Ue Character Movement

UE Character Movement

You are an expert in Unreal Engine's UCharacterMovementComponent (CMC), the core system that drives character locomotion, floor detection, network prediction, and root motion integration. You understand the full Phys* pipeline, custom movement mode implementation, and the FSavedMove_Character prediction architecture.

Context Check

Read .agents/ue-project-context.md to determine:

• Whether the project uses ACharacter or a custom pawn with its own movement
• The UE version (UE 5.4+ adds GravityDirection support, UE 5.5 changes DoJump signature)
• Whether multiplayer is involved (affects prediction pipeline complexity)
• Any existing CMC subclass or custom movement modes already in use

Information Gathering

Ask the developer:

1. Are you extending UCharacterMovementComponent or configuring the default one?
2. Do you need custom movement modes (wall-running, climbing, dashing)?
3. Is this multiplayer? If so, do custom abilities need network prediction?
4. Are you integrating root motion from animations or gameplay code?
5. Do you need custom gravity directions (UE 5.4+)?

CMC Architecture

UCharacterMovementComponent sits at the end of a four-level class hierarchy:

UMovementComponent
  -> UNavMovementComponent
    -> UPawnMovementComponent
      -> UCharacterMovementComponent

CMC also implements IRVOAvoidanceInterface and INetworkPredictionInterface. It is declared UCLASS(MinimalAPI).

CMC lives as a default subobject on ACharacter, created in the constructor. ACharacter provides the capsule, skeletal mesh, and high-level actions (Jump, Crouch, LaunchCharacter), while CMC handles the actual physics simulation, floor detection, and network prediction.

Movement Modes

CMC dispatches movement logic through EMovementMode:

Change modes with SetMovementMode(EMovementMode, uint8 CustomMode = 0). The CMC calls OnMovementModeChanged(PreviousMode, PreviousCustomMode) after every transition, which is the correct place to handle enter/exit logic for custom modes.

Phys* Movement Pipeline

Every tick, CMC processes movement through a strict pipeline. Understanding this flow is essential for writing correct custom movement or debugging unexpected behavior.

PerformMovement(float DeltaTime) is the main entry point (protected). It calls StartNewPhysics(), which dispatches to the appropriate Phys* function based on the current EMovementMode. Each Phys* function is protected virtual:

• PhysWalking(float deltaTime, int32 Iterations) — ground movement
• PhysNavWalking(float deltaTime, int32 Iterations) — navmesh-projected walking
• PhysFalling(float deltaTime, int32 Iterations) — airborne/gravity
• PhysSwimming(float deltaTime, int32 Iterations) — fluid movement
• PhysFlying(float deltaTime, int32 Iterations) — free flight
• PhysCustom(float deltaTime, int32 Iterations) — your code here

Inside each Phys* function, two core methods do the heavy lifting:

`CalcVelocity` computes the velocity for this frame:

// BlueprintCallable
void CalcVelocity(float DeltaTime, float Friction, bool bFluid, float BrakingDeceleration);

`SafeMoveUpdatedComponent` moves the capsule and resolves penetration:

virtual bool SafeMoveUpdatedComponent(
    const FVector& Delta,
    const FQuat& NewRotation,
    bool bSweep,
    FHitResult& OutHit,
    ETeleportType Teleport = ETeleportType::None
);

It wraps MoveUpdatedComponent and automatically handles depenetration if the move results in an overlap. Always prefer SafeMoveUpdatedComponent over MoveUpdatedComponent in custom Phys* functions.

When a sweep hits a surface, SlideAlongSurface projects movement along it. When hits occur in a corner (two blocking surfaces), CMC calls TwoWallAdjust (virtual on UMovementComponent) to compute a safe movement direction that avoids both walls. During PhysWalking, ComputeGroundMovementDelta (virtual) adjusts the velocity delta to follow the floor slope — it projects horizontal input onto the floor plane so the character walks along inclines rather than into them.

See references/movement-pipeline.md for the full flow diagram and per-mode breakdown.

Floor Detection

CMC's walking mode relies on continuous floor detection to determine whether the character is grounded.

FFindFloorResult

struct FFindFloorResult
{
    uint32 bBlockingHit : 1;    // Sweep hit something
    uint32 bWalkableFloor : 1;  // Hit surface passes walkability test
    uint32 bLineTrace : 1;      // Result came from line trace (not sweep)
    float FloorDist;             // Distance from capsule bottom to floor
    float LineDist;              // Distance from line trace
    FHitResult HitResult;        // Full hit result data

    bool IsWalkableFloor() const { return bBlockingHit && bWalkableFloor; }
};

Floor Detection Methods

FindFloor is the primary method:

void FindFloor(
    const FVector& CapsuleLocation,
    FFindFloorResult& OutFloorResult,
    bool bCanUseCachedLocation,
    const FHitResult* DownwardSweepResult = nullptr
);

It delegates to ComputeFloorDist(), which performs a downward capsule sweep followed by a line trace. The sweep finds the floor surface, and the line trace validates walkability at the exact contact point.

Walkable Floor Angle

Two linked properties control what counts as "walkable":

• WalkableFloorAngle (default 44.765 degrees) — the maximum surface angle in degrees
• WalkableFloorZ — the corresponding Z component of the surface normal (auto-calculated from the angle)

Set the angle, not the Z value directly. SetWalkableFloorAngle() updates both.

Custom Movement Modes

MOVE_Custom with a uint8 sub-mode is the standard way to add new movement types. This gives you up to 256 custom modes while reusing CMC's full network prediction pipeline.

Implementation Steps

1. Define custom mode constants:

UENUM(BlueprintType)
enum class ECustomMovementMode : uint8
{
    WallRun = 0,
    Climb   = 1,
    Dash    = 2
};

1. Override PhysCustom in your CMC subclass:

virtual void PhysCustom(float deltaTime, int32 Iterations) override;

1. Enter the mode using SetMovementMode:

SetMovementMode(MOVE_Custom, static_cast<uint8>(ECustomMovementMode::WallRun));

1. Handle transitions in OnMovementModeChanged:

virtual void OnMovementModeChanged(EMovementMode PrevMode, uint8 PrevCustomMode) override;

Inside PhysCustom, dispatch on CustomMovementMode and implement your simulation. Call CalcVelocity for acceleration, SafeMoveUpdatedComponent for capsule movement, and SetMovementMode when transitioning out.

See references/cmc-extension-patterns.md for a complete wall-run implementation.

Network Prediction

CMC uses a client-side prediction and server reconciliation model. The client runs movement locally, saves inputs, sends them to the server, and corrects if the server disagrees. This is why custom movement must integrate with the prediction pipeline to work in multiplayer.

FSavedMove_Character

Each client tick generates a saved move that records the input state:

Key fields: bPressedJump, bWantsToCrouch, StartLocation, StartVelocity, SavedLocation, Acceleration, MaxSpeed.

Key virtuals to override for custom data: