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I asked this in p.general in a thread, but no-one has answered, so I'll ask
it here in its own thread:
What do vista and light buffers do and how they work? A precise answer from
someone who knows well the algorithm, please.
I'm very interested in knowing this.
--
main(i,_){for(_?--i,main(i+2,"FhhQHFIJD|FQTITFN]zRFHhhTBFHhhTBFysdB"[i]
):_;i&&_>1;printf("%s",_-70?_&1?"[]":" ":(_=0,"\n")),_/=2);} /*- Warp -*/
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On 30 Aug 2000 10:30:51 -0400, Warp wrote:
> I asked this in p.general in a thread, but no-one has answered, so I'll ask
>it here in its own thread:
>
> What do vista and light buffers do and how they work? A precise answer from
>someone who knows well the algorithm, please.
> I'm very interested in knowing this.
Not a precise answer, but...
The vista buffer is a 2-d representation of the locations of the objects in
the scene, as seen from the camera. When tracing camera rays, you need only
check the objects at that location in the vista buffer.
The light buffers are similar, one per light, and are used for tracing
shadow rays.
--
Ron Parker http://www2.fwi.com/~parkerr/traces.html
My opinions. Mine. Not anyone else's.
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> The light buffers are similar, one per light, and are used for tracing
> shadow rays.
Don't know well the algo though...
For lights these are not only 2D but 3D: a box which
faces have a 2D representation of the objects around. Using light
buffers can be greatly memory expensive if a lot of lights are used
(as in my unique IRTC entry 2 years ago:
http://oz.irtc.org/ftp/pub/stills/1998-08-31/afterain.jpg
) but should speed up almost all scenes. However sometimes light
buffers are not desirable for instance when some objects are not
well projected on the light boxes (it happened me once, but don't
remember exactly how).
*** Nicolas Calimet
*** http://pov4grasp.free.fr
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On Wed, 30 Aug 2000 19:34:39 +0200, Nicolas Calimet wrote:
>> The light buffers are similar, one per light, and are used for tracing
>> shadow rays.
>
> Don't know well the algo though...
> For lights these are not only 2D but 3D: a box which
>faces have a 2D representation of the objects around. Using light
That's still 2D.
--
Ron Parker http://www2.fwi.com/~parkerr/traces.html
My opinions. Mine. Not anyone else's.
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Ron Parker <ron### [at] povray org> wrote:
: The vista buffer is a 2-d representation of the locations of the objects in
: the scene, as seen from the camera.
How does povray determine those 2D areas?
--
main(i,_){for(_?--i,main(i+2,"FhhQHFIJD|FQTITFN]zRFHhhTBFHhhTBFysdB"[i]
):_;i&&_>1;printf("%s",_-70?_&1?"[]":" ":(_=0,"\n")),_/=2);} /*- Warp -*/
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On 30 Aug 2000 18:40:54 -0400, Warp wrote:
>Ron Parker <ron### [at] povrayorg> wrote:
>: The vista buffer is a 2-d representation of the locations of the objects in
>: the scene, as seen from the camera.
>
> How does povray determine those 2D areas?
By projecting the bounding boxes onto a sphere, I suspect. I've never looked.
--
Ron Parker http://www2.fwi.com/~parkerr/traces.html
My opinions. Mine. Not anyone else's.
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On 30 Aug 2000 23:55:38 -0400, ron### [at] povrayorg (Ron Parker)
wrote:
>>: The vista buffer is a 2-d representation of the locations of the objects in
>>: the scene, as seen from the camera.
>>
>> How does povray determine those 2D areas?
>
>By projecting the bounding boxes onto a sphere, I suspect. I've never looked.
That's one way to put it but maybe it only stores the bounding box
vertices in spherical coordinates with respect to every light source?
That would be faster and less memory consuming, I think.
Peter Popov ICQ : 15002700
Personal e-mail : pet### [at] usanet
TAG e-mail : pet### [at] tagpovrayorg
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Ron Parker <ron### [at] povrayorg> wrote:
: The light buffers are similar, one per light, and are used for tracing
: shadow rays.
What about area lights?
--
main(i,_){for(_?--i,main(i+2,"FhhQHFIJD|FQTITFN]zRFHhhTBFHhhTBFysdB"[i]
):_;i&&_>1;printf("%s",_-70?_&1?"[]":" ":(_=0,"\n")),_/=2);} /*- Warp -*/
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> : The light buffers are similar, one per light, and are used for tracing
> : shadow rays.
