I know you can have particles emitted from the follow; point, sphere, box, layer, layer grid. I would like to have the particles emit from a ring or something with a whole in it. Is this possible? I can not seem to get it to work.
Ken, the ring tutorial by Andrew Kramer shows you how to emit particles in a circle based on emitter movement. I think your question was how do you emit particles from a custom shape layer. The answer to your question is simple - precompose. I bet you are using a shape layer or other masked layer in the same comp as particular. Particular looks at the layer without any of the effects or transforms applied in that comp. That means, if you apply a shape mask on the layer, Particular will read the entire layer, before it is masked, resulting in particles emitted from everywhere. All you need to do is build your shape in a seperate precomp and then place it in the comp with particular, make it 3d and then set particular's emitter to layer or layer grid and select your shape layer as the source.
I hope this helps. Sorry it took so long to get a response. I will be here almost everyday if you have any other questions.