes the transparent part visible. It's apparently linked
with fog turbulence.
The second bug makes the normals behind look weird when the transparency
texture is scaled very unevenly (pure 100% transparent texture is not
affected).
Can other people confirm that these problems exist and that they are really
bugs (they were reported by a Moray/POV-Ray 3.1 user)?
camera {location -z*35}
light_source {(x+y-z)*50 rgb 1}
fog {
fog_type 1
distance 30
color rgb 1
// turbulence makes the transparent part visible
turbulence 0.8
}
sphere{0,8 pigment{rgb x+y} normal{bumps 1}}
union{
triangle{-x,-x+y,x+y}
triangle{-x,x,x+y}
hollow
texture{
pigment_pattern{
bozo color_map{[0.4 rgb 1][0.4 rgb 0]}
}
texture_map{
[0.5 pigment{rgb x} finish{ambient 0 diffuse 1}]
[0.5 pigment{rgbt 1} finish{ambient 0 diffuse 0}]
}
// uneven scaling makes the normals behind look weird
scale <1,1,0.001>
}
scale 2
translate -z*20
}
--
**********************
http://www.oyonale.com
**********************
- Graphic experiments
- POV-Ray and Poser computer images
- Posters
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From: Mick Hazelgrove
Subject: Re: Possible pair of bugs affecting transparency.
Date: 22 Sep 2002 03:54:33
Message: <3d8d7739@news.povray.org>
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I can confirm both bugs. Windows XP & pov3.5
Mick
"Gilles Tran" <git### [at] wanadoo fr> wrote in message
news:3d8d447b@news.povray.org...
> The code below shows 2 potential bugs affecting transparency.
> These have been observed on 3.1 (using material_map) and 3.5, at least on
a
> Windows version, running XP.
> The first bug makes the transparent part visible. It's apparently linked
> with fog turbulence.
> The second bug makes the normals behind look weird when the transparency
> texture is scaled very unevenly (pure 100% transparent texture is not
> affected).
>
> Can other people confirm that these problems exist and that they are
really
> bugs (they were reported by a Moray/POV-Ray 3.1 user)?
>
>
> camera {location -z*35}
> light_source {(x+y-z)*50 rgb 1}
>
> fog {
> fog_type 1
> distance 30
> color rgb 1
> // turbulence makes the transparent part visible
> turbulence 0.8
> }
> sphere{0,8 pigment{rgb x+y} normal{bumps 1}}
> union{
> triangle{-x,-x+y,x+y}
> triangle{-x,x,x+y}
> hollow
> texture{
> pigment_pattern{
> bozo color_map{[0.4 rgb 1][0.4 rgb 0]}
> }
> texture_map{
> [0.5 pigment{rgb x} finish{ambient 0 diffuse 1}]
> [0.5 pigment{rgbt 1} finish{ambient 0 diffuse 0}]
> }
> // uneven scaling makes the normals behind look weird
> scale <1,1,0.001>
> }
> scale 2
> translate -z*20
>
> }
>
>
> --
> **********************
> http://www.oyonale.com
> **********************
> - Graphic experiments
> - POV-Ray and Poser computer images
> - Posters
>
>
>
>
>
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Gilles Tran wrote:
> The first bug makes the transparent part visible. It's apparently linked
> with fog turbulence.
This has been a known limitation of fog and transparent objects for many years.
It came up several times during the beta of 3.5 and I seem to recall the
general consensus and official response was that media should be used instead.
--
Ken Tyler
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From: Gilles Tran
Subject: Re: Possible pair of bugs affecting transparency.
Date: 22 Sep 2002 09:11:01
Message: <3d8dc165@news.povray.org>
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3D8D9CEB.D3830FD5@pacbell.net...
> This has been a known limitation of fog and transparent objects for many
years.
> It came up several times during the beta of 3.5 and I seem to recall the
> general consensus and official response was that media should be used
instead.
Well thanks, the first bug rang a (dim) bell.
Does the second one deserve a formal bug report ?
It's less a problem than the first one but it's really weird anyway. I
scratched my head for hours figuring it out (the initial problem was
submitted by an user, not by me, so I have to tell him something).
G.
--
**********************
http://www.oyonale.com
**********************
- Graphic experiments
- POV-Ray and Poser computer images
- Posters
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In article <3d8d447b@news.povray.org>,
"Gilles Tran" <git### [at] wanadoo fr> wrote:
> The code below shows 2 potential bugs affecting transparency.
> These have been observed on 3.1 (using material_map) and 3.5, at least on a
> Windows version, running XP.
> The first bug makes the transparent part visible. It's apparently linked
> with fog turbulence.
It isn't a bug, just a limitation of fog. Fog is really a cheat, it uses
the distance along the ray to figure out how much fog it goes through
assuming constant or gradient fog, and then uses turbulence with the
intersection point scaled by the turbulence amount and some other tricks
to mess with the real fog value. The result is nothing like real fog,
but usually looks good and is fast to compute.
"Fixing" this would require making fog into a more limited media, if you
need accurate results in this kind of situation just use scattering
media.
> The second bug makes the normals behind look weird when the transparency
> texture is scaled very unevenly (pure 100% transparent texture is not
> affected).
I haven't had a chance to render this, but it seems very unlikely that
there is some problem with scaling of normals, or even scaling of normal
patterns. Maybe there is a problem with the ray directions not being
normalized for some reason...
--
Christopher James Huff <cja### [at] earthlink net>
http://home.earthlink.net/~cjameshuff/
POV-Ray TAG: chr### [at] tag povray org
http://tag.povray.org/
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From: Warp
Subject: Re: Possible pair of bugs affecting transparency.
Date: 22 Sep 2002 12:44:55
Message: <3d8df386@news.povray.org>
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Christopher James Huff <chr### [at] mac com> wrote:
> It isn't a bug, just a limitation of fog. Fog is really a cheat
This could be a good proverb for CG: "Don't expect a trick to work like
the real thing." :)
--
#macro N(D)#if(D>99)cylinder{M()#local D=div(D,104);M().5,2pigment{rgb M()}}
N(D)#end#end#macro M()<mod(D,13)-6mod(div(D,13)8)-3,10>#end blob{
N(11117333955)N(4254934330)N(3900569407)N(7382340)N(3358)N(970)}// - Warp -
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