Hi, I want to make poker card rain in after effect with CC Particle world. I have 12 card images to be shown as particle, but currently it can only select 1 image as texture [Quadpolygon texture]. Can I make the particle randomly pick one image from the 12 card layer when 'birth' ? any expression to do that?
Not really. You can play around with longevity, death and opacity parameters and set the sampling to birth to somewhat fake it, but it's severely limited. You would have your 12 cards in a pre-comp with each only visible for a few frames, but have the particles in the main comp live for rather long while at the same time creating an extrem short visibility period with the opacity gradient. That's as good as it gets and of course it won't be that random and lots of duplicate images show up. For anything beyond that you have to resort to tools liek particular that support actual random sampling of the source frame.
It might be worth exploring both Card Dance and Shatter effects, with all your cards on a single layer, and use either of these effects to split up the deck and then animate them falling.
Alternatively, you could make a precomp of one card falling, then use Essential Graphics to add this precomp multiple times, staggering their start times, to get the rain, swapping each face out using the Image property in EG.
CC Particle World is easy enough to use multiple times without slowing down your computer, so you could have each on its own layer.