"ryan constantine" <rco### [at] yahoocom> wrote in message
news:39C08E5D.682CD947@yahoo.com...
| > Unfortunately I don't think it's possible.  Area lights only effect
shadows
| > as they fall onto other objects not the object creating the shadow.
|
| i do remember that limitation of area lights, but that makes them faster
| than a bunch of points right?  but how about a small array of points for
| this?  or maybe spots?  can an angle of close to 180 be specified?  are
| there any calculation speed ups with spots since light obviously can't
| go behind them?  or are light calculations done another way?  and can
| spot lights have their penumbra (is that the right word?) set to zero so
| all light from the spot light is of the same intensity (ie no lateral
| falloff)?  let's say i make a planet 70000 units in radius, how should i
| go about finding the minimum acceptable distance (given the
| size/distance ratio of 1/100 in christopher's post)?  would i use
| different distances for spots than i would for points?  and what about
| all those new keywords in megapov like circular and parallel?  might
| they be of any use here?  has anyone ever done a looks_like to make a
| sun?

Wow, so many questions :-)
I just noticed you said before that you thought the Sun is 2 degrees across.
Wrong.  It's closer to 0.5 degree, but then there is the surrounding
brightness in the air.  Still probably not 2 degrees wide of a source of
light enough to contribute to the main source, I wouldn't think anyway.
So the Sun is 1/360th of the arc of the whole sky.
Not sure what is meant by that 1:100 ratio.  The Sun being about 864,000
miles across and 93 million miles away and the Earth being about 8,000 miles
across makes for about a 1:11,625 ratio of Earth diameter to Sun distance,
with about a 1:107 ratio for Sun diameter to Earth distance.  Must be the
Sun then eh? :-)
70,000 unit planet isn't the thing to figure from anyway, just the sun(s)
size(s) and that's still solar system-like.
All moot if Tatooine and it's system is totally different, but judging from
the movie the ratios are probably going to be similar.  Simply add the
second sun.
Anyhow, back to the spotlight question(s).
You can go up to but not quite 90 for the both radius and falloff (same
value each), that's what you'd want to do for the non-penumbra form (not
certain of use of that word concerning lights, umbra should mean the unlit
area though and penumbra the partially lit).  But you really wouldn't need
it that wide I'd think.  If everything were to scale then a 1 degree light
ought to be fine for the distance you would have.
Not sure if it matters at all as long as no other object is in the scene
away from the planet, concerning the speed of render.  Also 'tightness 1'
(or zero?) will close the penumbral part of a spotlight if you were to use a
falloff larger than the radius.
You do know of course that area_light using spotlight will be the same way
as a point light too.  That array of spotlights could be a real slowdown but
maybe it wouldn't be too slow.

Bob

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