Cover system¶

The cover system lets a character take cover against walls and low obstacles, move along them, run from cover to cover, turn around corners, vault over cover and aim from it. It works on both sample pawns and in multiplayer.

Kinds of cover¶

What the player can do¶

The cover marker (a widget on the targeted wall) and a green crosshair show where the cover button will take the character.

How it works¶

The core component evaluates cover every frame on the owning machine, then hands the result to the movement back end.

flowchart LR
    Input[Move input<br>camera, cover button] --> Eval[EvaluateCover<br>AC_CoverSystem_Base]
    Eval -->|Mover| MoverIn[S_MoverCustomInputs_Cover<br>in the Mover input]
    MoverIn --> Mode[BP_MovementMode_Cover<br>along-wall movement, wall spring]
    Eval -->|CMC| Shape[ShapeCoverMoveInput<br>shaped acceleration]
    Shape --> CMC[Character Movement Component]
    Eval --> Facing[GetCoverOrientationIntent<br>facing]
    Eval --> Cam[GetCoverCameraState<br>camera director offsets]
    Eval --> Pose[GetCoverLowerAmount<br>CR_Humanoid_CoverLower]

1. Sensing. Sphere traces (Cover Trace Radius) in the move direction find a wall within Cover Enter Distance. A second trace at High Cover Height decides high or low cover. Probes at Edge Probe Offset to each side find the wall ends and corners.
2. Deciding. The move input must point into the wall (Cover Enter Input Dot). Cover is kept while the wall is within Cover Hold Distance, and left after the input points away from it (Cover Exit Input Dot) for Cover Exit Delay.
3. Moving. In cover, the move input is turned into movement along the wall, and a spring holds the capsule at the Wall Distance gap for the current case (stand or crouch, soft or sticky).
   • Mover: the cover data travels in the Mover input (S_MoverCustomInputs_Cover). BP_MovementTransition_Cover switches between Walking and the Cover mode; BP_MovementMode_Cover moves along the wall (walk 150 cm/s, run and sprint 250 cm/s) and runs the wall spring.
   • CMC: AC_CoverSystem_CMC shapes the acceleration before the Character Movement Component runs, and turns the mesh to the cover facing.
4. Facing. Four settings pick the facing per case: FaceWall, ShoulderToWall (along the wall, in the move direction) or BackToWall.
5. Camera. The camera director reads GetCoverCameraState: it raises the camera behind low cover (CameraRig_TP_Offset_CoverLow), offsets it at wall ends (CameraRig_TP_Offset_CoverEdgeLeft/Right) and swaps the shoulder toward the open side.
6. Pose. CR_Humanoid_CoverLower lowers the pelvis so the head stays under the cover top, and plants the legs on the animated feet.

Features in detail¶

Cover run¶

Hold the cover button while the crosshair is on cover beyond Sticky Cover Reach. The character sprints along a navigation path to a stand point 60 cm in front of the wall, slows down for the arrival (Cover Run Arrive Speed, Cover Run Brake Decel) and snaps into sticky cover at Cover Run Arrive Distance. Released button, blocked path or a time limit (path length at 5 m/s plus Cover Run Max Time) cancel the run.

The path comes from the navigation mesh (FindPathToLocationSynchronously). Without a navmesh, or when no path is found, the character runs in a straight line and can get blocked. Clients build their own path, which needs bAllowClientSideNavigation=True in the project settings.

Corner turn¶

In sticky cover, hold the move input toward a wall end. If the wall continues around the corner (an outside corner up to Corner Turn Angle, 100 degrees between the two wall normals, with at least Corner Turn Min Width of wall), the character walks around it and stays in cover. The held input keeps working after the turn, so a round pillar or a run of corners is followed in one go.

Vault from cover¶

Jump in cover asks for a vault (RequestCoverVault). If the character does not face the wall within Vault Facing Dot, it turns first (up to Vault Facing Timeout). The component then fires the OnCoverVaultReady dispatcher; the pawn handles it and starts the traversal. If the traversal finds nothing to vault, the Mover pawn falls back to a jump.

