feat(ecs): new (simple) implementation without entt

modules/ecs/private/entity.cpp

@@ -1,10 +0,0 @@
-#include <ecs/entity.hpp>
-#include <ecs/scene.hpp>
-
-namespace lt {
-
-Entity::Entity(entt::entity handle, Scene *scene): m_handle(handle), m_scene(scene)
-{
-}
-
-} // namespace lt

modules/ecs/private/registry.test.cpp

@@ -0,0 +1,349 @@
+#include <ecs/registry.hpp>
+#include <ranges>
+#include <test/expects.hpp>
+#include <test/test.hpp>
+
+using lt::test::Case;
+using lt::test::expect_unreachable;
+using lt::test::Suite;
+
+using lt::test::expect_eq;
+using lt::test::expect_ne;
+using lt::test::expect_throw;
+
+using lt::test::expect_false;
+using lt::test::expect_true;
+
+using lt::ecs::Entity;
+using lt::ecs::Registry;
+
+struct Component
+{
+	int m_int;
+	std::string m_string;
+
+	[[nodiscard]] friend auto operator==(const Component &lhs, const Component &rhs) -> bool
+	{
+		return lhs.m_int == rhs.m_int && lhs.m_string == rhs.m_string;
+	}
+};
+template<>
+struct std::formatter<Component>
+{
+	constexpr auto parse(std::format_parse_context &context)
+	{
+		return context.begin();
+	}
+
+	auto format(const Component &val, std::format_context &context) const
+	{
+		return std::format_to(context.out(), "{}, {}", val.m_int, val.m_string);
+	}
+};
+
+struct Component_B
+{
+	float m_float;
+
+	[[nodiscard]] friend auto operator==(const Component_B lhs, const Component_B &rhs) -> bool
+	{
+		return lhs.m_float == rhs.m_float;
+	}
+};
+template<>
+struct std::formatter<Component_B>
+{
+	constexpr auto parse(std::format_parse_context &context)
+	{
+		return context.begin();
+	}
+
+	auto format(const Component_B &val, std::format_context &context) const
+	{
+		return std::format_to(context.out(), "{}", val.m_float);
+	}
+};
+
+Suite raii = [] {
+	Case { "happy path won't throw" } = [] {
+		std::ignore = Registry {};
+	};
+
+	Case { "many won't throw" } = [] {
+		for (auto idx : std::views::iota(0, 100'000))
+		{
+			std::ignore = Registry {};
+		}
+	};
+
+	Case { "unhappy path throws" } = [] {
+	};
+
+	Case { "post construct has correct state" } = [] {
+		auto registry = Registry {};
+		expect_eq(registry.get_entity_count(), 0);
+	};
+};
+
+Suite entity_raii = [] {
+	Case { "create_entity returns unique values" } = [] {
+		auto registry = Registry {};
+		auto set = std::unordered_set<Entity> {};
+
+		for (auto idx : std::views::iota(0, 10'000))
+		{
+			auto entity = registry.create_entity();
+			expect_false(set.contains(entity));
+
+			set.insert(entity);
+			expect_eq(set.size(), idx + 1);
+		}
+	};
+
+	Case { "post create/destroy_entity has correct state" } = [] {
+		auto registry = Registry {};
+
+		auto entities = std::vector<Entity> {};
+		for (auto idx : std::views::iota(0, 10'000))
+		{
+			entities.emplace_back(registry.create_entity());
+			expect_eq(registry.get_entity_count(), idx + 1);
+		}
+
+		for (auto idx : std::views::iota(0, 10'000))
+		{
+			auto entity = entities.back();
+			registry.destroy_entity(entity);
+
+			entities.pop_back();
+			expect_eq(registry.get_entity_count(), 10'000 - (idx + 1));
+		}
+	};
+};
+
+Suite component_raii = [] {
+	Case { "add has correct state" } = [] {
+		auto registry = Registry {};
+		for (auto idx : std::views::iota(0, 100'000))
+		{
+			auto entity = registry.create_entity();
+			auto &component = registry.add<Component>(
+			    entity,
+			    { .m_int = idx, .m_string = std::to_string(idx) }
+			);
+
+			expect_eq(component.m_int, idx);
+			expect_eq(component.m_string, std::to_string(idx));
+		}
+	};
+
+	Case { "remove has correct state" } = [] {
+		auto registry = Registry {};
+		for (auto idx : std::views::iota(0, 100'000))
+		{
+			auto entity = registry.create_entity();
+			auto &component = registry.add<Component>(
+			    entity,
+			    { .m_int = idx, .m_string = std::to_string(idx) }
+			);
+
+			expect_eq(component.m_int, idx);
+			expect_eq(component.m_string, std::to_string(idx));
+		}
+	};
+};
+
+Suite callbacks = [] {
+	Case { "connecting on_construct/on_destruct won't throw" } = [] {
+		auto registry = Registry {};
+		registry.connect_on_construct<Component>([&](Registry &, Entity) {});
+		registry.connect_on_destruct<Component>([&](Registry &, Entity) {});
+	};
+
+	Case { "on_construct/on_destruct won't get called on unrelated component" } = [] {
+		auto registry = Registry {};
+		registry.connect_on_construct<Component>([&](Registry &, Entity) { expect_unreachable(); });
+		registry.connect_on_destruct<Component>([&](Registry &, Entity) { expect_unreachable(); });
+
+		for (auto idx : std::views::iota(0, 100'000))
+		{
+			registry.add<Component_B>(registry.create_entity(), {});
+		}
+	};
+
+	Case { "on_construct/on_destruct gets called" } = [] {
