Nieminen Mika <war### [at] assaricctutfi> wrote in article
<35f65710.0@news.povray.org>...
> Johannes Hubert <jhu### [at] algonetse> wrote:
> : Create your neonsign object.
> : Give it an ambient value of 1, so that it glows by itself. Also set the
> : "no_shadow" property.
> [snip]
> : Note: This workaround will not light up objects close to the sign in a
> : realistic manner
> 
>   This can be achieved with (surprise!) radiosity :)
>   A very bright object (like one with ambient set to 1) emits lots of its
> color to its surroundings, so with proper radiosity settings it will look
> like it's actually emitting light.
>   This effect can be seen in the images at
> http://iki.fi/warp/pics/Radiosity_test/
> 

	Is there a description of these images and the objects in the scene
available any where ? Like which use this high ambient technique (I think I
can work it out from the 'without radiosity' pictures, but it would be nice
to know for sure) and what radiosity settings were used ? etc, etc.

-- 
Scott Hill
Sco### [at] DDLinkscouk
Software Engineer (and all round nice guy)
Company homepage : http://www.ddlinks.demon.co.uk

"The best trick the devil ever pulled was convincing people he didn't
exist..."
								- Verbal Kint.

"the Internet is here so we can waste time talking about nothing in 
 particular when we should be working" - Marcus Hill.

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Tried to put everyones ideas together - what do you reckon.

Mick
 
camera
{
  location  <0.0, 0.0, -15.0>
  look_at   <0.0, 5.0,  0.0>
}

background{color rgb<0,0,0>}
light_source {<20,5,-20> color rgb 0.25 }
// ----------------------------------------

#declare nmb=0;
#while (nmb<=10)
   light_source { nmb*y color rgb 0.1 }
   #declare nmb=nmb+1;
#end
cylinder { <0,-0.5,0>, <0,10.5,0>, 0.2 pigment { color rgbf <20,2,5,0.5> }
finish{specular 0.5}
 }

Edward Lotter <_lot### [at] loopcom> wrote in article
<01bddbb0$052ffd00$693ed3cf@edward.loop.com>...
> Try as I might (and search as I might) I have not been able to find a
> solution to this one!
> 
> My first thought (when learning POV-Ray) was a light that looked like a
> cyclinder.
> The docs do NOT tell you that the light will ONLY emit from the source,
not
> the
> entire object.
> 
> Okay, next try. Halos! Many frustrated hours later. NOPE!
> 
> Finally, linear area lights!! Even more frustrated hours later. I don't
> think so!!
> 
> Since I'm not a fundi with POV-Ray, it's entirely possible I have missed
a
> salient
> point in one or a combination of the above which would have solved my
> dilemma, but
> what it is eludes me!
> 
> How does one render a visible flourescent tube (like those in an office
> ceiling)?
> Or even a neon sign??
> 
> Thanks in advance for any pointers and help.
> 
> Cheers
> Eddie
> 
>

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> Tried to put everyones ideas together - what do you reckon.
> 
> Mick
>  
>
camera
{
  location  <0.0, 0.0, -15.0>
  look_at   <0.0, 0.0,  0.0>
}

background{color rgb<0,0,0>}
light_source {<0,5,-20> color rgb 0.25 }
// ----------------------------------------

#declare nmb=-15;
#while (nmb<=15)
   light_source { nmb*x color rgb <0.2,0,0.1> }
   #declare nmb=nmb+0.33;
#end
cylinder { <-5,0,0>, <5,0,0>, 0.2 pigment { color rgbf <20,2,5,0.5> }
finish{specular 0.5}
 }

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Edward Lotter <_lot### [at] loopcom> wrote in article
<01bddbb0$052ffd00$693ed3cf@edward.loop.com>...
> Try as I might (and search as I might) I have not been able to find a
> solution to this one!
> [...]

You guys are the greatest. Thanks to everyone for such a quick and
thorough response. (Especially, Mick. Thanks for successfully 
rising to the challenge.)

You will see examples of my work on the web (eventually) and
probably in the IRTC.

Thanks again, one and all.

Cheers
Eddie

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Edward Lotter wrote:
> 
> Try as I might (and search as I might) I have not been able to find a
> solution to this one!
> 
> My first thought (when learning POV-Ray) was a light that looked like a
> cyclinder.
> The docs do NOT tell you that the light will ONLY emit from the source, not
> the
> entire object.
> 
> Okay, next try. Halos! Many frustrated hours later. NOPE!
> 
> Finally, linear area lights!! Even more frustrated hours later. I don't
> think so!!

