Can anyone please explain why this:

density { checker }

and this

density { checker rgb <1,0,0>, rgb <0,0,0> }

give errors, while this:

density { checker density { rgb <1,0,0> }, density { rgb <0,0,0> } }

works just fine?

Here's the whole scene:

// scene starts here
// ------------------

#include "colors.inc"

box
{
  -.99, .99
  interior
  {
    media
    {
      emission 1
      absorption 2
      intervals 20
      samples 10, 20
      variance 1/255
      confidence 0.999
      density { checker density { color White }, density { color Black
} }
    }
  }
  
  hollow
  pigment { Clear }
}

camera
{
  location  <1.0 , 2.0 ,-3.0>*.8
  right x
  look_at   <0.0 , 0.0 , 0.0>
}

background { color red 0.1 green 0.3 blue 0.8 }

// scene ends here
// ------------------

Thanks in advance.


---------
Peter Popov
ICQ: 15002700

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Peter Popov wrote:
> 
> Can anyone please explain why this:
> 
> density { checker }
> 
> and this
> 
> density { checker rgb <1,0,0>, rgb <0,0,0> }
> 
> give errors, while this:
> 
> density { checker density { rgb <1,0,0> }, density { rgb <0,0,0> } }
> 
> works just fine?
> 
> Here's the whole scene:

That is the correct behaviour as detailed in the docs. It is the exact
same syntax necessary to use color list patterns in a texture statement.
There is one very short 2 line mention of this in the docs that is a bit
hard to find. The second example you provided is the correct way of
specifying color list patterns in media.


P.S. About a month ago I posted a study of this in povray.binaries.images.
It provides example images and the source code showing how to use the three
different color list patterns in a media statement.





-- 
Ken Tyler

mailto://tylereng@pacbell.net

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To my surprise I just uncovered something myself (using POV-Win 3.1e).
Try rendering this simple thing with and without a comma inbetween the
rgb colors in this checker pattern:

//BEGIN

#version 3.1

global_settings {assumed_gamma 1.0}
// ----------------------------------------
camera {
  location  <0.0, 0.5, -4.0>
  direction 1.5*z
  right     4/3*x
  look_at   <0.0, 0.0,  0.0>
}

sky_sphere {
  pigment {
    gradient y
    color_map { [0.0 color blue 0.6] [1.0 color rgb 1] }
  }
}

light_source {
  0*x // light's position (translated below)
  color rgb 1  // light's color
  translate <-30, 30, -30>
}
// ----------------------------------------
plane { y, -1 pigment {rgb <0.7,0.5,0.3>}}

#declare MyColor1=rgb<1,.5,.25>
#declare MyColor2=rgb<.25,.5,1>

sphere { 0, 1
 pigment {checker rgb 1, rgb 0} //remove comma, add comma to correct
  finish{specular 1} }

//END


Ken wrote:
> 
> Peter Popov wrote:
> >
> > Can anyone please explain why this:
> >
> > density { checker }
> >
> > and this
> >
> > density { checker rgb <1,0,0>, rgb <0,0,0> }
> >
> > give errors, while this:
> >
> > density { checker density { rgb <1,0,0> }, density { rgb <0,0,0> } }
> >
> > works just fine?
> >
> > Here's the whole scene:
> 
> That is the correct behaviour as detailed in the docs. It is the exact
> same syntax necessary to use color list patterns in a texture statement.
> There is one very short 2 line mention of this in the docs that is a bit
> hard to find. The second example you provided is the correct way of
> specifying color list patterns in media.
> 
> P.S. About a month ago I posted a study of this in povray.binaries.images.
> It provides example images and the source code showing how to use the three
> different color list patterns in a media statement.
> 
> --
> Ken Tyler
> 
> mailto://tylereng@pacbell.net

-- 
 omniVERSE: beyond the universe
  http://members.aol.com/inversez/homepage.htm
 mailto:inv### [at] aolcom?Subject=PoV-News

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Bob Hughes wrote:
> 
> To my surprise I just uncovered something myself (using POV-Win 3.1e).
> Try rendering this simple thing with and without a comma inbetween the
> rgb colors in this checker pattern:


