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Among other things, Warp saw fit to write:
> And sampling along a spline (iow. splitting the spline into very small
> parts and making a whole ray-scene intersection test for each small part)
> is exactly what would make it prohibitively slow.
> Would it really be worth the effort?
>
> Radiosity requires lots of sampling, but the results can be spectacular.
> Media also requires lots of sampling, but the results can also be quite
> spectacular. Variable IOR would probably require even more sampling, yet
> I highly doubt the end result will look any spectacular.
Could it maybe be "faked" in some way, similarly to how the caustics keyword
fakes photons?
I'm not sure what kind of effect it would give, I'm just throwing some white
noise into the discussion :-)
--
light_source{9+9*x,1}camera{orthographic look_at(1-y)/4angle 30location
9/4-z*4}light_source{-9*z,1}union{box{.9-z.1+x clipped_by{plane{2+y-4*x
0}}}box{z-y-.1.1+z}box{-.1.1+x}box{.1z-.1}pigment{rgb<.8.2,1>}}//Jellby
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In article <44014e05@news.povray.org>, war### [at] tag povrayorg says...
> Patrick Elliott <sha### [at] hotmailcom> wrote:
> > Now... A Spline Path could work though, maybe?
>
> And sampling along a spline (iow. splitting the spline into very small
> parts and making a whole ray-scene intersection test for each small part)
> is exactly what would make it prohibitively slow.
> Would it really be worth the effort?
>
But, is it actually slower than for a regular line? I mean, sure, the
calculation may require a few more math steps, but intersections still
require the same sort of testing, even for a straight line right? Maybe I
am wrong.
> Radiosity requires lots of sampling, but the results can be spectacular.
> Media also requires lots of sampling, but the results can also be quite
> spectacular. Variable IOR would probably require even more sampling, yet
> I highly doubt the end result will look any spectacular.
>
Depends. What about an object where the variable IOR is based on a
pattern, similar to what you can do with media? Right now you can't even
simulate that, at least unless you wanted to glue together hundreds of
discrete objects, all approximate shapes and all with different IORs. We
really can't be sure what effect would result, without trying it. And for
that matter, from what I understand, there are real world materials that
actually have a "different" IOR depending on the angle of incidence of
the light hitting it (I think I remember reading about some anyway).
--
void main () {
call functional_code()
else
call crash_windows();
}
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In article <l2l### [at] badulaqueunexes>, me### [at] privacynet says...
> Among other things, Warp saw fit to write:
>
> > And sampling along a spline (iow. splitting the spline into very small
> > parts and making a whole ray-scene intersection test for each small part)
> > is exactly what would make it prohibitively slow.
> > Would it really be worth the effort?
> >
> > Radiosity requires lots of sampling, but the results can be spectacular.
> > Media also requires lots of sampling, but the results can also be quite
> > spectacular. Variable IOR would probably require even more sampling, yet
> > I highly doubt the end result will look any spectacular.
>
> Could it maybe be "faked" in some way, similarly to how the caustics keyword
> fakes photons?
>
> I'm not sure what kind of effect it would give, I'm just throwing some white
> noise into the discussion :-)
>
Well, as I pointed out in a reply, yeah, for some cases, others, like a
complex pattern based IOR would be either impossible or prohibitively
complex to manage, nor could any simulation deal with materials with odd
properties, like IOR differing by the angle light enters.
--
void main () {
call functional_code()
else
call crash_windows();
}
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Patrick Elliott <sha### [at] hotmailcom> wrote:
> But, is it actually slower than for a regular line? I mean, sure, the
> calculation may require a few more math steps, but intersections still
> require the same sort of testing, even for a straight line right? Maybe I
> am wrong.
You have to test a straight line against the scene once. A spline would
have to be tested hundreds or thousands of times.
--
- Warp
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Warp wrote:
> Radiosity requires lots of sampling, but the results can be spectacular.
> Media also requires lots of sampling, but the results can also be quite
> spectacular. Variable IOR would probably require even more sampling, yet
> I highly doubt the end result will look any spectacular.
This is probably the best argument against it I've heard. I'm sure
someone will eventually write a patch to do it, and we'll see at that
point whether your argument is justified.
