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13 Apr 2024 13:11:28 EDT (-0400)
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From: Bald Eagle
Subject: Wet paper texture
Date: 18 Jan 2024 21:55:00
Message: <web.65a9e42e59f07cd41f9dae3025979125@news.povray.org>
So, I wasted half the day doing ridiculous things with cross products, dot
products, and rotating graphs of scattering functions.

Then I just decided to experiment with faking it from scratch.

After wrestling with the aoi and slope patterns, I got something that more or
less works as a basic concept.

I have no real idea what I'm doing with the filter and transmit values, and I
can't achieve any transparency no matter what values I use.

Anyway, here's a quick animation I threw together to adequately show how it
works.

It's just "one" texture and 2 light sources to provide adequate illumination of
both sides.

- BE


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Attachments:
Download 'wetpaper.mp4.dat' (1595 KB)

From: William F Pokorny
Subject: Re: Wet paper texture
Date: 19 Jan 2024 06:45:33
Message: <65aa60dd$1@news.povray.org>
On 1/18/24 21:53, Bald Eagle wrote:
> I have no real idea what I'm doing with the filter and transmit values, and I
> can't achieve any transparency no matter what values I use.

In v3.8 (v3.7?) there is that second finish { difuse } specification?

diffuse 0.6, 0.3

Bill P.


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From: And
Subject: Re: Wet paper texture
Date: 19 Jan 2024 10:10:00
Message: <web.65aa906a9bc1d8da97dafaf4aa81652d@news.povray.org>
"Bald Eagle" <cre### [at] netscapenet> wrote:
> So, I wasted half the day doing ridiculous things with cross products, dot
> products, and rotating graphs of scattering functions.
>
> Then I just decided to experiment with faking it from scratch.
>
> After wrestling with the aoi and slope patterns, I got something that more or
> less works as a basic concept.
>
> I have no real idea what I'm doing with the filter and transmit values, and I
> can't achieve any transparency no matter what values I use.
>
> Anyway, here's a quick animation I threw together to adequately show how it
> works.
>
> It's just "one" texture and 2 light sources to provide adequate illumination of
> both sides.
>
> - BE

Wow, your ridiculous thing is really attractive.


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From: Thomas de Groot
Subject: Re: Wet paper texture
Date: 20 Jan 2024 02:24:21
Message: <65ab7525$1@news.povray.org>
Op 19/01/2024 om 12:45 schreef William F Pokorny:
> On 1/18/24 21:53, Bald Eagle wrote:
>> I have no real idea what I'm doing with the filter and transmit 
>> values, and I
>> can't achieve any transparency no matter what values I use.
> 
> In v3.8 (v3.7?) there is that second finish { difuse } specification?
> 
> diffuse 0.6, 0.3
> 
> Bill P.

I was going to suggest that too indeed. I use that for simulating 
semitransparent cloth combined with backside illumination. Is also 
available in v3.7.

-- 
Thomas


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From: Bald Eagle
Subject: Re: Wet paper texture
Date: 20 Jan 2024 10:10:00
Message: <web.65abe1419bc1d8da1f9dae3025979125@news.povray.org>
Thomas de Groot <tho### [at] degrootorg> wrote:

> I was going to suggest that too indeed. I use that for simulating
> semitransparent cloth combined with backside illumination. Is also
> available in v3.7.

Unexplored territory for me.


So, my texture is

texture {
     slope {}
     texture_map {
          [0 pigment {
               average
               pigment_map {
                    [Entries]
               }
          ]
          [0 pigment {
               average
               pigment_map {
                    [Entries]
               }
          ]
     }
}

I've tried plugging in a finish statement, but the parser squawks "no }, found
finish instead"

Where does the finish GO?

I was also thinking about how to go about making a user defined finish function,
and that will probably have to be done with another map, since we don't have
function controlled finish parameters

- BW


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From: Bald Eagle
Subject: Re: Wet paper texture
Date: 20 Jan 2024 10:40:00
Message: <web.65abe8d39bc1d8da1f9dae3025979125@news.povray.org>
OK, so I finally got the finish in the right place

texture {
     slope {}
     texture_map {
          [0 pigment {
               average
               pigment_map {
                    [Entries]
               }
               finish {}
          ]
          [0 pigment {
               average
               pigment_map {
                    [Entries]
               }
               finish {}
          ]
     }
}

But no matter what I do with those 2 diffuse values, I don't get anything like
that translucent effect.  I'm also still puzzled why filter and transmit don't
seem to work at all - it doesn't result in a totally transparent region even if
I hard code the function pigment map entry to 1.
I do seem to get more "light" coming through, but strangely, it doesn't look
like the usual filtered or transmissive appearance that I normally expect.
It tried getting rid of those entries entirely, and that didn't seem to help
either.

