I thought I used this before and it was working, but I can't seem to get it to work now. Is it changed in the latest update? Check this (different setup) out. The opacity and colors fed by same world scale fractal, but they differ in outcome.
On a related note. I believe that in Terragen 2 the sphere, plane, and rock used to handle opacity changes with proper shadows to match any opacity changes. Now in Terragen 3 you can apply opacity changes to the sphere, plane, or rock but the shadows are calculated for the unchanged objects.
The first example shows a few nested spheres with an image mask Y projected on them for opacity which was done in Terragen 2. The shadows are correct for the shapes.
The second example shows a sphere with an image mask Y projected on it for opacity and the unchanged shadow it makes in Terragen 3.
The work around is simple enough since a simple sphere, plane, or rock can be modeled elsewhere and imported, but it does seem that perhaps T3 calculates the shadows of it's own sphere, rock, and plane at a different time than it used to.
Good of you to chime in. I indeed think some changes have been made to this, and I hope it can be remodded.
I haven't had a chance to look at your project file yet, but I will do so.
I think your TG2 render might be using either an OBJ or a Rock object, because I can see that it's faceted at the edges. OBJ Reader, TGO Reader, Card, Rock and Grass Clump render using one method, while Sphere, Plane, Disc and Lake use a separate method. There are problems with opacity on that second kind of object. As far as I can remember, this was a problem in TG2 as well, but if you're using an OBJ or Rock it should work correctly in both TG2 and TG3.
Apparently I must have used the rock object in that T2 render but I don't have that file anymore.
Tried the rock in T3 and it shadows fine with an opacity mask applied.