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
};

2. Override PhysCustom in your CMC subclass:

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

3. Enter the mode using SetMovementMode:

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

4. 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:

• Clear() — reset your custom fields
• SetMoveFor(ACharacter*, float, FVector const&, FNetworkPredictionData_Client_Character&) — capture your custom state from the CMC before the move executes
• PrepMoveFor(ACharacter*) — restore your custom state before replaying a move
• GetCompressedFlags() const — pack custom booleans into the uint8 flags
• CanCombineWith(const FSavedMovePtr&, ACharacter*, float) — return true only if two moves are identical (enables bandwidth optimization)
• PostUpdate(ACharacter*, EPostUpdateMode) — called after the move executes
• IsImportantMove(const FSavedMovePtr&) — prevent combining if this move carries significant state

CompressedFlags

The uint8 returned by GetCompressedFlags has a fixed layout:

You get four custom bits. For more complex state, use FCharacterNetworkMoveData.

FNetworkPredictionData_Client_Character

Override AllocateNewMove() to return your custom FSavedMove subclass:

class FMyNetworkPredictionData : public FNetworkPredictionData_Client_Character
{
public:
    FMyNetworkPredictionData(const UCharacterMovementComponent& ClientMovement)
        : FNetworkPredictionData_Client_Character(ClientMovement) {}

    virtual FSavedMovePtr AllocateNewMove() override;
};

The CMC exposes this via GetPredictionData_Client(), which you override to lazy-init your custom prediction data class.

Modern Packed RPCs

UE5 uses packed move RPCs on ACharacter:

• ServerMovePacked(FCharacterServerMovePackedBits) — client to server
• ClientMoveResponsePacked(FCharacterMoveResponsePackedBits) — server to client

The old RPCs (ServerMove, ServerMoveDual, ClientAdjustPosition) are DEPRECATED_CHARACTER_MOVEMENT_RPC. For custom network data beyond CompressedFlags, derive FCharacterNetworkMoveData (override ClientFillNetworkMoveData, Serialize), derive FCharacterNetworkMoveDataContainer, and call SetNetworkMoveDataContainer() in your CMC constructor.

See references/cmc-extension-patterns.md for full FSavedMove and network data implementation templates.

Root Motion

Root motion allows animations or gameplay code to drive character movement directly. CMC integrates root motion through FRootMotionSource and its subclasses.

FRootMotionSource

Base class fields:

• Priority — higher priority sources override lower
• LocalID — unique ID returned by ApplyRootMotionSource
• InstanceName — FName for retrieval and removal
• Duration — total time in seconds; negative Duration means infinite (runs until explicitly removed)
• AccumulateMode — Override (replaces other sources) or Additive (stacks)

Subclasses

CMC Methods

// Returns uint16 LocalID for tracking
uint16 ApplyRootMotionSource(TSharedPtr<FRootMotionSource> Source);

// Retrieve by InstanceName
TSharedPtr<FRootMotionSource> GetRootMotionSource(FName InstanceName);

// Remove by InstanceName
void RemoveRootMotionSource(FName InstanceName);

Apply a constant knockback:

auto Knockback = MakeShared<FRootMotionSource_ConstantForce>();
Knockback->InstanceName = TEXT("Knockback");
Knockback->Duration = 0.3f;
Knockback->Force = KnockbackDirection * KnockbackStrength;
Knockback->AccumulateMode = ERootMotionAccumulateMode::Override;
CMC->ApplyRootMotionSource(Knockback);

Key Properties

Rotation

bOrientRotationToMovement and bUseControllerDesiredRotation are mutually exclusive in practice. The first rotates the character toward its velocity direction (third-person), the second smoothly rotates toward where the controller is facing (strafing shooter). Set one, not both.

Gravity Direction (UE 5.4+)

virtual void SetGravityDirection(const FVector& GravityDir);
FVector GetGravityDirection() const;
bool HasCustomGravity() const;
// Transform helpers (fields are protected — access via accessors)
FQuat GetWorldToGravityTransform() const;
FQuat GetGravityToWorldTransform() const;

Custom gravity reorients the entire movement simulation. Walking, falling, and floor detection all respect the gravity direction when HasCustomGravity() returns true.

