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(using Windows 7 64-bit)
I haven't used a light_group in a long time, so I can't remember exactly what
its behavior was in v3.62, but I don't think it's working correctly in the beta.
I've included a test scene below.
Although the light_group's light does not appear on objects outside the group
(which is correct), it's still casting shadows from those objects, onto the
object in the light_group. Is that proper behavior? I don't recall a similar
problem in v3.62 (although I could be wrong.) The included documentation doesn't
mention shadow behavior (except as relates to scattering media.)
Also, the light's looks_like object (yellow sphere) is showing lighting effects
from the extra 'global light', even with 'global_lights off' in the light_group
(although there's no shadow from that sphere, as far as I can tell.) I don't
know if that is correct behavior or not.
--------
#version 3.71;
global_settings{assumed_gamma 1.0 max_trace_level 5}
camera {
perspective
location <0, 0, -3.5>
look_at <0, 0, 0>
right x*image_width/image_height
angle 35
}
background {rgb .2}
// the extra 'global light'-- up and to the left
light_source {
0*x
color rgb <1,1,1>
translate <-30, 30, -10>
}
light_group{
light_source {
0*x
color rgb 80000*<1,.5,.5>
fade_power 1.5
fade_distance .001
looks_like{
sphere{0,.03 texture{pigment{rgb <1,.8,0>}finish{ambient 0 diffuse .9}}}
}
translate <.09, .2, -.06>
}
plane{y,-.61
texture{
pigment{
cells
scale .5
color_map{
[0 rgb .5]
[1 rgb 1]
}
}
finish{
ambient 0
diffuse .4
}
}
}
// global_lights on
}
// tall thin box
#declare TALL_BOX =
box{<-.02,-1,-.02>, <.02,1,.02>
texture{
pigment{rgb <.4,1,.4>}
finish{ambient 0 diffuse .9}
}
rotate 30*y
}
object{TALL_BOX}
object{TALL_BOX
rotate 80*x
translate <-.3,-.3,.3>
}
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Le 17-04-30 à 11:04, Kenneth a écrit :
> (using Windows 7 64-bit)
>
> I haven't used a light_group in a long time, so I can't remember exactly what
> its behavior was in v3.62, but I don't think it's working correctly in the beta.
> I've included a test scene below.
>
> Although the light_group's light does not appear on objects outside the group
> (which is correct), it's still casting shadows from those objects, onto the
> object in the light_group. Is that proper behavior? I don't recall a similar
> problem in v3.62 (although I could be wrong.) The included documentation doesn't
> mention shadow behavior (except as relates to scattering media.)
This is the correct and expected behaviour and did not change since
light_group have been introduced.
>
> Also, the light's looks_like object (yellow sphere) is showing lighting effects
> from the extra 'global light', even with 'global_lights off' in the light_group
> (although there's no shadow from that sphere, as far as I can tell.) I don't
> know if that is correct behavior or not.
Can't tell for that part, but it brobably did not change.
>
> --------
> #version 3.71;
>
> global_settings{assumed_gamma 1.0 max_trace_level 5}
>
> camera {
> perspective
> location <0, 0, -3.5>
> look_at <0, 0, 0>
> right x*image_width/image_height
> angle 35
> }
>
> background {rgb .2}
>
> // the extra 'global light'-- up and to the left
> light_source {
> 0*x
> color rgb <1,1,1>
> translate <-30, 30, -10>
> }
>
>
> light_group{
> light_source {
> 0*x
> color rgb 80000*<1,.5,.5>
> fade_power 1.5
> fade_distance .001
> looks_like{
> sphere{0,.03 texture{pigment{rgb <1,.8,0>}finish{ambient 0 diffuse .9}}}
> }
> translate <.09, .2, -.06>
> }
> plane{y,-.61
> texture{
> pigment{
> cells
> scale .5
> color_map{
> [0 rgb .5]
> [1 rgb 1]
> }
> }
> finish{
> ambient 0
> diffuse .4
> }
> }
> }
> // global_lights on
> }
>
>
> // tall thin box
> #declare TALL_BOX =
> box{<-.02,-1,-.02>, <.02,1,.02>
> texture{
> pigment{rgb <.4,1,.4>}
> finish{ambient 0 diffuse .9}
> }
> rotate 30*y
> }
>
> object{TALL_BOX}
>
> object{TALL_BOX
> rotate 80*x
> translate <-.3,-.3,.3>
> }
>
>
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Alain <kua### [at] videotron ca> wrote:
>
> This is the correct and expected behaviour and did not change since
> light_group have been introduced.
>
I'm having trouble understanding the logic of this; but maybe it will become
clearer to me, as I continue to think about it. ;-)
Long ago, I wrote and archived several light_group 'test scenes' (with lots of
notes to myself about its behavior), but I can't find the files. :-(
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On 1-5-2017 1:40, Kenneth wrote:
> Alain <kua### [at] videotronca> wrote:
>
>>
>> This is the correct and expected behaviour and did not change since
>> light_group have been introduced.
>>
>
> I'm having trouble understanding the logic of this; but maybe it will become
> clearer to me, as I continue to think about it. ;-)
>
> Long ago, I wrote and archived several light_group 'test scenes' (with lots of
> notes to myself about its behavior), but I can't find the files. :-(
>
>
I agree with you. Intuitively I would say that this shadow behaviour is
not correct. It annihilates imho one of the fundamental reasons to use
light_group in the first place.