+		auto registry = Registry {};
+		auto all_entities = std::vector<Entity> {};
+		auto on_construct_called = std::vector<Entity> {};
+		auto on_destruct_called = std::vector<Entity> {};
+
+		registry.connect_on_construct<Component>([&](Registry &, Entity entity) {
+			on_construct_called.emplace_back(entity);
+		});
+		registry.connect_on_destruct<Component>([&](Registry &, Entity entity) {
+			on_destruct_called.emplace_back(entity);
+		});
+
+		expect_true(on_construct_called.empty());
+		expect_true(on_destruct_called.empty());
+		for (auto idx : std::views::iota(0, 100'000))
+		{
+			auto entity = all_entities.emplace_back(registry.create_entity());
+			registry.add<Component>(entity, {});
+		}
+		expect_eq(on_construct_called, all_entities);
+		expect_true(on_destruct_called.empty());
+
+		for (auto &entity : all_entities)
+		{
+			registry.remove<Component>(entity);
+		}
+		expect_eq(on_construct_called, all_entities);
+		expect_eq(on_destruct_called, all_entities);
+	};
+};
+
+Suite each = [] {
+	auto registry = Registry {};
+
+	auto shared_entity_counter = 0u;
+
+	auto component_map_a = std::unordered_map<Entity, Component> {};
+	auto entities_a = std::vector<Entity> {};
+
+	for (auto idx : std::views::iota(0, 10'000))
+	{
+		auto entity = entities_a.emplace_back(registry.create_entity());
+		auto &component = registry.add<Component>(
+		    entity,
+		    { .m_int = idx, .m_string = std::to_string(idx) }
+		);
+
+		component_map_a[entity] = component;
+	}
+
+	auto component_map_b = std::unordered_map<lt::ecs::Entity, Component_B> {};
+	for (auto idx : std::views::iota(0, 10'000))
+	{
+		auto entity = Entity {};
+		if (idx % 3 == 0)
+		{
+			entity = entities_a[idx];
+			++shared_entity_counter;
+		}
+		else
+		{
+			entity = registry.create_entity();
+		}
+		auto &component = registry.add<Component_B>(
+		    entity,
+		    { .m_float = static_cast<float>(idx) / 2.0f }
+		);
+
+		component_map_b[entity] = component;
+	}
+
+	Case { "each one element" } = [&] {
+		auto counter = 0u;
+		registry.each<Component>([&](Entity entity, Component &component) {
+			++counter;
+			expect_eq(component_map_a[entity], component);
+		});
+
+		expect_eq(component_map_a.size(), counter);
+
+		counter = 0u;
+		registry.each<Component_B>([&](Entity entity, Component_B &component) {
+			++counter;
+			expect_eq(component_map_b[entity], component);
+		});
+		expect_eq(component_map_b.size(), counter);
+	};
+
+	Case { "each two element" } = [&] {
+		auto counter = 0u;
+		registry.each<Component, Component_B>(
+		    [&](Entity entity, Component &component_a, Component_B &component_b) {
+			    expect_eq(component_map_a[entity], component_a);
+			    expect_eq(component_map_b[entity], component_b);
+			    ++counter;
+		    }
+		);
+
+		expect_eq(counter, shared_entity_counter);
+	};
+};
+
+Suite views = [] {
+	auto registry = Registry {};
+
+	auto shared_entity_counter = 0u;
+
+	auto component_map_a = std::unordered_map<Entity, Component> {};
+	auto entities_a = std::vector<Entity> {};
+
+	for (auto idx : std::views::iota(0, 10'000))
+	{
+		auto entity = entities_a.emplace_back(registry.create_entity());
+		auto &component = registry.add<Component>(
+		    entity,
+		    { .m_int = idx, .m_string = std::to_string(idx) }
+		);
+
+		component_map_a[entity] = component;
+	}
+
+	auto component_map_b = std::unordered_map<Entity, Component_B> {};
+	for (auto idx : std::views::iota(0, 10'000))
+	{
+		auto entity = Entity {};
+		if (idx % 3 == 0)
+		{
+			entity = entities_a[idx];
+			++shared_entity_counter;
+		}
+		else
+		{
+			entity = registry.create_entity();
+		}
+		auto &component = registry.add<Component_B>(
+		    entity,
+		    { .m_float = static_cast<float>(idx) / 2.0f }
+		);
+
+		component_map_b[entity] = component;
+	}
+
+
+	Case { "view one component" } = [&] {
+		for (const auto &[entity, component] : registry.view<Component>())
+		{
+			expect_eq(component_map_a[entity], component);
+		}
+
+		for (const auto &[entity, component] : registry.view<Component_B>())
+		{
+			expect_eq(component_map_b[entity], component);
+		}
+	};
+
+	Case { "view two component" } = [&] {
+		auto counter = 0u;
+		for (const auto &[entity, component, component_b] : registry.view<Component, Component_B>())
+		{
+			expect_eq(component_map_a[entity], component);
+			expect_eq(component_map_b[entity], component_b);
+			++counter;
+		}
+		expect_eq(counter, shared_entity_counter);
+
+		counter = 0u;
+		for (const auto &[entity, component_b, component] : registry.view<Component_B, Component>())
+		{
+			expect_eq(component_map_b[entity], component_b);
+			expect_eq(component_map_a[entity], component);
+			++counter;
+		}
+		expect_eq(counter, shared_entity_counter);
+	};
+};

