【Unreal Engine】Level Blueprint vs Blueprint Class: Differences and Selection Criteria

Overview of Level Blueprint and Blueprint Class

When building game logic in Unreal Engine (UE), there are primarily two choices:

• Level Blueprint: A blueprint specific to that level, controlling the entire level.
• Blueprint Class: A reusable blueprint defining actor and component behaviors.

This article explains the fundamental differences between these two, their advantages and disadvantages, and criteria for choosing between them.

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What is Level Blueprint

Basic Concepts of Level Blueprint

Level Blueprint is, as the name suggests, a blueprint specific to a particular level (map).

It exists for writing logic that automatically executes when the level opens. Level Blueprint serves as a "command center" that references multiple actors within the level and coordinates them.

Characteristics:

1. Bound to level: Cannot be used in other levels.
2. Easy actor referencing: Can directly reference actors placed in the level and call their events.
3. Singleton: Only one exists per level.

Level Blueprint Use Cases

Level Blueprint shines brightest when controlling one-time events unique to that level.

Example: Level Start Sequence and Door Opening

For example, consider logic where "when the player enters a specific trigger volume, open a specific door in the level."

// Level Blueprint example: Door opening logic

// 1. Trigger volume (TriggerBox_Door) Overlap event
Event OnActorBeginOverlap (Other Actor == PlayerCharacter)
    // 2. Call custom event on door actor (Door_BP)
    Call Custom Event: OpenDoor (Target: Door_BP)
    // 3. If event should only fire once, disable this trigger
    Disable Input (Target: TriggerBox_Door)

This logic applies only to this door in this level, so writing it in Level Blueprint is the simplest and most intuitive approach.

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What is Blueprint Class

Basic Concepts of Blueprint Class

Blueprint Class is a reusable blueprint that defines the behavior of in-game Actors and Components.

It's used to encapsulate common functionality and properties for objects that appear repeatedly in games, such as "explosive barrels," "collectible items," "moving platforms," etc.

Characteristics:

1. Reusability: Can be instantiated and used across multiple levels and projects.
2. Encapsulation: Data (variables) and functionality (functions/events) are bundled together.
3. Inheritance: Can create child classes that add new functionality with existing Blueprint Classes as parents.

Blueprint Class Use Cases

Blueprint Class is suited for defining fundamental game elements and functionality you want to reuse.

Example: Barrel Actor That Takes Damage

When creating "a barrel that explodes when the player attacks it," create the barrel itself as a Blueprint Class.

// Blueprint Class (BP_ExplosiveBarrel) example: Damage processing

// 1. Event when damage is received
Event AnyDamage (Damage Amount, Damage Type, Instigator, Damage Causer)
    // 2. Reduce health variable (Health)
    Set Health = Health - Damage Amount
    // 3. Check if health is 0 or below
    If (Health <= 0)
        // 4. Call custom event to execute explosion processing
        Call Custom Event: Explode

This BP_ExplosiveBarrel behaves the same wherever it's placed in the level. This reusability is Blueprint Class's greatest strength.

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Comparing Level Blueprint and Blueprint Class

Item	Level Blueprint	Blueprint Class
Purpose	Control specific level events, coordinate actors within level	Define reusable actor/component behavior
Reusability	Not possible (level-specific)	Possible (instantiate and use anywhere)
Encapsulation	Low (depends on external actors within level)	High (data and logic are self-contained in class)
Inheritance	Not possible	Possible (extend parent class functionality)
References	Easy to directly reference actors within level	Indirect methods like Get All Actors Of Class needed to reference other actors
Performance	As complexity grows, references multiply making management and optimization difficult	Structured and easier to optimize for performance
Recommendation	Limited (restrict to level-specific events)	High (foundation for game logic)

Note: Get All Actors Of Class traverses all actors, so it negatively impacts performance in levels with many actors. For frequent calls, consider caching references or tag-based searches.

Selection Criteria

When in doubt, follow this "golden rule" for selection.

Scenario	Blueprint to Choose	Reason
In-game "things" behavior (barrels, doors, enemies, items)	Blueprint Class	Reusability, encapsulation, efficient development through inheritance.
Level-specific "direction" and "flow" (level-start camera work, level completion detection)	Level Blueprint	Level-specific logic with no need for reuse.
Complex logic coordinating multiple actors	Blueprint Class + Interface	Before Level Blueprint becomes complex, structure inter-actor communication using Blueprint Class and Blueprint Interface.

Common Mistake: Concentrating Logic in Level Blueprint

A common beginner trap is writing core game logic (e.g., player health management, score systems) in Level Blueprint. This requires copying and pasting logic every time you change levels, becoming a breeding ground for bugs.

❌ Bad example: Writing player damage processing in Level Blueprint. ✅ Good example: Writing damage processing in the player character's Blueprint Class.

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Coordination Pattern Using Interface

To minimize Level Blueprint usage while coordinating actors within levels, utilizing Blueprint Interface is key.

Here's an example of achieving "open a specific door from Level Blueprint" in a more structured way.

Define the Interface

First, create a Blueprint Interface (BPI_Interactable) that serves as the "contract" for opening doors.

Function Name	Input	Output	Purpose
OpenDoor	None	None	Tell the door to "open"

Implement in Blueprint Class

The door actor (BP_Door) implements this interface.

// BP_Door (Blueprint Class)

// Implement BPI_Interactable's OpenDoor event
Event OpenDoor (Interface Message)
    // Play Timeline or Animation to open door
    Play Timeline: DoorOpenAnimation
    // Log: Door opened
    Print String: "Door Opened by Interface Call"

Call from Level Blueprint

In Level Blueprint, instead of directly referencing the door actor, send interface messages.

// Level Blueprint

// 1. Trigger volume (TriggerBox_Door) Overlap event
Event OnActorBeginOverlap (Other Actor == PlayerCharacter)
    // 2. Reference door actor (Door_BP)
    // 3. Send interface message
    Call OpenDoor (Target: Door_BP) // Call as interface function

The benefit of this approach is that Level Blueprint doesn't need to know the door's internal implementation (Timeline or animation). Level Blueprint simply communicates "I want this actor to execute OpenDoor," achieving logic separation.

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Guidelines for Choosing Level Blueprint or Blueprint Class

Level Blueprint and Blueprint Class are like two wheels of a car in Unreal Engine development. Both are powerful, but understanding their roles and using them appropriately determines project quality.

Blueprint	Role	Selection Criteria
Blueprint Class	Game parts (actors, components)	Logic requiring reuse, behavior that should be encapsulated
Level Blueprint	Level direction (level-specific events)	Logic that occurs only in that level and doesn't need reuse

Especially as projects grow larger, having the awareness to make Blueprint Class the main focus and limit Level Blueprint usage to level-specific coordination and direction is the first step toward professional development.

Apply this knowledge to build more organized, extensible Unreal Engine projects.