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We know that almost every item needs a corresponding item baked model (or item model for short), and an item models definition since 1.21.4. Each block needs a block baked model (or block model for short) and a block states definition, and a corresponding item baked model or item models definition. A simple block requires so much complicated JSON files! Obviously, it's too hard to build each file manually. Therefore, we use data generator to generate models for blocks and items.

In data generator, models and definitions are generated together. Usually, when generation a model, a model id is returned, which will be used in the block states definition or item models definition. We will go into that from simple ones to details.

Note: In the tutorials created previously, there may be some JSON files already created in the resources folder. When the data generator generates a JSON file with a same filename, the file will conflict with our manually-created JSONs. Therefore, before running data generators, please delete them.

Note: Since 1.21.4, data generation are divided into client and server. In vanilla, classes related to models will be annotated @Environment(EnvType.CLIENT) which will be available only in client environment. If you find errors due to server environments when you run data generator, please refer to datagen_setup, and modify the fabricApi block in the build.gradle to enable client environment, and regenerate IDE's run configs.

First, create a class that extends FabricModelProvider and register it in the datagen entrypoint:

TutorialModelGenerator.java

public static class TutorialModelGenerator extends FabricModelProvider {
  public TutorialModelGenerator(FabricDataOutput output) {
    super(output);
  }
 
 
  @Override
  public void generateBlockStateModels(BlockStateModelGenerator blockStateModelGenerator) {
    // ...
  }
 
 
  @Override
  public void generateItemModels(ItemModelGenerator itemModelGenerator) {
    // ...
  }
}

ExampleModDataGenerator.java

public class ExampleModDataGenerator implements DataGeneratorEntrypoint {
  @Override
  public void onInitializeDataGenerator(FabricDataGenerator generator) {
    // ...
 
    pack.addProvider(TutorialModelGenerator::new);
  }
}

We have already created an example block in the blocks tutorial. We just use several short codes to create block states definition and block model:

TutorialModelGenerator.java

  @Override
  public void generateBlockStateModels(BlockStateModelGenerator blockStateModelGenerator) {
    blockStateModelGenerator.registerSimpleCubeAll(TutorialBlocks.EXAMPLE_BLOCK);
  }

The line of code creates a simplest block model, which is a full block, in which all sides use the texture identical to its id: tutorial:block/example_block. Note that the texture is a picture and is usually not generated with data generator. It will also create a simplest block states definition which directly uses its block model.

You can also write like this (the following code is also in the generateBlockStateModels method), which allows you to specify a different block model type. The returned value in the first line is the model id, which will be used when generating block states definitions:

    final Identifier exampleBlockModelId = TexturedModel.CUBE_ALL.upload(TutorialBlocks.EXAMPLE_BLOCK, blockStateModelGenerator.modelCollector);
    blockStateModelGenerator.registerParentedItemModel(TutorialBlocks.EXAMPLE_BLOCK, exampleBlockModelId);

To specify a different texture, you can create a block model manually (for example, all six faces using the mangrove log's top texture):

    final Identifier exampleBlockModelId = Models.CUBE_ALL.upload(TutorialBlocks.EXAMPLE_BLOCK, TextureMap.all(Identifier.ofVanilla("block/mangrove_log_top")), blockStateModelGenerator.modelCollector);
    blockStateModelGenerator.registerParentedItemModel(TutorialBlocks.EXAMPLE_BLOCK, exampleBlockModelId);

Generating an item model is also quite simple:

TutorialModelGenerator.java

  @Override
  public void generateItemModels(ItemModelGenerator itemModelGenerator) {
    itemModelGenerator.register(TutorialItems.CUSTOM_ITEM, Models.GENERATED);
  }

The item model will use the simplest item models mappings, with item model item/generated and a texture identical to its id (tutorial:item/custom_item). Of course, you can also change Models.GENERATED to other values according to your needs.

If you do not provide the second parameter in itemModelGenerator.register, only the item models definition will be generated, without an item model.

To specify a different texture (in this example, directly use vanilla white wool texture), you can also manually create models and models definitions (the following code is also in the generateItemModels method).

TutorialModelGenerator.java

    itemModelGenerator.register(TutorialItems.CUSTOM_ITEM, Models.GENERATED);
    final Identifier modelId = Models.GENERATED.upload(TutorialItems.CUSTOM_ITEM, TextureMap.layer0(Identifier.of("block/white_wool")), itemModelGenerator.modelCollector);
    itemModelGenerator.output.accept(TutorialItems.CUSTOM_ITEM, ItemModels.basic(modelId));

Sometimes a block model is not so simple, because it is related to complicated block states. For example, stairs can have multiple facings, can be facing E/S/W/N, can be placed upright or upside, and can even be corner. It will definitely be troublesome to create models and block states definitions for these blocks. Luckily Minecraft has written for these common blocks well, and what we need to do is directly use them. Here we take stairs and slabs as an example, and create stairs and slabs for diamond blocks. First, let's quickly create the blocks:

For versions after 1.21.2:

