unreal-blueprint-integration

C++ and Blueprint Integration - Unreal Engine 5.7

Exposing Variables to Blueprint

• Use UPROPERTY(BlueprintReadWrite) for editable variables
• Use UPROPERTY(BlueprintReadOnly) for read-only variables
• Use Category = "CategoryName" to organize in editor
• Use meta = (AllowPrivateAccess = "true") to expose private variables

Exposing Functions to Blueprint

• UFUNCTION(BlueprintCallable) - Function callable from Blueprint
• UFUNCTION(BlueprintImplementableEvent) - Implementation only in Blueprint
• UFUNCTION(BlueprintNativeEvent) - Default implementation in C++, can be overridden

BlueprintNativeEvent Pattern

// Header
UFUNCTION(BlueprintNativeEvent, Category = "Gameplay")
void OnPlayerHit(float DamageAmount);

// Cpp - Default implementation
void AMyActor::OnPlayerHit_Implementation(float DamageAmount)
{
    // Default implementation in C++
    Health -= DamageAmount;
}

Blueprint Events

• Use BlueprintImplementableEvent when logic should be only in Blueprint
• Use BlueprintNativeEvent when there's default logic in C++ that can be extended

Best Practices

• ALWAYS test changes in C++ classes that are used in Blueprints
• Document functions exposed to Blueprint
• Use categories to organize properties in editor
• Consider performance: frequently called functions should be pure C++
• Use BlueprintCallable for functions that need to be called from Blueprint
• Use BlueprintImplementableEvent for events that only make sense in Blueprint

Compatibility

• When modifying C++ classes used in Blueprints, verify:
  • Removed properties will break Blueprints
  • Type changes can break connections
  • Removed functions will break Blueprint calls
  • ALWAYS test after changes