OpenColloq WS24 ECS

OpenColloq/WS24_EntityComponentSystem/content/_index.md

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++++
+title = "Entity Component System - It's not a system"
+outputs = ["Reveal"]
++++
+
+# Entity Component System
+
+---
+
+## What is (an) ECS?
+- {{< frag c="unnecessary" >}}
+- {{< frag c="useful" >}}
+- {{< frag c="not a system" >}}
+
+{{% note %}}
+
+Talk about structure of presentation here:
+- define terms like "entity", "component", "system"
+- go over other approaches to "motivate" ECS
+- main 3 game engines will be mentioned (Unity, Unreal, Godot)
+- talking about the level of programming engines, not games
+
+{{% /note %}}
+
+---
+
+## What are entities?
+![lol](lol.jpg)[^1]
+
+[^1]: https://br.ign.com/league-of-legends-wild-rift/89123/feature/wild-rift-tudo-sobre-o-lol-mobile ; Image: Riot Games
+
+---
+
+## What are entities?
+![aoe](aoe.jpg)[^2]
+
+[^2]: https://pressakey.com/gameinfos,4981,screenshots,,,Age-of-Empires-Definitive-Edition,.html
+
+---
+
+## What are entities?
+- Objects in a game (or simulation)
+- Can have different behaviours
+- {{< frag c="Basically everything" >}}
+
+---
+
+# INHERITANCE
+
+---
+
+{{% section %}}
+
+{{< slide transition="none" >}}
+
+## Inheritance
+```mermaid
+graph TD;
+    Entity-->MoveableEntity;
+    Entity-->PhysicsEntity;
+```
+
+{{% note %}}
+
+Entity: Basic information like transform and mesh in our example
+MoveableEntity: Entity with functions to move with and support animations
+PhysicsEntity: Walls, Falling Boulders and stuff; Colliders and Gravity
+
+{{% /note %}}
+
+---
+
+{{< slide transition="none" >}}
+
+## Inheritance
+```mermaid
+graph TD;
+    Entity-->MoveableEntity;
+    Entity-->PhysicsEntity;
+    MoveableEntity-->Character;
+    PhysicsEntity-->BoxColliderEntity;
+```
+
+{{% note %}}
+
+Entity: Basic information like transform and mesh in our example
+MoveableEntity: Entity with functions to move with and support animations
+PhysicsEntity: Walls, Falling Boulders and stuff; Colliders and Gravity
+
+{{% /note %}}
+
+---
+
+{{< slide transition="none" >}}
+
+## Inheritance
+```mermaid
+graph TD;
+    Entity-->MoveableEntity;
+    Entity-->PhysicsEntity;
+    MoveableEntity-->Character;
+    Character-->Player;
+    Character-->NPC;
+    PhysicsEntity-->BoxColliderEntity;
+```
+
+{{% note %}}
+
+Entity: Basic information like transform and mesh in our example
+MoveableEntity: Entity with functions to move with and support animations
+PhysicsEntity: Walls, Falling Boulders and stuff; Colliders and Gravity
+
+{{% /note %}}
+
+{{% /section %}}
+
+---
+
+## Godot
+![GodotInheritance](./GodotInheritanceEditor.png)
+[^3]
+
+[^3]: Screenshot: Godot Engine
+
+---
+
+![](godot_news.png)
+
+---
+
+## Godot Code
+```cpp
+class Node2D : public CanvasItem {
+...
+}
+.
+.
+.
+class PhysicsBody2D : public CollisionObject2D {
+...
+}
+class CharacterBody2D : public PhysicsBody2D {
+...
+}
+```
+[^4]
+
+[^4]: https://github.com/godotengine/godot
+
+---
+
+{{% section %}}
+{{< slide transition="none" >}}
+
+## Inheritance
+```mermaid
+graph TD;
+    Entity-->MoveableEntity;
+    Entity-->PhysicsEntity;
+    MoveableEntity-->Character;
+    Character-->Player;
+    Character-->NPC;
+    PhysicsEntity-->BoxColliderEntity;
+    MoveableEntity-->Vehicle;
+```
+
+---
+
+{{< slide transition="none" >}}
+
+## Multiple Inheritance
+```mermaid
+graph TD;
+    Entity-->MoveableEntity;
+    Entity-->PhysicsEntity;
+    MoveableEntity-->Character;
+    Character-->Player;
+    Character-->NPC;
+    PhysicsEntity-->BoxColliderEntity;
+    MoveableEntity-->Vehicle;
+    BoxColliderEntity-->Vehicle;
+```
+
+{{% /section %}}
+
+---
+
+<section data-noprocess>
+<h1>Godot</h1>
+<div style="display: flex; flex-direction: row; justify-content: center; align-items: center;">
+  <img style="margin-right: 10%;" src="Godot_player_scene_nodes.webp">
+  <ul>
+    <li class="fragment" >uses hierarchy instead</li>
+    <li class="fragment" >child nodes as "components"</li>
+  </ul>
+</div>
+</section>
+
+---
+
+## What are components?
