Networking in UE 4 Joe Graf Epic Cog

Networking in UE 4 Joe Graf @Epic. Cog

Introduction • Network topology and NATs • C++ Replication • Blueprint Replication • Low Level Networking • Diagnostic Tools

Network Topologies Client / Server Peer to Peer

Network Address Translation (NAT) • Three types to think about – Open • Can accept unsolicited connections – Moderate • Can sometimes accept unsolicited connections – Strict • Can only accept connections from known addresses

Gears of War 3 NAT Analytics

NAT Implications • Client/Server – Server should have Open NAT – Client can be any NAT type • Peer to Peer – All clients need Open NATs – ~20% of players can’t play your game

Server Authoritative Client / Server • Clients only talk to Server • Server replicates to Clients • Data flow is Server->Clients • RPCs are bidirectional

C++ Replication

Basic Gameplay Classes Server • Game. Mode • Game. State • Player. Controller – One for each player • Player. State – One for each player Client • Game. State • Player. Controller – One for each local player • Player. State – One for each player

Gameplay Classes • Game. Mode – Rules for your game • Game. State – Replicated information about your Game. Mode

Gameplay Classes (cont) • Player. Controller – Primary interaction with your Game. Mode • Player. State – Replicated information about your player

Data Replication • b. Replicates – Set as part of the Actor’s construction • UPROPERTY Macro – Replicated. Using • Get. Lifetime. Replicated. Props Function – Determines the set of properties for replication

b. Replicates ACool. Actor: : ACool. Actor(…) : Super( PCIP ) { b. Replicates = true; }

Replicated Example /** number of kills */ UPROPERTY(Transient, Replicated) int 32 Num. Kills;

Replicated. Using Example /** team number */ UPROPERTY(Transient, Replicated. Using=On. Rep_Team. Color) int 32 Team. Number; void AShooter. Player. State: : On. Rep_Team. Color() { Update. Team. Colors(); }

Get. Lifetime. Replicated. Props Example void AShooter. Player. State: : Get. Lifetime. Replicated. Props( TArray<FLifetime. Property>& Out. Lifetime. Props) const { Super: : Get. Lifetime. Replicated. Props(Out. Lifetime. Props); DOREPLIFETIME( AShooter. Player. State, Team. Number ); DOREPLIFETIME( AShooter. Player. State, Num. Kills ); DOREPLIFETIME( AShooter. Player. State, Num. Deaths ); }

Conditional Replication • Property is only replicated when a condition is met • Can reduce bandwidth consumed • Done via a similar macro

Conditional Replication Example void AMy. Player. State: : Get. Lifetime. Replicated. Props( TArray<FLifetime. Property>& Out. Lifetime. Props) const { Super: : Get. Lifetime. Replicated. Props(Out. Lifetime. Props); DOREPLIFETIME_CONDITION(AMy. Player. State, Some. Owner. Only. Val, COND_Owner. Only); }

Common Replication Conditions • COND_Initial. Only – • COND_Owner. Only – • This property send to every connection EXCEPT the owner COND_Simulated. Only – • This property will only send to the actor's owner COND_Skip. Owner – • This property will only attempt to send on the initial replication This property will only send to simulated actors COND_Autonomous. Only – This property will only send to autonomous actors

Function Replication • UFUNCTION Macro – – – – Reliable Unreliable Client Server Net. Multicast With. Validation Blueprint. Authority. Only Blueprint. Cosmetic

Reliable • Function is guaranteed to be called • Resent when an error is present • Delayed when bandwidth is saturated

Reliable Example /** notify player about started match */ UFUNCTION(Reliable, Client) void Client. Game. Started(); void AShooter. Player. Controller: : Client. Game. Started_Implementation() { b. Allow. Game. Actions = true; // Enable controls and disable cinematic mode now the game has started Set. Cinematic. Mode(false, true, true); AShooter. HUD* Shooter. HUD = Get. Shooter. HUD(); if (Shooter. HUD) { Shooter. HUD->Set. Match. State(EShooter. Match. State: : Playing); Shooter. HUD->Show. Scoreboard(false); } … }

Unreliable • Function is attempted to be sent • Not sent again when an error is present • Skipped when bandwidth is saturated

Unreliable Example /** Replicated function sent by client to server - contains client movement and view info. */ UFUNCTION(Unreliable, Server, With. Validation) virtual void Server. Move(float Time. Stamp, …); void UCharacter. Movement. Component: : Server. Move_Implementation( float Time. Stamp, …) { … }