 There is mention in the docs in several places about the importance
of using commas in color list pigments to ensure the correct results.
I believe what you are seeing when you don't include the comma is
a combination of the default checker colors which are blue/green
and your listed colors black/white. Which ever color that is dominate
for that segment of the pattern will either prevail of become an
additive of the two. My recommendation regardless is to follow the
advice in the docs and ensure you have included the comma if you
want your checker pattern to perform as expected. But this should
apply without having to mention it. ;^ )

-- 
Ken Tyler

mailto://tylereng@pacbell.net

Post a reply to this message

On Sat, 10 Apr 1999 11:56:53 -0700, Ken <tyl### [at] pacbellnet> wrote:

>Peter Popov wrote:
>> 
>> Can anyone please explain why this:
>> 
>> density { checker }
>> 
>> and this
>> 
>> density { checker rgb <1,0,0>, rgb <0,0,0> }
>> 
>> give errors, while this:
>> 
>> density { checker density { rgb <1,0,0> }, density { rgb <0,0,0> } }
>> 
>> works just fine?
>> 
>> Here's the whole scene:
>
>That is the correct behaviour as detailed in the docs. It is the exact
>same syntax necessary to use color list patterns in a texture statement.
>There is one very short 2 line mention of this in the docs that is a bit
>hard to find. The second example you provided is the correct way of
>specifying color list patterns in media.

From the POV-Ray docs:

-------------------
For block pattern types checker, hexagon, and brick you may specify a
color list such as this:

  density{checker rgb<1,0,0>, rgb<0,0,0>}

See "Color List Pigments" which describes how pigment uses a color
list. The same principles apply when using them with density.
--------------------

The example shown above does not work. Under "Color List Pigments" it
is written that the two entries must be separated by a comma and the
color keyword must be used, like this:

density { checker color White, color Black }

This gives the same error:

} expected, color found instead

So, what am I doing wrong?

>P.S. About a month ago I posted a study of this in povray.binaries.images.
>It provides example images and the source code showing how to use the three
>different color list patterns in a media statement.

I will try and locate your post. It should prove useful.

---------
Peter Popov
ICQ: 15002700

Post a reply to this message

Peter Popov wrote:

> So, what am I doing wrong?
> 
> >P.S. About a month ago I posted a study of this in povray.binaries.images.
> >It provides example images and the source code showing how to use the three
> >different color list patterns in a media statement.
> 
> I will try and locate your post. It should prove useful.
> 
> ---------
> Peter Popov
> ICQ: 15002700


Also straight from the docs:

--
Density maps may be nested to any level of complexity you desire. The
densities in a map may have color maps or density maps or any type of
density you want.

Entire densities may also be used with the block patterns such as
checker, hexagon and brick. For example...

  density {
    checker
    density { Flame scale .8 }
    density { Fire scale .5 }
  }

Note that in the case of block patterns the density wrapping is required
around the density information.
--


The other two examples you quoted must be generic examples for the color
list patterns and are incorrect for use inside a media density statement.

-- 
Ken Tyler

mailto://tylereng@pacbell.net

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Ah, yes. When I saw green and black checker colors I suspected as much.
Going from POV version 1 (I came in late on 1.0) to 3 has been heck
though hasn't it...?;) My kingdom for a semi-colon auto-attacher!


Ken wrote:
> 
> I believe what you are seeing when you don't include the comma is
> a combination of the default checker colors which are blue/green
> and your listed colors black/white. Which ever color that is dominate
> for that segment of the pattern will either prevail of become an
> additive of the two. My recommendation regardless is to follow the
> advice in the docs and ensure you have included the comma if you
> want your checker pattern to perform as expected. But this should
> apply without having to mention it. ;^ )
> 
> --
> Ken Tyler
> 
> mailto://tylereng@pacbell.net

-- 
 omniVERSE: beyond the universe
  http://members.aol.com/inversez/homepage.htm
 mailto:inv### [at] aolcom?Subject=PoV-News

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