The Invisible Walls: How to Build Constraints in Verse

So you’ve built a map. You’ve placed some traps, added some loot, and maybe even coded a respawn system. But let’s be honest: if a player can just walk from the spawn point to the finish line without hitting a single obstacle, you haven’t made a game. You’ve made a hallway with good lighting.

In Fortnite, we call this "challenging." In Verse, we call it Constraints.

Think of constraints as the invisible rules of your universe. They are the boundaries that tell the game, "This value can’t be negative," or "This timer can’t run past 60 seconds," or "This player can’t hold more than 100 ammo." Without constraints, your code is like a storm circle with no radius limit—it just expands forever until the server crashes.

Today, we’re going to stop letting our variables go wild. We’re going to build a "Limit Breaker" system where we define strict boundaries for our gameplay elements, ensuring that no matter what chaos the players bring, your logic stays solid.

What You'll Learn

• What a Constraint Is: Why limits make games fun (and code stable).
• The constrained Keyword: How to tell Verse, "Hey, this value has a max and a min."
• Safety Checks: Preventing your game from breaking when a player tries to break the rules.
• Scene Graph Context: Where these rules live in your island’s hierarchy.

How It Works

The "Storm" Analogy

Remember the Storm? It has a safe zone and a damage zone. The storm doesn’t just shrink to "whatever size it feels like." It has specific radius limits. If the radius went negative, your players would fall into the void of bad math.

In Verse, a constraint is exactly that: a set of boundaries for a value.

When you declare a variable in Verse, you can optionally attach constraints to it. This tells the compiler (the code-checker) and the runtime (the game engine) that this specific piece of data is not allowed to go outside a certain range.

Why Bother?

You might think, "I’ll just check if the value is too high in my logic." And you could. But constraints are proactive. They act like a bouncer at a club. If someone tries to enter with a fake ID (a negative number where only positives are allowed), the bouncer (Verse) stops them before they even get inside the party (your game logic). This prevents bugs, crashes, and weird glitches where a player has -5 health or 1,000,000 coins.

The Scene Graph Connection

In the Unreal Engine scene graph, every object (an Entity) has properties. When you use Verse to script these entities, you are defining how those properties behave. A constraint is a property of the data itself, not just the visual model. It’s part of the "skeleton" of your logic. If you’re building a loot box that only spawns rare items after 10 minutes, the "10 minutes" is a constrained value. It can’t be -10 minutes. It can’t be 1000 minutes (unless you want the game to take a decade to complete).

Let's Build It

We’re going to build a Score Limiter. Imagine a game mode where players earn points for eliminations, but the leaderboard only shows the top 100 points. If a player scores 150, their score should cap at 100. We’ll use a constraint to enforce this "max score" rule automatically.

The Setup

1. Open UEFN and create a new Verse script.
2. We’ll define a global constant for the max score (this never changes).
3. We’ll create a variable for the current score, but we’ll apply a constraint to it so it can never exceed that max.

The Code

# Import the core Verse library
using /Fortnite.com/Verse

# Import the game framework for interacting with players
using /Fortnite.com/GameFramework

# 1. Define the MAX_SCORE constant.
# This is like the "Win Condition" points. It’s set once in the editor and never changes.
const MAX_SCORE: int = 100

# 2. Define the current score variable.
# We use 'constrained' to set limits.
# min: 0 (You can't have negative points)
# max: MAX_SCORE (You can't have more than 100 points)
var Current_Score: int = constrained(0, MAX_SCORE)

# This function simulates a player getting an elimination.
# In a real game, this would be triggered by an Elimination Event.
function Add_Points(points: int) -> void:
    # Calculate the new potential score
    new_score: int = Current_Score + points
    
    # Here’s the magic: We try to assign the new score to our constrained variable.
    # If new_score is 150, Verse will automatically clamp it to 100 because of the constraint.
    # If new_score is -5, it will clamp to 0.
    Current_Score = new_score
    
    # Let's print what happened so we can see the constraint in action
    Print("Score updated to: " + Current_Score)

# This function is called when the game starts.
function On_Game_Start() -> void:
    # Reset score to 0
    Current_Score = 0
    Print("Game Started! Score is now: " + Current_Score)
    
    # Simulate some eliminations
    Add_Points(50)   # Score becomes 50
    Add_Points(60)   # Score becomes 100 (capped, because 50+60=110, but max is 100)
    Add_Points(-10)  # Score becomes 0 (capped, because 100-10=90... wait, no, 100-10=90. 
                     # Let's try adding -200. Score becomes 0 because min is 0)
    Add_Points(-200) # Score becomes 0 (clamped to min)

Walkthrough

1. const MAX_SCORE: This is your "Hard Cap." Think of it like the Battle Bus altitude. It’s fixed. You can’t change it during the game.
2. constrained(0, MAX_SCORE): This is the bouncer. When we declare Current_Score, we’re telling Verse: "This variable is allowed to exist, but only between 0 and 100."
3. Current_Score = new_score: When you assign a value to a constrained variable, Verse checks the boundaries. If the value is outside the range, Verse doesn’t crash. It clamps the value to the nearest valid boundary.
   • If you try to set it to 150, it becomes 100.
   • If you try to set it to -5, it becomes 0.

This is powerful because you don’t need if statements to check every time. The constraint handles the validation for you.

Try It Yourself

Now that you’ve seen how constraints cap your score, let’s try something more interactive.

Challenge: Build a Health Regenerator.

1. Create a variable for Current_Health constrained between 0 and 100.
2. Write a function Take_Damage(amount: int) that subtracts from Current_Health.
3. Write a function Heal(amount: int) that adds to Current_Health.
4. The Twist: Try calling Take_Damage(200) when health is 50. What happens? Try calling Heal(50) when health is 100. What happens?

Hint: Don’t worry about complex UI or player interaction yet. Just focus on the math and the constraints. If you get stuck, remember: the constraint is the bouncer. It won’t let the value go outside the door.

Recap

• Constraints are boundaries for your data, just like the storm limits your movement.
• Use the constrained(min, max) syntax to define these limits when declaring a variable.
• Constraints prevent bugs by automatically clamping values to valid ranges, so you don’t have to write endless if checks.
• They are part of the Scene Graph’s logic layer, keeping your game’s rules tight and predictable.

References

• https://dev.epicgames.com/documentation/en-us/fortnite/constrained
• https://dev.epicgames.com/documentation/en-us/fortnite-creative/how-to-design-a-game-in-fortnite-creative
• https://dev.epicgames.com/documentation/en-us/fortnite/how-to-design-a-game-in-fortnite-creative
• https://dev.epicgames.com/documentation/fortnite/verse-glossary
• https://dev.epicgames.com/documentation/en-us/uefn/verse-glossary