>
> What about area lights?
From the POV docs:
"The light buffer is created by enclosing each light source in an
imaginary box and projecting the bounding box hierarchy onto each of its
six sides. Since this relies on a fixed light source, light buffers will
not be used for area lights."
*** Nicolas Calimet
*** http://pov4grasp.free.fr
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Nicolas Calimet wrote:
> From the POV docs:
> "The light buffer is created by enclosing each light source in an
> imaginary box and projecting the bounding box hierarchy onto each of its
> six sides. Since this relies on a fixed light source, light buffers will
> not be used for area lights."
Hey Warp, RTFM !
TeeHee
--
Ken Tyler - 1400+ POV-Ray, Graphics, 3D Rendering, and Raytracing Links:
http://home.pacbell.net/tylereng/index.html http://www.povray.org/links/
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On Thu, 31 Aug 2000 09:17:50 +0300, Peter Popov wrote:
>On 30 Aug 2000 23:55:38 -0400, ron### [at] povrayorg (Ron Parker)
>wrote:
>
>>>: The vista buffer is a 2-d representation of the locations of the objects in
>>>: the scene, as seen from the camera.
>>>
>>> How does povray determine those 2D areas?
>>
>>By projecting the bounding boxes onto a sphere, I suspect. I've never looked.
>
>That's one way to put it but maybe it only stores the bounding box
>vertices in spherical coordinates with respect to every light source?
I fail to see a difference between what I said and what you said.
--
Ron Parker http://www2.fwi.com/~parkerr/traces.html
My opinions. Mine. Not anyone else's.
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On 31 Aug 2000 12:28:07 -0400, Ron Parker wrote:
>On Thu, 31 Aug 2000 09:17:50 +0300, Peter Popov wrote:
>>On 30 Aug 2000 23:55:38 -0400, ron### [at] povrayorg (Ron Parker)
>>wrote:
>>
>>>>: The vista buffer is a 2-d representation of the locations of the objects in
>>>>: the scene, as seen from the camera.
>>>>
>>>> How does povray determine those 2D areas?
>>>
>>>By projecting the bounding boxes onto a sphere, I suspect. I've never looked.
I was wrong. It projects the bounding boxes onto the faces of a box. I
suspect it's done this way because planar polygons are easier to deal with.
--
Ron Parker http://www2.fwi.com/~parkerr/traces.html
My opinions. Mine. Not anyone else's.
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> (as in my unique IRTC entry 2 years ago:
> http://oz.irtc.org/ftp/pub/stills/1998-08-31/afterain.jpg
Hey, that's really beautiful... got the source code? :)
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> Hey, that's really beautiful... got the source code? :)
Thanks ;-)
Source code is given on the IRTC website (www.irtc.org)
if you look to the July-August 1998 results for still images;
alternatively you can get the .zip directly from here:
http://oz.irtc.org/ftp/pub/stills/1998-08-31/afterain.zip
Beware that it needed more than 4 days to render on a
fast machine at that time (was a Digital Alpha) because of the
atmosphere effect combined to focal blur. I didn't tried to
render it again, but it should be at least as long on a PC
PIII/500. Could be a little faster if using +ul switch to turn
on light buffers, but then it requires about 250 MB of memory :-)
For more details:
http://oz.irtc.org/ftp/pub/stills/1998-08-31/afterain.txt
*** Nicolas Calimet
*** http://pov4grasp.free.fr
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On 31 Aug 2000 12:28:07 -0400, ron### [at] povrayorg (Ron Parker)
wrote:
>>>By projecting the bounding boxes onto a sphere, I suspect. I've never looked.
>>
>>That's one way to put it but maybe it only stores the bounding box
>>vertices in spherical coordinates with respect to every light source?
>
>I fail to see a difference between what I said and what you said.
There might be none, it's just that when I read "projected onto
something" I still see that something as an object in 3D and thus the
points on it have 3D coordinates. Technically, though, you're right,
there's no difference, it's just the way it sounds.
Peter Popov ICQ : 15002700
Personal e-mail : pet### [at] usanet
TAG e-mail : pet### [at] tagpovrayorg
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