- BW


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From: Thomas de Groot
Subject: Re: Wet paper texture
Date: 20 Jan 2024 10:56:15
Message: <65abed1f$1@news.povray.org>
Op 20-1-2024 om 16:05 schreef Bald Eagle:
> Thomas de Groot <tho### [at] degrootorg> wrote:
> 
>> I was going to suggest that too indeed. I use that for simulating
>> semitransparent cloth combined with backside illumination. Is also
>> available in v3.7.
> 
> Unexplored territory for me.
> 
> 
> So, my texture is
> 
> texture {
>       slope {}
>       texture_map {
>            [0 pigment {
>                 average
>                 pigment_map {
>                      [Entries]
>                 }
>            ]
>            [0 pigment {
>                 average
>                 pigment_map {
>                      [Entries]
>                 }
>            ]
>       }
> }
> 
> I've tried plugging in a finish statement, but the parser squawks "no }, found
> finish instead"
> 
> Where does the finish GO?
> 
> I was also thinking about how to go about making a user defined finish function,
> and that will probably have to be done with another map, since we don't have
> function controlled finish parameters
> 
> - BW
> 
I have no access presently to the PC where I have stored my stuff (and 
it is some years since last I used backside illumination). First thing 
in the morning, on my ToDo. Sorry for the delay!
-- 
Thomas


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From: Bald Eagle
Subject: Re: Wet paper texture
Date: 20 Jan 2024 11:15:00
Message: <web.65abf1629bc1d8da1f9dae3025979125@news.povray.org>
Thomas de Groot <tho### [at] degrootorg> wrote:

> I have no access presently to the PC where I have stored my stuff (and
> it is some years since last I used backside illumination). First thing
> in the morning, on my ToDo. Sorry for the delay!

Never fear, intrepid renderer - I figgered it out.

I just needed to add the ft values in, using a constant function in the pigment
map.

So, it works, but probably could use a fair bit of improvement.

- BW


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Attachments:
Download 'wetpaper.mp4.dat' (1599 KB)

From: Thomas de Groot
Subject: Re: Wet paper texture
Date: 21 Jan 2024 02:28:51
Message: <65acc7b3@news.povray.org>
Op 20/01/2024 om 17:14 schreef Bald Eagle:
> Thomas de Groot <tho### [at] degrootorg> wrote:
> 
>> I have no access presently to the PC where I have stored my stuff (and
>> it is some years since last I used backside illumination). First thing
>> in the morning, on my ToDo. Sorry for the delay!
> 
> Never fear, intrepid renderer - I figgered it out.
> 
> I just needed to add the ft values in, using a constant function in the pigment
> map.
> 
> So, it works, but probably could use a fair bit of improvement.
> 
> - BW
> 
Excellent!

Just in case you want to play with those diffuse parameters, here is 
some code (+ an image map) I used a long time ago in my window scene 
with the Sultana (Gancaloon Project):

//==================================================
#declare p_curtain_1 = pigment {image_map {png 
"Orange_Gold_Damask_by_R2krw9.png" gamma srgb interpolate 2 filter all 0.5}}
#declare p_curtain_2 = pigment {image_map {png 
"Orange_Gold_Damask_by_R2krw9.png" gamma srgb interpolate 2 filter all 0.0}}
#declare p_curtain_sat = pigment {image_map {png 
"Orange_Gold_Damask_by_R2krw9_sat.png" gamma 1 interpolate 2}}

//==================================================
//Material definitions
#declare Curtain_=
#declare f_curtain_1 =
finish {
   specular 0.0
   roughness 0.0005
   diffuse 0.8, 0.2  //using backside illumination
   conserve_energy
}

#declare f_curtain_2 =
finish {
   specular 0.25
   roughness 0.002
   diffuse 0.8, 0.3  //using backside illumination
   conserve_energy
}

material {
   texture {uv_mapping
     pigment_pattern {p_curtain_sat}
     texture_map {
       [0.0 pigment {p_curtain_1}
            finish {f_curtain_1}
       ]
       [1.0 pigment {p_curtain_2}
            finish {f_curtain_2}
       ]
     }
   }
}
//==================================================

-- 
Thomas


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Attachments:
Download 'orange_gold_damask_by_r2krw9.png' (402 KB)

Preview of image 'orange_gold_damask_by_r2krw9.png'
orange_gold_damask_by_r2krw9.png


 

From: Thomas de Groot
Subject: Re: Wet paper texture
Date: 21 Jan 2024 02:31:37
Message: <65acc859@news.povray.org>
forgot to add the saturation map.

-- 
Thomas


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Attachments:
Download 'orange_gold_damask_by_r2krw9_sat.png' (281 KB)

Preview of image 'orange_gold_damask_by_r2krw9_sat.png'
orange_gold_damask_by_r2krw9_sat.png


 

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