Behavior Tree

I have been experimenting with behavior trees for a bit now, always finding I am over complicating things or that I did not prepare to solve all my needs with them, but the potential exists.

Right now I am working on a flash game along side an artist (I am so glad I don't have to draw) and I implemented an straight forward almost component like behavior system, such as "I give you the draw behavior, therefore you draw".

This was great to start, I didn't put too much thought into it and I ended creating some pretty cool behaviors, like interpolations (much like the tween class in Unity, but not as huge, of course), recycling routines, click events, functions proxy (Delegate like things, but in As3), collision responses, sequences, etc.

The problem was there was no stop at some behavior, once the entity got the behavior there was no way to stop the behavior from happening, since there was no real condition evaluation unless I went out of my way and filled the behavior with possibilities within its routine (which is dirty).

So I created 2 supporting templates that would work together to make my behaviors only fire when the conditions apply.

First, I created a "BaseCondition":

public class BaseCondition implements IBehavior
 {
  static var Head:BaseCondition;
  var Next:BaseCondition;
  var Self:BaseCondition;

The first part explains that this class is the type of IBeahvior (To comply with my Entity IBehavior collection, and to not disturb what was already in place and working properly).

The Head, Next and Self are the elements used to keep this class pooled, if you would like to know more about it please check my previous post here

The IBehavior interface contains 2 functions, Update():void and Recycle():void, pretty simple.

var Condition:ICondition;
  
  public var TrueConditions:Vector.<BaseCondition>
  public var FalseConditions:Vector.<BaseCondition>
  
  public var TrueActions:Vector.<IBehavior>
  public var FalseActions:Vector.<IBehavior>
  
  public function BaseCondition()
  {
   Self = this;
   TrueConditions = new Vector.<BaseCondition>();
   FalseConditions = new Vector.<BaseCondition>();
   TrueActions = new Vector.<IBehavior>();
   FalseActions = new Vector.<IBehavior>();
  }

Then we have a field for the condition, this condition is what makes the base condition unique, depending on this ICondition we will be able to tell what we are looking for, such as "Is this element inside the view frustum?".

Then we have 4 collections, one for the true branch (in case the condition is true, follow up with these conditions), another for the false conditions and 2 more of the true and false actions, meaning that depending on the residing condition in this base condition we will execute either the actions in the true collection or in the false collection, this proves to be very useful as you start evolving your behaviors.

Coming next we have the factory patterns I use, they are essentially the same with one another except for a small difference, this is done for convenience when creating behaviors (to avoid a mess of having to create things, link them and then reuse them).

public static function Create(Condition:ICondition):BaseCondition
  {
   var Vessel:BaseCondition;
   if (Head != null)
   {
    Vessel = Head;
    Head = Head.Next;
   }
   else
   {
    Vessel = new BaseCondition();
   }
   
   Vessel.Condition = Condition;
   
   return Vessel;
  }
  
  public static function CreateRoot(Owner:Entity, Condition:ICondition):BaseCondition
  {
   var Vessel:BaseCondition;
   if (Head != null)
   {
    Vessel = Head;
    Head = Head.Next;
   }
   else
   {
    Vessel = new BaseCondition();
   }
   
   Vessel.Condition = Condition;
   Owner.BehaviorList.push(Vessel);
   
   return Vessel;
  }
  
  public static function CreateTrueBranch(PreviousBranch:BaseCondition, Condition:ICondition)
  {
   var Vessel:BaseCondition;
   if (Head != null)
   {
    Vessel = Head;
    Head = Head.Next;
   }
   else
   {
    Vessel = new BaseCondition();
   }
   
   Vessel.Condition = Condition;
   PreviousBranch.TrueConditions.push(Vessel);
   
   return Vessel;
  }
  
  public static function CreateFalseBranch(PreviousBranch:BaseCondition, Condition:ICondition)
  {
   var Vessel:BaseCondition;
   if (Head != null)
   {
    Vessel = Head;
    Head = Head.Next;
   }
   else
   {
    Vessel = new BaseCondition();
   }
   
   Vessel.Condition = Condition;
   PreviousBranch.FalseConditions.push(Vessel);
   
   return Vessel;
  }

There's nothing really special to tell, if the factory pattern is not really clear to you please read my last post, there I explain my pool system and the factory pattern used in it.

