Working with WorldGeneratorModifiers

For a brief overview of the World Generation process in Sponge, please read World Generation. Now, let’s show how you can begin making your mark on world generation. All plugins wishing to make changes to a worlds generator must register a WorldGeneratorModifier. These modifiers are registered globally with a unique id, which must be added to the config of a world by a server admin. With the id specified in the world config, a WorldGeneratorModifer will be automatically called when the generator for that world is set up, allowing it to make changes to the generator.

Creating a WorldGeneratorModifier

Let’s start with the format of a WorldGeneratorModifier. First, you need a class which implements the WorldGeneratorModifier interface:

import org.spongepowered.api.world.gen.WorldGeneratorModifier;

private class MyModifier implements WorldGeneratorModifier {

        @Override
        public String getId() {
                return "pluginid:mymodifier";
        }

        @Override
        public String getName() {
                return "My Modifier";
        }

        @Override
        public void modifyWorldGenerator(WorldCreationSettings world, DataContainer settings, WorldGenerator worldGenerator) {

        }

}

As you can see, WorldGeneratorModifier has three methods which we override. getId() must be overridden to return a constant and unique identifier for your WorldGeneratorModifier, this is the identifier which will be used in the world configration to specify which worlds your modifer should be applied to. getName() must be overriden with a constant and simple human-readable name for your modifier.

The third overridden method is where you make your changes to the world generator. This method is called by the implementation when it is creating the world generator for a world which has specified that your WorldGeneratorModifier should be applied.

The WorldGenerationSettings and a DataContainer of additional properties for the world are passed to this method in order to give context for your changes. For instance, you can use the WorldCreationSettings to only apply your generator changes to nether worlds.

Registering a WorldGeneratorModifier

Now that you have created our modifier, you need to register it. A good place to do this is in an GameInitializationEvent. To register it, simply call GameRegistry.registerWorldGeneratorModifier.

@Listener
public void onGameInitialization(GameInitializationEvent event) {
        Sponge.getGame().getRegistry().registerWorldGeneratorModifier(new MyModifier());
}

To apply your WorldGeneratorModifier to a world you must add it to the world-generation-modifiers array within the world config file found at config/sponge/worlds/[dimension]/[worldName]/world.conf. For example to apply the skylands WorldGeneratorModifier to a world you would add the skylands modifier’s id to the modifiers list.

    # WorldGenerationModifiers to apply to the world
    world-generation-modifiers=[
"sponge:skylands"
    ]

Note that the world-generation-modifers list may not be there, as by default there are no modifiers applied to a world and therefore the value is not created when the configuration file is created.

In the next articles we will look deeper at the changes we can make from our WorldGeneratorModifer.