On 01/23/2018 03:28 PM, clipka wrote:
> Am 23.01.2018 um 16:57 schrieb William F Pokorny:
> 
...
> I'd say yes, that would be quite useful indeed.
> 
> (And maybe also `media_attenuation on` for light sources inside the
> media container.)
> 

I have been weeks now on and off digging into media and media code. It 
turns out there are scenes - abyss.pov for example - where the 
light_source IS inside the media container. We get no attenuation no 
matter other settings in those cases and often a washed out visual 
result. I'm starting to wonder if this lack of attenuation is behind the 
struggles with contrast in some media scenes.

Anyway, I want to immediately let folks know there is a way to get 
media_attenuation on in cases where your light source(s) are inside your 
media container. If you set up a difference creating either a small void 
or small divot around your light source(s) - presto media_attenuation is 
on.

It's an obvious idea since for lights outside the media container in my 
original posting the attenuation is always on. Of course, the small void 
idea didn't work when I first tried it...

Turns out in the global - the post transforms - scene coordinate space, 
the distance from the light outside to surface of the media container 
must be >= 0.001. This value appears to come from '#define 
SHADOW_TOLERANCE 1.0e-3' value being used in trace.cpp, but I've not 
spent time hacking at that code to be 100% sure.

Getting the lights outside the container >= 0.001 for attenuation works 
all the way back to 3.6.1 in my testing.

Bill P.

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Le 18-02-11 à 09:47, William F Pokorny a écrit :
> On 01/23/2018 03:28 PM, clipka wrote:
>> Am 23.01.2018 um 16:57 schrieb William F Pokorny:
>>
> ...
>> I'd say yes, that would be quite useful indeed.
>>
>> (And maybe also `media_attenuation on` for light sources inside the
>> media container.)
>>
> 
> I have been weeks now on and off digging into media and media code. It 
> turns out there are scenes - abyss.pov for example - where the 
> light_source IS inside the media container. We get no attenuation no 
> matter other settings in those cases and often a washed out visual 
> result. I'm starting to wonder if this lack of attenuation is behind the 
> struggles with contrast in some media scenes.
> 
> Anyway, I want to immediately let folks know there is a way to get 
> media_attenuation on in cases where your light source(s) are inside your 
> media container. If you set up a difference creating either a small void 
> or small divot around your light source(s) - presto media_attenuation is 
> on.
> 
> It's an obvious idea since for lights outside the media container in my 
> original posting the attenuation is always on. Of course, the small void 
> idea didn't work when I first tried it...
> 
> Turns out in the global - the post transforms - scene coordinate space, 
> the distance from the light outside to surface of the media container 
> must be >= 0.001. This value appears to come from '#define 
> SHADOW_TOLERANCE 1.0e-3' value being used in trace.cpp, but I've not 
> spent time hacking at that code to be 100% sure.
> 
> Getting the lights outside the container >= 0.001 for attenuation works 
> all the way back to 3.6.1 in my testing.
> 
> Bill P.
> 

So, we should add :
looks_like{sphere{0, 0.001 pigment{rgbt 1}}}
to the lights that are inside some media container.

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Alain <kua### [at] videotronca> wrote:

>
> So, we should add :
> looks_like{sphere{0, 0.001 pigment{rgbt 1}}}
> to the lights that are inside some media container.

I just tried that, and it doesn't work, unfortunately. (And the placement of the
looks_like(..) entry in the light code doesn't fix it either, relative to the
light's translation statement; I thought it might, but no luck.)

Apparently, Bill's successful trick needs an actual CGS difference of a tiny
object from the media container; then media_attenuation comes back on (as if the
light was again outside the media.) Very nice! By the way, here's an interesting
little detail about that small void. My media object code looks like this:

difference{
sphere{0,1}
sphere{0, .005 translate <-.2, 0, .9>} // translation same as light's position
hollow on
.....

The hollow keyword applies to BOTH objects AFAIK-- meaning both objects will
'contain' media. Yet the CSG-difference trick works anyway-- even though the
light is again 'inside a media container' rather than outside it. I don't know
what to make of that, re: a required media-free(?) void , but it's interesting.

My tests so far have been with object media, and with the camera outside the
object. I haven't yet tested atmospheric media. Or a situation where the camera
is *inside* the media object.

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On 02/12/2018 01:16 PM, Alain wrote:
> Le 18-02-11 à 09:47, William F Pokorny a écrit :
> 
> So, we should add :
> looks_like{sphere{0, 0.001 pigment{rgbt 1}}}
> to the lights that are inside some media container.
> 

Ah, good thought. I see Kenneth already tried it last night without 
success. Thanks Kenneth - saved me the time.

Longer term the aim is to be able to control whether media attenuation 
is on or off when using media containers by some explicit SDL mechanism. 
We've also got the problem we cannot turn it off when the light is 
outside, but to the quality of the end result it matters less I think.

