View Full Version : volumetrics don't work

10-22-2003, 02:21 AM
Hi there,
Anybody could help me to solve a big trouble :
I have lot of spotlights in a scene nd all have volumetric lights
Volumetrics are checked of course in the GI panel.

What is very strange is that the volumetrics are rendered
correctly when I disable the Ray Trace shadows,
but not when I enable them…!!!!!

Has this something to do with the Ray recursion limit ?
(it's at 16 currently)
See the pic below…

Any advice appreciated

10-22-2003, 02:49 AM

It could be that your lights origins are just behind some of you models geometry which when shadows are enabled means the light won't pass through it so you get no lights and no volumetric cones.

hope this helps



10-22-2003, 02:53 AM
OK I think I got a beginning of answer :
if the vol. lights don't appear it's because the spotlights
are always INSIDE my lamps (models) so when RT shadows
are enabled the light can't go through the faces (polys) of
the lamp heads.
But what is still strange is that the light itself works,
it goes through these surfaces or else the whole image would be dark.

So should I conclude that the light can go through a surface but not
the volumetric ???
Any idea of a simple way to solve this issue ???

10-22-2003, 03:25 AM
Is it your light or does it have a very bright surface?

this is what should happen. With shadows on lights shouldn't pass through objects unless they are set to ignore them.



10-22-2003, 04:28 AM
Issue solved !!!!

thanks Munky,
the issue was near of what you said : the light did'nt go through some
surfaces as soon as the RT shadows were enabled.

I first thought of excluding objects from lights but would have to
separate objects more and more for this : very annoying.

I eventually did the opposite : exclude lights FROM the objects !!!
Now it will be all right.

However it's not the first time I meet such issues
and I must say this exclusion tip is still quite long to set with many objects :

Newtek please could we be able to exclude SURFACES from lights,
instead of only OBJECTS !!!!

10-22-2003, 04:37 AM
For casting light, LW light ignores a single sided surface facing away from it - so a spotlight in a box can shine out through the sides.
Volumetrics treat a surface as something they can't shine through.
Unfortunately volumetrics try to start from a point, so a volumetric source has to be well behind the light fitting. So you generally have to exclude the object from it's own lights and turn off it's shadows.
I use a lot of light beams for my Rock'n roll visualisations, I keep a library of scenes containing ready set up 'Luminairs' - moving light fixtures, complete with three lights - on for actually lighting with, one for the beam, and one for the glow.
Have a look at the attatched scene with object.
(sorry, It'll ask for a reflection image - any fracref will do)

10-22-2003, 04:43 AM
Looks like This: