v7 - particle volume shader transparency / FG lighting

[Martin Winkler]

Dear list,

I ran into a few issues while using the new particle volume shader of v7.

1. I wasnt able to convince the particles to pick up FG lighting. The
environment picks up the irradiance bounce from the particles very well (for
example lighting a dark room with a red glowing fire), but i couldnt get it to
work the other way round (for example lighting a particle cloud with the
physical sky). The volume just stays at its ambience value. Any hints on this?

2. So far i was unsuccessful to make the clouds fade to transparent. All my
attempts to pass alpha values to the volume shader resulted in cutting the
cloud off where transparency occurs (which i guess is a feature). But i wasn't
able to lets say have a gradient over a cloud from 100% solid to fully
transparent. Probably i'm just missing a switch..

Any hints would be appreciated.

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Best regards,
Martin mailto:mar...@exposure-vfx.com

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[phil harbath]

2.) I believe you have to set the "Per Cloud or Gradient: Color/Density"
intensity density to 1.
then feed the values from a particle gradient into the "density" port.

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[Martin Winkler]

Hi phil,

Sunday, September 7, 2008, 4:33:53 AM, you wrote:

> 2.) I believe you have to set the "Per Cloud or Gradient: Color/Density"
> intensity density to 1.
> then feed the values from a particle gradient into the "density" port.

Thanks for your suggestion, I was struggling because I couldnt get the particle
gradient to influence the whole span of the cloud and not just the span of one
particle..

So I did it like this: I stopped trying to generate the transparency from
within the rendertree, but rather used a gradient in the icetree, driven by the
particle position and rescaled the whole value range to 0 - 1.. the "1"-value
on the ice gradient then got an alpha of 0...

So my cloud nicely fades off to zero.

As soon as I'm done with this whole thing I'll have a closer look at your
method, since I need to fully understand the whole density concept sooner or
later.