Personally, I think that if used well, it could aid in realism the same
way that radiosity, focal blur, et al can - that is, when the viewer
doesn't realize that the effect is there, that's when it has the
greatest benefit.
...Chambers
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Warp nous apporta ses lumieres en ce 27/02/2006 01:09:
> Patrick Elliott <sha### [at] hotmailcom> wrote:
>
>>But, is it actually slower than for a regular line? I mean, sure, the
>>calculation may require a few more math steps, but intersections still
>>require the same sort of testing, even for a straight line right? Maybe I
>>am wrong.
>
>
> You have to test a straight line against the scene once. A spline would
> have to be tested hundreds or thousands of times.
>
You'd need some spacing for the tests. To small and it takes for ever. To large and
you can go right
trough several objects. Then, it a test get inside an object, take a new point between
the last and
next to last, test again until you reach a sufficient confidence value.
It will take very long if you only have simple primitives, and now the fun beggin when
you add
torus, superellipsoids, sphere_sweeps and the nightmare is on you as soon as you add
some
isosurfaces. And you *think* that radiosity with photons, scathering media,
reflections and
transparcy, togheter with many area_lights, and area_light photons make for long
render time? Does
anybody have a cluster of 100GHz computers at hand?
--
Alain
-------------------------------------------------
REMEMBER: WHATEVER HAPPENS, HAPPENS FOR A REASON.
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"Jellby" <me### [at] privacynet> wrote in message
news:l2l### [at] badulaqueunexes...
> Could it maybe be "faked" in some way, similarly to how the caustics
> keyword
> fakes photons?
>
The Pov Reference Manual says under "Language Things that don't work as one
expects":
"
"Can I specify variable IOR for an object? Is there any patch that can do
this? Is it possible?"
Short answer: No.
Long answer:
There are basically two ways of defining variable IOR for an object: IOR
changing on the surface of the object and IOR changing throughout inside the
object.
The first one is physically incorrect. For uniform IOR it simulates physical
IOR quite correctly since for objects with uniform density the light bends
at the surface of the object and nowhere else. However if the density of the
object is not uniform but changes throughout its volume, the light will bend
inside the object, while travelling through it, not only on the surface of
the object.
This is why variable IOR on the surface of the object is incorrect and the
possibility of making this was removed in POV-Ray 3.1. "
I wonder why they kept faked caustics in Pov-Ray when we have photons that
can do it better, and took out surface variable ior leaving us with no
replacement.
--
-Nekar Xenos-
----------------------------------------
"The truth is out there..."
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Nekar Xenos nous apporta ses lumieres en ce 01/03/2006 10:40:
> I wonder why they kept faked caustics in Pov-Ray when we have photons that
> can do it better, and took out surface variable ior leaving us with no
> replacement.
>
>
Faked caustics are way faster and good enough in many situations. A prime example been
the light
play on the bottom of a water body.
--
Alain
-------------------------------------------------
'I can resist anything but temptation.'
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We've all been thinking along the lines of doing it with a statement similar
to media which is very complex. How about something simpler, like
fade_colour? If the ior gets denser at a specific rate like fade_colour
does, will this not make it more feasable to do?
--
-Nekar Xenos-
----------------------------------------
"The truth is out there..."
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"Nekar Xenos" <go_### [at] yahoocom> wrote:
> We've all been thinking along the lines of doing it with a statement similar
> to media which is very complex. How about something simpler, like
> fade_colour? If the ior gets denser at a specific rate like fade_colour
> does, will this not make it more feasable to do?
>
>
> --
> -Nekar Xenos-
> ----------------------------------------
> "The truth is out there..."
The effect of a changing ior is not so much affected by the rate of change
of its value, but its change relative to the direction of travel of the
light ray. In order for it to affect the direction, it needs to interact
with a change in iro along a surface not perpendicular to its line of
travel. So this would require, not only discrete sampling to determine the
ior along the light path, but also some sort of adaptive sampling to
determine an effective angle of incidence for the change in ior. This
would not be entrely impossible, however, it would significantly increase
the calculations and overead involved and probably not give significantly
noticeable results versus what could be faked much more easily.
-tgq
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