Hi, I hope someone can help me.

There's a couple of things I'm not sure about with respect to looks_like.

Firstly there are two locations: the location of the light source and the
location of the object. I'm not sure if the light source gets transposed,
or if it only appears to shine through the object.

Secondly, what's the difference between looks_like and just putting a
light source at the centre of an object and making the object no_shadow?

Many aTdHvAaNnKcSe :-)

-- 
Bill Hails

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"Bill Hails" <bil### [at] europeyahoo-inccom> wrote in message
news:3f85d88c@news.povray.org...
>
> There's a couple of things I'm not sure about with respect to looks_like.
>
> Firstly there are two locations: the location of the light source and the
> location of the object. I'm not sure if the light source gets transposed,
> or if it only appears to shine through the object.
>
> Secondly, what's the difference between looks_like and just putting a
> light source at the centre of an object and making the object no_shadow?

Ack! I sure can foul up when I jump to quickly to answer things like this.
Don't know why my memory fails so badly sometimes. Unless you can't guess, I
had already posted an incorrect reply here and then cancelled it.

Let me see if I can manage to do better this time. It does indeed move the
object to the light's position.

Other than that, no, it doesn't shine light through it as though it were a
hole in an otherwise solid universe. Only allows light to pass without any
shadowing attached. What I mean by this, there isn't any projected light
through the looks_like object in the sense that if it were offset from the
light source location light would not beam outward from the object.

projected_through could help to pipe the light through an object if you
wanted the light shining from elsewhere but through the object.  Either way
you lose any filtered or transmitted coloring due to lack of shadow.

It's essentially what no_shadow does, just tied to the light more directly
than if were by a union instead.

Sorry for the mistake before, if anyone saw that too.  :-X  Again, if I'm
wrong in any way about the above answer maybe the POV-gods will take pity on
me.  :-)

Bob H.

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These two constructs are practically identical in functionality:

light_source
{ LIGHT_LOCATION, COLOR
  looks_like { OBJECT }
}

=

union
{ light_source { LIGHT_LOCATION, COLOR }
  object { OBJECT shadowless translate LIGHT_LOCATION }
}

  I hope this helps clearing out how looks_like works.

  (The bit that confuses most new (and even some old) users is the
implicit translation of the looks_like object.)

-- 
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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In article <3f85d88c@news.povray.org>,
 Bill Hails <bil### [at] europeyahoo-inccom> wrote:

> Secondly, what's the difference between looks_like and just putting a
> light source at the centre of an object and making the object no_shadow?

The looks_like object is shadowless to its light, but can cast shadows 
from other lights. Otherwise, it behaves like any other object.

-- 
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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Christopher James Huff wrote:

> In article <3f85d88c@news.povray.org>,
>  Bill Hails <bil### [at] europeyahoo-inccom> wrote:
> 
>> Secondly, what's the difference between looks_like and just putting a
>> light source at the centre of an object and making the object no_shadow?
> 
> The looks_like object is shadowless to its light, but can cast shadows
> from other lights. Otherwise, it behaves like any other object.
> 

Ah, that's the point I was missing, thanks.

-- 
Bill Hails

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Warp wrote:

>   These two constructs are practically identical in functionality:
> 
> light_source
> { LIGHT_LOCATION, COLOR
>   looks_like { OBJECT }
> }
> 
> =
> 
> union
> { light_source { LIGHT_LOCATION, COLOR }
>   object { OBJECT shadowless translate LIGHT_LOCATION }
> }
> 
>   I hope this helps clearing out how looks_like works.
> 
>   (The bit that confuses most new (and even some old) users is the
> implicit translation of the looks_like object.)
> 

Thanks, I'd kind of assumed it was the light source that got
translated to the object's position, but then in my current use of it
I have the two locations the same to start off with.

-- 
Bill Hails

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Thanks for your reply, things are a lot clearer (and brighter :-)
now

Hughes, B. wrote:

> "Bill Hails" <bil### [at] europeyahoo-inccom> wrote in message
> news:3f85d88c@news.povray.org...
>>
>> There's a couple of things I'm not sure about with respect to looks_like.
>>
>> Firstly there are two locations: the location of the light source and the
>> location of the object. I'm not sure if the light source gets transposed,
>> or if it only appears to shine through the object.
>>
>> Secondly, what's the difference between looks_like and just putting a
>> light source at the centre of an object and making the object no_shadow?
> 
> Ack! I sure can foul up when I jump to quickly to answer things like this.
> Don't know why my memory fails so badly sometimes. Unless you can't guess,
> I had already posted an incorrect reply here and then cancelled it.
> 
> Let me see if I can manage to do better this time. It does indeed move the
> object to the light's position.
> 
> Other than that, no, it doesn't shine light through it as though it were a
> hole in an otherwise solid universe. Only allows light to pass without any
> shadowing attached. What I mean by this, there isn't any projected light
> through the looks_like object in the sense that if it were offset from the
> light source location light would not beam outward from the object.
> 
> projected_through could help to pipe the light through an object if you
> wanted the light shining from elsewhere but through the object.  Either
> way you lose any filtered or transmitted coloring due to lack of shadow.
> 
> It's essentially what no_shadow does, just tied to the light more directly
> than if were by a union instead.
> 
> Sorry for the mistake before, if anyone saw that too.  :-X  Again, if I'm
> wrong in any way about the above answer maybe the POV-gods will take pity
> on
> me.  :-)
> 
> Bob H.