TutorialBlocks.json

  public static final Block DIAMOND_STAIRS = register("diamond_stairs",
      settings -> new StairsBlock(Blocks.DIAMOND_BLOCK.getDefaultState(), settings),
      AbstractBlock.Settings.copy(Blocks.DIAMOND_BLOCK));
  public static final Block DIAMOND_SLAB = register("diamond_slab",
      SlabBlock::new,
      AbstractBlock.Settings.copy(Blocks.DIORITE_SLAB));

For versions before 1.21.2:

TutorialBlocks.json

  public static final Block DIAMOND_STAIRS = register("diamond_stairs",
      new StairsBlock(Blocks.DIAMOND_BLOCK.getDefaultState(),
      AbstractBlock.Settings.copy(Blocks.DIAMOND_BLOCK)));
  public static final Block DIAMOND_SLAB = register("diamond_slab",
      new SlabBlock(AbstractBlock.Settings.copy(Blocks.DIORITE_SLAB)));

And then we create regular stairs model, inner corner stairs model, outer corner stairs model, bottom slab model and top slab model. For double slab model we directly use vanilla diamond block model. When creating models for these blocks, the id of the models will be returned, and we create block states definitions with the utility methods in BlockStateModelGenerator, using the model ids that are returned before. We also need to use the regular stairs model and bottom slab model for the item model.

TutorialModelGenerator.json

    final TextureMap diamondTexture = TextureMap.all(Identifier.ofVanilla("block/diamond_block"));
 
    final Identifier stairsModelId = Models.STAIRS.upload(TutorialBlocks.DIAMOND_STAIRS, diamondTexture, blockStateModelGenerator.modelCollector);
    final Identifier innerStairsModelId = Models.INNER_STAIRS.upload(TutorialBlocks.DIAMOND_STAIRS, diamondTexture, blockStateModelGenerator.modelCollector);
    final Identifier outerStairsModelId = Models.OUTER_STAIRS.upload(TutorialBlocks.DIAMOND_STAIRS, diamondTexture, blockStateModelGenerator.modelCollector);
    blockStateModelGenerator.blockStateCollector.accept(
        BlockStateModelGenerator.createStairsBlockState(TutorialBlocks.DIAMOND_STAIRS,
            BlockStateModelGenerator.createWeightedVariant(innerStairsModelId),
            BlockStateModelGenerator.createWeightedVariant(stairsModelId),
            BlockStateModelGenerator.createWeightedVariant(outerStairsModelId)));
    blockStateModelGenerator.registerParentedItemModel(TutorialBlocks.DIAMOND_STAIRS, stairsModelId);
 
    final Identifier slabBottomModelId = Models.SLAB.upload(TutorialBlocks.DIAMOND_SLAB, diamondTexture, blockStateModelGenerator.modelCollector);
    final Identifier slabTopModelId = Models.SLAB_TOP.upload(TutorialBlocks.DIAMOND_SLAB, diamondTexture, blockStateModelGenerator.modelCollector);
    blockStateModelGenerator.blockStateCollector.accept(
        BlockStateModelGenerator.createSlabBlockState(TutorialBlocks.DIAMOND_SLAB,
            BlockStateModelGenerator.createWeightedVariant(slabBottomModelId),
            BlockStateModelGenerator.createWeightedVariant(slabTopModelId),
            BlockStateModelGenerator.createWeightedVariant(Identifier.ofVanilla("block/diamond_block")))
    );
    blockStateModelGenerator.registerParentedItemModel(TutorialBlocks.DIAMOND_SLAB, slabBottomModelId);

In versions before 1.21.4, we do not need to call BlockStateModelGenerator.createWeightedVariant, but pass ids as parameters directly instead.

Well done! We successfully added all models, block states definitions and item models definitions needed with several lines of code.

A directional block usually uses one block model, but in the block states definition, different model variants will be mapped into, such as different x-rotation, y-rotation and uvlock. (These words seem similar when we used to manually write block states definitions JSONs?)

Taking a vertical slab block we created in the directionalblock tutorial as an example, we generate models and block states definitions with data generator.

We have created a tutorial:block/vertical_slab model before, as a template for vertical slab block models. These template models are usually not generated with a data generator. Then we create a model with name tutorial:block/polished_andesite_vertical_slab for the vertical polished andesite slab, inheriting the template model we mentioned, and provide texture variables.

To inherit this template model in the data generator, we create a Model object for this template model. The model's JSON use three texture variables: bottom, top and side, so we also depend the three texture variables here. The data generator will assign values for the variables when generating models.

TutorialModelGenerator.java

public class TutorialModelGenerator extends FabricModelProvider {
  public static final Model VERTICAL_SLAB = new Model(
      Optional.of(Identifier.of("tutorial", "block/vertical_slab")),
      Optional.empty(),
      TextureKey.BOTTOM, TextureKey.TOP, TextureKey.SIDE);
 
  // ...
}

Then we call the upload method, which generates a block model and returns the model's id. Here, we make item models definitions as well so that the item also directly uses this block model.

