How to edit C++ variables in runtime using blueprints?

Development Programming & Scripting C++
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1

I started C++ in Unreal Engine yesterday and made a function to replace the blueprint version of it.

up3
up31152×500 112 KB

This is the blueprint function I am trying to replace with C++ code.

Below is the entire code(cpp, header) I made

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

#pragma once

#include "CoreMinimal.h"
#include "GameFramework/Pawn.h"
#include "UpdatePositionPawn.generated.h"

UCLASS()
class CTEST_API AUpdatePositionPawn : public APawn
{
	GENERATED_BODY()


public:
	// Sets default values for this pawn's properties
	AUpdatePositionPawn();

protected:
	// Called when the game starts or when spawned
	virtual void BeginPlay() override;



	//Function #1: UpdatePosition. If other functions need to be added, add it right below this function.
	UFUNCTION(BlueprintCallable)
		void UpdatePosition();




public:	
	// Called every frame
	virtual void Tick(float DeltaTime) override;

	// Called to bind functionality to input
	virtual void SetupPlayerInputComponent(class UInputComponent* PlayerInputComponent) override;


protected:
	UPROPERTY(BlueprintReadOnly, Category = "Position")
		float Drag=0.25;

	UPROPERTY(EditAnywhere, BlueprintReadWrite, Category = "Position")
		float CurrentSpeed=7500;

	UPROPERTY(EditAnywhere, BlueprintReadWrite, Category = "Position")
		float ThrustSpeed=7500;

};


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


#include "UpdatePositionPawn.h"

#include "Kismet/KismetMathLibrary.h"
#include "Math/UnrealMathUtility.h"
#include "GameFramework/Actor.h"
#include "Kismet/GameplayStatics.h"

// Sets default values
AUpdatePositionPawn::AUpdatePositionPawn()
{
 	// Set this pawn to call Tick() every frame.  You can turn this off to improve performance if you don't need it.
	PrimaryActorTick.bCanEverTick = true;

}

// Called when the game starts or when spawned
void AUpdatePositionPawn::BeginPlay()
{
	Super::BeginPlay();
	
}

// Called every frame
void AUpdatePositionPawn::Tick(float DeltaTime)
{
	Super::Tick(DeltaTime);

}

// Called to bind functionality to input
void AUpdatePositionPawn::SetupPlayerInputComponent(UInputComponent* PlayerInputComponent)
{
	Super::SetupPlayerInputComponent(PlayerInputComponent);

}

void AUpdatePositionPawn::UpdatePosition()
{
	
	AddActorWorldOffset(UKismetMathLibrary::SelectFloat(ThrustSpeed, UKismetMathLibrary::FInterpTo(CurrentSpeed, ThrustSpeed,GetWorld()->DeltaTimeSeconds, Drag), (ThrustSpeed <= CurrentSpeed)) * GetWorld()->DeltaTimeSeconds * GetActorForwardVector(), true);
}

The UpdatePosition function right above is equal to all the blueprints in the image.
Values of ‘CurrentSpeed’ and ‘ThrustSpeed’ should be edited in runtime by any other blueprints

up2
up2989×272 69.8 KB

Like this.

But even I wrote EditAnywhere, BlueprintReadWrite in UPROPERTY, the value of each variables aren’t changing from the first 7500(I tried public instead of protected for the variables and it didn’t work).

Why can’t I change the values by blueprint in runtime?

2

The parameters should update with no problem. Your blueprints parent is your c++ class right?

What is connected to your finterp function?
Is it driven by a tick function or timeline?

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3

Yes the C++ class is set as parent of an actor, and the image with the finterp is part of a ‘switch on int’ running every tick. So that is connected with the tick event and also the ‘UpdatePosition’ made by C++ is too.

4

Oh I figured it out it was my mistake sorry
I had to set CurrentSpeed before addActorWorldOffset like this because FInterp uses CurrentSpeed and ThrustSpeed as current and target.

void AUpdatePositionPawn::UpdatePosition()
{
	CurrentSpeed=UKismetMathLibrary::SelectFloat(ThrustSpeed, UKismetMathLibrary::FInterpTo(CurrentSpeed, ThrustSpeed,GetWorld()->DeltaTimeSeconds, Drag), (ThrustSpeed <= CurrentSpeed));
	AddActorWorldOffset(CurrentSpeed * GetWorld()->DeltaTimeSeconds * GetActorForwardVector(), true);
}
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