120 - Syncing Client and Server Time

Source/Blaster/PlayerController/BlasterPlayerController.cpp

@@ -22,6 +22,8 @@ void ABlasterPlayerController::Tick(float DeltaSeconds)
 	Super::Tick(DeltaSeconds);
 
 	SetHUDTime();
+
+	CheckTimeSync(DeltaSeconds);
 }
 
 void ABlasterPlayerController::OnPossess(APawn* InPawn)
@@ -34,15 +36,56 @@ void ABlasterPlayerController::OnPossess(APawn* InPawn)
 	}
 }
 
+void ABlasterPlayerController::ReceivedPlayer()
+{
+	Super::ReceivedPlayer();
+
+	if (IsLocalController())
+	{
+		ServerRequestServerTime(GetWorld()->GetTimeSeconds());
+	}
+}
+
+void ABlasterPlayerController::CheckTimeSync(float DeltaSeconds)
+{
+	TimeSyncRunningTime += DeltaSeconds;
+	if (IsLocalController() && TimeSyncRunningTime > TimeSyncFrequency)
+	{
+		ServerRequestServerTime(GetWorld()->GetTimeSeconds());
+		TimeSyncRunningTime = 0.f;
+	}
+}
+
+float ABlasterPlayerController::GetServerTime()
+{
+	if (HasAuthority()) return GetWorld()->GetTimeSeconds();
+	
+	return GetWorld()->GetTimeSeconds() + ClientServerDelta;
+}
+
+void ABlasterPlayerController::ServerRequestServerTime_Implementation(float TimeOfClientRequest)
+{
+	const float ServerTimeOfReceipt = GetWorld()->GetTimeSeconds();
+	ClientReportServerTime(TimeOfClientRequest, ServerTimeOfReceipt);
+}
+
+void ABlasterPlayerController::ClientReportServerTime_Implementation(float TimeOfClientRequest, float TimeServerReceivedClientRequest)
+{
+	const float RoundTripTime = GetWorld()->GetTimeSeconds() - TimeOfClientRequest;
+	const float CurrentServerTime = TimeServerReceivedClientRequest + 0.5f * RoundTripTime;
+
+	ClientServerDelta = CurrentServerTime - GetWorld()->GetTimeSeconds();
+}
+
 void ABlasterPlayerController::SetHUDTime()
 {
-	const uint32 SecondsLeft = FMath::CeilToInt(MatchTime - GetWorld()->GetTimeSeconds());
+	const uint32 SecondsLeft = FMath::CeilToInt(MatchTime - GetServerTime());
 
 	if (CountdownInt != SecondsLeft)
 	{
-		SetHUDMatchCountdown(MatchTime - GetWorld()->GetTimeSeconds());
+		SetHUDMatchCountdown(MatchTime - GetServerTime());
 	}
-	
+
 	CountdownInt = SecondsLeft;
 }
 
@@ -54,7 +97,7 @@ void ABlasterPlayerController::SetHUDHealth(float Health, float MaxHealth)
 		BlasterHUD->CharacterOverlay &&
 		BlasterHUD->CharacterOverlay->HealthBar &&
 		BlasterHUD->CharacterOverlay->HealthText;
-	
+
 	if (bHUDValid)
 	{
 		const float HealthPercent = Health / MaxHealth;
@@ -136,7 +179,7 @@ void ABlasterPlayerController::SetHUDMatchCountdown(float CountdownTime)
 	{
 		int32 Minutes = FMath::FloorToInt(CountdownTime / 60);
 		int32 Seconds = CountdownTime - Minutes * 60;
-		
+
 		const FString CountdownText = FString::Printf(TEXT("%02d:%02d"), Minutes, Seconds);
 		BlasterHUD->CharacterOverlay->MatchCountdownText->SetText(FText::FromString(CountdownText));
 	}

Source/Blaster/PlayerController/BlasterPlayerController.h

@@ -18,6 +18,7 @@ public:
 
 	virtual void Tick(float DeltaSeconds) override;
 	virtual void OnPossess(APawn* InPawn) override;
+	virtual void ReceivedPlayer() override; // Sync with server clock as soon as possible
 	
 	void SetHUDHealth(float Health, float MaxHealth);
 	void SetHUDScore(float Score);
@@ -25,12 +26,33 @@ public:
 	void SetHUDWeaponAmmo(int32 Ammo);
 	void SetHUDCarriedAmmo(int32 Ammo);
 	void SetHUDMatchCountdown(float CountdownTime);
+
+	// Synced with server world clock
+	virtual float GetServerTime();
 	
 protected:
 
 	virtual void BeginPlay() override;
+	void CheckTimeSync(float DeltaSeconds);
 	void SetHUDTime();
-	
+
+	// Sync time between client and server
+
+	// Requests the current server time, passing in the client's time when the request was sent
+	UFUNCTION(Server, Reliable)
+	void ServerRequestServerTime(float TimeOfClientRequest);
+
+	// Reports the current server time to the client in response to ServerRequestServerTime
+	UFUNCTION(Client, Reliable)
+	void ClientReportServerTime(float TimeOfClientRequest, float TimeServerReceivedClientRequest);
+
+	// Difference between client and server time
+	float ClientServerDelta = 0;
+
+	UPROPERTY(EditAnywhere, Category = Time)
+	float TimeSyncFrequency = 10.f;
+
+	float TimeSyncRunningTime = 0.f;
 private:
 
 	UPROPERTY()