how about a real answer?
What I'm asking isn't available through f1
If your background layer has an alpha channel then you can apply your particles on a layer beneath it. You could also duplicate your background layer and then use the duplicate as a track matte for a particle layer below. You just can't do this easily using a single layer.
If that won't do it I don't understand your question.
Thanks for the reply Rick.
It does in fact work like you suggest. The problem is that in order to do it this way I need to generate particles to cover the entire page
and then I mask so that I only see the small area I want instead of just generating particles based on my shape, mask, etc.
All I want is for CC snow to only spawn within my shape or mask
What I am really after is setting up a shape and having it look like it is filled with mud that is circulating throughout the shape
as in an oil well.
Using a new solid for the vertical borehole, cc snow, blur and colorama I can get some decent looking 'mud'
but when the borehole turns to a horizontal I can't use a solid shape so the snow isn't dense enough and it doesn't look muddy at all.
maybe there's another way I haven't thought of.
If I'm following you I'd suggest that you try some displacement mapping or take a look at Free Form (now included with AE) to apply something like a bump map to your layer. This will give it the illusion of depth.