+- {{< frag c="Split entities from behaviour" >}}
+- {{< frag c="Data associated with a certain \"behaviour\"" >}}
+
+---
+
+# COMPOSITION
+
+---
+
+# Composition
+```mermaid
+graph LR;
+    EntityA-->BoxColliderComponent;
+    EntityA-->StaticMeshComponent;
+    EntityB-->SphereColliderComponent;
+    EntityB-->DynamicMeshComponent;
+    EntityB-->PlayerControllerComponent;
+linkStyle default stroke:lime,stroke-width:4px;
+```
+
+---
+
+## Composition
+- {{< frag c="Entities have minimal data and behaviour" >}}
+- {{< frag c="Entities hold their components or references to them" >}}
+
+{{% fragment %}}
+```cpp
+class Component;
+
+class Entity {
+//...
+private:
+    std::unordered_map<std::type_info, Component*> m_components;
+}
+```
+{{% /fragment %}}
+
+{{% note %}}
+
+Wanted to have a look at Unreal Source code, but...
+
+{{% /note %}}
+
+---
+
+![](gnupolice_unreal.png)
+
+---
+
+## Unreal
+
+Code in Unreal's AActor class[^5]:
+
+```cpp
+/**
+* All ActorComponents owned by this Actor. Stored as a Set as actors may have a large number of components
+* @see GetComponents()
+*/
+TSet<TObjectPtr<UActorComponent>> OwnedComponents;
+
+/**
+* Get all components derived from class 'ComponentType' and fill in the OutComponents array with the result.
+* It's recommended to use TArrays with a TInlineAllocator to potentially avoid memory allocation costs.
+* TInlineComponentArray is defined to make this easier, for example:
+* {
+*     TInlineComponentArray<UPrimitiveComponent*> PrimComponents(Actor);
+* }
+*
+* @param bIncludeFromChildActors   If true then recurse in to ChildActor components and find components of the appropriate type in those Actors as well
+*/
+template<class ComponentType, class AllocatorType>
+void GetComponents(TArray<ComponentType, AllocatorType>& OutComponents, bool bIncludeFromChildActors = false) const
+{
+    typedef TPointedToType<ComponentType> T;
+
+    OutComponents.Reset();
+    ForEachComponent_Internal<T>(T::StaticClass(), bIncludeFromChildActors, [&](T* InComp)
+    {
+        OutComponents.Add(InComp);
+    });
+}
+```
+
+[^5]: Engine/Source/Runtime/Engine/Classes/GameFramework/Actor.h
+
+{{% note %}}
+
+next, Unity, but...
+
+*b. Distributing Examples
+You may Distribute Examples (including as modified by you) in Source Code or object code to any third party.*
+
+{{% /note %}}
+
+---
+
+![](gnupolice_unity.png)
+
+---
+
+## Unity
+![](unity_inspector.jpg)[^6]
+
+[^6]:https://docs.unity3d.com/6000.0/Documentation/Manual/UsingTheInspector.html
+
+{{% note %}}
+
+- can't confirm what Unity uses (no source found)
+- interface suggests composition
+- Unity DOTS?
+
+{{% /note %}}
+
+---
+
+![](mario_ecs_castle.png)
+
+---
+
+## What are systems?
+- {{< frag c="███████████████████" >}}
+- {{< frag c="█████████████████" >}}
+- {{< frag c="████████████████████" >}}
+
+{{% note %}}
+We'll talk about it later.