modules/ecs/private/scene.cpp

@@ -1,31 +0,0 @@
-#include <ecs/components.hpp>
-#include <ecs/entity.hpp>
-#include <ecs/scene.hpp>
-
-namespace lt {
-
-auto Scene::create_entity(const std::string &name, const TransformComponent &transform) -> Entity
-{
-	return create_entity_with_uuid(name, UUID(), transform);
-}
-
-auto Scene::get_entity_by_tag(const std::string &tag) -> Entity
-{
-	return {};
-}
-
-auto Scene::create_entity_with_uuid(
-    const std::string &name,
-    UUID uuid,
-    const TransformComponent &transform
-) -> Entity
-{
-	auto entity = Entity { m_registry.create(), this };
-	entity.add_component<TagComponent>(name);
-	entity.add_component<TransformComponent>(transform);
-	entity.add_component<UUIDComponent>(uuid);
-
-	return entity;
-}
-
-} // namespace lt

modules/ecs/private/sparse_set.test.cpp

@@ -0,0 +1,138 @@
+#include <ecs/sparse_set.hpp>
+#include <ranges>
+#include <test/expects.hpp>
+#include <test/test.hpp>
+
+using lt::test::Case;
+using lt::test::Suite;
+
+using lt::test::expect_eq;
+using lt::test::expect_false;
+using lt::test::expect_ne;
+using lt::test::expect_throw;
+using lt::test::expect_true;
+
+using Set = lt::ecs::SparseSet<int>;
+constexpr auto capacity = 100;
+
+Suite raii = [] {
+	Case { "happy path won't throw" } = [] {
+		std::ignore = Set {};
+		std::ignore = Set { Set::max_capacity };
+	};
+
+	Case { "unhappy path throws" } = [] {
+		expect_throw([] { std::ignore = Set { Set::max_capacity + 1 }; });
+	};
+
+	Case { "post construct has correct state" } = [&] {
+		auto set = Set { capacity };
+		expect_eq(set.get_size(), 0);
+		expect_eq(set.get_capacity(), capacity);
+	};
+};
+
+Suite element_raii = [] {
+	Case { "many inserts/removes won't throw" } = [] {
+		auto set = Set {};
+		for (auto idx : std::views::iota(0, 10'000))
+		{
+			set.insert(idx, {});
+		}
+
+		for (auto idx : std::views::iota(0, 10'000))
+		{
+			set.remove(idx);
+		}
+	};
+
+	Case { "insert returns reference to inserted value" } = [] {
+		auto set = Set {};
+		for (auto idx : std::views::iota(0, 10'000))
+		{
+			const auto val = Set::Dense_T { idx, {} };
+			expect_eq(set.insert(val.first, val.second), val);
+		}
+	};
+
+	Case { "post insert/remove has correct state" } = [] {
+		auto set = Set {};
+		for (auto idx : std::views::iota(0, 10'000))
+		{
+			set.insert(idx, idx * 2);
+			expect_eq(set.get_size(), idx + 1);
+			expect_eq(set.at(idx), Set::Dense_T { idx, idx * 2 });
+			expect_true(set.contains(idx));
+		}
+
+		for (auto idx : std::views::iota(0, 10'000))
+		{
+			expect_eq(set.at(idx), Set::Dense_T { idx, idx * 2 });
+			expect_true(set.contains(idx));
+		}
+
+		for (auto idx : std::views::iota(0, 10'000))
+		{
+			set.remove(idx);
+
+			expect_eq(set.get_size(), 10'000 - (idx + 1));
+			expect_throw([&] { std::ignore = set.at(idx); });
+			expect_false(set.contains(idx));
+		}
+	};
+};
+
+Suite getters = [] {
+	Case { "get_size returns correct values" } = [] {
+		auto set = Set {};
+		for (auto idx : std::views::iota(0, 10'000))
+		{
+			expect_eq(set.get_size(), idx);
+			set.insert(idx, {});
+		}
+
+		expect_eq(set.get_size(), 10'000);
+	};
+
+	Case { "get_capacity returns correct values" } = [] {
+		auto set = Set { 10'000 };
+		for (auto idx : std::views::iota(0, 10'000))
+		{
+			expect_eq(set.get_capacity(), 10'000); // are we testing std::vector's implementation?
+			set.insert(idx, {});
+		}
+
+		expect_eq(set.get_capacity(), 10'000);
+
+		set.insert(set.get_size(), {});
+		expect_ne(set.get_capacity(), 10'000);
+	};
+
+	Case { "at throws with out of bound access" } = [] {
+		auto set = Set {};
+
+		for (auto idx : std::views::iota(0, 50))
+		{
+			expect_throw([&] {
+				set.insert(idx, {});
+				std::ignore = set.at(50);
+			});
+		}
+
+		set.insert(50, {});
+		std::ignore = set.at(50); // should not throw
+	};
+};
+
+Suite clear = [] {
+	Case { "post clear has correct state" } = [] {
+		auto set = Set { 0 };
+		for (auto idx : std::views::iota(0, 10'000))
+		{
+			set.insert(idx, {});
+		}
+
+		set.clear();
+		expect_eq(set.get_size(), 0);
+	};
+};

