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Now that I have rechecked into this I see how I misinterpreted what I was
seeing. What I had thought was a "artifact" must be a place where the
negatively colored light source has its own shadow region, thus not
counteracting the positive light at that place. I figure I better post this
anyway to show others how this kind of thing looks and acts.
Top rendering shows the everyday kind of spotlight (rgb +1) pointed downward
but pretty much at full wide angle (the orientation is a little off from the
y plane). Shadow of the sphere appears as it should.
Middle render is the negative color light (rgb -1) also pointed downward but
shifted slightly lower than where the other is placed. Looks okay again. The
ambient light is from a dim shadowless light source.
Bottom render shows the interactions of both lights within a shadow region
of the sphere. The negative light, having a shadow of sorts too, doesn't
fully match up with the positive light's shadow so they are offset some. I
had thought this was wrong before since I expected no light to be anywhere
the negative light source covered, even in shadow. In other words, negative
lights do have shadows.
Sorry about the confusion.
--
Farewell,
Bob
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Attachments:
Download '-lights_shadow.jpg' (15 KB)
Preview of image '-lights_shadow.jpg'
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hughes, b. wrote:
> In other words, negative lights do have shadows.
That's because the object is blocking the 'energy' from the negative
light, so there's an area in shadow.
--
Tim Cook
http://empyrean.scifi-fantasy.com
mirror: http://personal.lig.bellsouth.net/lig/z/9/z993126
-----BEGIN GEEK CODE BLOCK-----
Version: 3.12
GFA dpu- s: a?-- C++(++++) U P? L E--- W++(+++)>$
N++ o? K- w(+) O? M-(--) V? PS+(+++) PE(--) Y(--)
PGP-(--) t* 5++>+++++ X+ R* tv+ b++(+++) DI
D++(---) G(++) e*>++ h+ !r--- !y--
------END GEEK CODE BLOCK------
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From: Andrew Coppin
Subject: Re: example of negative lights [~18KB jpg]
Date: 16 Oct 2002 07:48:06
Message: <3dad51f6@news.povray.org>
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You crazy people...
Andrew.
PS. Apparently cat's pee glows under black light. (Wonder who they paid to
find that out...)
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Could this be used to make lights for the nightside of a planet not visible
on the dayside?
Rohan _e_ii
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"Rohan Bernett" <rox### [at] yahoo com> wrote in message
news:web.3db3743a71f60fbad02c7b870@news.povray.org...
> Could this be used to make lights for the nightside of a planet not
visible
> on the dayside?
That's an idea alright, sure. How to go about that? Using actual light
sources numbering in the hundreds is slow, even if a negative color I think.
But then individual light sources can be diminished to rgb 0 dependant on
placement so negative lights aren't needed anyway.
It's probably more common that nightside lights are faked with image
mapping, hence texturing so it's faster.
A negative light shone onto the daylight side and "lights" image map, which
is layered atop the rest of the planet texture and transparent everywhere
but the lights themselves, coupled together in a light_group would work I
think; with the image map fully ambient so it shows on the dark side of the
planet.
--
Farewell,
Bob
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From: Sir Charles W Shults III
Subject: Re: example of negative lights [~18KB jpg]
Date: 21 Oct 2002 01:20:11
Message: <3db38e8b$1@news.povray.org>
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Personally, I make an opaque shell with holes in it and contain a light
source within to make city lights. Or, a white shell with a high ambient can be
contained within. The does not appreciably slow the render time.
Cheers!
Chip Shults
My robotics, space and CGI web page - http://home.cfl.rr.com/aichip
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In article <3db383cb$1@news.povray.org>,
"hughes, b." <omn### [at] charternet> wrote:
> A negative light shone onto the daylight side and "lights" image map, which
> is layered atop the rest of the planet texture and transparent everywhere
> but the lights themselves, coupled together in a light_group would work I
> think; with the image map fully ambient so it shows on the dark side of the
> planet.
Just use a "lights" layer, and only put it on the night side. No need to
mess with hundreds of lights that don't illuminate more than tiny specks
or negative lights (I still don't see where they apply here anyway).
--
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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