Contexts

Usage of Contexts in Nova

Contexts are currently only used for block-related events, but it is planned to expand them to other aspects in the future.

A Context, at its core, is a simple key-value storage for (ContextParamType<T>, T) pairs and a ContextIntention, which defines the allowed parameters.

You can find a list of default context intentions here.
You can find a list of default context param types here.
The documentation also notes which types are parameter types are required for which ContextIntention and which are optional.

The context system can also infer parameters from other parameters, for example, you don't need to provide a BLOCK_WORLD parameter if you provide a BLOCK_POS parameter, and you can still read BLOCK_WORLD from the context. Which parameters are inferred from other parameters is also noted in the context param type documentation.

Creating and using a Context

And this is how you create and use a Context:

// create a context to place EXAMPLE_BLOCK at pos
val context = Context.intention(DefaultContextIntentions.BlockPlace)
    .param(DefaultContextParamTypes.BLOCK_POS, pos)
    .param(DefaultContextParamTypes.BLOCK_TYPE_NOVA, Blocks.EXAMPLE_BLOCK)
    .build()

// read BLOCK_WORLD from context, which is inferred from BLOCK_POS
val world: World = context.getOrThrow(DefaultContextParamTypes.BLOCK_WORLD)

// place block
BlockUtils.placeBlock(context)

Custom ContextParamType

In the example below I've created a custom ContextParamType that can be used in the BlockPlace, BlockBreak, BlockInteract default intentions. It represents the name of the target block and is autofilled through either the BLOCK_TYPE_NOVA or BLOCK_TYPE_VANILLA parameter.

val BLOCK_NAME: ContextParamType<Component> =
    ContextParamType.builder<Component>(Machines, "block_name")
        .optionalIn(BlockPlace, BlockBreak, BlockInteract)
        .autofilledBy(DefaultContextParamTypes::BLOCK_TYPE_NOVA) { type: NovaBlock -> type.name }
        .autofilledBy(DefaultContextParamTypes::BLOCK_TYPE_VANILLA) { type: Material -> Component.translatable(type.blockTranslationKey!!) }
        .build()