som### [at] microsoftcom news:412c7013@news.povray.org

> I just combined a Looks_Like, Area_Light, Fade_Distance, what a fantastic
> result.

Btw, I think it would be much more natural if *all* lights (not only 
light_sources direct rays, but also radiosity and photons rays) would have 
fade_power 3 and some arbitrary fade_distance. This is the correct phisical 
model AFAIR?

Currenlty - a small lightbull could lighten as well a small box and a 
spaceship hangar with is not true. 

In fade_power 3 case,  color rgb of light_source would mean color and 
light power, not color/brighntess.

It should give nice results with exposure (from MegaPov 1.1)

FUT: povray.general

-- 
http://www.raf256.com/3d/
Rafal Maj 'Raf256', home page - http://www.raf256.com/me/
Computer Graphics

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> In fade_power 3 case,  color rgb of light_source would mean color and
> light power, not color/brighntess.

I think actual light has an inverse square fade thing ( not very
knowledgeable) so they should all have  fade_power 2, I think.

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>>In fade_power 3 case,  color rgb of light_source would mean color and
>>light power, not color/brighntess.
> 
> 
> I think actual light has an inverse square fade thing ( not very
> knowledgeable) so they should all have  fade_power 2, I think.

As you move further away from the light source, the light is spread over 
a greater area. Since area is the square of length, it should indeed by 
fade_power 2.

Andrew @ work.

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voi### [at] devnull news:412c9f67@news.povray.org

> As you move further away from the light source, the light is spread over 
> a greater area. Since area is the square of length, it should indeed by 
> fade_power 2.

Yes, indeed - this is correct.

AFAIK even after manualy adding fade_power 2 to evey light_source it still 
will not solve problem - since diffused rays (in radiosity calculations) 
and direct media rays (radiosiy from ambient-media) as well as photons will 
not fade that way...? Or perhaps radiosity is behaving as fade_power 2 by 
default - because of way how rays are shooted? Hmm I must check that...

-- 
http://www.raf256.com/3d/
Rafal Maj 'Raf256', home page - http://www.raf256.com/me/
Computer Graphics

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"Rafal 'Raf256' Maj" <spa### [at] raf256com> wrote in message
news:Xns9550876BCF335raf256com@203.29.75.35...
> som### [at] microsoftcom news:412c7013@news.povray.org
>
> > I just combined a Looks_Like, Area_Light, Fade_Distance, what a
fantastic
> > result.
>
> Btw, I think it would be much more natural if *all* lights (not only
> light_sources direct rays, but also radiosity and photons rays) would have
> fade_power 3 and some arbitrary fade_distance. This is the correct
phisical
> model AFAIR?
>

the only problem i can see by having a default fade_power and fade_distance
other than what it is would be new users having objects outside the distance
that light reaches, causing confusion. "why isn't my sphere showing up? i
have a light and a camera" they can gradually learn that there are more
advanced options that simulate reality a little better.

by your argument, photons and radiosity would be on by default, but that
just doesn't make sense since every scene has different needs for photon
count.

i usually leave fade_power and fade_distance out of my scenes until towards
the end, if i change them at all.

good points, but i just think it would lead to much confusion to new users.
you could of course define an include file that creates realistic light
objects, and use those instead of adding fade_power/distance to each of your
lights in every scene.

-ross

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"Rafal 'Raf256' Maj" <spa### [at] raf256com> wrote in message
news:Xns9550A7D16A272raf256com@203.29.75.35...
> voi### [at] devnull news:412c9f67@news.povray.org
>
> > As you move further away from the light source, the light is spread over
> > a greater area. Since area is the square of length, it should indeed by
> > fade_power 2.
>
> Yes, indeed - this is correct.
>
> AFAIK even after manualy adding fade_power 2 to evey light_source it still
> will not solve problem - since diffused rays (in radiosity calculations)
> and direct media rays (radiosiy from ambient-media) as well as photons
will
> not fade that way...? Or perhaps radiosity is behaving as fade_power 2 by
> default - because of way how rays are shooted? Hmm I must check that...
>

refracted light is not governed by fade_distance/fade_power is it? i think i
recall reading that in the docs of 3.5. (opening docs for 3.6...) i always
wondered why. for instance if you have a candle (point light) in a glass
candle holder, nearly all the light would be defracted, and therefore, not
fade with distance.

from the documentation "Reflected or refracted light is not attenuated by
distance." is this because it is computationally too expensive, or is this
just how light works in nature?

