DragonECS/README.md

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# DragonECS - C# Entity Component System Framework

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The [ECS](https://en.wikipedia.org/wiki/Entity_component_system) Framework aims to maximize usability, modularity, extensibility and performance for dynamic entity changes, without code generation or external dependencies. Inspired by [LeoEcs Lite](https://github.com/Leopotam/ecslite).

> [!WARNING]
> The project is a work in progress; the API may change.
>
> The most current version of the README is in [Russian version](https://github.com/DCFApixels/DragonECS/blob/main/README-RU.md).
>
> If there are unclear points, you can ask questions here [Feedback](#Feedback)

## Table of Contents
- [Installation](#installation)
- [Extensions](#extensions)
- [Basic Concepts](#basic-concepts)
  - [Entity](#entity)
  - [Component](#component)
  - [System](#system)
- [Framework Concepts](#framework-concepts)
  - [Pipeline](#pipeline)
    - [Building](#building)
    - [Dependency Injection](#dependency-injection)
    - [Modules](#modules)
    - [Sorting](#sorting)
  - [Processes](#Processes)
  - [World](#World)
  - [Pool](#Pool)
  - [Mask](#mask)
  - [Aspect](#aspect)
  - [Queries](#queries)
  - [Collections](#collections)
  - [ECS Root](#ecs-root)
- [Debug](#debug)
  - [Meta Attributes](#meta-attributes)
  - [EcsDebug](#ecsdebug)
  - [Profiling](#profiling)
- [Define Symbols](#define-symbols)
- [Framework Extension Tools](#framework-extension-tools)
  - [World Components](#world-components)
  - [Configs](#configs)
- [Projects powered by DragonECS](#projects-powered-by-dragonecs)
- [Extensions](#extensions)
- [FAQ](#faq)
- [Feedback](#feedback)

</br>

# Installation
Versioning semantics - [Open](https://gist.github.com/DCFApixels/af79284955bf40e9476cdcac79d7b098#file-dcfapixels_versioning-md)
## Environment
Requirements:
* Minimum C# version: 7.3.

Supported:
* NativeAOT;
* Game engines with C#: Unity, Godot, MonoGame, etc.

Tested with:
* **Unity:** Minimum version 2021.2.0.

## Unity Installation
> It is also recommended to install the Unity engine integration extension [Unity integration](https://github.com/DCFApixels/DragonECS-Unity)
* ### Unity package
Installation as a Unity package is supported by adding the Git URL [in PackageManager](https://docs.unity3d.com/2023.2/Documentation/Manual/upm-ui-giturl.html):
```
https://github.com/DCFApixels/DragonECS.git
```
Or add the package entry to `Packages/manifest.json`:
```
"com.dcfa_pixels.dragonecs": "https://github.com/DCFApixels/DragonECS.git",
```

* ### As source code
The framework source code can also be copied directly into the project.


# Extensions
* Integrations:
    * [Unity](https://github.com/DCFApixels/DragonECS-Unity)
    * [Godot](https://gitlab.com/InauniusOwn/Libraries/DraGodot)
* Packages:
    * [Dependency autoinjections](https://github.com/DCFApixels/DragonECS-AutoInjections)
    * [Classic C# multithreading](https://github.com/DCFApixels/DragonECS-ClassicThreads)
    * [Recursivity](https://github.com/DCFApixels/DragonECS-Recursivity)
    * [Hybrid](https://github.com/DCFApixels/DragonECS-Hybrid)
    * [Graphs](https://github.com/DCFApixels/DragonECS-Graphs)
* Utilities:
    * [Simple syntax](https://gist.github.com/DCFApixels/d7bfbfb8cb70d141deff00be24f28ff0)
    * [EcsRefPool](https://gist.github.com/DCFApixels/73e392ccabdd98b3d4a517017d8a3f22)
    * [Timers](https://gist.github.com/DCFApixels/71a416275660c465ece76242290400df)
    * [One-Frame Components](https://gist.github.com/DCFApixels/46d512dbcf96c115b94c3af502461f60)
    * [Code Templates for IDE](https://gist.github.com/ctzcs/0ba948b0e53aa41fe1c87796a401660b) and [for Unity](https://gist.github.com/ctzcs/d4c7730cf6cd984fe6f9e0e3f108a0f1)
> *Your extension? Extensions for DragonECS are welcome, you can share it [here](#feedback).

