It is possible to add models to the game using block model JSON files, but it is also possible to render them through Java code. In this tutorial, we will add a four-sided furnace model to the game.

When a model is first registered in Minecraft, its raw data is contained in an UnbakedModel. This data can include shapes or texture names for example. Later during the initialization, UnbakedModel::bake() creates a BakedModel, ready for rendering. For rendering to be as fast as possible, as many operations as possible need to be done during baking. We will also implement FabricBakedModel to make use of the Fabric Renderer API. Let's create a single FourSidedFurnace model that will implement all three interfaces.

public class FourSidedFurnaceModel implements UnbakedModel, BakedModel, FabricBakedModel {

A Sprite is necessary for rendering a texture. We must first create a SpriteIdentifier and then get the corresponding Sprite while baking the model. Here, we will use two furnace textures. They are block textures, so they must be loaded from the block atlas SpriteAtlasTexture.BLOCK_ATLAS_TEX.

    private static final SpriteIdentifier[] SPRITE_IDS = new SpriteIdentifier[]{
            new SpriteIdentifier(SpriteAtlasTexture.BLOCK_ATLAS_TEX, new Identifier("minecraft:block/furnace_front_on")),
            new SpriteIdentifier(SpriteAtlasTexture.BLOCK_ATLAS_TEX, new Identifier("minecraft:block/furnace_top"))
    };
    private Sprite[] SPRITES = new Sprite[2];

A Mesh is a game shape that is ready for rendering with the Fabric Rendering API. We will add one to our class, and we will build it during model baking.

    private Mesh mesh;

    @Override
    public Collection<Identifier> getModelDependencies() {
        return Collections.emptyList(); // This model does not depend on other models.
    }
 
    @Override
    public Collection<SpriteIdentifier> getTextureDependencies(Function<Identifier, UnbakedModel> unbakedModelGetter, Set<Pair<String, String>> unresolvedTextureReferences) {
        return Arrays.asList(SPRITE_IDS); // The textures this model depends on.
    }
 
 
    @Override
    public BakedModel bake(ModelLoader loader, Function<SpriteIdentifier, Sprite> textureGetter, ModelBakeSettings rotationContainer, Identifier modelId) {
        // Get the sprites
        for(int i = 0; i < 2; ++i) {
            SPRITES[i] = textureGetter.apply(SPRITE_IDS[i]);
        }
        // Build the mesh
        Renderer renderer = RendererAccess.INSTANCE.getRenderer();
        MeshBuilder builder = renderer.meshBuilder();
        QuadEmitter emitter = builder.getEmitter();
 
        for(Direction direction : Direction.values()) {
            int spriteIdx = direction == Direction.UP || direction == Direction.DOWN ? 1 : 0;
            // Add a new face to the mesh
            emitter.square(direction, 0.0f, 0.0f, 1.0f, 1.0f, 0.0f);
            // Set the sprite of the face, must be calld after .square()
            emitter.spriteBake(0, SPRITES[spriteIdx], MutableQuadView.BAKE_LOCK_UV); // TODO: bake flags?
            // Enable texture usage
            emitter.spriteColor(0, -1, -1, -1, -1);
            emitter.emit();
        }
        mesh = builder.build();
 
        return this;
    }

TODO: check this The methods here are not used by the Fabric Renderer, so we don't really care about the implementation.

@Override
    public List<BakedQuad> getQuads(BlockState state, Direction face, Random random) {
        return null; // Don't need because we use FabricBakedModel instead
    }
 
    @Override
    public boolean useAmbientOcclusion() {
        return false;
    }
 
    @Override
    public boolean hasDepth() {
        return false;
    }
 
    @Override
    public boolean isSideLit() {
        return false;
    }
 
    @Override
    public boolean isBuiltin() {
        return false;
    }
 
    @Override
    public Sprite getSprite() {
        return SPRITES[1]; // Block break particle, let's use furnace_top
    }
 
    @Override
    public ModelTransformation getTransformation() {
        return null;
    }
 
    @Override
    public ModelOverrideList getOverrides() {
        return null;
    }

    @Override
    public boolean isVanillaAdapter() {
        return false; // False to trigger FabricBakedModel rendering
    }
 
    @Override
    public void emitBlockQuads(BlockRenderView blockRenderView, BlockState blockState, BlockPos blockPos, Supplier<Random> supplier, RenderContext renderContext) {
        // Render function
 
        // We just render the mesh
        renderContext.meshConsumer().accept(mesh);
    }
 
    @Override
    public void emitItemQuads(ItemStack itemStack, Supplier<Random> supplier, RenderContext renderContext) {
 
    }
}

Let's first register a ModelResourceProvider. Add this to your client initializer. TODO add a link explaining this

ModelLoadingRegistry.INSTANCE.registerResourceProvider(rm -> new TutorialModelProvider());

Let's register the model under the name tutorial:block/four_sided_furnace using the model provider. TODO explain this

public class TutorialModelProvider implements ModelResourceProvider {
    public static final Identifier FOUR_SIDED_FURNACE_MODEL = new Identifier("tutorial:block/four_sided_furnace");
    @Override
    public UnbakedModel loadModelResource(Identifier identifier, ModelProviderContext modelProviderContext) throws ModelProviderException {
        if(identifier.equals(FOUR_SIDED_FURNACE_MODEL)) {
            return new FourSidedFurnaceModel();
        } else {
            return null;
        }
    }
}

You can now register your block to use our new model, for example if your block only has one block state, put this in `assets/your_mod_id/blockstates/your_block_id.json`.

{
  "variants": {
    "": { "model": "tutorial:block/four_sided_furnace" }
  }
}
 
Of course, you can implement much more complex behavior!