From 6161b1a75105448731062fdae2544d598f58a450 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?J=C3=A9r=C3=B4me=20Leclercq?=
 <jerome.leclercq@fullcycle.games>
Date: Thu, 8 Feb 2018 15:15:56 +0100
Subject: [PATCH] Sdk/World: Use a Bitset to store free entity id

---
 ChangeLog.md              |  1 +
 SDK/include/NDK/World.hpp |  2 +-
 SDK/include/NDK/World.inl |  2 +-
 SDK/src/NDK/World.cpp     | 15 +++++++++------
 4 files changed, 12 insertions(+), 8 deletions(-)

diff --git a/ChangeLog.md b/ChangeLog.md
index 89ad63f04..4b5545f15 100644
--- a/ChangeLog.md
+++ b/ChangeLog.md
@@ -95,6 +95,7 @@ Nazara Development Kit:
 - Add ConstraintComponent2D class
 - Fix CollisionComponent3D initialization (teleportation to their real coordinates) which could sometimes mess up the physics scene.
 - ⚠️ Renamed World::Update() to World::Refresh() for more clarity and to differentiate it from World::Update(elapsedTime)
+- World entity ids are now reused from lowest to highest (they were previously reused in reverse order of death)
 
 # 0.4:
 
diff --git a/SDK/include/NDK/World.hpp b/SDK/include/NDK/World.hpp
index 694457412..1ee35979b 100644
--- a/SDK/include/NDK/World.hpp
+++ b/SDK/include/NDK/World.hpp
@@ -96,9 +96,9 @@ namespace Ndk
 			std::vector<EntityBlock> m_entities;
 			std::vector<EntityBlock*> m_entityBlocks;
 			std::vector<std::unique_ptr<EntityBlock>> m_waitingEntities;
-			std::vector<EntityId> m_freeIdList;
 			EntityList m_aliveEntities;
 			Nz::Bitset<Nz::UInt64> m_dirtyEntities;
+			Nz::Bitset<Nz::UInt64> m_freeEntityIds;
 			Nz::Bitset<Nz::UInt64> m_killedEntities;
 			bool m_orderedSystemsUpdated;
 	};
diff --git a/SDK/include/NDK/World.inl b/SDK/include/NDK/World.inl
index 4ddc2638f..87aee67d3 100644
--- a/SDK/include/NDK/World.inl
+++ b/SDK/include/NDK/World.inl
@@ -288,7 +288,7 @@ namespace Ndk
 		m_aliveEntities         = std::move(world.m_aliveEntities);
 		m_dirtyEntities         = std::move(world.m_dirtyEntities);
 		m_entityBlocks          = std::move(world.m_entityBlocks);
-		m_freeIdList            = std::move(world.m_freeIdList);
+		m_freeEntityIds         = std::move(world.m_freeEntityIds);
 		m_killedEntities        = std::move(world.m_killedEntities);
 		m_orderedSystems        = std::move(world.m_orderedSystems);
 		m_orderedSystemsUpdated = world.m_orderedSystemsUpdated;
diff --git a/SDK/src/NDK/World.cpp b/SDK/src/NDK/World.cpp
index dd99fee54..beb6a7d3b 100644
--- a/SDK/src/NDK/World.cpp
+++ b/SDK/src/NDK/World.cpp
@@ -61,11 +61,14 @@ namespace Ndk
 	{
 		EntityId id;
 		EntityBlock* entBlock;
-		if (!m_freeIdList.empty())
+
+		std::size_t freeEntityId = m_freeEntityIds.FindFirst();
+		if (freeEntityId != m_freeEntityIds.npos)
 		{
 			// We get an identifier
-			id = m_freeIdList.back();
-			m_freeIdList.pop_back();
+			m_freeEntityIds.Reset(freeEntityId); //< Remove id from free entity id
+
+			id = static_cast<EntityId>(freeEntityId);
 
 			entBlock = &m_entities[id];
 			entBlock->handle.Reset(&entBlock->entity); //< Reset handle (as it was reset when entity got destroyed)
@@ -81,7 +84,7 @@ namespace Ndk
 			{
 				NazaraAssert(m_waitingEntities.empty(), "There should be no waiting entities if space is available in main container");
 
-				m_entities.push_back(Entity(this, id)); //< We can't use emplace_back due to the scope
+				m_entities.emplace_back(Entity(this, id)); //< We can't make our vector create the entity due to the scope
 				entBlock = &m_entities.back();
 			}
 			else
@@ -124,11 +127,11 @@ namespace Ndk
 		m_entityBlocks.clear();
 
 		m_entities.clear();
-		m_freeIdList.clear();
 		m_waitingEntities.clear();
 
 		m_aliveEntities.Clear();
 		m_dirtyEntities.Clear();
+		m_freeEntityIds.Clear();
 		m_killedEntities.Clear();
 	}
 
@@ -207,7 +210,7 @@ namespace Ndk
 			entity->Destroy();
 
 			// Send back the identifier of the entity to the free queue
-			m_freeIdList.push_back(entity->GetId());
+			m_freeEntityIds.UnboundedSet(entity->GetId());
 		}
 		m_killedEntities.Reset();