Not entirely sure how to concisely describe this (or what to Google for). I guess it can be done somehow by using conditionals on the light path..?
I have this scene:
Basically, a "terrain" mesh, and two flat planes intersecting it. Now, I would like to apply a certain texture on the "Yellow" plane, but only on the area directly over the terrain, not over the blue plane.
It's probably clearer what I mean in a top view:
(The clearly yellow area).
The idea is to get some combination of nodes that will give me a
1 result I can use as "factor" to a mix shader.. but I got stuck trying to find how that could actually be done.
Update: to clarify, I want to apply the texture in the region hit by "vertical" rays, i.e. parallel to the object normals / Z axis, not the camera ray.