In Flow Core, a Trigger is essentially an external entry point into the graph, rather than a regular input to a flow node. The clearest evidence is that a Trigger normally has no In port and only exposes output ports. A standard Trigger has a single Out, while Input, UI, and Blackboard trigger nodes are simply variants built on the same entry-point mechanism.

It can be understood this way:

• Enter means you explicitly invoke a specific entry inside the graph.
• Trigger means the runtime registers a listener first, and when an external event occurs, execution automatically enters the chain.
• Remote In / Remote Out are used for internal graph routing, not for receiving external runtime events.

Within Flow Node Kind, standard Trigger, system Trigger, UI Trigger, input Trigger, and Blackboard Trigger are represented as separate node categories. At runtime, however, they are all compiled into the same trigger-slot structure.

Mechanism

The core execution path works like this:

• During graph compilation, all Trigger nodes are collected and compiled into trigger slots. Their runtime metadata is recorded at the same time, including Invoke Mode, Bus type, event name, and ticker parameters.
• After the runtime starts, RegisterTriggers registers listeners based on trigger type. Standard Triggers are registered to Unity, Global, Local, or Ticker sources. UI Triggers bind to Unity UI or Event System callbacks. Input Old Trigger and Input New Trigger enter the input polling pipeline. On Blackboard Value Changed Trigger subscribes to the Blackboard’s OnSet.
• When an event occurs, execution is funneled through TryExecuteTrigger(...). At that point, the payload and signal context are written into FlowContext, and execution begins from the corresponding trigger slot.
• A standard Trigger usually continues through a single Next connection. Multi-output Triggers, such as Input- or Blackboard-related ones, instead use Trigger Output Index to select Nexts[outputIndex].

There are several important points to keep in mind:

• Invoke Mode determines how a Trigger behaves when the system is already busy. In Queue mode, incoming executions are queued. In other modes, they may be skipped or bypassed when the runtime is occupied. This behavior is also explicitly described in the Trigger help text in the editor.
• Payload is strongly typed. Subsequent instructions read it through FlowValueSource.Payload and TriggerPayloadValueMode, rather than through an arbitrary object container. For more details, refer to Payload.
• A standard Trigger supports four Bus types: Unity, Global, Local, and Ticker.

UI

In the editor, the UI for Trigger-related nodes is not a single fixed panel. Instead, it is built dynamically based on the specific node type.