From 642f8df4d52aae980ea03f8e2c82c63e4425dfe2 Mon Sep 17 00:00:00 2001
From: Evan Hemsley <evan@moonside.games>
Date: Fri, 20 Dec 2019 11:28:56 -0800
Subject: [PATCH] pooling bit arrays

---
 encompass-cs/Collections/BitArrayPool.cs   | 33 ++++++++++++++++++++++
 encompass-cs/Collections/ComponentStore.cs |  2 +-
 encompass-cs/ComponentBitSet.cs            | 17 ++++++++---
 3 files changed, 47 insertions(+), 5 deletions(-)
 create mode 100644 encompass-cs/Collections/BitArrayPool.cs

diff --git a/encompass-cs/Collections/BitArrayPool.cs b/encompass-cs/Collections/BitArrayPool.cs
new file mode 100644
index 0000000..0f0165f
--- /dev/null
+++ b/encompass-cs/Collections/BitArrayPool.cs
@@ -0,0 +1,33 @@
+using System.Collections;
+using System.Collections.Generic;
+
+namespace Encompass
+{
+    internal class BitArrayPool
+    {
+        private Stack<BitArray> bitArrays;
+
+        public BitArrayPool(int capacity)
+        {
+            bitArrays = new Stack<BitArray>(capacity);
+
+            for (var i = 0; i < capacity; i++)
+            {
+                bitArrays.Push(new BitArray(128));
+            }
+        }
+
+        public BitArray Obtain(int size)
+        {
+            var bitArray = bitArrays.Pop();
+            bitArray.Length = size;
+            bitArray.SetAll(false);
+            return bitArray;
+        }
+
+        public void Free(BitArray bitArray)
+        {
+            bitArrays.Push(bitArray);
+        }
+    }
+}
diff --git a/encompass-cs/Collections/ComponentStore.cs b/encompass-cs/Collections/ComponentStore.cs
index f5c3b31..88c4d12 100644
--- a/encompass-cs/Collections/ComponentStore.cs
+++ b/encompass-cs/Collections/ComponentStore.cs
@@ -81,7 +81,7 @@ namespace Encompass
             {
                 entry.Remove(entity);
             }
-            componentBitSet.DestroyEntity(entity);
+            componentBitSet.RemoveEntity(entity);
         }
 
         public bool Any<TComponent>() where TComponent : struct, IComponent
diff --git a/encompass-cs/ComponentBitSet.cs b/encompass-cs/ComponentBitSet.cs
index ea44dc4..38c0000 100644
--- a/encompass-cs/ComponentBitSet.cs
+++ b/encompass-cs/ComponentBitSet.cs
@@ -6,6 +6,7 @@ namespace Encompass
 {
     internal class ComponentBitSet
     {
+        BitArrayPool bitArrayPool = new BitArrayPool(32768); // todo: set entity cap
         Dictionary<Entity, BitArray> entities = new Dictionary<Entity, BitArray>();
         Dictionary<Type, int> typeToIndex = new Dictionary<Type, int>();
         BitArray queryArray;
@@ -26,13 +27,17 @@ namespace Encompass
 
         public void Clear()
         {
+            foreach (var kvp in entities)
+            {
+                bitArrayPool.Free(kvp.Value);
+            }
             entities.Clear();
         }
 
         public void AddEntity(Entity entity)
         {
-            var bitArray = new BitArray(typeToIndex.Count);
-            entities.Add(entity, bitArray); // this is gonna create garbage!! fuck!!
+            var bitArray = bitArrayPool.Obtain(typeToIndex.Count);
+            entities.Add(entity, bitArray);
         }
 
         public void Set<TComponent>(Entity entity) where TComponent : struct, IComponent
@@ -46,9 +51,13 @@ namespace Encompass
             entities[entity].Set(typeToIndex[typeof(TComponent)], false);
         }
 
-        public void DestroyEntity(Entity entity)
+        public void RemoveEntity(Entity entity)
         {
-            entities.Remove(entity);
+            if (entities.ContainsKey(entity))
+            {
+                bitArrayPool.Free(entities[entity]);
+                entities.Remove(entity);
+            }
         }
 
         public IEnumerable<Entity> EntitiesWithComponents(IEnumerable<Type> types)