Quote from: Oshyan on February 20, 2019, 06:31:17 PM
How are the Parts Shaders determined/derived in the first place then?
There are various ways that object materials or groups can be defined in an OBJ file. If the OBJ has lines beginning with "usemtl" or "usemap", Terragen interprets those as material assignments and creates a "part" for each one. For example "usemtl leaf", "usemtl trunk" and so on. Also, OBJs sometimes contain "groups", and Terragen looks at those if it doesn't find any material-related commands that it knows about.
UVs are a completely different concept. They are the X,Y texture coordinates for each vertex. Every vertex should have a UV value attached if you want to do texture mapping.
UVs can be used to texture map an OBJ even if there was no material description. And materials/groups can be used to set up different shaders even if there are no UVs, as long as you don't need any texture maps.
Of course, most OBJs have both of these sets of data.