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Basic

How work the Group Param Handler on Specie

It's this system which manage all stuff from creation data

This mean you can add your own stuff thanks to this

Abbreviation

I'll use PHD for ParamHandlerDataAsset

GPHD for GroupParamHandlerDataAsset

PH for ParamHandler

Group Param Handler Content​

A GPH DataAsset (GPHD) is a container that holds a list of Param Handler Descriptors (PHDs).
This structure is used to organize and manage parameter handling by category.

Example: EpicHmn​

Screenshot

In this example, we can see parameters grouped by logical areas:

  • Head Creation Data
  • Hair Creation Data
  • Body Creation Data

Inspecting a PHD​

If we open the Head PHD, we see:

Screenshot

It contains a list of keys (parameter names) associated with handler classes.

For instance, whenever the HeadStyle parameter changes, the system will call the handler object BP_ACC_PH_HeadStyle.

Inspecting a Param Handler (PH) Object​

Each Param Handler class defines 4 event methods that are called when a data value changes:

  • OnReceiveInt
  • OnReceiveFloat
  • OnReceiveColor
  • OnReceiveTag

These functions allow you to implement logic specific to the type of parameter being received.

BP Version (deprecated)​

In the BP_ACC_PH_HeadStyle we can see i do stuff when i receive Int Value from HeadStyle key :

Blueprint Deprecated

The default Blueprint version of the ParamHandler has been migrated to C++.
It remains available only as a reference to understand the logic, but it is not used in the official template project.

Screenshot

CPP Version (used)​

FACCParamHandlerResult UACCParamHandler_HairStyle::OnReceiveInt_Implementation(UACCCreationComponent* CreationComponent, const FACCIntParam& IntParam, bool bRemoved)
{
	// Step 1: Use the CustomInfo as the hair part key (e.g., "FrontHair", "BackTailHair")
	FName HairPartName = IntParam.CustomInfo;

	// Remove Hair ?
	if (bRemoved)
	{
		CreationComponent->RemoveInstance(IntParam.CustomInfo);
		UE_LOG(LogACC, Log, TEXT("HairStyle: Removed '%s'"), *HairPartName.ToString());

		return FACCParamHandlerResult::MakeSuccess();
	}
	
	// Step 2: Retrieve mesh data for the selected hair ID
	FACCMeshData MeshData;
	if (!CreationComponent->CurrentGender->GetMeshData("Hair", IntParam.Value, MeshData))
	{
		// Optionally remove the current hair part if invalid data
		if (bRemoveHairPartIfInvalid)
		{
			CreationComponent->RemoveInstance(HairPartName);
			UE_LOG(LogACC, Warning, TEXT("HairStyle: Removed invalid hair part '%s'"), *HairPartName.ToString());
		}
		return FACCParamHandlerResult::MakeError(TEXT("Hair mesh data is missing or invalid for gender '%s'."),
		                                         *GetNameSafe(CreationComponent->CurrentGender));
	}
    ...