public function Update():void
  {
   if (Condition.CheckCondition())
   {
    var count:int = TrueActions.length;
    for (var i:int = 0; i < count; i++)
    {
     TrueActions[i].Update();
    }
    
    count = TrueConditions.length;
    for (var i:int = 0; i < count; i++)
    {
     TrueConditions[i].Update();
    }
   }
   else
   {
    var count:int = FalseActions.length;
    for (var i:int = 0; i < count; i++)
    {
     FalseActions[i].Update();
    }
    
    count = FalseConditions.length;
    for (var i:int = 0; i < count; i++)
    {
     FalseConditions[i].Update();
    }
   }
  }

And here we have the heart of this behavior tree, where we check the condition and depending on the outcome we will either do the true reaction or false reaction, and follow the proper path in the behavior.

public function Recycle():void
  {
   Next = Head;
   Head = Self;
   
   var count:int = TrueActions.length;
   for (var i:int = 0; i < count; i++)
   {
    TrueActions[i].Recycle();
   }
   
   count = TrueConditions.length;
   for (var i:int = 0; i < count; i++)
   {
    TrueConditions[i].Recycle();
   }
   
   count = FalseActions.length;
   for (var i:int = 0; i < count; i++)
   {
    FalseActions[i].Recycle();
   }
   
   count = FalseConditions.length;
   for (var i:int = 0; i < count; i++)
   {
    FalseConditions[i].Recycle();
   }
   
   TrueActions.length = 0;
   FalseActions.length = 0;
   TrueConditions.length = 0;
   FalseConditions.length = 0;
  }
 
 }

Finally we have our recycle method, pretty essential to my system, we have to make sure to recycle absolutely every single behavior and condition, for reuse. And this concludes the BaseCondition, it is not complicated but we haven't really seen it in action, in order to make this work we require a "ICondition" as well as another "IBehavior" to append to one of the action branches, let's start with the condition:

public class Con_CollidedWith implements ICondition
 {
  static var Head:Con_CollidedWith;
  var Next:Con_CollidedWith;
  var Self:Con_CollidedWith;
  
  var Target:PhysicsComponent; //Contains all the physics info.

  
  public function Con_CollidedWith()
  {
   Self = this;
  }
  
  public static function Create(Target:PhysicsComponent):Con_CollidedWith
  {
   var Vessel:Con_CollidedWith;
   if(Head != null)
   {
    Vessel = Head;
    Head = Head.Next;
   }
   else
   {
    Vessel = new Con_CollidedWith();
   }
   
   Vessel.Target = Target;

   return Vessel;
  }

This is pretty much the same pattern I follow for almost everything that requires to be pooled, in there you can see an object of type of "PhysicsComponent", in there I store variables that represent the entity in the physical world, such as position, body type (Rectangle, poly, circle, etc), a collision list, etc.

  public function CheckCondition():Boolean
  {
   return Target.CollisionList.length > 0;
  }
  
  
  public function Recycle():void
  {
   Next = Head;
   Head = Self;
  }
  
 }

Finally we have the CheckCondition (which is part of the ICondition interface) where I test the condition at hand, in this case if we have something in our collision collection (meaning we have collided with something in the collision phase) it will return true, otherwise false. That concludes an example of a condition, you can create all sort of conditions, you can test if an enemy has certain amount of HP, or if a button has been clicked, etc. Now we move to the last piece of the puzzle, the Action, for this example I will use a function proxy action:

public class Act_ExecuteFunction implements IBehavior
 {
  static var Head:Act_ExecuteFunction;
  var Next:Act_ExecuteFunction;
  var Self:Act_ExecuteFunction;
  
  var Execute:Function;
  
  public function Act_ExecuteFunction()
  {
   Self = this;
  }
  
  public static function Create(Execute:Function):Act_ExecuteFunction
  {
   var Vessel:Act_ExecuteFunction;
   if(Head != null)
   {
    Vessel = Head;
    Head = Head.Next;
   }
   else
   {
    Vessel = new Act_ExecuteFunction();
   }
   
   Vessel.Execute = Execute;
   
   return Vessel;
  }
  
  public function Update():void
  {
   Execute.call();
  }
  
  
  public function Recycle():void
  {
   Execute = null;
   Next = Head;
   Head = Self;
  }
  
