Layering Animations with Blend Per Bone

In this lesson, you will learn how to use Layered Blend per Bone to play two different animations simultaneously on specific parts of your character's body.

The Concept of Layering

In many games, you want your character to maintain their walking or running animation (the lower body) while performing a secondary action like waving, reloading, or aiming a weapon (the upper body). If you simply switched the animation state, the legs would stop moving. To solve this, we use the Layered Blend per Bone node in the AnimGraph.

This node takes two inputs: a "Base Pose" (usually your locomotion state machine) and a "Blend Pose" (the action you want to overlay). It then looks at the Skeletal Hierarchy you learned about earlier to decide where to "cut" the character and blend the animations.

Setting Up the Blend

1. Open your Animation Blueprint and go to the AnimGraph.
2. Add a Layered Blend per Bone node.
3. Plug your locomotion state machine into the Base Pose and your upper-body animation (e.g., an Aiming sequence) into the Blend Pose 0 input.
4. In the node’s Details panel, expand the Layer Setup and add an element to the Branch Filters.
5. Type in the Bone Name where the blend should start—for example, spine_01.

By setting the bone name to spine_01, you tell Unreal Engine: "Keep playing the walking animation for the hips and legs, but use the aiming animation for everything from the spine upward."

You can also adjust the Blend Depth, which determines how smoothly the transition happens at the joint, and toggle Mesh Space Rotation Blend to ensure the limbs align correctly during the transition. This technique keeps your character looking dynamic and fluid, rather than stiff or disjointed, as they interact with the world while moving.

Key Takeaway: The Layered Blend per Bone node allows you to split your character's skeleton into distinct regions, enabling independent animations for the upper and lower body to occur at the same time.