# Basic Concepts
## Entity
Container for components. Two identifier types are used to reference entities:
* `int` - short-lived identifier, valid within a single tick. Not recommended for long-term storage;
* `entlong` - long-term identifier that includes a generation tag, making it unique across entity lifetimes. Suitable for long-term storage.
```c#
// Creating a new entity in the world.
int entityID = _world.NewEntity();

// Deleting an entity.
_world.DelEntity(entityID);

// Copying components from one entity to another.
_world.CopyEntity(entityID, otherEntityID);

// Cloning an entity.
int newEntityID = _world.CloneEntity(entityID);
```

<details>
<summary>Working with entlong</summary>
 
```c#
// Convert int to entlong.
entlong entity = _world.GetEntityLong(entityID);
// or
entlong entity = (_world, entityID);

// Check that the entity is still alive.
if (entity.IsAlive) { }

// Converting entlong to int. Throws an exception if the entity no longer exists.
int entityID = entity.ID;
// or
var (entityID, world) = entity;
 
// Converting entlong to int. Returns true and the int identifier if the entity is still alive.
if (entity.TryGetID(out int entityID)) { }
```
 
 </details>
 
> Entities cannot exist without components. Removing the last component automatically deletes the entity along with it.

## Component
Data for entities.
```c#
// IEcsComponent components are stored in regular storage.
struct Health : IEcsComponent
{
    public float health;
    public int armor;
}
// Components with IEcsTagComponent are stored in tag-optimized storage.
struct PlayerTag : IEcsTagComponent {}
```

## System
Represents the core logic defining entity behaviors. Systems are implemented as user-defined classes that implement one or more process interfaces. Key processes include:
```c#
class SomeSystem : IEcsPreInit, IEcsInit, IEcsRun, IEcsDestroy
{
    // Called once during EcsPipeline.Init() and before IEcsInit.Init().
    public void PreInit () { }
    
    // Called once during EcsPipeline.Init() and after IEcsPreInit.PreInit().
    public void Init ()  { }
    
    // Called each time during EcsPipeline.Run().
    public void Run () { }
    
    // Called once during EcsPipeline.Destroy().
    public void Destroy () { }
}
```
> For implementing additional processes, refer to the [Processes](#Processes) section.

</br>

# Framework Concepts
## Pipeline
Container and engine of systems. Responsible for setting up the system call queue, providing mechanisms for communication between systems, and dependency injection. Implemented as the `EcsPipeline` class.
### Building
Builder is responsible for building the pipeline. Systems are added to the Builder, and the pipeline is built at the end. Example:
```c#
EcsPipeline pipeline = EcsPipeline.New() // Creates a pipeline builder.
    // Adds System1 to the systems queue.
    .Add(new System1())
    // Adds System2 to the queue after System1.
    .Add(new System2())
    // Adds System3 to the queue after System2, as a unique instance.
    .AddUnique(new System3())
    // Completes the pipeline building and returns its instance.
    .Build(); 
pipeline.Init(); // Initializes the pipeline.
```

```c#
class SomeSystem : IEcsRun, IEcsPipelineMember
{
    // Gets the pipeline instance to which the system belongs.
    public EcsPipeline Pipeline { get ; set; }

    public void Run () { }
}
```
> For simultaneous building and initialization, use `Builder.BuildAndInit()`.

