Is there any way to limit a shader/population etc. to slopes that are upside down?
e.g. I have some wacky displacement (twist and shear) and so I have an overhang. What I want to do is put a certain shader on the underside of this overhang. Is this possible?
EDIT: also - what if you have several over-hangs that actually overhang each other? would it be possible then, since you'd effectively have two upside down surface in the same XZ space.
Well, when you think about it, upside down surfaces are essentially surfaces with slopes higher than 90 degrees. I don't think the issue you described in your edit would pose a problem, but give it a go and let us know how it turns out ;).
K, I'll be back in half an hour with the results.
Yup, just set your shader to be on slopes greater than 90 degrees. Cheers for the help!