Thanks for the posts guys.
What I really want to do is animate a certain layer and have its displacement affected by the current color values of the layer underneath it (as it may or may not be animated itself)
Sounds like there should be a very simple way to do this – the problem is when I use a displacement map on my top layer it actually embeds the selected map to the top layer. I understand how pre-comping the animated map would give animated displacement motion but I want it to be able to continually change as I move the displaced image around.
Is the only way to do this to actually keyframe my top layer motion along the (visual representation of my) displacement map and then precomp that same motion path to the animated map so they match?
It just seems like there should be a simpler way – am I missing something?
Cheers!
Cosmo