+{{% /note %}}
+
+---
+
+# Entity Component System
+
+---
+
+![](dracula_ecs.png)
+
+{{% note %}}
+
+ECS is Data-Oriented rather than Object-Oriented
+
+{{% /note %}}
+
+---
+
+## Entity Component System
+- {{< frag c="split components even more from entities" >}}
+- {{< frag c="entities are minimal data" >}}
+- {{< frag c="components store data associated with certain behaviours" >}}
+- {{< frag c="components aren't managed by their entities" >}}
+
+{{% note %}}
+
+-
+- entities can just be ids
+- component manager
+
+
+{{% /note %}}
+
+---
+
+![](zerowing_component_manager.png)
+
+---
+
+## What are systems?
+- {{< frag c="main way of interacting with components" >}}
+- {{< frag c="loop over every component of a type" >}}
+- {{< frag c="e.g. Rendering System, Physics System..." >}}
+
+{{% note %}}
+
+- due to systems, want to optimise for iterating over components of a type
+
+{{% /note %}}
+
+---
+
+## Examples:
+
+- [Unity DOTS](https://unity.com/dots)
+- [Bevy](https://bevyengine.org/)
+- [EnTT](https://github.com/skypjack/entt)
+
+{{% fragment %}}
+
+> One thing known to most is that *EnTT* is also used in Minecraft.
+> Given that the game is available literally everywhere, I can confidently say that the library has been sufficiently tested on every platform that can come to mind.
+
+{{% /fragment %}}
+
+{{% note %}}
+
+Bevy ECS used for [Tiny Glade](https://store.steampowered.com/app/2198150/Tiny_Glade/)
+
+{{% /note %}}
+
+---
+
+## Cache
+
+CPU          |L1     |L2     |L3
+-------------|-------|-------|-----
+Pentium N4200|96 KiB |128 KiB|2 MiB
+i7 14700HX   |1800 KB|28 MB  |33 MB
+
+{{% note %}}
+
+top: silas' laptop
+bottom: mine
+
+Mine are probably also KiB/MiB, because Windows is doing Windows things
+
+Cache Locality less important with newer cpus, but will probably still lead to benefits.
+Storing data contigous should reduce cache misses, since accesses are more predictable.
+Collider Component may have 3\*float64 position + 4\*float64 rotation + 3\*float64 size + 10\*float64 miscellanious = 160 Byte
+300 of those = 48 KB
+500 of those = 80 KB
+
+{{% /note %}}
+
+---
+
+## How to implement it in C++
+### Entities:
+```cpp
+//one possibility
+typedef uint_32t UID;
+
+typedef UID Entity;
+```
+
+---
+
+## How to implement it in C++
+### Components:
+A [std::flat_map](https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2022/p0429r9.pdf) is a fitting datatype.
+
+{{% fragment %}}
+
+GCC libstdc++  | Clang libc++        | MSVC STL
+---------------|---------------------|---------------
+not implemented|partially implemented|not implemented
+
+{{% /fragment %}}
+
+[^7]
+[^7]: https://en.cppreference.com/w/cpp/compiler\_support/23
+
+---
+
+## How to implement it in C++
+### Components:
+
+```cpp
+class ComponentManager{
+    template<typename comp_type> requires std::is_base_of<Component, comp_type>
+    foreachComponent(std::function func){
+    //...
+    }
+
+    template<typename comp_type> requires std::is_base_of<Component, comp_type>
+    addComponentToEntity(Entity entity){
+    //...
+    }
+
+    //some type of ComponentMap store
+}
+```
+
+{{% note %}}
+
+possible ComponentMap store:
+```cpp
+std::unordered_map<std::typeid, std::size_t> m_typeOffsetMap;
+void* m_componentMaps;
+```
+
+{{% /note %}}
+
+---
+
+## How to implement it in C++
+### ComponentMap:
+
+```cpp
+template <typename component_type>
+class ComponentMap
+    std::vector<component_type> m_values;
+    std::unordered_map<Entity, size_type> m_mapping;
+```
+
+---
+
+![](metroid_ending.gif)
+
+---
+
+## Links
+- Images from [deathgenerator.com](https://deathgenerator.com)
+- Helpful [thesis by Toni Härkönen](https://trepo.tuni.fi/bitstream/handle/123456789/27593/H%C3%A4rk%C3%B6nen.pdf)
+- [Data Structures for Entity Systems: Contiguous memory](https://t-machine.org/index.php/2014/03/08/data-structures-for-entity-systems-contiguous-memory/)
+

OpenColloq/WS24_EntityComponentSystem/content/_index.md~

@@ -0,0 +1,520 @@
++++
+title = "Entity Component System - It's not a system"
+outputs = ["Reveal"]
++++
+
+# Entity Component System
+
+---
+
+## Why am I doing this?