 }

As you can see in our Update function (this will only get called if the condition fell in the action branch where this action resided in) we call the function we appended to this action, much like a delegate. But we still don't know how to put all of this together, so allow me to make an example, in my current game there is "Honey" in the air and you require to collide with it in order to acquire it, here is how I make a honey:

public static function CreateHoneyItem(X:Number, Y:Number):void
  {
   var Honey:Entity = Entity.Create(World.InGameGroup);
   var Graphics:GraphicsComponent = GraphicsComponent.Create(Honey, AnimationLibrary.HONEY_GRAPHICS);
   var Physics:PhysicsComponent = PhysicsComponent.Create(Honey, X, Y, PhysicsComponent.ITEM);
   Physics.TurnIntoCircle(16);
   
   var Drawer:B_Draw = B_Draw.CreateOwnerless(1, Graphics, Physics); //gets recycled upon collision by the honey collision response
   
   var Condition_Collision:BaseCondition = BaseCondition.CreateRoot(Honey,Con_CollidedWith.Create(Physics));
   Condition_Collision.TrueActions.push(Act_ExecuteFunction.Create(HoneyCollisionResponse));

}

public static function HoneyCollisionResponse():void
{
    //Do your response here
}

So in order to make a honey I call the factory method for the honey, this will create a honey, and give it's behavior. The behavior says that it will Draw (B_Draw), Also says that if the honey collides with something then execute the function proxy (HoneyCollisionResponse).

There's more behind the scene, such as the collision system, the render system, etc, but it is not hard to get the idea on how the behavior tree works. Using this you can come up with all sort of complex behaviors, but the main issue with this is that they are inflexible upon creation, there won't be learning of AI, it will just run the routine over and over, but that doesn't have to be that way, there are methods to make this work the way you want to, implementing weight based decisions instead of just conditionals could be a way, there's a lot of things that can be implementing using this Behavior Tree pattern, but that would be another post for another time.

Final pool version

Since I went from C# to AS3 in order to complete web games I realized that the lack of generics in AS3 was going to be a huge problem for my pooling system, this forced me to think things once again and the result was something more elegant, secure and completely contained within the pooled class.

Making use of the factory design pattern once again I was able to create a pool system within the same class (which is now a template in my IDE), here is how it goes:

public class PooledItem
{
   private static var PoolHead:PooledItem;
   private var Next:PooledItem;
   private var Self:PooledItem;

   public function PooledItem()
   {
      Self = this;
   }

   public static function Create():PooledItem
   {
      var Vessel:PooledItem;
      if(PooledHead != null)
      {
         Vessel = PoolHead;
         PoolHead = PoolHead.Next;
      }
      else
      {
         Vessel = new PooledItem();
      }
      
      return Vessel;
   }
}

The PoolHead is private and static, making it unique locally and impossible to access from outside this class, then we have the Next and the Self which are unique to each instance of the PooledItem, and finally we have a factory pattern which creates a new instance of a PooledItem if the head is null, but if the head is not null it will return it and set the new head as the next element in the queue.

One thing to have in mind is that AS3 does not allow to have private constructors, thus making it possible to create an instance of the PooledItem without the factory method, if this happens and you don't properly get rid of it by calling its recycle method then you will have an extra element (outside the pool) doing nothing, but even if you create it without the "create" function you can still put it back in the pool by calling recycle, so no real harm done if handled properly, still if this was not AS3 I would make the constructor private.

Going to the recycle function now, the recycle function is where I do all my clean up code (if required depending on the elements of the class) as well as to put elements back into the pool:

public function Recycle():void
{
   //Do clean up code, maybe recycle other pooled items that were created within this
   //class or release references of an element to let GC deal with it, etc.

   Next = PoolHead; //we set the next element as the current head.
   PoolHead = Self; //and finally we set the this element as the new head.
}

And that's it, it is amazing how essential and memory friendly this can be, allocating memory and deallocating memory can be very tasking in the system, specially if you are planning on putting your games in mobile devices, have in mind also that the more memory you use the more battery it might consume, so in order to have some balance make sure to maintain your pools, this can be achieve by an internal reference counter and releasing some of them if the number gets to a certain point, however you want to handle that I will leave to you.

My Factory Design Pattern

I will talk a bit about how I create my "Game objects".

The first thing you need to know is that I do not use the keyword "New" to instantiate a new object, this is because I need to have control over my game objects (coming from the pools), Let's create a quick example, I am going to assume that you know about my pool system, but if you don't please take a look at the previous post.

