QuoteThe Mesh Displacement input works for *non-displaceable* objects (any arbitrary imported geometry), but does not do any subdivision. It takes Displacement as input, not color. Force Displacement does not need to be on (not should it be) for it to work, though it won't break the effect if it is.
Thanks, Oshyan. That answers a couple of basic questions that I was having a hard time answering. Strange thing though is that the displacements appeared when I reopened the test file I had been working on.
Maybe it was a delayed effect of the connect/disconnect bug? Anyway everything is working as expected now.
Here are my results so far. I'm going into some detail in case anyone else might find this info useful. If I've gotten anything wrong, please feel free to correct it.
The displacements are centered at the imported object's pivot point and are proportional to the distance between the pivot point and the surface of the mesh. This means that nothing will happen if you displace a basic plane with a centered pivot because the pivot and the mesh are coplanar. If you want the displacement to affect any 3D shape as a whole – instead of merely displacing the surfaces out from the center – the pivot must be moved outside of the mesh before the object is imported into Terragen. Once I realized this I moved the pivot for my test objects –100m on the Y axis in Maya before freezing transforms and exporting.
Even so, with displacement in the source node set to Vertical Only or Normal, the resulting displacements were all angular based on the distance from the pivot point to the mesh. Here's a displacement from a plane, based on a circular Simple Shape:
[attachimg=1]
Setting the displacement type to Normal and piping the output through a Redirect shader fixes this.
[attachimg=2]
X and Z are set to 0, with the displacement going through Y.
[attachimg=3]
Does this sound right? Everything is working as expected so far. Here is a power fractal displacement applied to a plane.
[attachimg=4]
And the same displacement applied to a cuboid with 1 x 1 x 100 faces.
[attachimg=5]
So the moral is, be careful what you ask for. This is the exact result that I was looking for, but it clearly won't work well for railroad tracks! But it's cool to know how this feature works, and I'm sure I'll find other uses for it.
[Edit: I wasn't able to figure out a way to use a heightfield as the displacement source. That would be useful indeed.]