Rendering Blocks and Items Dynamically using a custom Model

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.

Note that models are rendered when the chunks are rebuilt. If you need more dynamic rendering, you can use a BlockEntityRenderer: blockentityrenderers.

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.

@Environment(EnvType.CLIENT)
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 PlayerScreenHandler.BLOCK_ATLAS_TEXTURE.

    // for versions before 1.21, replace `Identifier.ofVanilla` with `new Identifier`.
    private static final SpriteIdentifier[] SPRITE_IDS = new SpriteIdentifier[]{
            new SpriteIdentifier(PlayerScreenHandler.BLOCK_ATLAS_TEXTURE, Identifier.ofVanilla("block/furnace_front_on")),
            new SpriteIdentifier(PlayerScreenHandler.BLOCK_ATLAS_TEXTURE, Identifier.ofVanilla("block/furnace_top"))
    };
    private final Sprite[] sprites = new Sprite[SPRITE_IDS.length];
 
    // Some constants to avoid magic numbers, these need to match the SPRITE_IDS
    private static final int SPRITE_SIDE = 0;
    private static final int SPRITE_TOP = 1;

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 List.of(); // This model does not depend on other models.
    }
 
    @Override
    public void setParents(Function<Identifier, UnbakedModel> modelLoader) {
        // This is related to model parents, it's not required for our use case
    }
 
 
    @Override
    public BakedModel bake(Baker baker, Function<SpriteIdentifier, Sprite> textureGetter, ModelBakeSettings rotationContainer) {
        // Get the sprites
        for(int i = 0; i < SPRITE_IDS.length; ++i) {
            sprites[i] = textureGetter.apply(SPRITE_IDS[i]);
        }
        // Build the mesh using the Renderer API
        Renderer renderer = RendererAccess.INSTANCE.getRenderer();
        MeshBuilder builder = renderer.meshBuilder();
        QuadEmitter emitter = builder.getEmitter();
 
        for(Direction direction : Direction.values()) {
            // UP and DOWN share the Y axis
            int spriteIdx = direction == Direction.UP || direction == Direction.DOWN ? SPRITE_TOP : SPRITE_SIDE;
            // 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 called after .square()
            // We haven't specified any UV coordinates, so we want to use the whole texture. BAKE_LOCK_UV does exactly that.
            emitter.spriteBake(sprites[spriteIdx], MutableQuadView.BAKE_LOCK_UV);
            // Enable texture usage
            emitter.color(-1, -1, -1, -1);
            // Add the quad to the mesh
            emitter.emit();
        }
        mesh = builder.build();
 
        return this;
    }

Not all the methods here are 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) {
        // Don't need because we use FabricBakedModel instead. However, it's better to not return null in case some mod decides to call this function.
        return List.of();
    }
 
    @Override
    public boolean useAmbientOcclusion() {
        return true; // we want the block to have a shadow depending on the adjacent blocks
    }
 
    @Override
    public boolean isBuiltin() {
        return false;
    }
 
    @Override
    public boolean hasDepth() {
        return false;
    }
 
    @Override
    public boolean isSideLit() {
        return false;
    }
 
    @Override
    public Sprite getParticleSprite() {
        return sprites[SPRITE_TOP]; // 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
        mesh.outputTo(context.getEmitter());
    }
 
    @Override
    public void emitItemQuads(ItemStack itemStack, Supplier<Random> supplier, RenderContext renderContext) {
 
    }
}

Note: Make sure you override the FabricBakedModel methods, the interface has default implementations!

In order for the model to be rendered in game we need to register it. In order to register it you need to create a ModelLoadingPlugin:

@Environment(EnvType.CLIENT)
public class TutorialModelLoadingPlugin implements ModelLoadingPlugin {
    public static final ModelIdentifier FOUR_SIDED_FURNACE_MODEL = new ModelIdentifier(Identifier.of("tutorial", "four_sided_furnace"), "");
 
    @Override
    public void onInitializeModelLoader(Context pluginContext) {
        // We want to add our model when the models are loaded
        pluginContext.modifyModelOnLoad().register((original, context) -> {
            // This is called for every model that is loaded, so make sure we only target ours
            final ModelIdentifier id = context.topLevelId();
            if(id != null && id.equals(FOUR_SIDED_FURNACE_MODEL)) {
                return new FourSidedFurnaceModel();
            } else {
                // If we don't modify the model we just return the original as-is
                return original;
            }
        });
    }
}

