StateTree

#unreal

Custom tasks, evaluators and conditions can be written both in C++ and BP’s. C++ offers better control, such as not making tasks tick.

• Custom StateTree tasks
• StateTree InstanceData
• StateTree design
• Troubleshooting State Trees
• State Tree Context

GetExternalData §

Usage §

This function can be used to load objects from outside the state tree. This works by defining a handle, and linking it:

//In your header
TStateTreeExternalDataHandle<AAIController> ControllerHandle;
 
virtual bool Link(FStateTreeLinker& Linker) override;
 
//.cpp file
bool FMySTT::Link(FStateTreeLinker& Linker)
{
	Linker.LinkExternalData(ControllerHandle);
	return true;
}
 
EStateTreeRunStatus FMySTT::EnterState(FStateTreeExecutionContext& Context, const FStateTreeTransitionResult& Transition) const
{
	AAIController& Controller = Context.GetExternalData(ControllerHandle);
	// ....
}

How it works §

The data available via GetExternalData is defined in UStateTreeComponent (if you use Mass state trees there’s probably different place which I’ve not looked at)

UStateTreeComponent has a function SetContextRequirements which is used to fill external data into the tree. Check its implementation for specifics.

State tree performance §

Measure with Unreal Insights. State Tree total seems to show up as “StateTree”. Blueprint based tasks seem to perform significantly worse than C++ based tasks, so depending on how often the tasks execute, using C++ may give decent performance benefits.

Other issues §

Issues valid at least for Unreal Engine 5.3

• State Trees cannot be changed at runtime if ran through the StateTreeComponent
• State Trees might be possible to run outside of the component, but no builtin support for it