Aim from cover¶

With Enable Cover Aim on (default), aiming in cover does not leave cover. The character takes the least exposed pose that can hit what the camera aims at, faces the aim direction, and walks back to its cover spot when aim is released.

The order is: in place, then the edge the aim points toward, then the other edge, then over. A pose "can hit" when a line from its muzzle position (Cover Aim Muzzle Height Stand/Crouch) reaches the target. The target is found along the camera direction from standing eye height above the cover spot, so the choice does not chase the camera as it moves with the pose. Aiming at your own cover counts as aiming past it.

Switching is damped so the pose does not flicker: a more exposed pose is taken only after the current one has been blocked for Cover Aim Blocked Delay, and a safer pose is taken back only after it has been clearly valid for Cover Aim Return Delay. With Cover Aim Keep Standing (default), a character standing over low cover only crouches back down, never side-steps to an edge.

While aiming, pushing away from the wall leaves cover and keeps aiming. Lateral input is ignored. The camera drops its low-cover offset and takes the shoulder of the side the character stepped out to. Turn on Cover Aim Debug to print every pose change and draw the target.

Pose lowering¶

CR_Humanoid_CoverLower runs at the end of SandboxCharacter_Mover_ABP and SandboxCharacter_CMC_ABP. It measures the cover top with a trace down into the wall and lowers the pelvis until the capsule top is Cover Lower Head Clearance (5 cm) under it, clamped to Cover Lower Max Stand (10 cm) or Cover Lower Max Crouch (15 cm). Behind cover taller than the character it lowers nothing, and it does not lower while standing over low cover to aim. The amount is computed on every machine from the replicated cover state, so remote players look the same.

The rig uses the UEFN mannequin bone names (pelvis, thigh_l, calf_l, foot_l...). Retargeted characters get it through the animation skeleton.

First person in cover¶

Cover marker¶

With Show Cover Marker on, the local player sees W_CoverMarker on the cover under the crosshair, and the crosshair turns green. The marker is a widget component the system creates on demand; restyle it by editing W_CoverMarker.

Configuration¶

All settings are on the cover component of the pawn. Select AC_CoverSystem in the pawn's Components panel and look under GASPALS > Cover in the Details panel. The categories are:

Every setting with its default is in the Cover reference. Recipes for common setups (no auto cover, Gears-style sticky only, crouch-only cover, wider wall gaps) are in Configure cover behavior.

Networking¶

• Mover pawn. The cover state is part of the Mover input, so the server and the other clients run the same cover movement as the owner. Simulated proxies get it through the synced inputs. No extra replication is needed.
• CMC pawn. The owner shapes its own acceleration (replicated by the CMC). The cover state is sent to the server about 20 times a second (ServerUpdateCover) and replicated to other machines, which apply it in ApplyRemoteCoverState. Small corrections (2 to 4 cm) can happen at sticky edge stops and corners.
• Aim from cover runs on the owner only. Other machines see its result: position, crouch and facing.
• Cover run paths are built on each client, so bAllowClientSideNavigation must be on.

Using cover from Blueprints¶

The CMC pawn's state is also readable on any machine from the component's CoverState. To put cover on your own pawn, follow Add the systems to your own pawn.

Limitations¶

• Cover needs walls the traces can hit (the Visibility channel by default). Very thin walls (under 10 cm) count as tall for the pose lowering.
• Peek (leaning out without aiming) is not implemented.
• The cover run runs straight when no navmesh path exists, and can then be blocked.
• The pose-lowering rig expects the UEFN mannequin bone names.
• In first person, only the two behaviors of the First Person settings are available.
• The CMC pawn shows small corrections at sticky edge stops and corners in network play.

Related¶

• Set up cover in a level
• Configure cover behavior
• Camera system for the cover camera rigs
• Traversal system for vaulting