Item Property Overrides

Item properties are a way for the “properties” of items to be exposed to the model system. An example is the bow, where the most important property is how far the bow has been pulled. This information is then used to choose a model for the bow, creating an animation for pulling it. This is different from assigning ModelResourceLocations directly to items through ModelLoader.setCustomModelResourceLocation or ModelLoader.setCustomMeshDefinition. These methods fix the possible set of models. Used on a bow, for example, these methods would permanently fix the number of frames in the pull animation to 4. However, properties are more flexible.

An item property assigns a certain float value to every ItemStack it is registered for, and vanilla item model definitions can use these values to define “overrides”, where an item defaults to a certain model, but if an override matches, it overrides the model and uses another. The format of item models, including overrides, can be found on the [wiki][]. They are useful mainly because of the fact that they are continuous. For example, bows use item properties to define their pull animation. Since the value of the property is a float, it increases continuously from 0 to 1. This allows resource packs to add as many models as they want for the bow pulling animation along that spectrum, instead of being stuck with four “slots” for their models in the animation. The same is true of the compass and clock.

Adding Properties to Items

Item::addPropertyOverride is used to add a property to an item. The ResourceLocation parameter is the name given to the property (e.g. new ResourceLocation("pull")). The IItemPropertyGetter is a function that takes the ItemStack, the World it’s in, and the EntityLivingBase that holds it, returning the float value for the property. Some examples are the "pulling" and “pull” properties in ItemBow, and the several static final ones in Item. For modded item properties, it is recommended that the modid of the mod is used as the namespace (e.g. examplemod:property and not just property, as that really means minecraft:property).

Using Overrides

The format of an override can be seen on the wiki, and a good example can be found in model/item/bow.json. For reference, here is a hypothetical example of an item with an examplemod:power property. If the values have no match, the default is the current model.

{
  "parent": "item/generated",
  "textures": {
    "__comment": "Default",
    "layer0": "examplemod:items/examplePartial"
  },
  "overrides": [
    {
      "__comment": "power >= .75",
      "predicate": {
        "examplemod:power": 0.75
      },
      "model": "examplemod:item/examplePowered"
    }
  ]
}

And here’s a hypothetical snippet from the supporting code. (This does not have to be client-only; it will work on a server too. In vanilla, properties are registered in the item’s constructor.)

item.addPropertyOverride(new IItemPropertyGetter() {
  @SideOnly(Side.CLIENT)
  @Override
  public float apply(ItemStack stack, @Nullable World world, @Nullable EntityLivingBase entity) {
    return (float)getPowerLevel(stack) / (float)getMaxPower(stack); // Some external methods
  }
}