I've been trying to figure out how to create a scene in which there is a
light shining through a white linen cloth. For example, if you were to
take a white bedsheet and hold it up near a lightbulb, you wouldn't see
the exact outline of the bulb but you would see the light being
dispersed through the sheet in a fuzzy outline.  (Am I making myself
clear?)  Anyone know how to accoplish this in POV?

Jason Scheuerman
mt### [at] nullnet

Post a reply to this message

Try giving the sheets pgiment a filter or transmit value, but that may be
too literal for a bedsheet, so it meay work to increaswe it's ambience a
bit.

Jason Scheuerman wrote:

> I've been trying to figure out how to create a scene in which there is a
> light shining through a white linen cloth. For example, if you were to
> take a white bedsheet and hold it up near a lightbulb, you wouldn't see
> the exact outline of the bulb but you would see the light being
> dispersed through the sheet in a fuzzy outline.  (Am I making myself
> clear?)  Anyone know how to accoplish this in POV?
>
> Jason Scheuerman
> mt### [at] nullnet

--
Josh English
eng### [at] spiritonecom
www.spiritone.com/~english

Post a reply to this message

Jason Scheuerman wrote:
> 
> I've been trying to figure out how to create a scene in which there is a
> light shining through a white linen cloth. For example, if you were to
> take a white bedsheet and hold it up near a lightbulb, you wouldn't see
> the exact outline of the bulb but you would see the light being
> dispersed through the sheet in a fuzzy outline.  (Am I making myself
> clear?)  Anyone know how to accoplish this in POV?
> 
> Jason Scheuerman
> mt### [at] nullnet


I would suggest trying to do this texturaly. It will be difficult
to get the material properties correct to allow light to pass
in one spot only without effecting the rest of the object.

Try something like a spotted pigment with a sloped color. By that
I mean if the sheet is to be white with the spot of light in the
middle you could make the first part of the color map white and
then change the entries color intensities slowly towards the end
of the map. If this method is used you will need to scale the
pigment large enough that it only covers the object once and will
have experiment to find the correct translations and finishes.

 Below is a totaly untested and incomplete example of a sloped
color map entry:

#declare Sheet_Pigment =
 pigment{
  spotted
   color_map{
   [.750 rgb<.900,.900,.900>]
   [.750 rgb<.900,.900,.900>]
   [.791 rgb<.916,.916,.916>]
   [.833 rgb<.933,.933,.933>]
   [.875 rgb<.950,.950,.950>]
   [.916 rgb<.966,.966,.966>]
   [.958 rgb<.983,.983,.983>]
   [1.00 rgb<1.00,1.00,1.00>]
  }
}

The above gives a slow ramp from very light gray
to white.

 There are some other things yuo can do to the above
to increase the look of the effect. By leaving the
blue component at .9 and increasing the red and green
equaly you will have it change slowly to a very light
yellow color towards the center of the spot. The
following example shows how you can phase from white
to light yellow and change the intensity of the spot
colors without changing the shade of the colors
choosen:

#declare Sheet_Pigment =
 pigment{
  spotted
   color_map{
   [.750 rgb<.900,.900,.900>*1.00]
   [.750 rgb<.900,.900,.900>*1.05]
   [.791 rgb<.916,.916,.900>*1.10]
   [.833 rgb<.933,.933,.900>*1.15]
   [.875 rgb<.950,.950,.900>*1.20]
   [.916 rgb<.966,.966,.900>*1.25]
   [.958 rgb<.983,.983,.900>*1.30]
   [1.00 rgb<1.00,1.00,9.00>*1.35]
  }
}


Again this is untested and a different pigment type may
be needed but it gives you something to start with.

Good luck !

-- 
Ken Tyler

tyl### [at] pacbellnet

Post a reply to this message

Hmm, if you have a cray computer, or lots of memory, you can use several
cylinders tightly packed in two directions, creating a grid wich will
look like the cloth. This is a very stupid way of doing it, but, I had
to suggest it. The voices of reality are forcing me to it :-)

//Spider

Post a reply to this message

Ken wrote:
> The following example shows how you can phase from white
> to light yellow and change the intensity of the spot
> colors without changing the shade of the colors
> choosen:

    ===>    [1.00 rgb<1.00,1.00,9.00>*1.35]

Ken let a typo creep in :)

Change that 9.00 to .900

-- 
Ken Tyler

tyl### [at] pacbellnet

Post a reply to this message

On Thu, 04 Feb 1999 13:06:00 -0800, Jason Scheuerman <mt### [at] nullnet>
wrote:

>I've been trying to figure out how to create a scene in which there is a
>light shining through a white linen cloth. For example, if you were to
>take a white bedsheet and hold it up near a lightbulb, you wouldn't see
>the exact outline of the bulb but you would see the light being
>dispersed through the sheet in a fuzzy outline.  (Am I making myself
>clear?)  Anyone know how to accoplish this in POV?
>
>Jason Scheuerman
>mt### [at] nullnet

Well, if you a hardcoding-only POV-Ray nutcake (my ICQ nick is
pov-nut) you could  try using the SuperPatch to create a function for
an isosurface and use it as 1) an ithersection of two isosurfaces
situated closely to make the sheet and 2) a density pattern for a
scattering media in the sheet to do the fuzzy light effect you are
after.

Just a thought.

Peter

Post a reply to this message

Hey, you _are_ a nut :)
I'd just make the sheet out of bezier patches and use a simple constant
scattering media inside. Probably not too dense, so that a little bit of
non-diffuse transparency would remain.

Margus

Peter Popov wrote:
> 
> Well, if you a hardcoding-only POV-Ray nutcake (my ICQ nick is
> pov-nut) you could  try using the SuperPatch to create a function for
> an isosurface and use it as 1) an ithersection of two isosurfaces
> situated closely to make the sheet and 2) a density pattern for a
> scattering media in the sheet to do the fuzzy light effect you are
> after.
> 
> Just a thought.
> 
> Peter

Post a reply to this message

Didn't try it and don't know if it works, but a texture map using the
spherical pattern could do the trick. The outer texture would have the
regular bedsheet texture while the inner texture would have a high ambient
value and some filter or transmit value. The spherical pattern is centered
at <0,0,0> so it's easy to position.

Gilles Tran

Post a reply to this message

Margus Ramst wrote
> 
> Hey, you _are_ a nut :)
> I'd just make the sheet out of bezier patches and use a simple constant
> scattering media inside. Probably not too dense, so that a little bit of
> non-diffuse transparency would remain.

the buzzer says : Wrooooong !
since a bezier hav no inside/outside, you can't put a media in it...

now, maybe an ordinary container with a dense marble media,
where a thin vein (in 3D) plays the piece of clothe...

Fabien.

Post a reply to this message

Yes you can. Just checked. Worked just fine. The patches simply have to make
up a closed volume. I'm not sure if it works well with very complicated
patches, but in principle, it works.
Your idea isn't too bad, but you have very little control over the shape of
the sheet.

Margus

Fabien Mosen <101### [at] compuservecom> wrote in message
<36BB3F4F.3463DBD0@compuserve.com>...

>the buzzer says : Wrooooong !
>since a bezier hav no inside/outside, you can't put a media in it...
>
>now, maybe an ordinary container with a dense marble media,
>where a thin vein (in 3D) plays the piece of clothe...
>
>Fabien.

Post a reply to this message