Custom Attachments

Custom attachments allow you to encapsulate your virtual entity behaviour, and provide methods for modifying your virtual entities. The benefit of doing this in your attachment implementation and not a parent virtual entity is because you'll usually want to keep track of your attachment to be able to remove it once you're done with it. Having to also then keep a reference to a specific virtual entity can start to get messy.

class CustomVirtualEntityAttachment(
    anchor: AttachmentAnchor,
    observers: ObserverTracker
): SimpleVirtualEntityAttachment(anchor, observers) {
    private val warnings = Object2ObjectOpenHashMap<BlockPos, SimpleVirtualTextDisplay>()

    private var tick = 0

    fun warn(position: BlockPos) {
        if (!this.warnings.containsKey(position)) {
            val entity = this.attach(::SimpleVirtualTextDisplay)
            entity.position = VirtualPosition.Absolute(position.center)
            entity.setText(Component.literal("!!").yellow())
            this.warnings[position] = entity
        }
    }

    fun unwarn(position: BlockPos) {
        val entity = this.warnings[position] ?: return
        this.detach(entity)
    }

    override fun updateAttached() {
        this.tick += 1
        val isBold = (this.tick / 20) % 2 == 0
        for (entity in this.warnings.values) {
            entity.modifyText { original ->
                original.copy().withStyle { s -> s.withBold(isBold) }
            }
        }
    }
}

In the example above we can place warnings (virtual text entity) at block positions. We cannot place multiple warnings at the same position and every second the warnings change boldness.

The example attachment could then be used as follows:

object OverworldWarningHandler {
    private lateinit var attachment: CustomVirtualEntityAttachment
    
    fun foo() {
        this.attachment.warn(BlockPos.ZERO)
    }
    
    fun registerEvents() {
        GlobalEventHandler.Server.register<ServerStartEvent> { (server) ->
            this.attachment = server.overworld().createVirtualEntityAttachment(::CustomVirtualEntityAttachment)
        }
    }
}