### Dependency Injection
The framework implements dependency injection for systems. Injection process occurs during pipeline initialization and injects data passed to the Builder.
> Built-in Dependency injection is optional.
```c#
class SomeDataA { /* ... */ }
class SomeDataB : SomeDataA { /* ... */ }

// ...
SomeDataB _someDataB = new SomeDataB();
EcsPipeline pipeline = EcsPipeline.New()
    // ...
    // Injects _someDataB into systems implementing IEcsInject<SomeDataB>.
    .Inject(_someDataB) 
    // Adds systems implementing IEcsInject<SomeDataA> to the injection tree,
    // now these systems will also receive _someDataB.
    .Injector.AddNode<SomeDataA>()
    // ...
    .Add(new SomeSystem())
    // ...
    .BuildAndInit();

// ...
// Injection uses the interface IEcsInject<T> and its method Inject(T obj).
class SomeSystem : IEcsInject<SomeDataA>, IEcsRun
{
    SomeDataA _someDataA;
    // obj will be an instance of type SomeDataB.
    public void Inject(SomeDataA obj) => _someDataA = obj;

    public void Run () 
    {
        _someDataA.DoSomething();
    }
}
```

### Modules
Groups of systems that implement a common feature can be grouped into modules and added to the Pipeline.
```c#
using DCFApixels.DragonECS;
class Module1 : IEcsModule 
{
    public void Import(EcsPipeline.Builder b) 
    {
        b.Add(new System1());
        b.Add(new System2());
        b.AddModule(new Module2());
        // ...
    }
}
```
``` c#
EcsPipeline pipeline = EcsPipeline.New()
    // ...
    .AddModule(new Module1())
    // ...
    .BuildAndInit();
```

### Sorting
To manage system order in the pipeline regardless of addition order, use Layers and Sorting Order.
#### Layers
Queues of systems can be segmented into layers. A layer defines a position in the queue for inserting systems. For example, to insert a system at the end of the queue regardless of where it is added, add it to the `EcsConsts.END_LAYER` layer.
``` c#
const string SOME_LAYER = nameof(SOME_LAYER);
EcsPipeline pipeline = EcsPipeline.New()
    // ...
    // Inserts a new layer before the end layer EcsConsts.END_LAYER
    .Layers.Insert(EcsConsts.END_LAYER, SOME_LAYER)
    // System SomeSystem will be added to the SOME_LAYER layer
    .Add(new SomeSystem(), SOME_LAYER) 
    // ...
    .BuildAndInit();
```
The built-in layers are arranged in the following order:
* `EcsConsts.PRE_BEGIN_LAYER`
* `EcsConsts.BEGIN_LAYER`
* `EcsConsts.BASIC_LAYER` (Systems are added here if no layer is specified during addition)
* `EcsConsts.END_LAYER`
* `EcsConsts.POST_END_LAYER`
#### Sorting Order
The sort order integer value is used to sort systems within a layer. By default, systems are added with `sortOrder = 0`.

```c#
EcsPipeline pipeline = EcsPipeline.New()
    // ...
    // System SomeSystem will be inserted into the layer EcsConsts.BEGIN_LAYER 
    // and placed after systems with sortOrder less than 10.
    .Add(new SomeSystem(), EcsConsts.BEGIN_LAYER, 10)
    // ...
    .BuildAndInit();
```

## Processes
Processes are queues of systems that implement a common interface, such as `IEcsRun`. Runners are used to start processes. Built-in processes are started automatically; custom processes can be implemented.

<details>
<summary>Built-in processes</summary>
 
* `IEcsPreInit`, `IEcsInit`, `IEcsRun`, `IEcsDestroy` - lifecycle processes of `EcsPipeline`.
* `IEcsInject<T>` - [Dependency Injection](#Dependency-Injection) processes.
* `IOnInitInjectionComplete` - Similar to the [Dependency Injection](#Dependency-Injection) process, but signals completion of initialization injection.