TutorialModelGenerator.java

  @Override
  public void generateBlockStateModels(BlockStateModelGenerator blockStateModelGenerator) {
    // ...
 
    final Identifier verticalSlabModelId = VERTICAL_SLAB.upload(TutorialBlocks.POLISHED_ANDESITE_VERTICAL_SLAB, TextureMap.all(Identifier.ofVanilla("block/polished_andesite")), blockStateModelGenerator.modelCollector);
    blockStateModelGenerator.registerParentedItemModel(TutorialBlocks.POLISHED_ANDESITE_VERTICAL_SLAB, verticalSlabModelId);
  }

It's now an important part — now we create a block states definition for a vertical slab block. Actually it's not so complicated, because we know each model is the same, with only a difference in rotation.

In 1.21.5, a block states definition is BlockModelDefinitionCreator, which are divided into two types:

• VariantsBlockModelDefinitionCreator: Assign one block model variant according to block state. Simple blocks use this type. The vertical slab block we discuss here also uses this type.
• MultipartBlockModelDefinitionCreator: A block that consists of multiple parts, each of which is a block model variant. Each part is decided whether to display according to its block state. Vanilla redstone write is this type.

For VariantsBlockModelDefinitionCreator, we need to define the relations between block states and block model variants, which means to clarify, whether model variants to be used for which block. Multiple block states may use one same model variant (for example, waterlogged blocks and blocks not waterlogged, use the same model), and one block state may also use multiple variants (such as the random rotation for dirt and sands) — but we must ensure there is no duplication or ignorance: we do not need to ensure each block state property to be used, but we need to ensure each possible block state should be contained without duplication, otherwise errors may be thrown. In 1.21.5, there are two ways to define the relations between block states and block model variants:

• Method one: Specify one model variant, and modify the variant according to block states, such as modifying x-rotation, y-rotation and uvlock. All block states use the same model id, with only possible different variants.
• Method two: Allocating model variants for different block states directly, and then you can also continue to modify variants. In this case, the block states may use different model ids.

Our vertical slab has two block state properties: facing and waterlogged. But the waterlogged property does not affect its model, so we only look at facing. As the model id is not influenced by directions, we use method one here:

TutorialModelGenerator.java

  @Override
  public void generateBlockStateModels(BlockStateModelGenerator blockStateModelGenerator) {
    // ...
 
    blockStateModelGenerator.blockStateCollector.accept(
        VariantsBlockModelDefinitionCreator.of(TutorialBlocks.POLISHED_ANDESITE_VERTICAL_SLAB,
                BlockStateModelGenerator.createWeightedVariant(verticalSlabModelId))
            .apply(BlockStateModelGenerator.UV_LOCK)
            .coordinate(BlockStateVariantMap.operations(VerticalSlabBlock.FACING)
                .register(Direction.NORTH, BlockStateModelGenerator.NO_OP)
                .register(Direction.EAST, BlockStateModelGenerator.ROTATE_Y_90)
                .register(Direction.SOUTH, BlockStateModelGenerator.ROTATE_Y_180)
                .register(Direction.WEST, BlockStateModelGenerator.ROTATE_Y_270)));
  }

The apply method will apply a same operation for all block states (such as all adding uvlock), while the coordinate method apply different operations according to different block states (such as setting different y-rotation values). BlockStateVariantMap.operations is only related to model variants, not related to model ids.

Can we use method two? Of course yes! The code is the following:

TutorialModelGenerator.java

    blockStateModelGenerator.blockStateCollector.accept(
        VariantsBlockModelDefinitionCreator.of(
            TutorialBlocks.POLISHED_ANDESITE_VERTICAL_SLAB)
            .with(BlockStateVariantMap.models(VerticalSlabBlock.FACING)
                .register(Direction.NORTH, BlockStateModelGenerator.createWeightedVariant(verticalSlabModelId))
                .register(Direction.EAST, BlockStateModelGenerator.createWeightedVariant(verticalSlabModelId).apply(BlockStateModelGenerator.ROTATE_Y_90))
                .register(Direction.SOUTH, BlockStateModelGenerator.createWeightedVariant(verticalSlabModelId).apply(BlockStateModelGenerator.ROTATE_Y_180))
                .register(Direction.WEST, BlockStateModelGenerator.createWeightedVariant(verticalSlabModelId).apply(BlockStateModelGenerator.ROTATE_X_270))
            )
            .apply(BlockStateModelGenerator.UV_LOCK)
    );

We find that in method two, when calling VariantsBlockModelDefinitionCreator.of, we do not pass WeightedVariant as the second parameter, but provide once for each block state later. We can also notice that, in method one, what was called is BlockStateVariantMap.operations, and it's only operations for model variants that was registered each time, while in method two, what was called is BlockStateVariantMap.models, and it's a full model variant that was registered each time. After allocating model variants through the with method, we can continue to modify the variants with apply or coordinate.

In the method one and method two described above, apart from registering model operations or model variants one by one with the register method, the generate method can also be used, specifying a model operation or model variants with a lambda, which is a function, taking the corresponding property value as parameter, and returning the model operation or model variant.

If a block state has multiple properties that affect model variants, you can provide multiple properties in BlockStateVariantMap.operations and BlockStateVariantMap.models, and specify or use multiple values in the register or generate method. You can also call coordinate twice, allowing each property decide their respective modifications to the model variant.