Animation pipeline¶

Each pawn runs one character Anim Blueprint. It is the Game Animation Sample's motion matching Anim Blueprint with GASPALS layering added: overlay poses blended per body part on top of locomotion, an aim offset, procedural IK and cover lowering.

Both are animated on the UEFN mannequin skeleton. Other characters (Manny, Quinn, the MetaHuman Kellan, or your own) copy or retarget that pose; see Characters and visual overrides.

The pose, step by step¶

flowchart TD
    MM[Locomotion<br>motion matching or hybrid] --> LB
    OP[Overlay pose layer<br>ALI_OverlayPose] --> LB
    OB[Overlay body layer<br>ALI_OverlayBody] --> LB
    LB[ABP_LayerBlending<br>per-bone blends by curves] --> AO[Additive leans<br>and aim offset]
    AO --> Slot[DefaultSlot<br>montages: traversal, interactions, get-up]
    Slot --> Root[Offset root bone]
    Root --> Proc[Procedural layers<br>foot placement, leg IK, hand IK, full body IK]
    Proc --> Hist[Pose history<br>for motion matching]
    Hist --> Cover[CR_Humanoid_CoverLower<br>cover lowering]
    Cover --> Out((Output pose))

1. Locomotion. Two locomotion setups exist, selected per pawn by a console variable:

   • Full motion matching: the motion matching node picks frames from the pose search databases to match the character's trajectory.
   • State machine / blend stack hybrid: a state machine (idle, locomotion and in-air loops, transitions, idle breaks, slide) whose states pick animations with choosers and play them through a blend stack.

   DDCvar.LocomotionSetupMover (default 1, hybrid) and DDCvar.LocomotionSetupCMC (default 0, full motion matching) choose the setup. The result is cached as the locomotion pose. 2. Overlays. Two linked anim layers produce the overlay poses: ALI_OverlayPose (what the hands hold: rifle, torch, box...) and ALI_OverlayBody (the body style: default, masculine, feminine). The Blueprints that implement them are linked at runtime by the overlay and equipment systems. Inertialization smooths the switch when a new layer is linked. 3. Layer blending. ABP_LayerBlending (a linked anim graph) blends the overlays onto the locomotion pose bone chain by bone chain: legs, pelvis, spine, head, each arm and hand, in local or mesh space, as additive or override. The weights come from curves on the overlay animations, so each overlay pose decides how much of the body it takes over (see below). 4. Leans and aim offset. Additive leans from the lateral acceleration, then the aim offset layer turns the spine toward the aim direction. 5. Montages. The DefaultSlot plays montages: traversal, takedowns and shoves, ragdoll get-ups. 6. Root and procedural. The offset root bone keeps the feet planted while the capsule turns. The procedural layers run foot placement and leg IK, the hand IK Control Rig (CR_Humanoid_HandIK), and on the Mover pawn a full-body IK pass for character interactions. 7. Pose history records the final pose for motion matching's next search. 8. Cover lowering. CR_Humanoid_CoverLower lowers the pelvis in cover. It runs last so it acts on the final pose.

The Mover and CMC Anim Blueprints differ in the procedural part: the Mover one splits it into Procedural_PreLayering, Procedural_Feet (the CR_Biped_FootPlacement Control Rig) and Procedural_FullBody; the CMC one runs a single Procedural layer with the Foot Placement node and leg IK.

Layering curves¶

Overlay animations carry curves that say how strongly each body part follows the overlay. The pose Anim Blueprints write them from a curve map on each pose (see Overlay system), and ABP_LayerBlending reads them:

A rifle ready pose, for example, takes the spine, arms and hands fully (layering_* = 1), keeps the head free, and turns the left hand IK on so the support hand stays on the handguard.

Aim offset and weapon aim¶

When the character aims, the upper body follows the aim direction in two steps:

1. The aim rotation (the control rotation for the local player) is smoothed in the character Anim Blueprint with a critically damped spring. The smoothed value drives the spine aim offset.
2. In the overlay Anim Blueprint, the aim pitch is mapped to 0..1 and blends the weapon's aim sweep animations, which raise and lower the arms.

The camera has no rotation smoothing of its own, so any body lag shows against the crosshair. The smoothing is therefore short for the player you control and longer for remote copies, where the aim arrives in network steps.

With the defaults the aim offset trails the mouse by about 1.4 degrees on average while turning at a steady rate. A sweep speed of 0 snaps the arm pitch.

Legs and foot placement¶

The overlay legs are blended in (layering_legs, layering_pelvis), so carry and ready stances such as the rifle's bent-knee stance show in the legs. Foot placement then plants the feet:

• Mover pawn: CR_Biped_FootPlacement (Control Rig). Its leg IK measures the leg bone lengths from the posed skeleton every frame, so skeletons with scaled leg bones (the UEFN mannequin's thighs and calves carry a 1.12 scale) keep their real leg length.
• CMC pawn: the engine's Foot Placement node, then leg IK.

On the Mover pawn, DDCvar.FootPlacementMode selects the foot placement method (0 off, 1 foot placement node, 2 biped Control Rig). To keep the locomotion legs for an overlay, lower its layering_legs and layering_pelvis curves.

Threads and update order¶

The Anim Blueprints use the thread-safe update (BlueprintThreadSafeUpdateAnimation): the game thread only copies the pawn's state (Update_PropertiesFromCharacter, which reads Get_PropertiesForAnimation from the pawn through BPI_SandboxCharacter_Pawn), and the worker thread computes the rest. DDCVar.ThreadSafeAnimationUpdate.Enable (default on) selects the path; GASPALS' overlay Anim Blueprints read it once at start and run their update on exactly one of the two paths.

Console variables that change the animation¶

The full list, with what reads each one, is in Console variables.

First person¶

First person uses its own Anim Blueprint (ABP_FirstPerson_UEFN) on generated first-person meshes. It copies the third-person pose and adds camera, aim down sights and arm aim Control Rigs. See First person system.

Related¶

• Overlay system: the overlay poses and how they are selected.
• Add an overlay state: author a new overlay pose.
• Characters and visual overrides: how other skeletons get this pose.