We will start with the body of the class.

public class Slime: PooleanNode<Slime> 
{
    static LinkedPoolean<Slime> Pool = new LinkedPoolean<Slime>();

    public Slime()
    {
    }
}

Here we have declared a "Slime class" that can be pooled with my pool class, as you can see the constructor is public so we can instantiate them with the activator class, also there's a static pool of slimes living inside this class, this will mean that in every single slime object you will have access to the same pool, this is important cause all the slimes need to come from the pool, now moving into the "creational" method.

public static Slime Create() //this function must live inside the slime class.
{
    Slime Vessel;
    Pool.Get(out Vessel); //if it doesn't live inside the class, the pool wouldn't be
    return Vessel;        //visible, you would have to make it public and access it
}                         //like "Slime.Pool", I don't recommend that. 

And done, we have create an static method that will take slimes out of the pool and return them, simple as that! now for some logic on why I do this, by making a new slime this way I make sure they come from the pool and that they are not generated outside of the pool, this is handy when we want to manage them and when we want to avoid tasking the garbage collector, since we are not allocating new memory.

Now let's expand on it, to make it useful, you can declare multiple creation methods to obtain different results, let's say that the Slime has some fields like position or maybe current hit points, etc, we can modify these elements like this:

public class Slime: PooleanNode<Slime> 
{
    static LinkedPoolean<Slime> Pool = new LinkedPoolean<Slime>();

    Vector2 Position;
    int HP;

    public Slime()
    {
        Position = Vector2.Zero;
        HP = 1;
    }

    public static Slime Create(Vector2 Position, int HP) 
    {
        Slime Vessel;
        Pool.Get(out Vessel); 
        Vessel.Position = Position;
        Vessel.HP = HP;
        return Vessel;       
    } 
}

By default the slime starts at position 0,0 and with 1 HP, but we can create any slime anywhere we want as well as giving it any amount of HP we want, we can create more methods to define things ever further.

Lastly I define a recycle method that I use when I need to get rid of the object and sent it back to the pool, like this:

public void Recycle()
{
    Pool.ReturnPoolable(this);
}

That makes sure that the object is sent back into the pool to be reused by the factory method, this is an overly simplified version of what I use in my current game, if you would like to check the game out, here:

Game

Thanks for reading!

Taking casting out of the picture

Once again! I have done another revision to the way I am doing pools, it is almost like an obsession, in any case, it has proven to be fantastic, onto the code:

public class LinkedPoolean<T> where T : PooleanNode<T>, new()
    {
        public T Head;

        public LinkedPoolean()
        {
            Head = Activator.CreateInstance<T>();
        }

        public void Get(out T Vessel)
        {
            if (Head != null)
            {
                Vessel = Head;
                Head = Head.Next;
            }
            else
            {
                Vessel = Activator.CreateInstance<T>();
            }
         
        }

        public void ReturnPoolable(T Return)
        {
            Return.Next = Head;
            Head = Return;
        }
    }

The Key change here is the way we access the "Activator", you see, there's a function to create an instance that takes a Generic parameter T, and there's another version of the function that takes an argument "Type" and returns an "Object", the object returned by the second function is sadly not the right type, so in order to use it I used to cast it, this would create a hit on the performance. The function that takes a parameter of type T returns an object of type T, making casting unnecessary.

This improvement was only possible though if the PooleanNode knew which "kind of poolean node" it was, new Poolean node class:

public class PooleanNode<T> where T: PooleanNode<T>
    {
        public T Next;
    }

This in turn makes the poolean node type safe, before hand it was potentially possible to subscribe a poolean node into a pool of another type, it was kind of weird at the beginning to see a class expecting itself to be the template, but it is kind of cool the way it works.

Thanks for reading~

The Pooling Redo

I can't believe that I first attempted to make a proper pool back in April, that's only 6 months ago! I learned so much and looking back I feel dumb, but that's the main purpose of this blog! I like to check out my learning curve.

Anyways, to the pools, not too long ago I read about intrusive lists and how they were awesome for managing your game objects, before that my take on recursions were weird as well, I abandon the method and just made a while loop scanning of the nodes to traverse the tree, so no more recursion because the Xbox hates you using memory!