-- 
Bill Hails

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"Bill Hails" <bil### [at] europeyahoo-inccom> wrote in message
news:3f870b82@news.povray.org...
> Christopher James Huff wrote:
> >
> >> Secondly, what's the difference between looks_like and just putting a
> >> light source at the centre of an object and making the object
no_shadow?
> >
> > The looks_like object is shadowless to its light, but can cast shadows
> > from other lights. Otherwise, it behaves like any other object.

Well, I was about to go ahead and take it for granted that this is true. I
just had to see it for myself. I didn't find any shadows from other light
sources, whether the looks_like object is semi-transparent or opaque. Also,
only has self-shadowing on a per primitive basis too. In a union of sphere
and cone, for example, each doesn't cast a shadow onto  the other.

Bob H.

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In article <3f871c85@news.povray.org>,
 "Hughes, B." <omn### [at] charternet> wrote:

> Well, I was about to go ahead and take it for granted that this is true. I
> just had to see it for myself. I didn't find any shadows from other light
> sources, whether the looks_like object is semi-transparent or opaque.

Hmm, that makes it pretty useless...apparently no different than a union 
of a light source and a shadowless object.


> Also, only has self-shadowing on a per primitive basis too. In a 
> union of sphere and cone, for example, each doesn't cast a shadow 
> onto  the other.

I'm not sure if you're describing what it does or what it should 
do...are you saying look_like objects cast shadows on themselves but not 
on other objects?

Unions are kind of tricky...they are internally split up into separate 
objects to make bounding more efficient. Manually bounding the union 
will disable this behavior unless the split unions option 
(Split_Unions=on or +SU for non-Mac versions) is turned on, in which 
case even bounded unions will be split. This burned me when I was 
experimenting with the proximity and curvature patterns...I have no idea 
how it interacts with looks_like, I'd need to take a close look at the 
code.

Anyway, I'd suggest you just use a union of the light source with the 
object representing the light. This gives you most control over what 
actually happens...you can make specific parts shadowless, etc. If we're 
going to talk about what looks_like *should* do, I think it should 
behave in exactly the same way as a union with the light source, but 
changing it at this point would probably cause more problems than it 
solves.

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

Post a reply to this message

"Christopher James Huff" <cja### [at] earthlinknet> wrote in message
news:cja### [at] netplexaussieorg...
> In article <3f871c85@news.povray.org>,
>  "Hughes, B." <omn### [at] charternet> wrote:
>
> > Also, only has self-shadowing on a per primitive basis too. In a
> > union of sphere and cone, for example, each doesn't cast a shadow
> > onto  the other.
>
> I'm not sure if you're describing what it does or what it should
> do...are you saying look_like objects cast shadows on themselves but not
> on other objects?

Themselves, yes; on a per individual primitive basis, having only a shadowed
side versus lit side. So what I was saying is that if a sphere and cone are
next to each other, in a union, they don't cast a shadow onto each other. I
guess your explanation about bounding below is the reason why.

> Unions are kind of tricky...they are internally split up into separate
> objects to make bounding more efficient. Manually bounding the union
> will disable this behavior unless the split unions option
> (Split_Unions=on or +SU for non-Mac versions) is turned on, in which
> case even bounded unions will be split. This burned me when I was
> experimenting with the proximity and curvature patterns...I have no idea
> how it interacts with looks_like, I'd need to take a close look at the
> code.
>
> Anyway, I'd suggest you just use a union of the light source with the
> object representing the light. This gives you most control over what
> actually happens...you can make specific parts shadowless, etc. If we're
> going to talk about what looks_like *should* do, I think it should
> behave in exactly the same way as a union with the light source, but
> changing it at this point would probably cause more problems than it
> solves.

I'll agree with that. Many times I've passed on using a looks_like and used
union with a light source instead, with the idea being to get more control
of the object appearance. I know people must've suggested a 'shadow on',  or
'no_shadow off', method before, for doing things like this, instead of being
stuck with the shadowless invocation caused by looks_like. Therefore being
able to force shadowing within an otherwise no_shadow CSG object. I can
imagine it being of some use. Due to the way all other light sources fail to
interact properly with the current way looks_like works.

Just to give it a try, I checked what you suggested about manual bounding
within the CSG union, except still for a looks_like object, and still aren't
any shadows. I think it's been said that looks_like is only a shortcut to
creating a light plus object, not the only way available and perhaps that's
why no one has deemed it necessary to change. Or, as you said, there might
be some difficulties is allowing shadowing via the internal bounding
hierarchy?

-- 
Bob H.
3digitaleyes.com

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