+
+- {{< frag c ="My own bad implementation" >}}
+{{% fragment %}}
+![](tino-animated.gif) {{% /fragment %}}
+
+{{% note %}}
+My implementation in GL3 (explain course shortly) was horrible.
+ECS was introduced in the middle of GL3.
+
+Tino said I could talk about very niche topics, so I'm talking about a very niche topic.
+{{% /note %}}
+
+---
+
+## What is (an) ECS?
+- {{< frag c="unnecessary" >}}
+- {{< frag c="useful" >}}
+- {{< frag c="not a system" >}}
+
+{{% note %}}
+
+Talk about structure of presentation here:
+- define terms like "entity", "component", "system"
+- go over other approaches to "motivate" ECS
+- main 3 game engines will be mentioned (Unity, Unreal, Godot)
+- talking about the level of programming engines, not games
+
+{{% /note %}}
+
+---
+
+## What are entities?
+![lol](lol.jpg)[^1]
+
+[^1]: https://br.ign.com/league-of-legends-wild-rift/89123/feature/wild-rift-tudo-sobre-o-lol-mobile ; Image: Riot Games
+
+---
+
+## What are entities?
+![aoe](aoe.jpg)[^2]
+
+[^2]: https://pressakey.com/gameinfos,4981,screenshots,,,Age-of-Empires-Definitive-Edition,.html
+
+---
+
+## What are entities?
+- Objects in a game (or simulation)
+- Can have different behaviours
+- {{< frag c="Basically everything" >}}
+
+---
+
+# INHERITANCE
+
+---
+
+{{% section %}}
+
+{{< slide transition="none" >}}
+
+## Inheritance
+```mermaid
+graph TD;
+    Entity-->MoveableEntity;
+    Entity-->PhysicsEntity;
+```
+
+{{% note %}}
+
+Entity: Basic information like transform and mesh in our example
+MoveableEntity: Entity with functions to move with and support animations
+PhysicsEntity: Walls, Falling Boulders and stuff; Colliders and Gravity
+
+{{% /note %}}
+
+---
+
+{{< slide transition="none" >}}
+
+## Inheritance
+```mermaid
+graph TD;
+    Entity-->MoveableEntity;
+    Entity-->PhysicsEntity;
+    MoveableEntity-->Character;
+    PhysicsEntity-->BoxColliderEntity;
+```
+
+{{% note %}}
+
+Entity: Basic information like transform and mesh in our example
+MoveableEntity: Entity with functions to move with and support animations
+PhysicsEntity: Walls, Falling Boulders and stuff; Colliders and Gravity
+
+{{% /note %}}
+
+---
+
+{{< slide transition="none" >}}
+
+## Inheritance
+```mermaid
+graph TD;
+    Entity-->MoveableEntity;
+    Entity-->PhysicsEntity;
+    MoveableEntity-->Character;
+    Character-->Player;
+    Character-->NPC;
+    PhysicsEntity-->BoxColliderEntity;
+```
+
+{{% note %}}
+
+Entity: Basic information like transform and mesh in our example
+MoveableEntity: Entity with functions to move with and support animations
+PhysicsEntity: Walls, Falling Boulders and stuff; Colliders and Gravity
+
+{{% /note %}}
+
+{{% /section %}}
+
+---
+
+## Godot
+![GodotInheritance](./GodotInheritanceEditor.png)
+[^3]
+
+[^3]: Screenshot: Godot Engine
+
+---
+
+![](godot_news.png)
+
+---
+
+## Godot Code
+```cpp
+class Node2D : public CanvasItem {
+...
+}
+.
+.
+.
+class PhysicsBody2D : public CollisionObject2D {
+...
+}
+class CharacterBody2D : public PhysicsBody2D {
+...
