Buff System with Scriptable Objects for Unity

In this tutorial, I will show you how to create a flexible buff system for Unity using scriptable objects. We will use scriptable objects as a way to quickly create and manage buffs without having to use external data types such as xml or a text file. This lets us separate our buff data such as duration and stat changes from the game logic. As you will see soon, this will also allow us to bind our scriptable objects as assets, using the CreateAssetMenu attribute.

Update: The buff system has been updated with effect and duration extending flags. The original interface for TimedBuff has been updated to reflect that. Tutorial and github repository has been updated to reflect the changes. 

The premise of our design will revolve around three classes. The player class, a buff class, and a buff scriptable object. The player class serves as our generic player model, it can have multiples buffs at the same time, as well as multiple buffs of the same type (stacking). The buff scriptable object acts as our data and the buff class is our bridge between the two, handling the logic of each individual buff.

Buff System Implementation

First we’ll create an abstract version of our buff scriptable object to build on. Every buff should have a duration, and we need a way to create this buff from our data.

ScriptableBuff.cs

public abstract class ScriptableBuff : ScriptableObject
{

    /**
     * Time duration of the buff in seconds.
     */
    public float Duration;

    /**
     * Duration is increased each time the buff is applied.
     */
    public bool IsDurationStacked;

    /**
     * Effect value is increased each time the buff is applied.
     */
    public bool IsEffectStacked;

    public abstract TimedBuff InitializeBuff(GameObject obj);

}

ScriptableBuff contains buff fields and values that can be used across multiple buffs. These are the duration, and two flags that determine whether the duration and effects re stacked. The TimedBuff is the bridge we need to link the data and played model. We will implement that next.

TimedBuff.cs

public abstract class TimedBuff
{
    protected float Duration;
    protected int EffectStacks;
    public ScriptableBuff Buff { get; }
    protected readonly GameObject Obj;
    public bool IsFinished;

    public TimedBuff(ScriptableBuff buff, GameObject obj)
    {
        Buff = buff;
        Obj = obj;
    }

    public void Tick(float delta)
    {
        Duration -= delta;
        if (Duration <= 0)
        {
            End();
            IsFinished = true;
        }
    }

    /**
     * Activates buff or extends duration if ScriptableBuff has IsDurationStacked or IsEffectStacked set to true.
     */
    public void Activate()
    {
        if (Buff.IsEffectStacked || Duration <= 0)
        {
            ApplyEffect();
            EffectStacks++;
        }
        
        if (Buff.IsDurationStacked || Duration <= 0)
        {
            Duration += Buff.Duration;
        }
    }
    protected abstract void ApplyEffect();
    public abstract void End();
}

Another abstraction! There’s a little more code for this class, so I will explain what’s going on. For our example, we assume all buffs have a duration, however you can change that pretty easily. We want all TimedBuff objects to store reference to the duration, the buff data, and the game object that is receiving the buff. There’s also the following methods:

void Tick(float delta) – call this within the player’s update loop. Used to keep a timer on the duration remaining and calls End() when completed.
void Activate() – call this after initialization to activate the buff logic.void End() – called when duration is finished. May also be called early to ‘end’ the buff.

Now we just need the player class. For this, we will create a MonoBehaviour component called BuffableEntity.

BuffableEntity.cs

public class BuffableEntity: MonoBehaviour
{
    private readonly Dictionary<ScriptableBuff, TimedBuff> _buffs = new Dictionary<ScriptableBuff, TimedBuff>();

    void Update()
    {
        //OPTIONAL, return before updating each buff if game is paused
        //if (Game.isPaused)
        //    return;

        foreach (var buff in _buffs.Values.ToList())
        {
            buff.Tick(Time.deltaTime);
            if (buff.IsFinished)
            {
                _buffs.Remove(buff.Buff);
            }
        }
    }

    public void AddBuff(TimedBuff buff)
    {
        if (_buffs.ContainsKey(buff.Buff))
        {
            _buffs[buff.Buff].Activate();
        }
        else
        {
            _buffs.Add(buff.Buff, buff);
            buff.Activate();
        }
    }
}

BuffableEntity keeps a dictionary of all its current buffs. Each update updates existing buffs and removes completed ones. Updating the individual buffs gives more flexibility and control on their lifecycle. For example: buff duration can be frozen when the game is paused or player is phased out.

Speed Buff Example

So how do we use this buff system? Let’s make a quick ‘speed boost’ buff together.

SpeedBuff.cs

[CreateAssetMenu(menuName = "Buffs/SpeedBuff")]
public class SpeedBuff: ScriptableBuff
{
    public float SpeedIncrease;

    public override TimedBuff InitializeBuff(GameObject obj)
    {
       return new TimedSpeedBuff(Duration, this, obj);
    }
}

This extends our ScriptableBuff to hold data on the SpeedIncrease. In addition, by calling the InitializeBuff, we can create a TimedSpeedBuff, which we will implement next. The CreateAssetMenu attribute allows the scriptable object to be created as an asset in the project menu.

TimedSpeedBuff.cs

public class TimedSpeedBuff : TimedBuff
{
    private readonly MovementComponent _movementComponent;

    public TimedSpeedBuff(ScriptableBuff buff, GameObject obj) : base(buff, obj)
    {
        //Getting MovementComponent, replace with your own implementation
        _movementComponent = obj.GetComponent();
    }

    protected override void ApplyEffect()
    {
        //Add speed increase to MovementComponent
        ScriptableSpeedBuff speedBuff = (ScriptableSpeedBuff) Buff;
        _movementComponent.MovementSpeed += speedBuff.SpeedIncrease;
    }

    public override void End()
    {
        //Revert speed increase
        ScriptableSpeedBuff speedBuff = (ScriptableSpeedBuff) Buff;
        _movementComponent.MovementSpeed -= speedBuff.SpeedIncrease * EffectStacks;
        EffectStacks = 0;
    }
}

This is just a simple buff, but as you can see, in the ApplyEffect() method, the speed of the MovementComponent is increased. End() reverts the buff effect. This is all you need to implement your speed buff.

You should now be able to create an asset labeled Buffs/SpeedBuff. You’ll be able to create different versions of the speed buff while using the same implementation! This is one of the benefits of using Scriptable Objects.

Conclusion

So to recap, if you want to implement different types of buffs, the steps you would take are:

1. Implement a new version of TimedBuff. This is where all the logic goes, if you have any stat changes, effects to generate, they all go here.
2. Implement a new version of ScriptableBuff. This is where all the logic goes, so the values of stat changes, art resources, sounds, etc should go here.

Hope this tutorial for a buff system in Unity helps, you can find the source on github. Feel free to leave a comment with any suggestions or questions you may have!

Interested in learning more about Unity? Check out my other Unity tutorials!

Change Log

• 12/30/16 – Added github repository
• 12/7/19 – Updated buff system with effect and duration stacking flags