modules/ecs/private/uuid.cpp

@@ -1,14 +0,0 @@
-#include <ecs/uuid.hpp>
-
-namespace lt {
-
-std::mt19937_64 UUID::s_engine = std::mt19937_64(std::random_device()());
-
-std::uniform_int_distribution<uint64_t>
-    UUID::s_distribution = std::uniform_int_distribution<uint64_t> {};
-
-UUID::UUID(uint64_t uuid /* = -1 */): m_uuid(uuid == -1 ? s_distribution(s_engine) : uuid)
-{
-}
-
-} // namespace lt

modules/ecs/public/components.hpp

@@ -1,6 +0,0 @@
-#pragma once
-
-#include <ecs/components/native_script.hpp>
-#include <ecs/components/sprite_renderer.hpp>
-#include <ecs/components/tag.hpp>
-#include <ecs/components/transform.hpp>

modules/ecs/public/components/native_script.hpp

@@ -1,28 +0,0 @@
-#pragma once
-
-#include <ecs/components/scriptable_entity.hpp>
-
-namespace lt {
-
-struct NativeScriptComponent
-{
-	NativeScript *(*CreateInstance)();
-
-	void (*DestroyInstance)(NativeScriptComponent *);
-
-	template<typename t>
-	void bind()
-	{
-		CreateInstance = []() {
-			return static_cast<NativeScript *>(new t());
-		};
-		DestroyInstance = [](NativeScriptComponent *nsc) {
-			delete (t *)(nsc->instance);
-			nsc->instance = nullptr;
-		};
-	}
-
-	NativeScript *instance;
-};
-
-} // namespace lt

modules/ecs/public/components/scriptable_entity.hpp

@@ -1,46 +0,0 @@
-#pragma once
-
-#include <ecs/entity.hpp>
-
-namespace lt {
-
-class NativeScript
-{
-public:
-	friend class Scene;
-
-	NativeScript() = default;
-
-	virtual ~NativeScript() = default;
-
-	[[nodiscard]] auto get_uid() const -> unsigned int
-	{
-		return m_unique_identifier;
-	}
-
-	template<typename t>
-	auto GetComponent() -> t &
-	{
-		return m_entity.get_component<t>();
-	}
-
-protected:
-	virtual void on_create()
-	{
-	}
-
-	virtual void on_destroy()
-	{
-	}
-
-	virtual void on_update(float ts)
-	{
-	}
-
-private:
-	Entity m_entity;
-
-	unsigned int m_unique_identifier = 0; // :#todo
-};
-
-} // namespace lt

