Particles generated by cast shadows?

Hello!

Is there any way to have particles generated only from
cast shadows? I have a character throwing shadow to a
wall, and from that wall, from the shadowed area,
some dust should be emanated.

I've tried PFlow with Position Object -operator, density
by Material (grayscale or opacity) combined with Falloff
-material on the wall, but somehow the fallof type
Shadow/Light does not get passed to the particle engine
(nor does it pass to much anything else for that matter :))

Copying the illumination of the wall to a vertex
channel is not a solution here since the shadow is
animated with the character. I also need to have multiple
scenes with the same setup, so I'm not too thrilled
about the prospect of having to bake the animated
illumination of all of them.

I've studied the possibility of scripting here, but have
not found a suitable tool yet. Any help is much appreciated.

seppo

This seems to be a pretty simple method (attached), using the object thats 
casting the shadow as an emitter, while using the speed along the icon arrow 
(which is linked to the light).

The particles then hit the surface and mirror the shadow, from there they can 
spawn whatever effect etc.  This only seems to work in this form with a 
direct light, but I'm sure it could be modified to work with a spot light 
with a few parameter wires / constraints / or script.

But yes, of course! Thank you Andrew. :) I had tried to
figure out all kinds of 'light masked by the shadow caster'
-type of solutions but never seeing the obvious.

Unfortunately your scene misses too many dlls from my Max7
to open, but I think I catch the drift from your explanation.
I'll let you know if I succeed with other than direct lights.

Thanks again!

Cheers,
Seppo


On 7/24/2006 5:04:31 AM, Andrew Lowell wrote:
>This seems to be a pretty simple method (attached),
>using the object thats casting the shadow as an emitter,
>while using the speed along the icon arrow (which is
>linked to the light).
>
>The particles then hit the surface and mirror the shadow,
>from there they can spawn whatever effect etc.  This
>only seems to work in this form with a direct light, but
>I'm sure it could be modified to work with a spot light with
>a few parameter wires /constraints / or script.

Yes indeed, Andrew, your solution rocks like a moose!

I tweaked it a bit by constraining a tiny primitive sphere
to the spotlight and used that as a Speed by Surface object
in the 'shadow casting' event. That way I got a nice fanning,
which coincides with the actual shadow remarkably well. And
If you need area lights you just increase the radius of the
sphere.

On the wall there is a simple deflector and the final dust is
spawned by collision to it. Voila!

seppo

Ah, glad to hear ... actually I thought I had an origional idea and then I 
realized when getting up this morning that I had just finished watching 
"Hero" the jet li movie where he gets hit with all the arrows and they
end up 
with a silhouette on the wall .. same concept.