Then you need to register the plugin we just created:

@Environment(EnvType.CLIENT)
public class ExampleModClient implements ClientModInitializer {
    @Override
    public void onInitializeClient() {
        ModelLoadingPlugin.register(new TutorialModelLoadingPlugin());
 
        /* Other client-specific initialization */
    }
}

Don't forget to register this entrypoint in fabric.mod.json if you haven't done it yet:

{
  [...]
  "entrypoints": {
    [...]
    "client": [
      "net.fabricmc.example.ExampleModClient"
    ]
  },
  [...]
}

You can now register your block to use your new model. We assume this block is with id tutorial:four_sided_furnace.

TutorialBlocks.java

public final class TutorialBlocks {
  [...]
  public static final Block FOUR_SIDED_FURNACE = register("four_sided_furnace", new Block(AbstractBlock.Settings.copy(Blocks.FURNACE).luminance(x -> 15)));
  [...]
}

src/main/resources/assets/tutorial/blockstates/four_sided_furnace.json

{
  "variants": {
    "": { "model": "tutorial:block/four_sided_furnace" }
  }
}

Of course, you can implement much more complex rendering. Have fun!

As you can see in the picture, the item is not rendered correctly. Let's fix this.

We will re-use the same model class, with just a small change:

• We will need a ModelTransformation that rotates/translates/scales the model depending on its position (in right hand, in left hand, in gui, in item frame, etc…). As we are creating a model for a regular block, we can use the transform provided by fabric in ModelHelper.MODEL_TRANSFORM_BLOCK.

We will update our FourSidedFurnaceModel class as follows:

    // We need to implement getTransformation() and getOverrides()
    @Override
    public ModelTransformation getTransformation() {
        return ModelHelper.MODEL_TRANSFORM_BLOCK;
    }
 
    @Override
    public ModelOverrideList getOverrides() {
        return ModelOverrideList.EMPTY;
    }
 
    // We will also implement this method to have the correct lighting in the item rendering. Try to set this to false and you will see the difference.
    @Override
    public boolean isSideLit() {
        return true;
    }
 
    // Finally, we can implement the item render function
    @Override
    public void emitItemQuads(ItemStack itemStack, Supplier<Random> supplier, RenderContext renderContext) {
        mesh.outputTo(context.getEmitter());
    }

Let's update the TutorialModelLoadingPlugin we created earlier:

@Environment(EnvType.CLIENT)
public class TutorialModelLoadingPlugin implements ModelLoadingPlugin {
  public static final ModelIdentifier FOUR_SIDED_FURNACE_MODEL = new ModelIdentifier(Identifier.of("tutorial", "four_sided_furnace"), "");
  public static final ModelIdentifier FOUR_SIDED_FURNACE_MODEL_ITEM = new ModelIdentifier(Identifier.of("tutorial", "four_sided_furnace"), "inventory");
 
  @Override
  public void onInitializeModelLoader(Context pluginContext) {
    // We want to add our model when the models are loaded
    pluginContext.modifyModelOnLoad().register((original, context) -> {
      // This is called for every model that is loaded, so make sure we only target ours
      final ModelIdentifier id = context.topLevelId();
      if (id != null && (id.equals(FOUR_SIDED_FURNACE_MODEL) || id.equals(FOUR_SIDED_FURNACE_MODEL_ITEM))) {
        return new FourSidedFurnaceModel();
      } else {
        // If we don't modify the model we just return the original as-is
        return original;
      }
    });
  }
}

Et voilà! Enjoy!

The renderContext parameter in emitBlockQuads and emitItemQuads contains a QuadEmitter which you can use to build a model on the fly.

    @Override
    public void emitBlockQuads(BlockRenderView blockRenderView, BlockState blockState, BlockPos blockPos, Supplier<Random> supplier, RenderContext renderContext) {
        QuadEmitter emitter = renderContext.getEmitter();
        /* With this emitter, you can directly append the quads to the chunk model. */
    }