modules/ecs/public/components/sprite_renderer.hpp

@@ -1,35 +0,0 @@
-#pragma once
-
-#include <math/vec4.hpp>
-#include <utility>
-
-namespace lt {
-
-class Texture;
-
-struct SpriteRendererComponent
-{
-	SpriteRendererComponent() = default;
-
-	SpriteRendererComponent(const SpriteRendererComponent &) = default;
-
-	SpriteRendererComponent(
-	    Ref<Texture> _texture,
-	    const math::vec4 &_tint = math::vec4 { 1.0f, 1.0f, 1.0f, 1.0f }
-	)
-	    : texture(std::move(std::move(_texture)))
-	    , tint(_tint)
-	{
-	}
-
-	operator Ref<Texture>() const
-	{
-		return texture;
-	}
-
-	Ref<Texture> texture;
-
-	math::vec4 tint {};
-};
-
-} // namespace lt

modules/ecs/public/components/tag.hpp

@@ -1,30 +0,0 @@
-#pragma once
-
-#include <utility>
-
-namespace lt {
-
-struct TagComponent
-{
-	TagComponent() = default;
-
-	TagComponent(const TagComponent &) = default;
-
-	TagComponent(std::string _tag): tag(std::move(_tag))
-	{
-	}
-
-	operator std::string() const
-	{
-		return tag;
-	}
-
-	operator const std::string &() const
-	{
-		return tag;
-	}
-
-	std::string tag = "Unnamed";
-};
-
-} // namespace lt

modules/ecs/public/components/transform.hpp

@@ -1,43 +0,0 @@
-#pragma once
-
-#include <math/mat4.hpp>
-#include <math/vec3.hpp>
-
-namespace lt {
-
-struct TransformComponent
-{
-	TransformComponent(const TransformComponent &) = default;
-
-	TransformComponent(
-	    const math::vec3 &_translation = math::vec3(0.0f, 0.0f, 0.0f),
-	    const math::vec3 &_scale = math::vec3(1.0f, 1.0f, 1.0f),
-	    const math::vec3 &_rotation = math::vec3(0.0f, 0.0f, 0.0f)
-	)
-
-	    : translation(_translation)
-	    , scale(_scale)
-	    , rotation(_rotation)
-	{
-	}
-
-	[[nodiscard]] auto get_transform() const -> math::mat4
-	{
-		return math::translate(translation)
-		       * math::rotate(rotation.z, math::vec3 { 0.0f, 0.0f, 1.0f }) //
-		       * math::scale(scale);
-	}
-
-	operator const math::mat4() const
-	{
-		return get_transform();
-	}
-
-	math::vec3 translation;
-
-	math::vec3 scale;
-
-	math::vec3 rotation;
-};
-
-} // namespace lt

modules/ecs/public/components/uuid.hpp

@@ -1,18 +0,0 @@
-#pragma once
-
-#include <ecs/uuid.hpp>
-
-namespace lt {
-
-struct UUIDComponent
-{
-	UUIDComponent(UUID _uuid): uuid(_uuid)
-	{
-	}
-
-	UUIDComponent(const UUIDComponent &) = default;
-
-	UUID uuid;
-};
-
-} // namespace lt

modules/ecs/public/entity.hpp

@@ -1,59 +1,5 @@
 #pragma once
 
-#include <ecs/components/uuid.hpp>
-#include <ecs/scene.hpp>
-#include <entt/entt.hpp>
-
 namespace lt {
 
-class Entity
-{
-public:
-	Entity(entt::entity handle = entt::null, Scene *scene = nullptr);
-
-	template<typename t, typename... Args>
-	auto add_component(Args &&...args) -> t &
-	{
-		return m_scene->m_registry.emplace<t>(m_handle, std::forward<Args>(args)...);
-	}
-
-	template<typename t>
-	auto get_component() -> t &
-	{
-		return m_scene->m_registry.get<t>(m_handle);
-	}
-
-	template<typename t>
-	auto has_component() -> bool
-	{
-		return m_scene->m_registry.any_of<t>(m_handle);
-	}
-
-	template<typename t>
-	void remove_component()
-	{
-		m_scene->m_registry.remove<t>(m_handle);
-	}
-
-	auto get_uuid() -> uint64_t
-	{
-		return get_component<UUIDComponent>().uuid;
-	}
-
-	[[nodiscard]] auto is_valid() const -> bool
-	{
-		return m_handle != entt::null && m_scene != nullptr;
-	}
-
-	operator uint32_t()
-	{
-		return (uint32_t)m_handle;
-	}
-
-private:
-	entt::entity m_handle;
-
-	Scene *m_scene;
-};
-
 } // namespace lt

