Is it possible to put multiple normal maps on one mesh?
Sure, just stack them up in the textures slots and cross-fade the Normal Ininfluence between the multiple normal maps when you want to show the next one.
I thought the OP was asking if there was a good way to combine two normal maps simultaneously, not animate between two. Which I’d be curious to know too, actually…
All you do is devote two or more slots to a normal map and use the normal slider to determine the visibility of each one, one of them can even use a mask to limit the area of application.
Doing it in Cycles meanwhile is mostly the same thing, only the node system allows use of the mix node directly to allow mixing possibilities that can’t be done with the legacy material stack (like creating masks for both maps).
One thing to note though when using Cycles, normal maps can only be mixed successfully if the mix node uses the ‘mix’ blending mode. (as it would otherwise alter the RGB data to where it’s no longer correct).
Ah-ha. That is exactly what I was wondering about. I just hadn’t had a chance to test it out. I have one normal map for the mid-level details, and I wanted to make a second one for the really fine details if I could (probably using a different computer with more memory :p). I just didn’t want to waste time without the answer you just gave.
I don’t know if that’s really what johnh was asking, but I hope it helped someone other than me!
Edit:
OK, I think I’ve found the simplest (and fastest) way. Not the most right but pretty good.
Just use the Overlay mode for the second map and disable Blue color channel at it.
The most proper method is described here: