Currently I am working to convert other game models to Freemode. Normal GTA Models have two material (ped and ped_default for example) But when I work with 3rd party models I can only attach one material.
this is normal gta model but when I attach materials to new model it only appears like this:
This "Scene selection" branch in materials editor shows a set of materials "currently assigned" on selection. If you assign other materials onto some polygons, the "Scene selection" will show these materials too.
In general, the upper image does not mean you have to use two materials for a ped component. The ped component uses two materials - that's what this branch tells you.
Even more, ped component can use as much materials as you need. The only limitation - all these materials must use the same texture on DETAIL texture slot. So, you can have several different shaders/materials on your component.
To assign material onto geometry, you should switch object to polygons level, select desired polygons and assign material onto these polygons (either via drag&drop onto "Scene selection" in materials editor; or via Properties window with Mesh->Polygons->Material property there).