modules/ecs/public/registry.hpp

@@ -0,0 +1,243 @@
+#pragma once
+
+#include <ecs/sparse_set.hpp>
+
+namespace lt::ecs {
+
+using Entity = uint32_t;
+
+/** A registry of components, the heart of an ECS architecture.
+ *
+ * @todo(Light): optimize multi-component views
+ * @todo(Light): support more than 2-component views
+ * @todo(Light): handle edge cases or specify the undefined behaviors
+ */
+class Registry
+{
+public:
+	using UnderlyingSparseSet_T = TypeErasedSparseSet<Entity>;
+
+	using Callback_T = std::function<void(Registry &, Entity)>;
+
+	template<typename Component_T>
+	void connect_on_construct(Callback_T callback)
+	{
+		m_on_construct_hooks[get_type_id<Component_T>()] = callback;
+	}
+
+	template<typename Component_T>
+	void connect_on_destruct(Callback_T callback)
+	{
+		m_on_destruct_hooks[get_type_id<Component_T>()] = callback;
+	}
+
+	template<typename Component_T>
+	void disconnect_on_construct()
+	{
+		m_on_construct_hooks.erase(get_type_id<Component_T>());
+	}
+
+	template<typename Component_T>
+	void disconnect_on_destruct()
+	{
+		m_on_destruct_hooks.erase(get_type_id<Component_T>());
+	}
+
+	auto create_entity() -> Entity
+	{
+		++m_entity_count;
+		return m_current++;
+	}
+
+	void destroy_entity(Entity entity)
+	{
+		for (const auto &[key, set] : m_sparsed_sets)
+		{
+			set->remove(entity);
+		}
+
+		--m_entity_count;
+	}
+
+	template<typename Component_T>
+	auto get(Entity entity) -> Component_T &
+	{
+		auto &derived_set = get_derived_set<Component_T>();
+		return derived_set.at(entity).second;
+	}
+
+	template<typename Component_T>
+	auto add(Entity entity, Component_T component) -> Component_T &
+	{
+		auto &derived_set = get_derived_set<Component_T>();
+		auto &added_component = derived_set.insert(entity, std::move(component)).second;
+
+		if (m_on_construct_hooks.contains(get_type_id<Component_T>()))
+		{
+			m_on_construct_hooks[get_type_id<Component_T>()](*this, entity);
+		}
+
+		return added_component;
+	};
+
+	template<typename Component_T>
+	void remove(Entity entity)
+	{
+		if (m_on_destruct_hooks.contains(get_type_id<Component_T>()))
+		{
+			m_on_destruct_hooks[get_type_id<Component_T>()](*this, entity);
+		}
+
+		auto &derived_set = get_derived_set<Component_T>();
+		derived_set.remove(entity);
+	}
+
+	template<typename Component_T>
+	auto view() -> SparseSet<Component_T, Entity>&
+	{
+		return get_derived_set<Component_T>();
+	};
+
+	template<typename ComponentA_T, typename ComponentB_T>
+	    requires(!std::is_same_v<ComponentA_T, ComponentB_T>)
+	auto view() -> std::vector<std::tuple<Entity, ComponentA_T &, ComponentB_T &>>
+	{
+		auto &set_a = get_derived_set<ComponentA_T>();
+		auto &set_b = get_derived_set<ComponentB_T>();
+		auto view = std::vector<std::tuple<Entity, ComponentA_T &, ComponentB_T &>> {};
+
+		/* iterate over the "smaller" component-set, and check if its entities have the other
+		 * component */
+		if (set_a.get_size() > set_b.get_size())
+		{
+			for (auto &[entity, component_b] : set_b)
+			{
+				if (set_a.contains(entity))
+				{
+					view.emplace_back(std::tie(entity, set_a.at(entity).second, component_b));
+				}
+			}
+		}
+		else
+		{
+			for (auto &[entity, component_a] : set_a)
+			{
+				if (set_b.contains(entity))
+				{
+					view.emplace_back(std::tie(entity, component_a, set_b.at(entity).second));
+				}
+			}
+		}
+
+		return view;
+	};
+
+	template<typename Component_T>
+	void each(std::function<void(Entity, Component_T &)> functor)
+	{
+		for (auto &[entity, component] : get_derived_set<Component_T>())
+		{
+			functor(entity, component);
+		}
+	};
+
+	template<typename ComponentA_T, typename ComponentB_T>
+	    requires(!std::is_same_v<ComponentA_T, ComponentB_T>)
+	void each(std::function<void(Entity, ComponentA_T &, ComponentB_T &)> functor)
+	{
+		auto &set_a = get_derived_set<ComponentA_T>();
+		auto &set_b = get_derived_set<ComponentB_T>();
+
+		/* iterate over the "smaller" component-set, and check if its entities have the other
+		 * component */
+		if (set_a.get_size() > set_b.get_size())
+		{
+			for (auto &[entity, component_b] : set_b)
+			{
+				if (set_a.contains(entity))
+				{
+					functor(entity, set_a.at(entity).second, component_b);
+				}
+			}
+
+			return;
+		}
+
+		for (auto &[entity, component_a] : set_a)
+		{
+			if (set_b.contains(entity))
+			{
+				functor(entity, component_a, set_b.at(entity).second);
+			}
+		}
+	};
+
+	[[nodiscard]] auto get_entity_count() const -> size_t
+	{
+		return static_cast<size_t>(m_entity_count);
+	}
+
+private:
+	using TypeId = size_t;
+
+	static consteval auto hash_cstr(const char *str) -> TypeId
+	{
+		constexpr auto fnv_offset_basis = size_t { 14695981039346656037ull };
+		constexpr auto fnv_prime = size_t { 1099511628211ull };
+
+		auto hash = fnv_offset_basis;
+
+		for (const auto &ch : std::string_view { str })
+		{
+			hash *= fnv_prime;
+			hash ^= static_cast<uint8_t>(ch);
+		}
+
+		return hash;
+	}
+
+	template<typename T>
+	static consteval auto get_type_id() -> TypeId
+	{
+#if defined _MSC_VER
+	#define GENERATOR_PRETTY_FUNCTION __FUNCSIG__
+#elif defined __clang__ || (defined __GNUC__)
+	#define GENERATOR_PRETTY_FUNCTION __PRETTY_FUNCTION__
+#else
+	#error "Compiler not supported"
+#endif
+		constexpr auto value = hash_cstr(GENERATOR_PRETTY_FUNCTION);
+
+#undef GENERATOR_PRETTY_FUNCTION
+
+		return value;
+	}
+
+	template<typename T>
+	auto get_derived_set() -> SparseSet<T, Entity> &
+	{
+		constexpr auto type_id = get_type_id<T>();
+		if (!m_sparsed_sets.contains(type_id))
+		{
+			m_sparsed_sets[type_id] = create_scope<SparseSet<T, Entity>>();
+		}
+
+		auto *base_set = m_sparsed_sets[type_id].get();
+		auto *derived_set = dynamic_cast<SparseSet<T, Entity> *>(base_set);
+		ensure(derived_set, "Failed to downcast to derived set");
+
+		return *derived_set;
+	}
+
+	Entity m_current;
+
+	TypeId m_entity_count;
+
+	std::flat_map<TypeId, Scope<UnderlyingSparseSet_T>> m_sparsed_sets;
+
+	std::flat_map<TypeId, Callback_T> m_on_construct_hooks;
+
+	std::flat_map<TypeId, Callback_T> m_on_destruct_hooks;
+};
+
+} // namespace lt::ecs

