Support entity removal & explicit traversal in util::ecs

libs/util/include/psemek/util/ecs.hpp

@@ -43,6 +43,12 @@ namespace psemek::util
 			virtual handle entity_count() const = 0;
 
 			virtual handle add_entity() = 0;
+			virtual void remove_entity(handle h) = 0;
+
+			bool entity_active(handle h)
+			{
+				return get_free_list()[h] == h;
+			}
 
 			template <typename Behavior>
 			void apply(Behavior & behavior)
@@ -52,6 +58,11 @@ namespace psemek::util
 
 			virtual ~species_base() {}
 
+			static constexpr handle null = static_cast<handle>(-1);
+
+			virtual handle const * get_free_list() = 0;
+			virtual std::size_t list_size() const = 0;
+
 		private:
 
 			template <typename Behavior, typename ... Components>
@@ -90,12 +101,16 @@ namespace psemek::util
 					((++ptrs), ...);
 				};
 
-				std::size_t const count = entity_count();
+				auto list = get_free_list();
+
+				std::size_t const count = list_size();
 
 				for (std::size_t i = 0; i < count; ++i)
 				{
-					std::apply(visit, cptrs);
+					if (*list == i)
+						std::apply(visit, cptrs);
 					std::apply(increment, cptrs);
+					++list;
 				}
 			}
 		};
@@ -129,20 +144,38 @@ namespace psemek::util
 
 			handle entity_count() const override
 			{
-				return std::get<0>(entity_components_).size();
+				return entity_count_;
 			}
 
 			handle add_entity() override
 			{
-				handle result = entity_count();
-				add_entity_impl(std::make_index_sequence<sizeof...(Components)>{});
-				return result;
+				return add_entity_impl(std::make_index_sequence<sizeof...(Components)>{});
+			}
+
+			void remove_entity(handle h) override
+			{
+				list_[h] = list_head_;
+				list_head_ = h;
+				--entity_count_;
+			}
+
+			handle const * get_free_list() override
+			{
+				return list_.data();
+			}
+
+			std::size_t list_size() const override
+			{
+				return list_.size();
 			}
 
 		private:
 			std::string name_;
 			std::tuple<Components...> species_components_;
 			std::tuple<std::vector<typename Components::data>...> entity_components_;
+			std::vector<handle> list_;
+			handle list_head_ = null;
+			std::size_t entity_count_ = 0;
 
 			template <std::size_t ... I>
 			void * get_species_component_impl(std::type_index component_type, std::index_sequence<I...>)
@@ -163,46 +196,30 @@ namespace psemek::util
 			}
 
 			template <std::size_t ... I>
-			void add_entity_impl(std::index_sequence<I...>)
+			handle add_entity_impl(std::index_sequence<I...>)
 			{
-				((std::get<I>(entity_components_).emplace_back()), ...);
+				if (list_head_ == null)
+				{
+					std::size_t const old_size = list_.size();
+					std::size_t const new_size = std::max<std::size_t>(16, old_size * 2);
+
+					list_.resize(new_size);
+					for (std::size_t i = old_size; i + 1 < new_size; ++i)
+						list_[i] = i + 1;
+					list_[new_size - 1] = null;
+					list_head_ = old_size;
+
+					((std::get<I>(entity_components_).resize(new_size)), ...);
+				}
+
+				auto result = list_head_;
+				list_head_ = list_[list_head_];
+				list_[result] = result;
+				entity_count_++;
+				return result;
 			}
 		};
 
-		template <>
-		struct species_impl<>
-			: species_base
-		{
-			species_impl(std::string name)
-				: name_(std::move(name))
-			{}
-
-			std::string_view name() const override
-			{
-				return name_;
-			}
-
-			using species_base::get_species_component;
-			using species_base::get_entity_component;
-
-			void * get_species_component(std::type_index) override { return nullptr; }
-			void * get_entity_component(std::type_index) override { return nullptr; }
-
-			virtual handle entity_count() const
-			{
-				return entity_count_;
-			}
-
-			virtual handle add_entity()
-			{
-				return entity_count_++;
-			}
-
-		private:
-			std::string name_;
-			std::size_t entity_count_ = 0;
-		};
-
 		template <typename Behavior>
 		using prepare_helper = decltype(std::declval<Behavior>().prepare());
 
@@ -227,6 +244,10 @@ namespace psemek::util
 
 		handle add_entity(handle species);
 		handle entity_count(handle species) const;
+		void remove_entity(handle species, handle entity);
+		bool entity_active(handle species, handle entity);
+
+		handle capacity(handle species) const { return species_[species]->list_size(); }
 
 		template <typename Component>
 		Component & get(handle species);
@@ -265,6 +286,16 @@ namespace psemek::util
 		return species_[species]->entity_count();
 	}
 
+	inline void ecs::remove_entity(handle species, handle entity)
+	{
+		species_[species]->remove_entity(entity);
+	}
+
+	inline bool ecs::entity_active(handle species, handle entity)
+	{
+		return species_[species]->entity_active(entity);
+	}
+
 	template <typename Component>
 	Component & ecs::get(handle species)
 	{