"If you set fade_power in the interior of an object at 1000 or above, a 
realistic exponential attenuation function will be used"

I didnt find more explanation in mannual - why this new forumla is more 
realistic, witch real-word materials have it, is this the best attenuation
forumla - or is it still not perfect in compare to phisics rights ?
How choose fade_power ? 1000 ? 1500 ? 10000 ? 
Should we always use new attenuation, or do some object look more realistic 
with old formula ?

-- 
#macro g(U,V)(.4*abs(sin(9*sqrt(pow(x-U,2)+pow(y-V,2))))*pow(1-min(1,(sqrt(
pow(x-U,2)+pow(y-V,2))*.3)),2)+.9)#end#macro p(c)#if(c>1)#local l=mod(c,100
);g(2*div(l,10)-8,2*mod(l,10)-8)*p(div(c,100))#else 1#end#end light_source{
y 2}sphere{z*20 9pigment{function{p(26252423)*p(36455644)*p(66656463)}}}//M

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"Rafal 'Raf256' Maj" <raf### [at] raf256com> wrote in message
news:Xns### [at] 204213191226...
>
> "If you set fade_power in the interior of an object at 1000 or above, a
> realistic exponential attenuation function will be used"
>
> I didnt find more explanation in mannual - why this new forumla is more
> realistic, witch real-word materials have it, is this the best attenuation
> forumla - or is it still not perfect in compare to phisics rights ?
> How choose fade_power ? 1000 ? 1500 ? 10000 ?
> Should we always use new attenuation, or do some object look more
realistic
> with old formula ?
 I believe it is independent of the actual value, it just uses one specific
model so it doesn't matter what value it is, as long as it's at or over
1000.  I could be mistaken though.

-tgq

Post a reply to this message

"Rafal 'Raf256' Maj" <raf### [at] raf256com> wrote
>
> "If you set fade_power in the interior of an object at 1000 or above, a
> realistic exponential attenuation function will be used"
>
> I didnt find more explanation in mannual - why this new forumla is more
> realistic, witch real-word materials have it, is this the best attenuation
> forumla - or is it still not perfect in compare to phisics rights ?
> How choose fade_power ? 1000 ? 1500 ? 10000 ?
> Should we always use new attenuation, or do some object look more
realistic
> with old formula ?

Hmmm... I don't know if that was supposed to make it into 3.5.

Anyway, if fade_power is >=1000, then the fade_power value itself is
ignored, and an exponential attenuation is applied.  Only fade_color and
fade_distance matter.  The exponential attenuation is almost identical to
constant attenuating media.

attenuation[] =
exp(-(1.0-Interior->Fade_Colour[])*Ray_Intersection->Depth/Interior->Fade_Di
stance);

Here it is as an ascii-art formula (fixed-width font preferred):


        / - Depth * (1.0 - Fade_Colour)\
       | ------------------------------ |
        \        Fade_Distance         /
att = e

This is applied separately to each color component (red, green, and blue).

-Nathan

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In article <3d3aef85$1@news.povray.org>,
 "Nathan Kopp" <nat### [at] koppcom> wrote:

> Hmmm... I don't know if that was supposed to make it into 3.5.

I think it was part of the fade_color patch, it would have had to be 
removed manually. It is useful as a substitute for constant absorbing 
media, especially for things like glass, I'm glad it wasn't removed. 
However, I would have preferred a different trigger...I don't like the 
1000 "magic number". -1 might have been better, or some special keyword.

-- 
Christopher James Huff <chr### [at] maccom>
POV-Ray TAG e-mail: chr### [at] tagpovrayorg
TAG web site: http://tag.povray.org/

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