modules/ecs/public/scene.hpp

@@ -1,65 +0,0 @@
-#pragma once
-
-#include <ecs/components/transform.hpp>
-#include <ecs/uuid.hpp>
-#include <entt/entt.hpp>
-#include <functional>
-
-namespace lt {
-
-class Entity;
-class Framebuffer;
-
-class Scene
-{
-public:
-	template<typename... T>
-	auto group()
-	{
-		return m_registry.group(entt::get<T...>);
-	}
-
-	template<typename T>
-	auto view()
-	{
-		return m_registry.view<T>();
-	}
-
-	auto create_entity(
-	    const std::string &name,
-	    const TransformComponent &transform = TransformComponent()
-	) -> Entity;
-
-	auto get_entity_by_tag(const std::string &tag) -> Entity;
-
-	auto get_entt_registry() -> entt::registry &
-	{
-		return m_registry;
-	}
-
-
-private:
-	friend class Entity;
-
-	friend class SceneSerializer;
-
-	friend class SceneHierarchyPanel;
-
-	entt::registry m_registry;
-
-	auto create_entity_with_uuid(
-	    const std::string &name,
-	    UUID uuid,
-	    const TransformComponent &transform = TransformComponent()
-	) -> Entity;
-};
-
-namespace ecs {
-
-using Registry = Scene;
-
-using Entity = ::lt::Entity;
-
-} // namespace ecs
-
-} // namespace lt

