Mapping Out The UE4 Animation Architecture Flow

UE4 Animation Subsystem Architecture

Animation Subsystem

AnimInstance is the runtime animation class that maintains runtime data & plays shit
	- This is the parent class of the animation blueprint
	- Get Bone Transforms from a specific time t:
		○ Sequence->GetAnimationPose(Output.Pose, Output.Curve, FAnimExtractContext(CurrentTime, Sequence->bEnableRootMotion));
		
	
UAnimationAsset is the classes that contain the actual data and also calculates bones & curves
	- UAnimSequence
	- UAnimComposite
		○ UAnimMontage

Two classes for each Anim Node; separated for optimization b/c node construction is expensive
	- UAnimGraphNode_Base: Anim Graph Node that's shown in editor
		○ Only exist in editor
		○ One way relationship with corresponding FAnimNode_Base counterpart
	- FAnimNode_Base: Anim Behavior node that is run time
		○ Initialize: Called whenever need to initialize/reinitialize (e.g. changing mesh instance)
		○ Update: Called to update current state (such as advancing playtime or updating blend weights)
			§ Takes FAnimationUpdateContext that knows the delta time for the update & the current nodes blend weight
			§ Might be where we hook in to do the forward time projection intersection
		○ Evaluate/EvaluateComponentSpace: Generates a 'pose' i.e. list of bone transforms
	- FAnimationRuntime has lots of good functions to look at and utility/helper functions

Sequence:
Update Functions:
[Should be called before RefreshBoneTransforms]USkinnedMeshComponent::TickPose()
[Should be atomic & not rely on Tick()] USkinnedMeshComponent::RefreshBoneTransforms()
USkinnedMeshComponent::FinalizeBoneTransform()


USkeletalMeshComponent::InitAnim: Called when component needs to initialize or reinitialize eg InitializeComponent() or SetSkeletalMesh()
	- USkeletalMeshComponent::InitializeAnimScriptInstance
		○ AnimInstance::InitializeAnimation
			- AnimInstance::NativeInitializeAnimation()
			- AnimInstance::BlueprintInitializeAnimation()



USkinnedMeshComponent::TickComponent()
	- USkinnedMeshComponent::TickPose()
		○ USkeletalMeshComponent::TickAnimation
			- AnimInstance::UpdateAnimation
				○ [Default does nothing] NativeUpdateAnimation: Only does something for UAnimSingleNodeInstance
				○ BlueprintUpdateAnimation: Main AnimBP entry point
				○ FAnimNode_Base::Update()
				○ UAnimInstance::Montage_Advance()
				○ UAnimInstance::TriggerAnimNotifies
				○ UAnimInstance::TriggerQueuedMontageEvents
				
	- USkinnedMeshComponent::RefreshBoneTransforms()
		○ USkinnedMeshComponent::PerformAnimationEvaluation()
			§ [Evaluate Animation System] USkeletalMeshComponent::EvaluateAnimation()
				○ AnimInstance::EvaluateAnimation()
					§ [Default does nothing] UAnimInstance::NativeEvaluateAnimation() AnimInstance can override animgraph evaluation completely. Ex: AnimSingleNodeInstance() doesn't eval the animgraph
					§ FAnimNode_Base::Evaluate(): This is the root of the anim graph. Called if NativeEvaluateAnimation returns false
					
		○ USkeletalMeshComponent::PostAnimEvaluation
			§ AnimInstance::UpdateCurves
			§ USkinnedMeshComponent::FinalizeBoneTransform()
				○ AnimInstance::PostEvaluateAnimation
					§ [Does nothing by default but virtual] AnimInstance::NativePostEvaluateAnimation
					§ BlueprintPostEvaluateAnimation
			§ UpdateComponentToWorld()
			§ UpdateOverlaps()
			
		○ [If RefreshBoneTransforms() not called from Tick()] USkinnedMeshComponent::FinalizeBoneTransform

			

		

Thanks!

best summary i've come across. thank you

your welcome!

P.S. I made a whole site with stuff like this:
https://bebylon.dev/ue4guide/gameplay-programming/animation-subsystem/animation-subsystem
with github repo: https://github.com/ikrima/gamedevguide