[snip]

> How does one render a visible flourescent tube (like those in an office
> ceiling)?
> Or even a neon sign??

Um... don't forget that neon tubes work differently from fluorescent
tubes. In a neon tube, the gas glows in the colour that you want. you
can see through the glass tube (I'm pretty sure about this, but not
absolutely.) I don't think they use tinted glass either.

In a fluorescent tube, the inside of the glass tube is coated with stuff
(magic powder, I guess) that absorbs the non-visible ultra-violet light
and emits it as visible not-quite-white light.

I guess that what I'm driving at is that a fluorescent light tube could
simply be an opaque cylinder with a high ambient, whereas the neon tube
should probably have something like a cylindrically-mapped halo, and the
glass tube itself really should be the difference between two cylinders,
with some refraction applied.

Of course this would only make a difference in extreme closeup views,
and I haven't even attempted to deal with how to make it look like a
convincing light source. (Although, somebody's idea of using greater
than 1 values in the colour vectors, and switching on radiosity sounds
pretty good, especially for the neon signs.)

Or... take a different tack:
Render a view of the neon sign only, possibly with an orthographic
camera. Use a black background. Take that image and run it several times
through a blur filter in PhotoShop (or whatever). If you don't have a
suitable image editor, then render the neon sign with a lot of
focal_blur [not sure of what the keyword really is, but you get the
idea].
Finally, take that blurry image and map it onto the wall or board that
the sign is attached to. I bet it would look pretty close, but I haven't
actually tried anything like it.

-jr- 

**********************************************
* Delete "spamBgone." to get my real address *
**********************************************

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> Ken <tyl### [at] pacbellnet> wrote in article

> >   Do you mean to tell me that it is possible to use an
> > ambient value higher than 1. If this is so why wasn't
> > I informed. I don't remember getting a memo !

Ken - We all voted not to tell you, in your own best interest.
Unfortunately, you have stumbled on our secret, so now you must die!

------------------------------
I hit on it by accident (a typo that parsed okay, but gave unexpected
results) and found it was useful when I was looking for a good way to
emulate a "candy-apple red" for something like a custom car paint job.

Here's a bit of it (from an early version): 

pigment {colour rgb <1.6, 0.4, 0.1 >}  // note high red, low blue
components
finish {
      ambient <0.2, -0.3, 2.0>       // note low red, high blue
component
      diffuse 0.5
      reflection 0.10
      specular 1.0
      roughness 0.001
      brilliance  3
      } 

The resulting effect is that whatever is directly illuminated by the
light_source comes out as a nice bright warm red hot-spot; everything
else (ie. the shaded areas) is given a slightly purple tinge, and still
looks fairly bright without the glow-in-the-dark effect of a high
ambient.
 
The high red component in the pigment is countered by the low red value
in the ambient, and vice-versa for the blue

A traditional trick in painting (oil, acrylic, etc) is to use a
complementary colour on the shaded side of objects. This trick is
something like that. My other option was to use a carefully scaled and
rotated gradient, but that scheme would fall apart as soon as a second
light_source is used.

It was also during this project that I realized that you can use a
multiplier with a colour vector, as in 

    colour rgb 0.9*<1.6, 0.4, 0.1 >   
or
    ambient 1.2*<0.2, -0.3, 2.0>

And, I was really surprised to see that this parsed:

    reflection (0.01 + 0.4*(<0.5, 0.15, 0.4 >))

It's all like using the visual equivalent of a graphic equalizer with a
series amplifier. If it evaluates to something greater than 1.0, then
you get "clipping" of the over-driven signal, which is what a fuzz-box
does.

one drawback is that if I want to change the base color, I have to go
through and "rotate" the components in each vector, to shift the colors.

Hmmm... now that I think of it, I could probably come up with a scheme
that uses sin or cos functions, and a "colour phase" variable, just like
in an NTSC video signal. change one #declare statement, and all of the
colour vectors shift. Once I get pleasing results, then I go through and
substitute calculated values (from a spreadsheet), so as to save a bit
of rendering time... hmmm... so crazy, it just might work.

-jr- 

**********************************************
* Delete "spamBgone." to get my real address *
**********************************************

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