void UGameEngine::Tick( float DeltaSeconds, bool bIdleMode )
{
	SCOPE_CYCLE_COUNTER(STAT_GameEngineTick);
	NETWORK_PROFILER(GNetworkProfiler.TrackFrameBegin());

	int32 LocalTickCycles=0;
	CLOCK_CYCLES(LocalTickCycles);
	
	// -----------------------------------------------------
	// Non-World related stuff
	// -----------------------------------------------------

	if( DeltaSeconds < 0.0f )
	{
#if (UE_BUILD_SHIPPING && WITH_EDITOR)
		// End users don't have access to the secure parts of UDN.  Regardless, they won't
		// need the warning because the game ships with AMD drivers that address the issue.
		UE_LOG(LogEngine, Fatal,TEXT("Negative delta time!"));
#else
		// Send developers to the support list thread.
		UE_LOG(LogEngine, Fatal,TEXT("Negative delta time! Please see https://udn.epicgames.com/lists/showpost.php?list=ue3bugs&id=4364"));
#endif
	}

	// Tick allocator
	if( GMalloc != NULL )
	{
		GMalloc->Tick( DeltaSeconds );
	}

	// Tick the module manager
	FModuleManager::Get().Tick();

	if (!IsRunningDedicatedServer() && !IsRunningCommandlet())
	{
		// Clean up the game viewports that have been closed.
		CleanupGameViewport();
	}

	// If all viewports closed, time to exit.
	if(GIsClient && GameViewport == NULL )
	{
		UE_LOG(LogEngine, Log,  TEXT("All Windows Closed") );
		FPlatformMisc::RequestExit( 0 );
		return;
	}

	if ( GameViewport != NULL )
	{
		// Decide whether to drop high detail because of frame rate.
		GameViewport->SetDropDetail(DeltaSeconds);
	}

	// Update subsystems.
	{
		// This assumes that UObject::StaticTick only calls ProcessAsyncLoading.
		StaticTick( DeltaSeconds );
	}

	// -----------------------------------------------------
	// Begin ticking worlds
	// -----------------------------------------------------

	int32 OriginalGWorldContext = INDEX_NONE;
	for (int32 i=0; i < WorldList.Num(); ++i)
	{
		if (WorldList[i].World() == GWorld)
		{
			OriginalGWorldContext = WorldList[i].ContextHandle;
			break;
		}
	}

	bool WorldWasPaused = false;

	for (int32 WorldIdx = 0; WorldIdx < WorldList.Num(); ++WorldIdx)
	{
		FWorldContext &Context = WorldList[WorldIdx];
		if (Context.World() == NULL)
		{
			continue;
		}

		WorldWasPaused |= Context.World()->IsPaused();

		GWorld = Context.World();

		// Tick all travel and Pending NetGames (Seamless, server, client)
		TickWorldTravel(Context, DeltaSeconds);

		if (!IsRunningDedicatedServer() && !IsRunningCommandlet())
		{
			// Only update reflection captures in game once all 'always loaded' levels have been loaded
			// This won't work with actual level streaming though
			if (Context.World()->AreAlwaysLoadedLevelsLoaded())
			{
				// Update sky light first because it's considered direct lighting, sky diffuse will be visible in reflection capture indirect specular
				USkyLightComponent::UpdateSkyCaptureContents(Context.World());
				UReflectionCaptureComponent::UpdateReflectionCaptureContents(Context.World());
			}
		}

		if (!bIdleMode)
		{
			// Tick the world.
			GameCycles=0;
			CLOCK_CYCLES(GameCycles);
			Context.World()->Tick( LEVELTICK_All, DeltaSeconds );
			UNCLOCK_CYCLES(GameCycles);
		}

		// Issue cause event after first tick to provide a chance for the game to spawn the player and such.
		if( Context.World()->bWorldWasLoadedThisTick )
		{
			Context.World()->bWorldWasLoadedThisTick = false;
			
			const TCHAR* InitialExec = Context.LastURL.GetOption(TEXT("causeevent="),NULL);
			ULocalPlayer* GamePlayer = Context.GamePlayers.Num() > 0 ? Context.GamePlayers[0] : NULL;
			if( InitialExec && GamePlayer )
			{
				UE_LOG(LogEngine, Log, TEXT("Issuing initial cause event passed from URL: %s"), InitialExec);
				GamePlayer->Exec( GamePlayer->GetWorld(), *(FString("CAUSEEVENT ") + InitialExec), *GLog );
			}

