Yes that's mostly it, in regard to displacement intersection (DI).
The shader uses the terrain's state from the last compute terrain. This compute terrain does NOT need to have smoothing enabled.
For best results the surface layer shader asks to enable smoothing, so do so.
The surface layer shader then generates a smoothed version of your last compute terrain before that surface layer shader.
The smoothed result's smoothness depends on the gradient patch size of that compute terrain.
Indeed, the smaller the gradient patch the more details the smoothed version of the terrain will have.
Yet, it will always be smoother than the unsmoothed, so with the right settings you will always see some kind of effect of IU with DI.
Now the intersection zone is a parameter which determines a kind of step size to read the smoothed version of the terrain as provided by the last compute terrain.
It will compare both states and determines where the two "intersect", which is mostly in depressions.
You can imagine this by having a sinus shaped terrain from -0.5 to 0.5m, which upon smoothing is flat @ 0m (for example).
With DI you can now "fill" the negative/depressed parts of the sinus shaped parts.
With correct settings you can even "fill" them completely.
Small values for intersection zone allow for detailled "filling" of smaller depressions.
High values for intersection zone uses large chunks of smoothed terrain and allows for filling large depressions, but as a consequence can also add a thick layer over non-depressed surfaces.
Now these things are nicely demonstrated by Matt's in progress documentation, so I'll leave the rest to Oshyan.
No need for NWDA here
Cheers,
Martin
