No - not talking about exporting alpha channels, but that could certainly be a cool future development.

Ok, now I'm beginning to suspect something might be wrong with prox. If I have image-from-file layers, I can't seem to grab any data from them in other layers.
Eg: in the layer that is supposed to mix them, I have:
@R=(EngPipe2Tex.r(x,y))*(EngPipe2Mask.r(x,y))
@G=(EngPipe2Tex.g(x,y))*(EngPipe2Mask.g(x,y))
@B=(EngPipe2Tex.b(x,y))*(EngPipe2Mask.b(x,y))
with both those layers being images from files (evaluated already), but all I get is solid black.
Then if I just have:
@R=(EngPipe2Tex.r(x,y))
@G=(EngPipe2Tex.g(x,y))
@B=(EngPipe2Tex.b(x,y))
I get solid white.
Since neither image is solid white or black, it has to be something else. :\