			Context.World()->bTriggerPostLoadMap = true;
		}

		// Tick the viewports.
		if ( GameViewport != NULL && !bIdleMode )
		{
			SCOPE_CYCLE_COUNTER(STAT_GameViewportTick);
			GameViewport->Tick(DeltaSeconds);
		}
	
		UpdateTransitionType(Context.World());
	
		// fixme: this will only happen once due to the static bool, but still need to figure out how to handle this for multiple worlds
		if (FPlatformProperties::SupportsWindowedMode())
		{
			// Hide the splashscreen and show the game window
			static bool bFirstTime = true;
			if ( bFirstTime )
			{
				bFirstTime = false;
				FPlatformSplash::Hide();
				if ( GameViewportWindow.IsValid() )
				{
					GameViewportWindow.Pin()->ShowWindow();
					FSlateApplication::Get().RegisterGameViewport( GameViewportWidget.ToSharedRef() );
				}
			}
		}

		if (!bIdleMode && !IsRunningDedicatedServer() && !IsRunningCommandlet())
		{
			// Render everything.
			RedrawViewports();
		}

		// Block on async loading if requested.
		if( Context.World()->bRequestedBlockOnAsyncLoading )
		{
			// Only perform work if there is anything to do. This ensures we are not syncronizing with the GPU
			// and suspending the device needlessly.
			bool bWorkToDo = IsAsyncLoading();
			if (!bWorkToDo)
			{
				Context.World()->UpdateLevelStreaming();
				bWorkToDo = Context.World()->IsVisibilityRequestPending();
			}
			if (bWorkToDo)
			{
				// tell clients to do the same so they don't fall behind
				for( FConstPlayerControllerIterator Iterator = Context.World()->GetPlayerControllerIterator(); Iterator; ++Iterator )
				{
					APlayerController* PlayerController = *Iterator;
					UNetConnection* Conn = Cast<UNetConnection>(PlayerController->Player);
					if (Conn != NULL && Conn->GetUChildConnection() == NULL)
					{
						// call the event to replicate the call
						PlayerController->ClientSetBlockOnAsyncLoading();
						// flush the connection to make sure it gets sent immediately
						Conn->FlushNet(true);
					}
				}

				FStreamingPause::GameThreadWantsToSuspendRendering( GameViewport ? GameViewport->Viewport : NULL );

				// Flushes level streaming requests, blocking till completion.
				Context.World()->FlushLevelStreaming();

				FStreamingPause::GameThreadWantsToResumeRendering();
			}
			Context.World()->bRequestedBlockOnAsyncLoading = false;
		}

		// streamingServer
		if( GIsServer == true )
		{
			SCOPE_CYCLE_COUNTER(STAT_UpdateLevelStreaming);
			Context.World()->UpdateLevelStreaming();
		}

		// Update Audio. This needs to occur after rendering as the rendering code updates the listener position.
		if( GetAudioDevice() )
		{
			GetAudioDevice()->Update( !Context.World()->IsPaused() );
		}

	

		if( GIsClient )
		{
			// GStreamingManager is updated outside of a world context. For now, assuming it needs to tick here, before possibly calling PostLoadMap. 
			// Will need to take another look when trying to support multiple worlds.

			// Update resource streaming after viewports have had a chance to update view information. Normal update.
			GStreamingManager->Tick( DeltaSeconds );

			if ( Context.World()->bTriggerPostLoadMap )
			{
				Context.World()->bTriggerPostLoadMap = false;

				// Turns off the loading movie (if it was turned on by LoadMap) and other post-load cleanup.
				PostLoadMap();
			}
		}

		UNCLOCK_CYCLES(LocalTickCycles);
		TickCycles=LocalTickCycles;

		// See whether any map changes are pending and we requested them to be committed.
		ConditionalCommitMapChange(Context);
	}

	// ----------------------------
	//	End per-world ticking
	// ----------------------------

	// Restore original GWorld*. This will go away one day.
	if (OriginalGWorldContext != INDEX_NONE)
	{
		GWorld = WorldContextFromHandle(OriginalGWorldContext).World();
	}

	// tell renderer about GWorld->IsPaused(), before rendering
	{
		ENQUEUE_UNIQUE_RENDER_COMMAND_ONEPARAMETER(
			SetPaused,
			bool, bGamePaused, WorldWasPaused,
		{
			GRenderingRealtimeClock.SetGamePaused(bGamePaused);
		});
	}