Still trying to get my brain to digest as much as possible of the whole 
of the media code, how it interacts with itself and how it interacts 
with the rest of POV-Ray...

"The circles rapidly grow small—we are plunging madly within the grasp 
of the whirlpool—and amid a roaring, and bellowing, and thundering of 
ocean and of tempest, the ship is quivering—oh God! and ——going down!"

:-) I'm making progress, but it's slow.

Bill P.

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William F Pokorny <ano### [at] anonymousorg> wrote:
>
> Still trying to get my brain to digest as much as possible of the whole
> of the media code, how it interacts with itself and how it interacts
> with the rest of POV-Ray...
>

I'm in the throes of doing some further tests (although still with a media
container-object and the camera outside it)-- and I'm seeing some rather odd
things (so far) having to do with scattering's 'extinction' value. The fact that
media_attenuation is currently ALWAYS on (for lights outside the media, and when
your 'void' difference trick is used for a light *inside* the media), it's
really difficult to tell the difference between the media_attenuation effect,
and the separate shadowing (and 'self-shadowing') effects that
scattering/extinction produces. Those effects can't currently be separated out.
I've had to resort to some animation tests of the media with a moving light
source, to try and understand what's going on. It's a  s-l-o-w  process... but
worth the effort ;-)

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William F Pokorny <ano### [at] anonymousorg> wrote:

> "The circles rapidly grow small—we are plunging madly within the grasp
> of the whirlpool—and amid a roaring, and bellowing, and thundering of
> ocean and of tempest, the ship is quivering—oh God! and ——going down!"

https://www.youtube.com/watch?v=AX0XDHF3M60

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On 13/02/2018 15:03, Bald Eagle wrote:
> William F Pokorny <ano### [at] anonymousorg> wrote:
> 
>> "The circles rapidly grow small—we are plunging madly within the grasp
>> of the whirlpool—and amid a roaring, and bellowing, and thundering of
>> ocean and of tempest, the ship is quivering—oh God! and ——going down!"
> 
> https://www.youtube.com/watch?v=AX0XDHF3M60
> 

A bit of a Whoosh!, there. But I enjoyed the clip. :-)


-- 

Regards
     Stephen

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Stephen <mca### [at] aolcom> wrote:
> On 13/02/2018 15:03, Bald Eagle wrote:
> > William F Pokorny <ano### [at] anonymousorg> wrote:
> >
> >> "The circles rapidly grow small—we are plunging madly within the grasp
> >> of the whirlpool—and amid a roaring, and bellowing, and thundering of
> >> ocean and of tempest, the ship is quivering—oh God! and ——going down!"
> >
> > https://www.youtube.com/watch?v=AX0XDHF3M60
> >
>
> A bit of a Whoosh!, there. But I enjoyed the clip. :-)

The Quote is from "The House of Usher" by Poe.
The character's name is _Roderick_ Usher.

Or Wodewick Usheww....  :D

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On 13-2-2018 16:55, Bald Eagle wrote:
> Stephen <mca### [at] aolcom> wrote:
>> On 13/02/2018 15:03, Bald Eagle wrote:
>>> William F Pokorny <ano### [at] anonymousorg> wrote:
>>>
>>>> "The circles rapidly grow small—we are plunging madly within the grasp
>>>> of the whirlpool—and amid a roaring, and bellowing, and thundering of
>>>> ocean and of tempest, the ship is quivering—oh God! and ——going down!"
>>>
>>> https://www.youtube.com/watch?v=AX0XDHF3M60
>>>
>>
>> A bit of a Whoosh!, there. But I enjoyed the clip. :-)
> 
> The Quote is from "The House of Usher" by Poe.
> The character's name is _Roderick_ Usher.
> 
> Or Wodewick Usheww....  :D
> 
> 



-- 
Thomas

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On 13/02/2018 15:55, Bald Eagle wrote:
> Stephen <mca### [at] aolcom> wrote:
>> On 13/02/2018 15:03, Bald Eagle wrote:
>>> William F Pokorny <ano### [at] anonymousorg> wrote:
>>>
>>>> "The circles rapidly grow small—we are plunging madly within the grasp
>>>> of the whirlpool—and amid a roaring, and bellowing, and thundering of
>>>> ocean and of tempest, the ship is quivering—oh God! and ——going down!"
>>>
>>> https://www.youtube.com/watch?v=AX0XDHF3M60
>>>
>>
>> A bit of a Whoosh!, there. But I enjoyed the clip. :-)
> 
> The Quote is from "The House of Usher" by Poe.
> The character's name is _Roderick_ Usher.
> 

Ah! literature. No wonder I didn't recognise it.


> Or Wodewick Usheww....  :D
> 
> 
> 

Wight! ;)


-- 

Regards
     Stephen

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