Net. Multicast • Sends to all clients – Reliable or Unreliable applies here too

Net. Multicast Example /** broadcast death to local clients */ UFUNCTION(Reliable, Net. Multicast) void Broadcast. Death(…); void AShooter. Player. State: : Broadcast. Death_Implementation(…) { for (auto It = Get. World()->Get. Player. Controller. Iterator(); It; ++It) { // all local players get death messages so they can update their huds. AShooter. Player. Controller* Test. PC = Cast<AShooter. Player. Controller>(*It); if (Test. PC && Test. PC->Is. Local. Controller()) { Test. PC->On. Death. Message(Killer. Player. State, this, Killer. Damage. Type); } } }

With. Validation • Called before the target function • Used to validate parameters of a function – Meant to detect cheating/hacking • Return value affects whether function is called – false skips the call and kills the connection

With. Validation Example bool UCharacter. Movement. Component: : Server. Move_Validate( float Time. Stamp, …) { bool b. Is. Valid. Move = false; // Perform move validation here return b. Is. Valid. Move; }

Blueprint. Authority. Only • UE 4 all are functions are Simulated – This is the opposite of UE 3 • Opt out via Blueprint. Authority. Only

Blueprint. Authority. Only Example UFUNCTION(Blueprint. Implementable. Event, Blueprint. Authority. Only, meta=(Friendly. Name = "Any. Damage"), Category="Damage") virtual void Receive. Any. Damage(float Damage, const UDamage. Type* Damage. Type, AController* Instigated. By, AActor* Damage. Causer);

Blueprint. Cosmetic • Opposite of Blueprint. Authority. Only – Runs on the client not server • An optimization to skip execution of slow cosmetic code on the server

Actor Relevancy • Trades CPU time for network bandwidth • Distance based – Are these actors close enough – Default implementation right now • Line of sight – Can these actors see each other – UE 3 default implementation • Always relevant is an option – Trades bandwidth for CPU time

Blueprint Replication

Actor Replication

Property Replication

Property Replication Notify

Function Replication

Low Level Details

Low Level Implementation • UNet. Driver • UNet. Connection • UChannel – UControl. Channel – UVoice. Channel – UActor. Channel

UNet. Driver • Contains a list of connections to Tick • On client, one connection • On Server, N connections

UNet. Connection • Contains a list of channels to replicate • UChild. Connection – Used as an optimization for split-screen games

UChannel Objects • Logical construct – Routes data to the proper object • Accessed by Channel. ID – Some channels have predefined IDs

UControl. Channel • Handles connection handshaking • Processes object loading requests • Deals with misc. non-gameplay communication

UVoice. Channel • Sends and receives voice data – Voice channel routes data to platform handler • Voice data is platform dependent • Voice data is sent as speaker ID and payload

UActor. Channel • Handles actor replication – Includes any replicated components • One actor channel for each replicated actor • Actors are replicated by channel ID – Dynamically assigned based upon array position

Voice Considerations • Game can choose to support or not • Platform can mute other players – Player muted another outside of the game • Players can mute other players • Gameplay can mute players – Team based, distance based, push to talk

Voice Functions UFUNCTION(Server, Reliable, With. Validation) virtual void Server. Mute. Player(FUnique. Net. Id. Repl Player. Id); UFUNCTION(Server, Reliable, With. Validation ) virtual void Server. Unmute. Player(FUnique. Net. Id. Repl Player. Id); UFUNCTION(Reliable, Client) virtual void Client. Mute. Player(FUnique. Net. Id. Repl Player. Id); UFUNCTION(Reliable, Client) virtual void Client. Unmute. Player(FUnique. Net. Id. Repl Player. Id); /** * Mutes a remote player on the server and then tells the client to mute * * @param Player. Net. Id the remote player to mute */ void Gameplay. Mute. Player(const FUnique. Net. Id. Repl& Player. Net. Id); /** * Unmutes a remote player on the server and then tells the client to unmute * * @param Player. Net. Id the remote player to unmute */ void Gameplay. Unmute. Player(const FUnique. Net. Id. Repl& Player. Net. Id);

Diagnostic Tools

Network Logging • Log. Net – Verbose information about the state of channels and connections • Log. Net. Player. Movement – Detailed information about movement from clients and corrections from server • Log. Net. Traffic – Verbose information about data sent on a connection

Network Statistics • Stat Net – Lists ping, channel count, in/out bytes, etc. • Stat Game – List of network processing information

Stat Net Example

Stat Game Example

Network Simulation Options • Pkt. Lag – Delays the sending of a packet by a N ms • Pkt. Lag. Variance – Provides some randomness to the Pkt. Lag option • Pkt. Loss – A percentage chance of not sending a packet

Network Simulation Options (cont) • Pkt. Dup – A percentage chance of sending duplicate packets • Pkt. Order – Sends packets out of order when enabled

Setting the Simulation Options • Console Net Pkt. Lag=100 • INI File [Packet. Simulation. Settings] Pkt. Lag=50 Pkt. Lag. Variance=10 Pkt. Loss=3 Pkt. Order=0 Pkt. Dup=10

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