Blueprints, Empower Your Entire Team With BlueprintImplementableEvent

Overview

Original Author: Rama (talk)

Dear Community,

Here is perhaps the most powerful thing you can do as a c++ programmer for blueprint programmers!

So you've created your awesome new amazing C++ system,

but how do you tell the blueprint world when critical events occur in your C++ system?

You need to not only be able to have blueprint programmers call functions that use your C++ system,

you need to be able to spontaneously provide info to blueprint graph system, based on Run-Time events.

This is where BlueprintImplementableEvents come into play!

Providing Blueprints With Data And Critical Timings

Using the BlueprintImplementableEvent you can not only tell blueprints when a critical game event has occurred that your awesome C++ system is tracking / creating,

you can also send variable data to blueprints!

Example code below!

PlayerController.h

.h

/** Player's Health is Currently Above 50! Returns 
player's exact current health for convenience. This 
function runs every tick that the player's health 
is high enough! Play healthy sounds here. */
UFUNCTION(BlueprintImplementableEvent, meta=(FriendlyName = "Player Health ~ Player Is Healthy Tick"))
void PlayerIsHealthyTick(float CurrentHealth);

.cpp

void AYourPlayerController::PlayerTick(float DeltaTime)
{
	Super::PlayerTick(DeltaTime);
	
	//========================
	// 	BP Interface
	if(Health >= 50) 
	{
		this->PlayerIsHealthyTick(Health);
	}
	//========================
}

This

 this->PlayerIsHealthyTick(Health);

I personally use this-> to tell myself I am not actually calling a C++ function, but am sending info to BP.

You could exclude the use of this->

Tick Function

Note that the sample code is sending an event to blueprints every tick!

You can call BlueprintImplementableEvent's any way you want,

but I used this example to show a constant interfacing from c++ to blueprint graphs.

Sending Data to Blueprints From C++

Notice how the player's current health is being sent to blueprints as a function parameter!

You can pass any data you want from C++ to blueprints this way!

Calling a BlueprintImplementableEvent in Blueprints

Make sure to include BlueprintCallable if you want to also call your event in Blueprints!

UFUNCTION(Category = "Player Health", BlueprintImplementableEvent, BlueprintCallable)
void PlayerIsHealthyTick(float CurrentHealth);

4.8+ Standard, Non Virtual

As of 4.8 BlueprintImplementableEvents should not be made virtual!

From the 4.8 Engine upgrade notes:

 Removed "virtual" keyword from several engine-level BlueprintImplementableEvents 
 to conform to the new "BlueprintImplementableEvents should not be virtual" standard.

C++ to BP Interface

I am using the term interface loosely here, to describe how it is that you as the C++ programmer of an awesome new game mechanic can give Blueprint users all the info they need about what your C++ system is doing!

You can do all the core calculations in C++, and just send blueprint graphs the results!

Debugging BlueprintImplementableEvent

If you are having trouble getting a BlueprintImplementableEvent to show up in the blueprint graph, it is probably because you have a return type!

If you do have a return type, your BP implementable event will show up in your bp's overrideable functions list!

Return Values

If you define a C++ BlueprintImplementableEvent event with a return value, you can then override it as a function in the BP of the C++ Class to return the value!

UFUNCTION(BlueprintImplementableEvent)
float GetBPAdjustedPlayerHealth();

Recall that non-const references are also return values:

UFUNCTION(BlueprintImplementableEvent)
void GetBPAdjustedPlayerName(FString& BPModifiedName);

Blueprints For More Than Prototyping

Using BlueprintImplementableEvent's I can now show you that blueprints are amazing for far more than just prototyping game logic that should then be re-written in C++.

Using BlueprintImplementableEvent's, you can actually build a complex low-level c++ system,

and then provide the blueprint graphs with all the critical access points and information needed,

so that blueprints can fully extend and utilize the core C++ system!

Use Blueprints & BlueprintImplementableEvent to Empower Your Entire Team

In this way, you as a C++ programmer can empower your entire team to access, utilize, and extend a core C++ system in blueprints!

This is my favorite thing about the synergy of C++ with Blueprints!

You can write the core system in C++, and then give all of its power and new creativity to the blueprint programmers to take in all sorts of new directions!

Enjoy!

Rama (talk)