+}
+```
+[^4]
+
+[^4]: https://github.com/godotengine/godot
+
+---
+
+{{% section %}}
+{{< slide transition="none" >}}
+
+## Inheritance
+```mermaid
+graph TD;
+    Entity-->MoveableEntity;
+    Entity-->PhysicsEntity;
+    MoveableEntity-->Character;
+    Character-->Player;
+    Character-->NPC;
+    PhysicsEntity-->BoxColliderEntity;
+    MoveableEntity-->Vehicle;
+```
+
+---
+
+{{< slide transition="none" >}}
+
+## Multiple Inheritance
+```mermaid
+graph TD;
+    Entity-->MoveableEntity;
+    Entity-->PhysicsEntity;
+    MoveableEntity-->Character;
+    Character-->Player;
+    Character-->NPC;
+    PhysicsEntity-->BoxColliderEntity;
+    MoveableEntity-->Vehicle;
+    BoxColliderEntity-->Vehicle;
+```
+
+{{% /section %}}
+
+---
+
+<section data-noprocess>
+<h1>Godot</h1>
+<div style="display: flex; flex-direction: row; justify-content: center; align-items: center;">
+  <img style="margin-right: 10%;" src="Godot_player_scene_nodes.webp">
+  <ul>
+    <li class="fragment" >uses hierarchy instead</li>
+    <li class="fragment" >child nodes as "components"</li>
+  </ul>
+</div>
+</section>
+
+---
+
+## What are components?
+- {{< frag c="Split entities from behaviour" >}}
+- {{< frag c="Data associated with a certain \"behaviour\"" >}}
+
+---
+
+# COMPOSITION
+
+---
+
+# Composition
+```mermaid
+graph LR;
+    EntityA-->BoxColliderComponent;
+    EntityA-->StaticMeshComponent;
+    EntityB-->SphereColliderComponent;
+    EntityB-->DynamicMeshComponent;
+    EntityB-->PlayerControllerComponent;
+linkStyle default stroke:lime,stroke-width:4px;
+```
+
+---
+
+## Composition
+- {{< frag c="Entities have minimal data and behaviour" >}}
+- {{< frag c="Entities hold their components or references to them" >}}
+
+{{% fragment %}}
+```cpp
+class Component;
+
+class Entity {
+//...
+private:
+    std::unordered_map<std::type_info, Component*> m_components;
+}
+```
+{{% /fragment %}}
+
+{{% note %}}
+
+Wanted to have a look at Unreal Source code, but...
+
+{{% /note %}}
+
+---
+
+![](gnupolice_unreal.png)
+
+---
+
+## Unreal
+
+Code in Unreal's AActor class[^5]:
+
+```cpp
+/**
+* All ActorComponents owned by this Actor. Stored as a Set as actors may have a large number of components
+* @see GetComponents()
+*/
+TSet<TObjectPtr<UActorComponent>> OwnedComponents;
+
+/**
+* Get all components derived from class 'ComponentType' and fill in the OutComponents array with the result.
+* It's recommended to use TArrays with a TInlineAllocator to potentially avoid memory allocation costs.
+* TInlineComponentArray is defined to make this easier, for example:
+* {
+*     TInlineComponentArray<UPrimitiveComponent*> PrimComponents(Actor);
+* }
+*
+* @param bIncludeFromChildActors   If true then recurse in to ChildActor components and find components of the appropriate type in those Actors as well
+*/
+template<class ComponentType, class AllocatorType>
+void GetComponents(TArray<ComponentType, AllocatorType>& OutComponents, bool bIncludeFromChildActors = false) const
+{
+    typedef TPointedToType<ComponentType> T;
+
+    OutComponents.Reset();
+    ForEachComponent_Internal<T>(T::StaticClass(), bIncludeFromChildActors, [&](T* InComp)
+    {
+        OutComponents.Add(InComp);
+    });
+}
+```
+
+[^5]: Engine/Source/Runtime/Engine/Classes/GameFramework/Actor.h
+
+{{% note %}}
+
+next, Unity, but...
+
+*b. Distributing Examples
+You may Distribute Examples (including as modified by you) in Source Code or object code to any third party.*
+
+{{% /note %}}
+
+---
+
+![](gnupolice_unity.png)
+
+---
+
+## Unity
+![](unity_inspector.jpg)[^6]
+
+[^6]:https://docs.unity3d.com/6000.0/Documentation/Manual/UsingTheInspector.html
+
+{{% note %}}
+
+- can't confirm what Unity uses (no source found)
+- interface suggests composition
+- Unity DOTS?
+
+{{% /note %}}
+
+---
+
+![](mario_ecs_castle.png)
+
+---
+
+## What are systems?
+- {{< frag c="███████████████████" >}}
+- {{< frag c="█████████████████" >}}
+- {{< frag c="████████████████████" >}}
+
+{{% note %}}
+We'll talk about it later.