</details>
 
<details>
<summary>Custom Processes</summary>
 
To add a new process, create an interface inheriting from `IEcsProcess` and create a runner for it. A runner is a class that implements the process interface and inherits from `EcsRunner<TInterface>`. Example:
``` c#
// Process interface.
interface IDoSomethingProcess : IEcsProcess
{
    void Do();
}
// Runner implementation. An example of implementation can also be seen in built-in processes.
sealed class DoSomethingProcessRunner : EcsRunner<IDoSomethingProcess>, IDoSomethingProcess
{
    public void Do() 
    {
        foreach (var item in Process) item.Do();
    }
}
```
``` c#
// Adding the runner when creating the pipeline
_pipeline = EcsPipeline.New()
    //...
    .AddRunner<DoSomethingProcessRunner>()
    //...
    .BuildAndInit();

// Running the runner if it was added
_pipeline.GetRunner<IDoSomethingProcess>().Do();

// or if the runner was not added (calling GetRunnerInstance will also add the runner to the pipeline).
_pipeline.GetRunnerInstance<DoSomethingProcessRunner>().Do();
```

<details>
<summary>Advanced Implementation of a Runner</summary>

``` c#
internal sealed class DoSomethingProcessRunner : EcsRunner<IDoSomethingProcess>, IDoSomethingProcess
{
    // RunHelper simplifies the implementation similar to the built-in processes implementation. 
    // It automatically triggers the profiler marker and also includes a try-catch block.
    private RunHelper _helper;
    protected override void OnSetup()
    {
        // The second argument specifies the name of the marker; if not specified, the name will be chosen automatically.
        _helper = new RunHelper(this, nameof(Do));
    }
    public void Do()
    {
        _helper.Run(p => p.Do());
    }
}
```

</details>

> Runner requirements:
> * Inheritance from `EcsRunner<T>` must be direct.
> * A runner may only contain one interface (excluding `IEcsProcess`).
> * The inheriting class of `EcsRunner<T>` must also implement the `T` interface.

</details>

## World
A container for entities and components.
``` c#
// Creating an instance of the world.
_world = new EcsDefaultWorld();
// Creating and deleting an entity as shown in the Entities section.
var e = _world.NewEntity();
_world.DelEntity(e);
```
> **NOTICE:** Call `EcsWorld.Destroy()` on the world instance when it is no longer needed to release resources. Otherwise it will remain in memory.

### World Configuration
To initialize the world with a required size upfront and reduce warm-up time, pass an `EcsWorldConfig` instance to the constructor.

``` c#
EcsWorldConfig config = new EcsWorldConfig(
    // Pre-initializes the world capacity for 2000 entities.
    entitiesCapacity: 2000, 
    // Pre-initializes the pools capacity for 2000 components.
    poolComponentsCapacity: 2000);  
_world = new EcsDefaultWorld(config);
```

## Pool
Stash of components, providing methods for adding, reading, editing, and removing components on entities. Several pool types are available:
* `EcsPool` - universal pool for struct components implementing `IEcsComponent`;
* `EcsTagPool` - pool optimized for tag components implementing `IEcsTagComponent`;

Pools provide 5 common methods and their variations:
``` c#
// One way to get a pool from the world.
EcsPool<Pose> poses = _world.GetPool<Pose>();
 
// Adds component to entity, throws an exception if the entity already has the component.
ref var addedPose = ref poses.Add(entityID);
 
// Returns existing component, throws an exception if the entity does not have this component.
ref var gottenPose = ref poses.Get(entityID);
 
// Returns a read-only component, throwing an exception if the entity does not have this component. 
ref readonly var readonlyPose = ref poses.Read(entityID);
 
// Returns true if the entity has the component, otherwise false.
if (poses.Has(entityID)) { /* ... */ }
 
// Removes component from entity, throws an exception if the entity does not have this component.
poses.Del(entityID);
```
> [!WARNING]
> Exceptions are disabled in the `Release` build.

> There are "Safe" methods that first check presence or absence of a component are prefixed with `Try`.

<details> 
<summary>Custom Pools</summary>

A pool can be any type that implements the IEcsPoolImplementation<T> interface and has a parameterless constructor.