My last revision on the pool was cool, managed and it served it's purpose pretty well, but then I read about recursive lists and I thought that I could use something like that in the pool, a linked list pretty much but instead of using the built in linked list I wanted to make the nodes of the pool the actual objects and not a sub object attached to a node.

public class LinkedPoolean<t> where T : PooleanNode, new()
    {
       Type TypeOfT;

        T Head;

        public LinkedPoolean()
        {
            TypeOfT = typeof(T);
            Head = (T)Activator.CreateInstance(TypeOfT);
        }

        public void Get(out T Vessel)
        {
            if (Head != null)
            {
                Vessel = Head;
                Head = (T)Head.Next;
            }
            else
            {
                Vessel = (T)Activator.CreateInstance(TypeOfT);
            }
        }

        public void ReturnPoolable(T Return)
        {
            Return.Next = Head;
            Head = Return;
        }
    }

The thing to note here is that it is so ridiculous simple in comparison to my first attempt, and I was thinking that the last attempt was short! now, in this case I made the "PooleanNode" a base class cause it bugs me to know that I would have to use a "Property" to fetch a single field (which is all that class has in it as for now), but if that doesn't bother you then you may as well make the class an interface.

Poolean class:

public class PooleanNode
    {
        public PooleanNode Next;
    }

Well more weird things will result out of this, I am going to be changing quite a bit of things in my engine, because this method it is not just about 10 times faster and more memory friendly but it is also a good design.

New Poolean

Looking back to when I made my first "Pool" (called Poolean) and the reasons why I made it the way it was I came to realize I was trying to avoid using "List.Remove(T)" besides avoiding to create new elements every time something was needed.

Some time after that I stumbled upon a performance problem that was going to 

hinder my game if the number of elements to be managed was going to be big, let'ssay that a pool is used a lot, meaning that the elements within the pool are

almost always "In use" and often the pool requires to expand (create new elementsto accommodate demand). Following the way the pool used to work, I would have to check if the "next" element was free, and if it was not continue until I ran out of space, then I started back from 0 to right before the element I just used, andif nothing was available then expand the pool.

The problem with this is that if I want something that requires big numbers (likeparticles) it would get hairy real quick.

I was trying to make a class that could hold a collection of objects and be able to remove the objects without having to shift things around (like List.Remove(T) does) because once again that would be very slow, I came with the idea of removing the certain element and swapping the last element in the collection to the position of the element we just removed, putting the count down by one and that would be all, in order to do this, the object I wanted to use in this "Collection" would have to contain an interface that allows access to certain index number, just a simple property to know in which position the element is in the collection. This methodology could fix my Poolean issue, by knowing how many items are in the pool, and knowing I always remove the last one, this made the entire "Searching for the next element" completely obsolete, which made me happy, so now the new Poolean looks like this:    

public class Poolean<T> where T: new()
    {
        public T[] Pool;
        public int Size;
        public int GrowthAmount;
        public int CurrentFreeIndex;
        public Type TypeOfT;

        public Poolean(int size, int Growth)
        {
            CurrentFreeIndex = size - 1;
            GrowthAmount = Growth;
            TypeOfT = typeof(T);

            Pool = new T[size];

            Size = size;

            for (int i = 0; i < Size; i++)
            {
                T NewElement = (T)Activator.CreateInstance(TypeOfT);
                Pool[i] = NewElement;
            }
        }

        public void Get(out T Vessel)
        {
            if (CurrentFreeIndex > -1)
            {
                Vessel = (T)Pool[CurrentFreeIndex];
                Pool[CurrentFreeIndex] = default(T);
                CurrentFreeIndex--;
            }
            else
            {
                //Expand
                CurrentFreeIndex += GrowthAmount;
                Size += GrowthAmount;
                Pool = new T[Size];
                for (int i = 0; i < GrowthAmount; i++)
                {
                    T NewItem = (T)Activator.CreateInstance(TypeOfT);
                    Pool[i] = NewItem;
                }

                //try again
                Vessel = (T)Pool[CurrentFreeIndex];
                Pool[CurrentFreeIndex] = default(T);
                CurrentFreeIndex--;
            }
        }

        public void ReturnPoolable(T Poolable)
        {
            CurrentFreeIndex++;
            Pool[CurrentFreeIndex] = Poolable;
        }
    }

As you can see it is a lot shorted and easier to understand, let's go over the Constructor first, in the constructor you specify how many elements do you want in the pool to begin with and in the event that the pool runs out of space, how many elements you want to add, pretty simple, there we define what type T is and then we populate the array of Ts with objects of type T. Then we have the "Get" function which takes an element out of the pool if it has any left and if it doesn't it expands, and finally we have the "ReturnPoolable" which adds the element back to the pool and gets the count up by one.

This made the pool lightning faster, but I hope I come up with an idea to make it even faster.

