6 files changed, 112 insertions, 1 deletions

diff --git a/CMakeLists.txt b/CMakeLists.txt
index 011126f..e90552d 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -14,6 +14,8 @@ set(CMAKE_CXX_FLAGS_RELEASE "-O3 -s DNDEBUG")
 set(PKE_SOURCE_FILES
 	src/main.cpp
 	src/macros.hpp
+	src/ecs.hpp
+	src/ecs.cpp
 	src/game.hpp
 	src/game.cpp
 	src/memory.hpp
diff --git a/src/ecs.cpp b/src/ecs.cpp
new file mode 100644
index 0000000..2c0a26f
--- /dev/null
+++ b/src/ecs.cpp
@@ -0,0 +1,71 @@
+
+#include "ecs.hpp"
+
+TypeSafeInt_B(EntityHandle);
+const uint64_t bucketItemCount = 256;
+
+struct EntityBucket{
+	Entity entities[bucketItemCount];
+};
+
+uint64_t entityBucketIncrementer = 2;
+EntityHandle_T entityBucketCounter{0};
+EntityHandle_T entityCounter{0};
+EntityBucket *entityBuckets = nullptr;
+DynArray<EntityHandle> entitiesMarkedForRemoval{16};
+DynArray<EntityHandle> EntitiesToBeRemoved{16};
+
+void ECS_Init() {
+	entityBuckets = pke::PkeNew<EntityBucket>(entityBucketIncrementer);
+}
+
+EntityHandle ECS_CreateEntity_Inner(EntityHandle parentEntityHandle) {
+	EntityHandle_T entityHandle_T{Buckets_NewHandle<EntityBucket>(bucketItemCount, entityBucketIncrementer, entityBucketCounter, entityCounter, entityBuckets)};
+	EntityHandle entityHandle{entityHandle_T};
+
+	Entity *entity = &entityBuckets[Buckets_GetBucketIndex(entityHandle_T)].entities[Buckets_GetItemIndex(entityHandle_T)];
+
+	entity->handle = entityHandle;
+	entity->parentHandle = parentEntityHandle;
+
+	return entityHandle;
+}
+
+EntityHandle ECS_CreateEntity(EntityHandle parentEntityHandle) {
+	return ECS_CreateEntity_Inner(parentEntityHandle);
+}
+
+void ECS_MarkForRemoval(EntityHandle entityHandle) {
+	auto b = Buckets_GetBucketIndex(static_cast<EntityHandle_T>(entityHandle));
+	auto e = Buckets_GetItemIndex(static_cast<EntityHandle_T>(entityHandle));
+	const Entity *ent = &entityBuckets[b].entities[e];
+	assert(ent->isMarkedForRemoval == false && "Entity already marked for removal");
+	entitiesMarkedForRemoval.Push(entityHandle);
+}
+
+void ECS_Tick(double delta) {
+	EntitiesToBeRemoved.Resize(0);
+	for (long b = 0; b <= entityBucketCounter; ++b) {
+		uint64_t entCount = b == entityBucketCounter ? entityCounter >> 32 : bucketItemCount;
+		for (long e  = 0; e < entCount; ++e) {
+			Entity *ent = &entityBuckets[b].entities[e];
+			if (ent->handle == EntityHandle{EntityHandle_T{0xFFFFFFFFFFFFFFFF}}) continue;
+			if (ent->isMarkedForRemoval) {
+				ent->handle = EntityHandle{EntityHandle_T{0xFFFFFFFFFFFFFFFF}};
+				ent->parentHandle = EntityHandle{EntityHandle_T{0xFFFFFFFFFFFFFFFF}};
+				ent->isMarkedForRemoval = false;
+			} else {
+				if (entitiesMarkedForRemoval.Has(ent->handle)) {
+					ent->isMarkedForRemoval = true;
+					EntitiesToBeRemoved.Push(ent->handle);
+					continue;
+				}
+				if (EntitiesToBeRemoved.Has(ent->parentHandle)) {
+					ent->isMarkedForRemoval = true;
+					EntitiesToBeRemoved.Push(ent->handle);
+				}
+			}
+		}
+	}	
+	entitiesMarkedForRemoval.Resize(0);
+}
diff --git a/src/ecs.hpp b/src/ecs.hpp
new file mode 100644
index 0000000..d37ff57
--- /dev/null
+++ b/src/ecs.hpp
@@ -0,0 +1,25 @@
+#ifndef PKE_ECS_HPP
+#define PKE_ECS_HPP
+
+#include "dynamic-array.hpp"
+#include "macros.hpp"
+#include "memory.hpp"
+
+#include "glm/vec3.hpp"
+
+TypeSafeInt_H(EntityHandle, uint64_t, UINT64_MAX);
+
+extern DynArray<EntityHandle> EntitiesToBeRemoved;
+
+struct Entity {
+	EntityHandle handle = EntityHandle{EntityHandle_T{0xFFFFFFFFFFFFFFFF}};
+	EntityHandle parentHandle = EntityHandle{EntityHandle_T{0xFFFFFFFFFFFFFFFF}};
+	bool isMarkedForRemoval = false;
+};
+
+void ECS_Init();
+void ECS_Tick(double delta);
+EntityHandle ECS_CreateEntity(EntityHandle parentEntityHandle = EntityHandle{EntityHandle_T{0xFFFFFFFFFFFFFFFF}});
+void ECS_MarkForRemoval(EntityHandle entityHandle);
+
+#endif /* PKE_ECS_HPP */
diff --git a/src/game.cpp b/src/game.cpp
index 3cf2109..cfb6d7c 100644
--- a/src/game.cpp
+++ b/src/game.cpp
@@ -3,3 +3,10 @@
 
 GameSettings pkeSettings{};
 
+void GameTick(double delta) {
+	/*
+	 * ECS_Tick() gets called first because it updates the public
+	 *  `EntitiesToBeRemoved` for all other ticks to use.
+	 */
+	ECS_Tick(delta);
+}
diff --git a/src/game.hpp b/src/game.hpp
index 4ab021b..fad551b 100644
--- a/src/game.hpp
+++ b/src/game.hpp
@@ -4,6 +4,8 @@
 #include <chrono>
 #include <cstdint>
 
+#include "ecs.hpp"
+
 using GameTimeDuration = std::chrono::duration<int64_t, std::nano>;
 using GameTimePoint = std::chrono::steady_clock::time_point;
 #define NANO_DENOM std::chrono::nanoseconds::period::den
@@ -21,4 +23,6 @@ struct GameSettings {
 
 extern GameSettings pkeSettings;
 
+void GameTick(double delta);
+
 #endif /* PKE_GAME_HPP */
diff --git a/src/main.cpp b/src/main.cpp
index 026ddb8..b5a0697 100644
--- a/src/main.cpp
+++ b/src/main.cpp
@@ -7,6 +7,7 @@
 #include <csignal>
 
 #include "asset-manager.hpp"
+#include "ecs.hpp"
 #include "game.hpp"
 #include "window.hpp"
 
@@ -18,7 +19,7 @@ void signal_handler(int signal_num) {
 PKEWindowProperties windowProps{};
 
 void Tick(double delta) {
-	/* no-op */
+	GameTick(delta);
 }
 
 int main() { 
@@ -27,6 +28,7 @@ int main() {
 	printf("PKE ENTERING\n");
 	try {
 		AssetManagerInit();
+		ECS_Init();
 		CreateWindow(&windowProps);
 
 		auto steadyClock = std::chrono::steady_clock();