Global Loot Modifiers

Global Loot Modifiers are a data-driven method of handling modification of harvested drops without the need to overwrite dozens to hundreds of vanilla loot tables or to handle effects that would require interactions with another mod's loot tables without knowing what mods may be loaded. Global Loot Modifiers are also stacking, rather than last-load-wins, similar to tags.

Registering a Global Loot Modifier

You will need 4 things:

1. Create a global_loot_modifiers.json.
   • This will tell NeoForge about your modifiers and works similar to tags.
2. A serialized json representing your modifier.
   • This will contain all of the data about your modification and allows data packs to tweak your effect.
3. A class that extends IGlobalLootModifier.
   • The operational code that makes your modifier work. Most modders can extend LootModifier as it supplies base functionality.
4. Finally, a map codec to encode and decode your operational class.
   • This is registered.

The global_loot_modifiers.json

The global_loot_modifiers.json represents all loot modifiers to be loaded into the game. This file MUST be placed within data/neoforge/loot_modifiers/global_loot_modifiers.json.

danger

global_loot_modifiers.json will only be read in the neoforge namespace. The file will be neglected if it is under the mod's namespace.

entries is an ordered list of the modifiers that will be loaded. The ResourceLocations specified points to their associated entry within data/<namespace>/loot_modifiers/<path>.json. This is primarily relevant to datapack makers for resolving conflicts between modifiers from separate mods.

replace, when true, changes the behavior from appending loot modifiers to the global list to replacing the global list entries entirely. Modders will want to use false for compatibility with other mod implementations. Datapack makers may want to specify their overrides with true.

{
    "replace": false, // Must be present
    "entries": [
        // Represents a loot modifier in 'data/examplemod/loot_modifiers/example_glm.json'
        "examplemod:example_glm",
        "examplemod:example_glm2"
        // ...
    ]
}

The Serialized JSON

This file contains all of the potential variables related to your modifier, including the conditions that must be met prior to modifying any loot. Avoid hard-coded values wherever possible so that data pack makers can adjust balance if they wish to.

type represents the registry name of the codec used to read the associated JSON file. This must always be present.

conditions should represent the loot table conditions for this modifier to activate. Conditions should avoid being hardcoded to allow datapack creators as much flexibility to adjust the criteria. This must also be always present.

caution

Although conditions should represent what is needed for the modifier to activate, this is only the case if using the bundled NeoForge classes. If using LootModifier as a subclass, all conditions will be ANDed together and checked to see if the modifier should be applied.

Any additional properties read by the serializer and defined by the modifier can also be specified.

// Within data/examplemod/loot_modifiers/example_glm.json
{
    "type": "examplemod:example_loot_modifier",
    "conditions": [
        // Normal loot table conditions
        // ...
    ],
    "prop1": "val1",
    "prop2": 10,
    "prop3": "minecraft:dirt"
}

IGlobalLootModifier

To supply the functionality a global loot modifier specifies, a IGlobalLootModifier implementation must be specified. These are instances generated each time a serializer decodes the information from JSON and supplies it into this object.

There are two methods that needs to be defined in order to create a new modifier: #apply and #codec. #apply takes in the current loot that will be generated along with the context information such as the currently level or additional defined parameters. It returns the list of drops to generate.

info

The returned list of drops from any one modifier is fed into other modifiers in the order they are registered. As such, modified loot can be modified by another loot modifier.

#codec returns the registered map codec used to encode and decode the modifier to/from JSON.

The LootModifier Subclass

LootModifier is an abstract implementation of IGlobalLootModifier to provide the base functionality which most modders can easily extend and implement. This expands upon the existing interface by defining the #apply method to check the conditions to determine whether or not to modify the generated loot.

There are two things of note within the subclass implementation: the constructor which must take in an array of LootItemConditions and the #doApply method.

The array of LootItemConditions define the list of conditions that must be true before the loot can be modified. The supplied conditions are ANDed together, meaning that all conditions must be true.

The #doApply method works the same as the #apply method except that it only executes once all conditions return true.

public class ExampleModifier extends LootModifier {

    public ExampleModifier(LootItemCondition[] conditionsIn, String prop1, int prop2, Item prop3) {
        super(conditionsIn);
        // Store the rest of the parameters
    }

    @NotNull
    @Override
    protected ObjectArrayList<ItemStack> doApply(ObjectArrayList<ItemStack> generatedLoot, LootContext context) {
        // Modify the loot and return the new drops
    }

    @Override
    public MapCodec<? extends IGlobalLootModifier> codec() {
        // Return the codec used to encode and decode this modifier
        return EXAMPLE_MODIFIER_MAP_CODEC.get();
    }
}

The Loot Modifier Map Codec

The connector between the JSON and the IGlobalLootModifier instance is a MapCodec<T>, where T represents the type of the IGlobalLootModifier to use.

For ease of convenience, a loot conditions codec has been provided for an easy addition to a record-like codec via LootModifier#codecStart. This is utilized for data generation of the associated loot modifier.

// For some DeferredRegister<MapCodec<? extends IGlobalLootModifier>> REGISTRAR
public static final RegistryObject<MapCodec<ExampleModifier>> EXAMPLE_MODIFIER_MAP_CODEC = REGISTRAR.register("example_codec", () ->
    RecordCodecBuilder.mapCodec(
        inst -> LootModifier.codecStart(inst).and(
            inst.group(
                Codec.STRING.fieldOf("prop1").forGetter(m -> m.prop1),
                Codec.INT.fieldOf("prop2").forGetter(m -> m.prop2),
                BuiltInRegistries.ITEM.byNameCodec().fieldOf("prop3").forGetter(m -> m.prop3)
            )
        ).apply(inst, ExampleModifier::new)
    )
);

Examples can be found on the NeoForge Git repository, including silk touch and smelting effects.