Key points when implementing a pool:

* For an example of a pool implementation, reference can be made to the implementation of the built-in EcsPool<T>.
* The IEcsPoolImplementation interface and its members are not intended for public use; the interface members should be implemented explicitly.
* The type T substituted in the IEcsPoolImplementation<T> interface and the type returned by the ComponentType and ComponentTypeID properties must match.
* All pool changes must be registered with the EcsWorld.PoolsMediator instance passed in the OnInit method.
* EcsWorld.PoolsMediator is intended for use only inside the pool.
* The DISABLE_POOLS_EVENTS define disables the implemented AddListener and RemoveListener methods.
* The static class EcsPoolThrowHelper defines throwing of the most common exception types.
* The OnReleaseDelEntityBuffer method handles cleanup of deleted entities.
* It is recommended to define an interface that marks components intended for the new pool. Based on this interface, extension methods such as GetPool<T>() can be implemented to simplify access to pools.
* Pools must implement locking. Pool locking works only in Debug mode and should throw exceptions when attempting to add or remove a component.

</details>

## Mask
Used to filter entities by presence or absence of components. Usually masks are not used standalone, they are part of `EcsAspect` and used by queries to filter entities.
``` c#
// Creating a mask that checks if entities have components 
// SomeCmp1 and SomeCmp2, but do not have component SomeCmp3.
EcsMask mask = EcsMask.New(_world)
    // Inc - Condition for the presence of a component.
    .Inc<SomeCmp1>()
    .Inc<SomeCmp2>()
    // Exc - Condition for the absence of a component.
    .Exc<SomeCmp3>()
    .Build();
```

<details>
<summary>Static Mask</summary>

`EcsMask` is tied to specific world instances, which need to be passed to `EcsMask.New(world)`. `EcsStaticMask` can be created without a world reference.

``` c#
class SomeSystem : IEcsRun 
{
    // EcsStaticMask can be created in static fields.
    static readonly EcsStaticMask _staticMask = EcsStaticMask.Inc<SomeCmp1>().Inc<SomeCmp2>().Exc<SomeCmp3>().Build();

    // ...
}
```
``` c#
// Converting to a regular mask.
EcsMask mask = _staticMask.ToMask(_world);
```

</details>
 
## Aspect
User-defined classes that inherit from `EcsAspect` and describe sets of components a system works with. An aspect serves two purposes:
- Mask — initializes and holds an `EcsMask` used by queries for filtering entities.
- Pool cache — provides fast access to component pools.

In short, an aspect is a convenient way to declare "which entities I work with and how to access their components." 

Simplified syntax:
``` c#
using DCFApixels.DragonECS;
// ...
class Aspect : EcsAspect
{
    // Caches the Pose pool and adds it to the inclusive constraint.
    public EcsPool<Pose> poses = Inc;
    // Caches the Velocity pool and adds it to the inclusive constraint.
    public EcsPool<Velocity> velocities = Inc;
    // Caches the FreezedTag pool and adds it to the exclusive constraint.
    public EcsTagPool<FreezedTag> freezedTags = Exc;

    // During queries, it checks for the presence of components
    // in the inclusive constraint and absence in the exclusive constraint.
    // Opt only caches the pool without affecting the mask.
}
```

Purpose of the static markers:
* `Inc` — component must be present (inclusive) and caches the pool.
* `Exc` — component must NOT be present (exclusive) and caches the pool.
* `Opt` — component may be present; does not affect filtering (only caches the pool).
* `Any` — at least one of the components marked with `Any` must be present; caches the pool.