+{{% /note %}}
+
+---
+
+# Entity Component System
+
+---
+
+![](dracula_ecs.png)
+
+{{% note %}}
+
+ECS is Data-Oriented rather than Object-Oriented
+
+{{% /note %}}
+
+---
+
+## Entity Component System
+- {{< frag c="split components even more from entities" >}}
+- {{< frag c="entities are minimal data" >}}
+- {{< frag c="components store data associated with certain behaviours" >}}
+- {{< frag c="components aren't managed by their entities" >}}
+
+{{% note %}}
+
+-
+- entities can just be ids
+- component manager
+
+
+{{% /note %}}
+
+---
+
+![](zerowing_component_manager.png)
+
+---
+
+## What are systems?
+- {{< frag c="main way of interacting with components" >}}
+- {{< frag c="loop over every component of a type" >}}
+- {{< frag c="e.g. Rendering System, Physics System..." >}}
+
+{{% note %}}
+
+- due to systems, want to optimise for iterating over components of a type
+
+{{% /note %}}
+
+---
+
+## Examples:
+
+- [Unity DOTS](https://unity.com/dots)
+- [Bevy](https://bevyengine.org/)
+- [EnTT](https://github.com/skypjack/entt)
+
+{{% fragment %}}
+
+> One thing known to most is that *EnTT* is also used in Minecraft.
+> Given that the game is available literally everywhere, I can confidently say that the library has been sufficiently tested on every platform that can come to mind.
+
+{{% /fragment %}}
+
+{{% note %}}
+
+Bevy ECS used for [Tiny Glade](https://store.steampowered.com/app/2198150/Tiny_Glade/)
+
+{{% /note %}}
+
+---
+
+## Cache
+
+CPU          |L1     |L2     |L3
+-------------|-------|-------|-----
+Pentium N4200|96 KiB |128 KiB|2 MiB
+i7 14700HX   |1800 KB|28 MB  |33 MB
+
+{{% note %}}
+
+top: silas' laptop
+bottom: mine
+
+Mine are probably also KiB/MiB, because Windows is doing Windows things
+
+Cache Locality less important with newer cpus, but will probably still lead to benefits.
+Storing data contigous should reduce cache misses, since accesses are more predictable.
+Collider Component may have 3\*float64 position + 4\*float64 rotation + 3\*float64 size + 10\*float64 miscellanious = 160 Byte
+300 of those = 48 KB
+500 of those = 80 KB
+
+{{% /note %}}
+
+---
+
+## How to implement it in C++
+### Entities:
+```cpp
+//one possibility
+typedef uint_32t UID;
+
+typedef UID Entity;
+```
+
+---
+
+## How to implement it in C++
+### Components:
+A [std::flat_map](https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2022/p0429r9.pdf) is a fitting datatype.
+
+{{% fragment %}}
+
+GCC libstdc++  | Clang libc++        | MSVC STL
+---------------|---------------------|---------------
+not implemented|partially implemented|not implemented
+
+{{% /fragment %}}
+
+[^7]
+[^7]: https://en.cppreference.com/w/cpp/compiler\_support/23
+
+---
+
+## How to implement it in C++
+### Components:
+
+```cpp
+class ComponentManager{
+    template<typename comp_type> requires std::is_base_of<Component, comp_type>
+    foreachComponent(std::function func){
+    //...
+    }
+
+    template<typename comp_type> requires std::is_base_of<Component, comp_type>
+    addComponentToEntity(Entity entity){
+    //...
+    }
+
+    //some type of ComponentMap store
+}
+```
+
+{{% note %}}
+
+possible ComponentMap store:
+```cpp
+std::unordered_map<std::typeid, std::size_t> m_typeOffsetMap;
+void* m_componentMaps;
+```
+
+{{% /note %}}
+
+---
+
+## How to implement it in C++
+### ComponentMap:
+
+```cpp
+template <typename component_type>
+class ComponentMap
+    std::vector<component_type> m_values;
+    std::unordered_map<Entity, size_type> m_mapping;
+```
+
+---
+
+![](metroid_ending.gif)
+
+---
+
+## Links
+- Images from [deathgenerator.com](https://deathgenerator.com)
+- Helpful [thesis by Toni Härkönen](https://trepo.tuni.fi/bitstream/handle/123456789/27593/H%C3%A4rk%C3%B6nen.pdf)
+- [Data Structures for Entity Systems: Contiguous memory](https://t-machine.org/index.php/2014/03/08/data-structures-for-entity-systems-contiguous-memory/)
+