#R3 Spotlights
15 messages in this thread
I'd like to know what method of decay spotlights in 3DS R3 use.
Do they:
a.) have no decay
b.) decrease in linear proportion to distance
c.) decrease inversely proportionally to the square of the distance
d.) another method
Thanks A Ton,
Paul
Spotlights (and omni lights) have no decay unless their Attunate attribute is
on (in which case the spotlight will have linear falloff between the inner
and outer range circles).
– Phil
Phillip,
Is that somewhere in the manual? I was curious because we're trying to match
the lighting in R3 with lights in a film piece and another unmentionable
program and after a very long discussion on light here, it seemed strange that
the spotlights would not use an inverse of the square formula like spots do in
life. Quite frankly, until now I've never had a need to concern myself with it.
Paul
Paul,
<< it seemed strange that the spotlights would not use an inverse of the square
formula like spots do in life. >>
I believe most 3D software does not use the inverse square method simply
because it just doesn't "look" right, FWIW.
BILL
Bill,
Actually several packages use the technique as a default. Most high end ray
tracers do. We happen to prefer the 3DS method, hence the questions. It's a
huge pain in the butt trying to get other packages to respond like 3DS.
Paul
Actually, I was referring to some higher-priced renderers as well. They call it
inverse square, but I *_believe_* they actually use the un-squared distance
parameter. Seems like I've read that 'way back – I could be wrong.
BILL
I was just repeating what I was told, two different SGI based companies sent me
tech sheets with explanations of their spotlights, and they both are set up so
that you can set decay to "decrease light intensity inversely proportional to
the square of the distance."
They also sent us example calculations to accompany the brief.
As a note you can also set the spots to higher or lower ranges of decay by
changing some parameters. The main options are, no decay, linear decay,
inversely proportional to the square, inversely proportional to the cube.
None of it makes alot of difference to us, we were just in need of matching
some 3DS lit scenes to work in some other packages and we were having alot of
trouble matching lighting. Hence the questions.
>spotlights, decay
Look at 7-158, and pages around it in the reference manual. Just looking up
spotlights myself.. Look especially at attenuate and the stuff referred to in
that paragraph
JNJ
You seem to be asking about penumbral decay of the spotlight, not attenuation
over distance for spot and omni lights. Given that, are you sure you _really_
want to know? <g> Basically, spotlight decay uses a cubic spline with hermite
interpolation that's shaped like an s, so that the spline is tangent to 1 and 0
(it has 0 first and second derivatives at the ends). The formula is:
u*u*(3-2*u) …where u is a number which goes from 1-0 as you go from the
hotspot to the falloff. (0 at the outer range and 1 at the inner range)
That's for circular spotlights. The rectangular ones are a hybrid variant
that's way too complex to explain in an email. (does anyone else do rectangular
lights?)
– G
Hey, I have no idea what formulea are involved, but I love rectangular spots.
Jeff
I'm glad to see that they're appreciated. They were a bear to implement.
– G
Gary,
Your rectacular spot came in real real handy for re-creating the glow from some
lines of neon on the outside of a building we recently did for a high profile
client. (With some luck they will be introducing thier stuff to the public
before SIGGRAPH so I can show some of the animations we did for them there.)
I also want to thank you and sing praises for the projection lights.
I haven't had time to get on the forum for a while. Is there going to be any
meetings or get together of the 3DS users in Orlando during SIGGRAPH?
Andrew McClary
Graphic Alchemy Productions, Inc.
Andrew,
<< Will there be any meetings or get together of the 3DS users in Orlando
during SIGGRAPH? >>
Autodesk is sponcering a party Wednesday nite at the Hilton Hotel, Walt Disney
World. All registered 3DS owners will be receiving invites in the mail.
Last year there was also a ASOFT'rs get together but I haven't heard anyone
organizing ont this year.
jonas[adesk]
As Jonas said, Wed evening 7-10pm. C'mon down! <g>
Glad to hear that you're grooving on the new light features.
– G
Hmmm… lessee now… penumbral decay… a cubic spline with hermite
interpolation… first and second derivatives at the ends… unh, hunh, unh,
hunh… u*u*(3-2*u) … (I should've taken a little more arithmetic at
college)… yup, I like them rectangular spots, too… a hybrid variant, eh?
<blink, blink….>