Choosing Between CharacterMovementComponent and Custom Pawn Movement for Multiplayer

The Networking Dilemma: Responsiveness vs. Control

In multiplayer games, the primary challenge of movement is latency. If a client waits for the server to confirm a movement input, the game feels sluggish. If the client moves instantly without server validation, players can cheat or desync. The decision between using the CharacterMovementComponent (CMC) and a custom Pawn movement system depends on whether your entity requires Client-Side Prediction and Server Reconciliation.

The takeaway: Use CharacterMovementComponent for any entity that requires tight, responsive controls in a networked environment. Use custom Pawn movement for simple entities, spectators, or non-humanoid physics objects where slight latency or simple interpolation is acceptable.

Comparison of Movement Architectures

Feature	CharacterMovementComponent	Custom Pawn / FloatingPawn
Network Prediction	Built-in (Client-side prediction)	None (Requires manual implementation)
Reconciliation	Automatic (Corrects client position)	Manual (Interpolation or snapping)
Movement States	Walking, Falling, Swimming, Flying	Generic / Custom
Collision Model	Fixed Capsule Component	Flexible (Box, Sphere, Mesh)
CPU Overhead	High (Complex state machine)	Low (Simple transform updates)

Trade-offs and Constraints

The Power of the CharacterMovementComponent

The CMC is a massive piece of engineering that solves the "rubber-banding" problem. It maintains a history of moves on the client. When the server sends a correction, the CMC doesn't just snap the player back; it re-runs all pending moves from the point of the error to the current time, making the correction nearly invisible to the player.

However, this comes with a "Capsule Tax." The CMC is tightly coupled to the ACharacter class and its UCapsuleComponent. If your game entity is a giant spider or a floating cube, forcing it into a capsule can lead to awkward collision behavior.

The Flexibility of Custom Pawn Movement

Using a Pawn with FloatingPawnMovement or a custom Tick-based movement allows for any collision shape and lower overhead. This is ideal for drones, ghosts, or vehicles where you can afford to use Linear Interpolation (Lerp) to smooth out the movement of other players on the screen.

The risk here is the "Input Lag." Without prediction, a player pressing 'W' will not see their character move until the packet reaches the server and returns, which is unacceptable for fast-paced action games.

Implementation: Validating Network Prediction

To determine if your chosen component is handling network latency correctly, you can test using the Unreal Engine network emulation tools. This allows you to simulate high ping and packet loss without needing a remote server.

Testing Steps

1. Open the Console (tilde key ~) while running the game in a 'Listen Server' configuration.
2. Run the following command to simulate 200ms of lag:
   Net PktLag=200
3. Move your character. If using CharacterMovementComponent, the movement should remain fluid.
4. If using a basic Pawn without custom prediction, you will notice a significant delay between key press and movement.

Diagnostic Check: Unreal Insights

To verify the bandwidth cost, run the game with -trace=frame,net and open the trace in Unreal Insights. Compare the NetDriver packets for a Character versus a Pawn. You will see that the CMC sends more frequent, smaller updates to maintain the move buffer, whereas a simple Pawn typically replicates the ActorTransform at a lower frequency.

Limitations and Verification

Limitations: Customizing the CMC's internal prediction logic requires modifying the engine source code (C++), as many of the SavedMove structures are not easily exposed to Blueprints. If you need a completely non-humanoid movement system with prediction, you may need to implement a custom UCharacterMovementComponent subclass.

Verification: To confirm the server is the authority, use the cheat.net.set_latency 200 command and intentionally move your client into a wall. If the server correctly pushes you back and the client snaps to the server position, the reconciliation loop is functioning.