Implementing Slot-Based Animation Overlays

Utilize animation slots within your AnimGraph to play specific montages over existing state machine locomotion without interrupting core movement.

In this lesson, you will learn how to use Animation Slots to overlay secondary actions, like waving or reloading, onto your character’s active locomotion without breaking their movement cycle.

The Concept of Animation Slots

When you have a State Machine handling your core locomotion (walking, running, idling), it outputs a final animation pose. If you want your character to perform a unique action—like a "Hello" gesture—without stopping them mid-run, you cannot simply swap states. Instead, you use an Animation Slot.

An Animation Slot acts as a "layer" that sits on top of your state machine. When you play an Animation Montage through a specific slot (e.g., "UpperBody"), the engine blends the slot’s animation into your existing pose based on the bone weights defined in your rig.

Implementing in the AnimGraph

To set this up, navigate to your Animation Blueprint’s AnimGraph. Instead of piping your State Machine directly into the Output Pose, you will insert a Slot node.

Right-click in the AnimGraph and add a Slot 'DefaultSlot' node.
Connect your State Machine result into the input of the Slot node.
Connect the output of the Slot node to the final Output Pose.

Your graph should look like this: State Machine → Slot Node → Output Pose

Playing the Overlay

Now, whenever you call Play Anim Montage from your Character Blueprint, you specify the Slot Name (e.g., "DefaultSlot"). Because the slot is placed after the locomotion logic, it overrides the pose generated by the state machine only for the duration of the montage. If you want to limit the overlay to specific parts of the body—like only the arms—you can set up Layered Blend per Bone nodes before the slot to ensure the legs keep running while the upper body performs the action.

By using slots, you preserve the fluidity of your locomotion while gaining the flexibility to trigger specific animations instantly.

Key Takeaway: Animation Slots allow you to inject episodic animations into your character's workflow by intercepting the final pose of your state machine and applying a dynamic layer on top.