Events

The event system lets you react to things happening in the game. Events are posted on the EventBus, and you listen to them by annotating methods with @SubscribeEvent.

Listening to events

Any object can register as a listener. Methods must take exactly one parameter (the event type) and return Unit:


EventBus.register(this)
 
// or in a Module's onEnable (auto-subscribes)


@SubscribeEvent
fun onTick(event: TickEvent.Start) {
    // runs every tick
}

Event annotations


@SubscribeEvent(
    priority = Event.Priority.MEDIUM,
    ignoreCancelled = false,
    once = false
)

priority – order of execution: HIGHEST, HIGH, MEDIUM, LOW, LOWEST
ignoreCancelled – if true, receives cancellable events even when cancelled
once – automatically unregisters after the first dispatch

Available events

TickEvent

Fired every game tick.


@SubscribeEvent
fun onTick(event: TickEvent.Start)
fun onTick(event: TickEvent.End)

RenderEvent

Fired when the HUD or notification layer is rendered.


@SubscribeEvent
fun onHud(event: RenderEvent.Hud) {
    // Access event.graphics (GuiGraphicsExtractor)
    // Access event.deltaTracker (DeltaTracker)
    // Use SkiaPIP.drawSkia(graphics) { ... }
}
 
@SubscribeEvent
fun onNotification(event: RenderEvent.Notification)

WorldEvent


@SubscribeEvent
fun onWorldChange(event: WorldEvent.Change)
 
@SubscribeEvent
fun onBeforeGizmos(event: WorldEvent.BeforeGizmos) {
    // Called before world gizmos render, after entities
    // Good time to do per-frame rotation updates
}

GuiEvent


@SubscribeEvent
fun onGuiOpen(event: GuiEvent.Open)   // screen opened
fun onGuiDraw(event: GuiEvent.Draw)   // screen drawn
fun onGuiClose(event: GuiEvent.Close) // screen closed

The screen is available via event.screen.

PacketEvent

For intercepting network traffic. Both Send and Receive are cancellable.


@SubscribeEvent
fun onPacketSend(event: PacketEvent.Send) {
    // event.packet is the Packet<?>
}
 
@SubscribeEvent
fun onPacketReceive(event: PacketEvent.Receive) {
    // Cancel it:
    event.setCancelled(true)
}

MouseEvent


@SubscribeEvent
fun onMouse(event: MouseEvent) {
    val button = event.button  // LEFT, RIGHT, or MIDDLE
    val action = event.action  // PRESS or RELEASE
}

MouseScrollEvent


@SubscribeEvent
fun onScroll(event: MouseScrollEvent) {
    val h = event.horizontalAmount
    val v = event.verticalAmount
}

ChatSendEvent


@SubscribeEvent
fun onChat(event: ChatSendEvent) {
    val msg = event.message
    event.setCancelled(true) // blocks the message
}

Lambda listeners

For quick one-off listeners without a full class:


val token = EventBus.registerLambda<TickEvent.Start>(
    priority = Event.Priority.HIGH,
    once = true // auto-removes after first fire
) { event ->
    println("First tick only!")
}
 
// Later:
EventBus.unregister(token)

Posting custom events

You can post your own events. Just implement the Event interface (or extend Event.Cancellable for cancellable events):


class MyCustomEvent(val data: String) : Event.Cancellable()
 
// Post it:
EventBus.post(MyCustomEvent("hello"))

Cancelling events

For cancellable events:


event.setCancelled(true)
event.isCancelled() // check if cancelled