ACharacter API

ACharacter provides high-level movement actions that delegate to CMC:

Jump

void Jump();           // Sets bPressedJump, CMC handles velocity
void StopJumping();    // Clears jump input
bool CanJump() const;  // Checks CanJumpInternal

Properties: bPressedJump, JumpMaxHoldTime, JumpMaxCount, JumpCurrentCount.

DoJump(bool bReplayingMoves, float DeltaTime) is the internal method called by CMC to apply the jump velocity. In UE 5.5+ it takes two parameters; the old DoJump(bool) is deprecated.

Crouch

void Crouch(bool bClientSimulation = false);
void UnCrouch(bool bClientSimulation = false);

bIsCrouched is the replicated state. CMC handles capsule resizing and checks for clearance before uncrouching. Note: CrouchedHalfHeight on CMC is deprecated as of UE 5.0 — use SetCrouchedHalfHeight() / GetCrouchedHalfHeight() on the CMC instead.

LaunchCharacter

void LaunchCharacter(FVector LaunchVelocity, bool bXYOverride, bool bZOverride);

When bXYOverride is true, replaces XY velocity entirely. When false, adds to existing velocity. Same logic for bZOverride on the Z axis. Automatically transitions to MOVE_Falling.

Landed

virtual void Landed(const FHitResult& Hit);

Called when the character lands after falling. Override this for landing effects, damage, or animation triggers.

Accessors

UCharacterMovementComponent* GetCharacterMovement() const;
UCapsuleComponent* GetCapsuleComponent() const;
USkeletalMeshComponent* GetMesh() const;

Common Mistakes

Modifying velocity directly instead of using CalcVelocity:

// WRONG: Bypasses friction, braking, and acceleration curves
Velocity = GetLastInputVector() * MaxWalkSpeed;

// RIGHT: Let CMC handle physics
CalcVelocity(DeltaTime, GroundFriction, false, BrakingDecelerationWalking);

Forgetting to call Super in PhysCustom:

// WRONG: Skips base class bookkeeping
void UMyCMC::PhysCustom(float DT, int32 Iter)
{
    MyCustomLogic(DT, Iter);
}

// RIGHT: Call Super first (base PhysCustom is empty but future-proofs)
void UMyCMC::PhysCustom(float DT, int32 Iter)
{
    Super::PhysCustom(DT, Iter);
    MyCustomLogic(DT, Iter);
}

Not saving custom state in FSavedMove: Custom movement flags that are not captured in SetMoveFor and restored in PrepMoveFor will be lost during server correction replays, causing desyncs.

Using MoveUpdatedComponent instead of SafeMoveUpdatedComponent: MoveUpdatedComponent does not resolve penetration. In custom Phys* functions, always use SafeMoveUpdatedComponent to prevent the character from getting stuck inside geometry.

Setting both rotation flags: bOrientRotationToMovement and bUseControllerDesiredRotation conflict. The character oscillates between two desired rotations each frame. Pick one based on your camera style.

Using deprecated old-style RPCs: ServerMove, ServerMoveDual, ClientAdjustPosition are DEPRECATED_CHARACTER_MOVEMENT_RPC. Use the packed RPC pipeline and FCharacterNetworkMoveData for custom data.

Reference Files

• references/cmc-extension-patterns.md — Complete CMC subclass templates: custom FSavedMove, prediction data, GetPredictionData_Client, wall-run PhysCustom, and custom network move data
• references/movement-pipeline.md — Phys* flow diagrams, floor detection chain, step-up logic, PhysWalking/PhysFalling breakdowns, and root motion replication flow

Related Skills

• ue-networking-replication — Replication fundamentals, RPCs, net roles; CMC prediction builds on this
• ue-animation-system — Root motion from AnimMontage, animation-driven movement
• ue-physics-collision — Sweep queries, collision channels used by CMC floor detection
• ue-gameplay-abilities — GAS abilities that trigger movement modes or root motion
• ue-ai-navigation — NavMesh integration, MOVE_NavWalking, RVO avoidance
• ue-input-system — Enhanced Input feeding movement input to CMC
• ue-actor-component-architecture — Component subobject patterns for CMC subclasses