(removed p.o-t from list, since this is becomming on-topic)

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In povray.general Rafal 'Raf256' Maj <spa### [at] raf256com> wrote:
> Btw, I think it would be much more natural if *all* lights (not only 
> light_sources direct rays, but also radiosity and photons rays) would have 
> fade_power 3 and some arbitrary fade_distance. This is the correct phisical 
> model AFAIR?

  Radiosity produces a physically correct lighting automatically because
it computes the percentage of the area of a surface with regard to all
the visible hemisphere. This automatically causes a surface to cast less
light on the current surface if it's farther away.

-- 
plane{-x+y,-1pigment{bozo color_map{[0rgb x][1rgb x+y]}turbulence 1}}
sphere{0,2pigment{rgbt 1}interior{media{emission 1density{spherical
density_map{[0rgb 0][.5rgb<1,.5>][1rgb 1]}turbulence.9}}}scale
<1,1,3>hollow}text{ttf"timrom""Warp".1,0translate<-1,-.1,2>}//  - Warp -

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rli### [at] everestkcnet news:412ca60c$1@news.povray.org

> from the documentation "Reflected or refracted light is not attenuated
> by distance." is this because it is computationally too expensive, or
> is this just how light works in nature?

So to summ up I suggest

1. global_settings { 
    global_light_fading on  
    global_light_distance 100 // adjust this depending on size of scene
  }

2. with #version <= 3.6 default is:  global_light_fading off

3. global_light_fading  
  a) overwrites light_source defaults to: 
    power   2  
    distance   global_light_distance
  b) make refracted rays also fade
  c) photons... are they acting as radiosity or do they also need fading? 
If they need - turn it on by default

4. defauls can be manualy overwriten ofcourse 

5. perhaps add option fade_refracted ON in light_source{} to allow manualy 
switching on/off fading of refracted ray of each light 


This will not brake old scenes 2),  it will add functionality  3.c)  and 
will make writting scene bit more comfortable  3.a) and 4)

Perhaps macros  will be usefull:
CALCULATE_LIGHT (designated_light, object_distance)  
CALCULATE_LIGHT2(designated_light, object_position, light_position)  


used as:

#local W = <200,0,0>;
#local L = <0,500,0>;
sphere { W 1 pigment { rgb 1 } }
light_source { CALCULATE_LIGHT2(0.5, W, L) }

and sphere would be have resulting color as it was lighten by 
light_source { rgb 0.5 }  no matter where we will put it.

If someone could implement this patch I can help to write manual on it and 
test it (and perhaps help coding) as I find it very usefull in creating 
photorealistick scenes (especialy togeather with radiostity and exposure)


-- 
http://www.raf256.com/3d/
Rafal Maj 'Raf256', home page - http://www.raf256.com/me/
Computer Graphics

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Have you ever tried Jaime's Lightsys for lighting? If not, you can 
download it at http://www.ignorancia.org

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Ross <rli### [at] everestkcnet> wrote:

> refracted light is not governed by fade_distance/fade_power is it? i think i
> recall reading that in the docs of 3.5. (opening docs for 3.6...) i always
> wondered why.

How bright an object appears depends on it's distance to the light source,
but it does NOT depend on it's distance to the camera!
(otherwise you wouldn't be able to see the moon, for example)

Since reflections/refractions can only occur in rays between camera and object,
but not between object/lightsource (without photon mapping, photon mapping 
should get the fading automatically correct, just like radiosity) it isn't 
necessary to handle light fading there.

Lutz-Peter

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