Rasagar/Library/PackageCache/com.unity.visualeffectgraph/Documentation~/Events.md

Events

Events define the inputs for a Visual Effect Graph's processing workflow. The Spawn and Initialize Contexts use Events as their inputs. Through Events, a Visual Effect Graph can:

• Start and stop spawning particles.
• Read Event Attribute payloads sent from C# scripts.

Creating Events

In general, an Event is just a string that represents the Event's name. To receive an Event in the Visual Effect Graph, create an Event Context and type the name of the Event you want to receive in the Event Name property. Event Contexts have no input flow ports and can only connect their output flow port to Spawn or Initialize Contexts.

To create an Event Context:

1. In the Visual Effect Graph window, right-click in an empty space.
2. From the menu, click Create Node.
3. In the Node Creation menu, click Contexts > Event (Context).
4. In the Event Name input field, type the name of your Event.

Default Events

The Visual Effect Graph provides two default Events:

• OnPlay: Enables the spawning of particles when Unity sends the Play Event to the Visual Effect. If you do not assign an Event to a Spawn Context's Start input flow port, the Visual Effect Graph implicitly binds this Event to that input flow port instead.
• OnStop: Disables the spawning of particles when Unity sends the Stop Event to the Visual Effect. If you do not assign an Event to a Spawn Context's Stop input flow port, the Visual Effect Graph implicitly binds this Event to that input flow port instead.

If you connect an Event Context to a Spawn Context's Start or Stop input flow port, this removes the implicit binding to the OnPlay and OnStop Events respectively.

Custom Events

If you do not want to use the default Events, you can use an Event Context to create your own custom Event.

To do this, first create an Event Context, then type the name of your custom Event in the Event Name property.

Event Attribute Payloads

Event Attribute payloads are attributes that you can attach to an Event. To set these attributes in a Visual Effect Graph, you can use the Set [Attribute] Blocks in Spawn Contexts, but you can also attach them to Events you send from C# scripts. For information on how to do that latter, see Component API .

Event Attribute Payloads are attributes that implicitly travel through the graph from Events, through Spawn Contexts, and eventually to an Initialize Context. To catch a payload in an Initialize Context, use Get Source Attribute Operators or Inherit [Attribute] Blocks.

Default Visual Effect Event

The default Visual Effect Event defines the name of the Event that the Visual Effect Graph implicitly sends when a Visual Effect instance Resets. This happens when the effect first starts, or when the effect restarts.

You can define the default Visual Effect Event for each Visual Effect Graph Asset independently. You can also override this value for every instance of the Visual Effect Graph Asset. To override the default Visual Effect Event for an instance, see Initial Event Name in the Visual Effect Inspector.

GPU Events

GPU Events are an Experimental feature of the Visual Effect Graph. They allow you to spawn particles based on other particles. To enable GPU Events, enable the Experimental Operators/Blocks checkbox in the Visual Effect Preferences.

GPU Events are Event Contexts that rely on data sent from other systems, for example, when a particle dies. The following Update Blocks can send GPU Event Data:

• Trigger Event On Die: Spawns N Particles on another system when a particle dies.
• Trigger Event Rate: Spawn N Particles per second (or per distance travelled), based on a particle from a system.
• Trigger Event Always: Spawns N Particles every frame.

These Blocks connect to a GPUEvent Context. This Context does not handle any Blocks, but instead connects to an Initialize Context of a child system.

To gather data from the parent particle, a child system must refer to Source Attributes in its Initialize Context. To do this, a child system can use a Get Source Attribute Operator, or an Inherit Attribute Block. For a visual example, see the image below.

In this example, the child System inherits the source position of the particle that creates it. It also inherit roughly 50% of the parent particle's speed.