Overlay system¶

An overlay is a pose layered on top of locomotion. The legs keep walking, running and turning with motion matching; the overlay decides how the upper body is held: a rifle at the ready, a torch held up, a box carried in both arms, hands tied, an injured stance. This is the layering approach of the Advanced Locomotion System (ALS), on the Game Animation Sample.

There are two independent overlays:

• Overlay pose: what the character holds or how it holds itself. Item poses come from the equipment system; stance poses (Default, Injured, HandsTied) from the overlay menu.
• Overlay body: a body style applied to the whole figure: Default, Masculine, Feminine.

How it works¶

The character Anim Blueprints call two linked anim layers, OverlayPose and OverlayBody. Which Anim Blueprint implements them is decided at runtime with Link Anim Class Layers on the character mesh:

• AC_OverlaySystem links ABP_Overlay_Default, _Injured or _HandsTied for the overlay pose menu, and ABP_OverlayBody_<Style> for the body.
• AC_EquipmentSystem links the item's pose (ABP_Overlay_Rifle...) from its data asset.

The last link wins: equipping an item replaces a stance pose, and choosing a stance in the menu replaces the item pose. At spawn the equipment system initializes after the overlay system and links its pose last (Unequip links ABP_Overlay_Default), so an Overlay Pose set on the pawn's component is replaced. Pick overlays through the menu or Select|NewOverlayPose once the pawn has spawned. Overlay changes are instant (no transition animation plays). Each linked Anim Blueprint outputs a pose; ABP_LayerBlending blends it onto locomotion per body part using curves. See Animation pipeline for where this sits in the full graph.

Pose Anim Blueprints¶

ABP_OverlayPose_Base holds the logic; its children only hold data. A state machine (SM_OverlayPose) chooses between three states:

With Can Aim off (box, barrel, default and the stance poses), the machine stays in Relaxed. Within each state, the pose is picked by stance (stand, crouch) and speed:

Each pose variable is a Struct_OverlayCurves: an animation (usually a single-frame pose) and a curve map (curve name to value). The pose Anim Blueprint writes the curve map onto the pose, and ABP_LayerBlending reads those curves.

Curves¶

The curve map decides how much of the body each pose takes over. Names are lowercase:

The rifle's ready pose, for reference: all layering_* at 1 except the head and the additive arms (0), right arm local space at 0.5, left hand IK on.

Aim sweep¶

While aiming, the arms follow the camera pitch through the aim sweep additive, blended by AimSweepValue (the pitch mapped from up to down). Aim Sweep Interp Speed Local (30) and Remote (10) set how fast it follows on the owning machine and on others. See Animation pipeline.

Body Anim Blueprints¶

ABP_OverlayBody_Base picks one of four poses by stance and movement: Pose Stand Idle, Pose Stand Move, Pose Crouch Idle, Pose Crouch Move. The children set those four animations.

First-person poses¶

ABP_OverlayFirstPerson_Base has the same pose variables (without the aim sweeps) for the first-person arms, with curves for the first-person rigs. The equipment data's Overlay Pose FP links it. See First person.

The menus¶

Hold V (pose) or B (body): the world slows to 0.35, a menu with one entry per enum value opens, the mouse wheel or D-pad moves the highlight, and releasing the key selects it. The entries come from Enum_OverlayPose (Default, Injured, HandsTied) and Enum_OverlayBody (Default, Masculine, Feminine).

If the pawn is destroyed while a menu is open, the component's EndPlay calls CloseOverlayMenus: it closes both menus, removes their widgets and sets the world speed back to normal.

Shipped overlays¶

Injured holds one hand to the side and HandsTied keeps the hands behind the back. Their relaxed standing poses use Pose_Injured_Stand / Pose_HandsTied_Stand and their relaxed crouch poses Pose_Injured_Crouch / Pose_HandsTied_Crouch, with the same layering curve values as the box. They are complete examples of a stance overlay: see Add an overlay state. Pistol1H has poses but no equipment slot uses it; link it from a data asset to try it.

Animation modifiers¶

AnimModifiers/ holds four animation modifiers for authoring: Create_LayeringCurves keys every layering curve (value 1) on an animation, Copy_Curves and Copy_Curves_Pose copy curves from another animation, and Create_Curves creates curves from parameters. Apply them from the animation's Animation Modifiers window. The shipped overlays use curve maps instead, so the modifiers are optional: use them if you prefer layering curves authored in the animations.

Settings¶

Networking¶

Overlay Pose and Overlay Body are replicated with RepNotify. The owner changes them locally and sends a reliable Server RPC; every machine links the Anim Blueprints in the RepNotify.

Limitations¶

• The menus slow the whole world while open.
• An Overlay Pose set on the pawn is replaced by the equipment pose at spawn (see How it works).
• The stance poses (Default, Injured, HandsTied) and the item poses share the pose layer, so a stance and an item cannot be combined.
• Adding a value to Enum_OverlayPose needs a matching case in AC_OverlaySystem.UpdateOverlayPose.
• Variables added to ABP_OverlayPose_Base do not reach existing children's class defaults: set them on each child.

Related¶

• Add an overlay state
• Add an equipment item
• Animation pipeline