--
Thomas
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"Kenneth" <kdw### [at] gmailcom> wrote:
> Alain <kua### [at] videotronca> wrote:
>
> >
> > This is the correct and expected behaviour and did not change since
> > light_group have been introduced.
> >
>
> I'm having trouble understanding the logic of this; but maybe it will become
> clearer to me, as I continue to think about it. ;-)
You need to consider the purpose of light groups: They exist to allow additional
local lights for objects, a technique that is frequently used in computer
animations to help make certain objects appear lit "better" - after all, there
is no physical equivalent of light groups in the real world.
What you are looking for is something like "shadow groups", though I suppose you
might want to rethink what you actually want to render.
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On 1-5-2017 9:40, Thorsten Froehlich wrote:
> "Kenneth" <kdw### [at] gmailcom> wrote:
>> Alain <kua### [at] videotronca> wrote:
>>
>>>
>>> This is the correct and expected behaviour and did not change since
>>> light_group have been introduced.
>>>
>>
>> I'm having trouble understanding the logic of this; but maybe it will become
>> clearer to me, as I continue to think about it. ;-)
>
> You need to consider the purpose of light groups: They exist to allow additional
> local lights for objects, a technique that is frequently used in computer
> animations to help make certain objects appear lit "better" - after all, there
> is no physical equivalent of light groups in the real world.
>
> What you are looking for is something like "shadow groups", though I suppose you
> might want to rethink what you actually want to render.
>
>
As for me, that clarifies a lot indeed. Use a bit different than I
expected. I have used light_group is a somewhat different context with a
reddish sundown landscape and a 'midday' lighted moon. I think I got
some unwanted artefacts but I resolved them with no_shadow and
no_reflection.
--
Thomas
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"Thorsten Froehlich" <nomail@nomail> wrote:
>
> You need to consider the purpose of light groups: They exist to allow additional
> local lights for objects, a technique that is frequently used in computer
> animations to help make certain objects appear lit "better" -
That's basically what the documentation says, although the behavior of shadows
vis-a-vis a light_group isn't discussed there-- which seems like an important
topic, as shadow behavior may be 'unexpected', in an intuitive sense. (Well, at
least for me-- and maybe Thomas as well.) My immediate intuition when reading
the docs is basically this: that a light_group should *only* light the objects
in the group, AND *only* those objects should cast shadows from that light.
Obviously, it doesn't work according to my intuition... ;-) I admit that I
haven't completely thought through the ramifications of my idea; there may
indeed be some logical conundrums with it. But its present behavior seems like a
conundrum (to me.)
>
> What you are looking for is something like "shadow groups", though I
> suppose you might want to rethink what you actually want to render.
That's very possible (and I could probably find a work-around to the scene
problem I encountered, using no_image and/or no_shadow as Thomas mentioned.) My
current scene-- which prompted me to post about this-- is an animation of an
expanding 'explosion' on the top of a tower (like the old A-bomb tests.) I
wanted a VERY bright fading light to flare on the ground (and only there), from
a position at the center of the explosion, so I made a light_group with the
ground-- but found that the explosion sphere and the tower were casting unwanted
harsh shadows... which I didn't expect (based on my... intuition...)
I think my past use of a light_group was always with a carefully-positioned
spotlight, so I probably never noticed the unexpected shadow behavior from other
scene objects. (Actually, I do recall once making a scene where I wanted a light
*underneath* the ground, to artifically light up some above-ground objects-- and
I did have to add no_shadow to the ground. But I thought that was because I had
made some kind of dumb mistake in my complex code.)
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Am 30.04.2017 um 18:15 schrieb Alain:
> This is the correct and expected behaviour and did not change since
> light_group have been introduced.
Kenneth and Tomas' posts are clear evidence (nay, proof) that it is
/not/ "expected behaviour" - or at least not universally so.
My personal guess is that light groups were originally implemented for a
use case where shadowing objects or media were a non-issue, and thus no
thought was given in that direction whatsoever. And that when the issue
first arose, light groups were well-established already, so that the
developers were reluctant to change the implementation, out of fear of
breaking existing scenes.
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Am 30.04.2017 um 17:04 schrieb Kenneth:
> Also, the light's looks_like object (yellow sphere) is showing lighting effects
> from the extra 'global light', even with 'global_lights off' in the light_group
> (although there's no shadow from that sphere, as far as I can tell.) I don't
> know if that is correct behavior or not.
I haven't examined the issue myself, but I wouldn't be surprised if
`looks_like` objects would always be hooked up into the global group
(again presumably because no thought had been given about the
interaction of these two features).
A workaround would be to replace the `looks_like` object with a
corresponding "regular" object in the same light group, with
`no_shadow`, `no_radiosity` and whatever other flags the `looks_like`
feature automatically sets.
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Am 03.05.2017 um 20:40 schrieb clipka:
> Kenneth and Tomas' posts are clear evidence (nay, proof) that it is
> /not/ "expected behaviour" - or at least not universally so.
(Sorry Tom, stole an "h" from you there...)
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