Reactive Programming and State Management in Unreal Engine

Development Programming & Scripting C++
#1

I am coming from an Angular/RxJs perspective and attempting to learn C++. I am getting to the point in my development journey where I need to understand and manage game and player state.

I found a library called RxCpp developed for reactive programming in C++, but the library seems inactive. There is even a wrapper for RxCpp and unreal engine, but that library is also inactive.

Is there anyone using reactive programming in Unreal Engine?

#2

Have u started using rxcpp in UE4

1 Like
#3

I am beginning to understand how UE handles event-driven design. The code below is probably bloated, but the goal is to create an NgRx-like environment.

Store = Player State
Action = public IncreaseCoinsAction()
Reducer = private IncreaseCoinsReducer()

Anytime a player collides with a coin, it dispatches the increaseCoinAction.

CoinGamePlayerState.h


#pragma once

#include "CoreMinimal.h"
#include "GameFramework/PlayerState.h"
#include "CoinGamePlayerState.generated.h"

DECLARE_DYNAMIC_MULTICAST_DELEGATE(FIncreaseCoinsDelegate);

UCLASS()
class COINCOLLECTOR_API ACoinGamePlayerState : public APlayerState
{
	GENERATED_BODY()

	// Create Coins property
	UPROPERTY(EditAnywhere)
	int32 Coins;

	// Create delegate for increase coins
	UPROPERTY(BlueprintAssignable)
	FIncreaseCoinsDelegate IncreaseCoinsDelegate;

	// Create function for broadcast increase coins
	UFUNCTION(BlueprintCallable)
	void IncreaseCoinsAction();

	// Create begin play function
	virtual void BeginPlay() override;

private:
	// Create reducer function for increase coins
	UFUNCTION()
	void IncreaseCoinsReducer();
};

CoinGamePlayerState.cpp

// Fill out your copyright notice in the Description page of Project Settings.

#include "CoinGamePlayerState.h"

// BeginPlay
void ACoinGamePlayerState::BeginPlay()
{
    Super::BeginPlay();

    // Set Coins to 0
    Coins = 0;

    // Bind IncreaseCoins function to delegate add dynamic
    IncreaseCoinsDelegate.AddDynamic(this, &ACoinGamePlayerState::IncreaseCoinsReducer);
}

// Create function for broadcast increase coins
void ACoinGamePlayerState::IncreaseCoinsAction()
{
    // Broadcast increase coins
    IncreaseCoinsDelegate.Broadcast();
}

// Bind increase coins action to increase coins
void ACoinGamePlayerState::IncreaseCoinsReducer()
{
    // Increase coins
    Coins++;

    // Print coins
    GEngine->AddOnScreenDebugMessage(-1, 5.f, FColor::Green, FString::Printf(TEXT("Coins: %d"), Coins));
}
#4

I have experience on RxJS and Angular 12.x too, however, RxCPP looks really awful to me, I believe not many people would use that on local machine gaming logic, unless for some network traffic applications. But C++ has lots of mature network libraries that can outperform everything else, whereas l believe lots of MMOs with heavy network traffic use their own C++ developed low-level protocols.

I think C++ is fast for linear tasks, and things in C++ tend to happen with low-level optimizations. ParallelFor() can do simple multi-threading tasks, and OpenMP can make things better.

I wish other people could write some insights into this since I’m also a newcomer to UE development.

#5

As I’m learning, just had another thought about this.
I coded a fairly complex gaming logic for a casual game.
Then I dropped into the trap of ‘Timeline cannot be inside a loop’.
Took me 1 week to figure out that the UE C++ compiler would do something unknown for the timeline animation inside any loop, it would make multiple timelines just run once and it would be after the loop !
Then I missed the reactive programming.

In the end, I solved this by recursive calling, the UE wouldn’t optimize that.