modules/ecs/public/sparse_set.hpp

@@ -0,0 +1,141 @@
+#pragma once
+
+namespace lt::ecs {
+
+/**
+ *
+ * @ref https://programmingpraxis.com/2012/03/09/sparse-sets/
+ */
+template<typename Identifier_T = uint32_t>
+class TypeErasedSparseSet
+{
+public:
+	TypeErasedSparseSet() = default;
+
+	TypeErasedSparseSet(TypeErasedSparseSet &&) = default;
+
+	TypeErasedSparseSet(const TypeErasedSparseSet &) = default;
+
+	auto operator=(TypeErasedSparseSet &&) -> TypeErasedSparseSet & = default;
+
+	auto operator=(const TypeErasedSparseSet &) -> TypeErasedSparseSet & = default;
+
+	virtual ~TypeErasedSparseSet() = default;
+
+	virtual void remove(Identifier_T identifier) = 0;
+};
+
+/**
+ *
+ * @todo(Light): implement identifier recycling.
+ */
+template<typename Value_T, typename Identifier_T = uint32_t>
+class SparseSet: public TypeErasedSparseSet<Identifier_T>
+{
+public:
+	using Dense_T = std::pair<Identifier_T, Value_T>;
+
+	static constexpr auto max_capacity = size_t { 1'000'000 };
+
+	static constexpr auto null_identifier = std::numeric_limits<Identifier_T>().max();
+
+	explicit SparseSet(size_t initial_capacity = 1)
+	{
+		ensure(
+		    initial_capacity <= max_capacity,
+		    "Failed to create SparseSet: capacity too large ({} > {})",
+		    initial_capacity,
+		    max_capacity
+		);
+
+		m_dense.reserve(initial_capacity);
+		m_sparse.resize(initial_capacity, null_identifier);
+	}
+
+	auto insert(Identifier_T identifier, Value_T value) -> Dense_T &
+	{
+		if (m_sparse.size() < identifier + 1)
+		{
+			auto new_capacity = std::max(static_cast<size_t>(identifier + 1), m_sparse.size() * 2);
+			new_capacity = std::min(new_capacity, max_capacity);
+
+			// log_dbg("Increasing sparse vector size:", m_dead_count);
+			// log_dbg("\tdead_count: {}", m_dead_count);
+			// log_dbg("\talive_count: {}", m_alive_count);
+			// log_dbg("\tsparse.size: {} -> {}", m_sparse.size(), new_capacity);
+
+			m_sparse.resize(new_capacity, null_identifier);
+		}
+
+		++m_alive_count;
+		m_sparse[identifier] = m_dense.size();
+		return m_dense.emplace_back(identifier, std::move(value));
+	}
+
+	void remove(Identifier_T identifier) override
+	{
+		auto &idx = m_sparse[identifier];
+		auto &[entity, component] = m_dense[idx];
+
+		idx = null_identifier;
+		++m_dead_count;
+		--m_alive_count;
+	}
+
+	void clear()
+	{
+		m_dense.clear();
+		m_sparse.clear();
+		m_alive_count = 0;
+	}
+
+	[[nodiscard]] auto contains(Identifier_T identifier) const -> bool
+	{
+		return m_sparse.size() > identifier               //
+		       && m_sparse[identifier] != null_identifier //
+		       && m_dense[m_sparse[identifier]].first == identifier;
+	}
+
+	auto begin() -> std::vector<Dense_T>::iterator
+	{
+		return m_dense.begin();
+	}
+
+	auto end() -> std::vector<Dense_T>::iterator
+	{
+		return m_dense.end();
+	}
+
+	[[nodiscard]] auto at(Identifier_T identifier) -> Dense_T &
+	{
+		return m_dense.at(m_sparse.at(identifier));
+	}
+
+	/** @warn unsafe, for bound-checked access: use `.at` */
+	[[nodiscard]] auto &&operator[](this auto &&self, Identifier_T identifier)
+	{
+		using Self_T = decltype(self);
+		return std::forward<Self_T>(self).m_dense[std::forward<Self_T>(self).m_sparse[identifier]];
+	}
+
+	[[nodiscard]] auto get_size() const noexcept -> size_t
+	{
+		return m_alive_count;
+	}
+
+	[[nodiscard]] auto get_capacity() const noexcept -> size_t
+	{
+		return m_sparse.capacity();
+	}
+
+private:
+	std::vector<Dense_T> m_dense;
+
+	std::vector<Identifier_T> m_sparse;
+
+	size_t m_alive_count {};
+
+	size_t m_dead_count {};
+};
+
+} // namespace lt::ecs

modules/ecs/public/uuid.hpp

@@ -1,38 +0,0 @@
-#pragma once
-
-#include <random>
-
-namespace lt {
-
-class UUID
-{
-public:
-	UUID(uint64_t uuid = -1);
-
-	operator uint64_t() const
-	{
-		return m_uuid;
-	}
-
-private:
-	static std::mt19937_64 s_engine;
-
-	static std::uniform_int_distribution<uint64_t> s_distribution;
-
-	uint64_t m_uuid;
-};
-
-} // namespace lt
-
-namespace std {
-
-template<>
-struct hash<lt::UUID>
-{
-	std::size_t operator()(const lt::UUID &uuid) const
-	{
-		return hash<uint64_t>()(static_cast<uint64_t>(uuid));
-	}
-};
-
-} // namespace std