I was reading the 1996 edition of Digital Character Animation.   They made a
passing remark that implied that the major 3D packages then all had the
ability to turn off light interactions with individual objects.  I request
this for povray because:

1) I saw an inference that the big guys had it in 1996.

2) The book pointed it as having some utility in faking radiosity.

3) It would allow me to do 2D toons, by cranking up the specular reflection
to max.

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In article <3daa2eea@news.povray.org>,
 "Greg M. Johnson" <gregj:-)56590@ao:-)l.com> wrote:

> I was reading the 1996 edition of Digital Character Animation.   They made a
> passing remark that implied that the major 3D packages then all had the
> ability to turn off light interactions with individual objects.  I request
> this for povray because:

Ever hear of light groups?

-- 
Christopher James Huff <cja### [at] earthlinknet>
http://home.earthlink.net/~cjameshuff/
POV-Ray TAG: chr### [at] tagpovrayorg
http://tag.povray.org/

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cool.  What'll they think of next?

Perhaps an example of this should go into that exhaustive and useful web
page of pov features (Christoph's??).
Perhaps an example scene file (perhaps even showing off cartoony effect
possible with specular 10000)  should be added to example scenes.

I may work on the latter, if just for my own fun...


"Christopher James Huff" <chr### [at] maccom> wrote in message
news:chr### [at] netplexaussieorg...
>
> Ever hear of light groups?
>

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"Greg M. Johnson" wrote:
> 
> Perhaps an example of this should go into that exhaustive and useful web
> page of pov features (Christoph's??).

What? My web page exhaustive? Probably only in terms of server space...

I never actually used light groups so i'm probably the wrong person to ask
for a tutorial on that.

There is a light groups sample scene in the distribution BTW.

Christoph

-- 
POV-Ray tutorials, IsoWood include,                 
TransSkin and more: http://www.tu-bs.de/~y0013390/  
Last updated 13 Aug. 2002 _____./\/^>_*_<^\/\.______

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On the topic of lighting, here's an idea for something to include in the
next version: Negative Lighting.

What this negative lighting would do is, it would make the texture
dark/transparent where it is hit by light, and bright in shadow. This would
be handy for making special effects, or for lights on the nightside of a
planet. In the case of the nightside lights, it would be a lot easier than
having to use objects for the different sides of the planet.

The option for using negative lighting would be something like this:

sphere{<0,0,0> 2
  pigment{
    image_map{
      png "nightlights.png"
      map_type 1 // I think that's spherical mapping
      }
    negative_light on
    }
  }

I don't know what kind of special effects could be made using this, but you
did include no_image, no_reflection, no_shadow, etc, and they can be used
to make special effects.

Rohan _e_ii

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> On the topic of lighting, here's an idea for something to include in the
> next version: Negative Lighting.


You mean like

light_source {
  Position,
  rgb -1
}

? =)

Try it. Make sure to have some positive light sources, or full ambient
lighting.

 - Slime
[ http://www.slimeland.com/ ]

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"Slime" <slm### [at] slimelandcom> wrote in message
news:3dab967d@news.povray.org...
> > On the topic of lighting, here's an idea for something to include in the
> > next version: Negative Lighting.
>
>
> light_source {
>   Position,
>   rgb -1
> }
>
> Try it. Make sure to have some positive light sources, or full ambient
> lighting.

Nope, sorry, doesn't work exactly right unfortunately. Shadows aren't
correct. This just came to my attention recently and before that I had never
noticed a problem using negative light source colors. So, I don't know if
something changed or I just had not seen a shadow of one under the right
circumstances. I've used positive and negative lights in v3.1 media without
any apparent problem, although I can't remember what shadows there might
have been from them.

That would mean a reworking of light sources to correct this problem (which
isn't one, being outside the usual usage).

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hughes, b. wrote:
> "Slime" <slm### [at] slimelandcom> wrote in message
>>Try it. Make sure to have some positive light sources, or full ambient
>>lighting.
> Nope, sorry, doesn't work exactly right unfortunately. Shadows aren't
> correct.

If I may ask, how do you tell if shadows are correct or not with
something that cannot exist in nature?  There is no such thing as
a negative light source, except perhaps a black hole, which emits
its own radiation.

-- 
Tim Cook
http://empyrean.scifi-fantasy.com
mirror: http://personal.lig.bellsouth.net/lig/z/9/z993126

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"Timothy R. Cook" <tim### [at] scifi-fantasycom> wrote in message
news:3dac0e32@news.povray.org...
> hughes, b. wrote:
> > Nope, sorry, doesn't work exactly right unfortunately. Shadows aren't
> > correct.
>
> If I may ask, how do you tell if shadows are correct or not with
> something that cannot exist in nature?  There is no such thing as
> a negative light source, except perhaps a black hole, which emits
> its own radiation.

In the context I meant it would just be anti-light for POV scenes, light
subtraction. No shadowing, only removal of positive color light. I guess if
negative lights were to do as expected of such a thing, though, then they'd
actually illuminate shadows, or be a anti-shadow. They currently don't do
either I think. But as they are now it does subtract positive color lights
and ambience from the scene, except for strange artifacts left in the shadow
regions I guess.

Far as reality goes...?

I suppose some analogy could be made to the wave properties of light. Black
holes don't really shine outward, they vacuum inward and remove ordinary
light, but the interfering waves of regular light can diminish the photons
in regions.

Although you could set up a series of positive color area-spotlights to get
some bright and dark boundaries, a negative color light can counteract
within the same area-spotlight instead of needing masking objects and such.
More of a CSG for light sources idea than anything else perhaps.

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In article <3dac17d4$1@news.povray.org>,
 "hughes, b." <omn### [at] charternet> wrote:

> I guess if negative lights were to do as expected of such a thing, 
> though, then they'd actually illuminate shadows, or be a anti-shadow.

Why? Ordinary lights don't darken shadows, they just fail to illuminate 
them.


> But as they are now it does subtract positive color lights and 
> ambience from the scene, except for strange artifacts left in the 
> shadow regions I guess.

What artifacts? Shadowed areas are shadowed from the "antilight" just as 
they are from light.

-- 
Christopher James Huff <cja### [at] earthlinknet>
http://home.earthlink.net/~cjameshuff/
POV-Ray TAG: chr### [at] tagpovrayorg
http://tag.povray.org/

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