Entity Pooling

Memory allocation in run time can be pretty heavy depending on how much you do it, getting rid of objects every loop will trigger the garbage collector (at 1 MB in the Xbox) often making you get lag spikes once in a while.

I encountered this issue with my engine, where entities were being created and deleted almost every frame, this made the lag unbearable. I knew from the start I had to pool the entities, so I did using this method:

static List EntityList = new List();

public static void GetEntity(out Entity Returnee)
{
        int Count = EntityList.Count;
        if(Count > 0)
        {
                  Returnee = EntityList[Count - 1];
                  EntityList.Remove(Returnee);
         }
         else
         {
                  Returnee = new Entity();
          }
}

Something I am not showing here is the way to return the entities to the list, that's by simply re adding them to list of entities, trivial.



The main issue with this way of pooling is that you are required to remove things from a list, this could get heavy if the list gets bigger, but for the time this method did improve my overall performance I thought I was happy with the results, until one day one of my class mates said something about how a pool can know what the next available index was instead of taking things out of a list, this made me really curious and I went on that to find a better way of pooling.

What I found is that removing things from the list was just wasteful and not necessarily, if I knew the next available index I could use that instead of removing the ones that were being used, this was possible by creating a base object that represents an item that can be activated when in the pool and "deactivated" or "unavailable" when "not" in the pool ("" because it is always in the pool at all times), the new pool looks like this:

public class Poolean where T: Poolable, new()
    {
        private List Pool;
        int MaxCount;
        int CurrentFreeIndex;
        bool SpecificType;
        Type ElementType;

        public Poolean(int BufferSize)
        {
            SpecificType = false;
            Pool = new List(BufferSize);
            MaxCount = 0;
            CurrentFreeIndex = 0;
            ExpandPool(BufferSize);
            
        }

        public Poolean(int BufferSize, Type typeOfElement)
        {
            ElementType = typeOfElement;
            SpecificType = true;
            Pool = new List(BufferSize);
            MaxCount = 0;
            CurrentFreeIndex = 0;
            ExpandPool(BufferSize);
        }

        private void ExpandPool(int size)
        {
            int start = MaxCount;
            MaxCount += size;

            if (SpecificType)
            {
                for (int i = start; i < MaxCount; i++)
                {
                    T NewPoolElement = (T)Activator.CreateInstance(ElementType);
                    NewPoolElement.Index = i;
                    NewPoolElement.InUse = false;
                    Pool.Add(NewPoolElement);
                }
            }
            else
            {
                
                for (int i = start; i < MaxCount; i++)
                {
                    T NewPoolElement = new T();
                    NewPoolElement.Index = i;
                    NewPoolElement.InUse = false;
                    Pool.Add(NewPoolElement);
                }
            }
        }

        public void ReturnPoolable(Poolable returnee)
        {
            returnee.InUse = false;
        }

        public void GetPoolable(out T vessel)
        {
            vessel = (T)Pool[CurrentFreeIndex];
            vessel.InUse = true;

            //find ther next available item
            int Next = vessel.Index + 1;
            GetNextAvailableElement(Next);
        }

        private void GetNextAvailableElement(int LastPlusOne)
        {
            for (int NextInLine = LastPlusOne; NextInLine < MaxCount; NextInLine++)
            {
                Poolable Current = Pool[NextInLine];
                if (!Current.InUse)
                {
                    CurrentFreeIndex = Current.Index;
                    return;
                }
            }

            //if it gets here then we need to start from the beginning of the list until we reach the last "Next", if this happens, 
            //then all elements are being used in the list, we need to increase the size of the list.

            for (int Start = 0; Start < LastPlusOne - 1; Start++)
            {
                Poolable Current = Pool[Start];
                if (!Current.InUse)
                {
                    CurrentFreeIndex = Current.Index;
                    return;
                }
            }

            //if we still here... then yes all the elements are being use, you need to inscrease the size of the pool.

            ExpandPool(MaxCount);
            GetNextAvailableElement(LastPlusOne);
        }
   
    }

As you can see, the new pool return references to the element in the pool, but it never ever removes that reference from the pool itself, instead it makes its "used" tag true, and looks for the next available from the index that was just taken out, in case the pool ever runs out of elements, it will double its size to continue working properly. A poolable base class looks like this:

public class Poolable
    {
        public int Index;
        public bool InUse;

        public Poolable()
        {

        }
    }

Real simple!


Well that's the cool thing I learned today, now all my entities are created really much much faster.