Multiplayer: Server RPC for damage, Multicast RPC for effects

Pattern for shooting in multiplayer: ON CLIENT: InputAction Shoot → ServerRPC_Shoot (Custom Event, Run On Server, Reliable). ServerRPC_Shoot (runs on SERVER): LineTraceByChannel → Branch(hit) → ApplyDamage → MulticastRPC_PlayEffect(ImpactPoint). MulticastRPC_PlayEffect (Custom Event, Multicast, Unreliable): SpawnNiagaraSystemAtLocation(NS_BulletImpact, ImpactPoint). Key rules: - Server RPC: Custom Event → Replicates='Run On Server', Reliable=true. - Multicast: Custom Event → Replicates='Multicast', Reliable=false (VFX can be dropped). - Client RPC: Custom Event → Replicates='Run On Owning Client'. - Never directly modify replicated vars on clients — always go through Server RPC.

HasAuthority — server-side authority check for multiplayer

Switch On HasAuthority: 'Authority' exec fires on server, 'Remote' fires on clients. Use to gate server-only logic like damage calculation, score updates, spawning.

Spawn system with wave management for enemies

Pattern: Variables CurrentWave(int)=0, EnemiesAlive(int)=0, EnemiesPerWave(Array<int>). StartWave: CurrentWave++ → SET EnemiesAlive=EnemiesPerWave[CurrentWave]. Timer looping: Branch(SpawnedThisWave < EnemiesPerWave[CurrentWave]) → SpawnActor(EnemyClass, RandomSpawnPoint) → SpawnedThisWave++. OnEnemyDeath: EnemiesAlive-- → Branch(EnemiesAlive <= 0) → StartNextWave or Victory.

Create a Blueprint for a health pickup that restores health when overlapped by the player

Respawn system: death → delay → respawn at PlayerStart

In Character BP: OnDied (custom event) → SetActorHiddenInGame(true) → SetActorEnableCollision(false) → Disable input: GetController → DisableInput → Delay(Duration=3.0) → GetGameMode → CastTo<BP_GameMode> → RestartPlayer(GetController) → SetActorHiddenInGame(false) → SetActorEnableCollision(true) → EnableInput. In GameMode RestartPlayer: Gets nearest PlayerStart → SetActorLocation to PlayerStart → calls OnPossess. OR manual: GetAllActorsOfClass(PlayerStart) → Random select → SetActorLocationAndRotation(PlayerStart.Location, PlayerStart.Rotation).

GameMode

Defines the rules + default classes (Pawn, PlayerController, GameState) for a level. Only exists on the server.

GetGameInstance — get persistent game instance

UGameplayStatics::GetGameInstance. Persists across level loads.

SetCollisionEnabled — enable, disable or set query-only collision

ECollisionEnabled values: NoCollision, QueryOnly, PhysicsOnly, QueryAndPhysics.

GetGameMode — get current game mode

UGameplayStatics::GetGameMode. Cast to your custom GameMode class.

Multicast

An RPC the server calls that runs on every connected client. Use for one-shot effects (explosions, sounds).