I have a block that has several variants:

 

1. The first variant has a simple "cross" model with a texture.  I finally have that block rendering in world as well as inventory.  Yay!

 

2. The second variant is an entirely different model.  What I want to do is use existing models from Vanilla as sub-models to build a composite.  (I want to make a bone pile using the item "bone" and "skull".)

 

I see that the blockstate json has this an ability to do sub-models based on state.  In my case I just want to build a model reusing existing models as building blocks, and refer to that composite model  from the blockstate.  The only attribute that can alter rendering of the model is a rotation around Y, but that can be handled easily up in the blockstate and would (generally) apply to any models that it refers to.

 

Anyways, I was wondering if what I want is possible, or do I need to go back and rethink this.  From Java implementation standpoint all these blocks have the same capabilities.  The only thing that is changing is what they look like in the world based on the variant type.

You will probably want to look at Forge's MultiLayerModels.

Some information, and examples, can be read here: WillieWillus : Forge Rendering Primer

Scroll down to where he talks about Aura Cascade’s Fortified Blocks.

 

Heavily recommend that you read the whole primer. It's good material to learn the system that has been used since 1.8 to render.

 

Edit: seems the link in the primer to Aura Cascade's multi-layer example returns a 404; so here's a direct link

The Forge documentation gives an example of using submodels here

Yes.  Saw that.  It shows it being used in the BlockState Json.  What I want to do is make a "normal" model file that has submodels, and then refer to *that* Json from the BlockState Json.  It's not clear to me if this is possible.

 

This being said I dropped back and punted to keep things simple.  I decided I didn't want to tackle this particular challenge for the moment.  What I wound up doing is using Choonster's BlockSappling example and modeled (no pun intended) my BlockState off of that.

 

The idea of "submodels" are specifically related to the Blockstate Json. You can't do "submodels" in a model JSON.