<details>
<summary>Initialization via a method (the result is identical to the example above):</summary>

Explicit syntax (equivalent result):
``` c#
using DCFApixels.DragonECS;
// ...
class Aspect : EcsAspect
{
    public EcsPool<Pose> poses;
    public EcsPool<Velocity> velocities;
    protected override void Init(Builder b)
    {
        poses = b.Inc<Pose>();
        velocities = b.Inc<Velocity>();
        b.Exc<FreezedTag>();
    }
}
```

</details>

<details>
<summary>Combining aspects</summary>

Aspects can be combined by adding other aspects; constraints are merged accordingly.
``` c#
using DCFApixels.DragonECS;
// ...
class Aspect : EcsAspect
{
    public OtherAspect1 otherAspect1;
    public OtherAspect2 otherAspect2;
    public EcsPool<Pose> poses;
 
    protected override void Init(Builder b)
    {
        // Combines with OtherAspect1.
        otherAspect1 = b.Combine<OtherAspect1>(1);
        // Although Combine was called earlier for OtherAspect1, it will first combine with OtherAspect2 because the default order is 0.
        otherAspect2 = b.Combine<OtherAspect2>();
        // If b.Exc<Pose>() was specified in OtherAspect1 or OtherAspect2, it will be replaced with b.Inc<Pose>() here.
        poses = b.Inc<Pose>();
    }
}
```

If conflicting constraints exist between combined aspects, the newer constraints replace earlier ones. Constraints from the root aspect always replace constraints from added aspects. Example of constraint combination:
| | cmp1 | cmp2 | cmp3 | cmp4 | cmp5 | Conflict resolution |
| :--- | :--- | :--- | :--- | :--- | :--- |:--- |
| OtherAspect2 | :heavy_check_mark: | :x: | :heavy_minus_sign: | :heavy_minus_sign: | :heavy_check_mark: | |
| OtherAspect1 | :heavy_minus_sign: | :heavy_check_mark: | :heavy_minus_sign: | :x: | :heavy_minus_sign: | For `cmp2`, :heavy_check_mark: will be chosen. |
| Aspect | :x: | :heavy_minus_sign: | :heavy_minus_sign: | :heavy_minus_sign: | :heavy_check_mark: | For `cmp1`, :x: will be chosen. |
| Final Constraints | :x: | :heavy_check_mark: | :heavy_minus_sign: | :x: | :heavy_check_mark: | |

</details>

## Queries
Filter entities and return collections of entities that match conditions. The built-in `Where` query filters by component mask and has several overloads:
+ `EcsWorld.Where(EcsMask mask)` - standard filtering by mask;
+ `EcsWorld.Where<TAspect>(out TAspect aspect)` - combines aspect mask filtering and returns the aspect;

`Where` can be applied to both `EcsWorld` and framework collections (similar to LINQ). Overloads for sorting using `Comparison<int>` are available.

Example system:
``` c#
public class SomeDamageSystem : IEcsRun, IEcsInject<EcsDefaultWorld>
{
    class Aspect : EcsAspect
    {
        public EcsPool<Health> healths = Inc;
        public EcsPool<DamageSignal> damageSignals = Inc;
        public EcsTagPool<IsInvulnerable> isInvulnerables = Exc;
        // The presence or absence of this component is not checked.
        public EcsTagPool<IsDiedSignal> isDiedSignals = Opt;
    }
    EcsDefaultWorld _world;
    public void Inject(EcsDefaultWorld world) => _world = world;

    public void Run()
    {
        foreach (var e in _world.Where(out Aspect a))
        {
            // Entities with Health, DamageSignal, and without IsInvulnerable will be here.
            ref var health = ref a.healths.Get(e);
            if(health.points > 0)
            {
                health.points -= a.damageSignals.Get(e).points;
                if(health.points <= 0)
                { // Create a signal to other systems that the entity has died.
                    a.isDiedSignals.TryAdd(e);
                }
            }
        }
    }
}
```

> You can use an [Extension](#extensions) to simplify query syntax and interactions with components - [Simplified Syntax](https://github.com/DCFApixels/DragonECS-AutoInjections).
 
## Collections

### EcsSpan
A `ref struct` collection of entities, available only for reading. Consists of a reference to an array, a length, and a world identifier. Similar to `ReadOnlySpan<int>`.
``` c#
// Where query returns entities as EcsSpan.
EcsSpan es = _world.Where(out Aspect a);
// Iteration is possible using foreach and for loops.
foreach (var e in es)
{
    // ...
}
for (int i = 0; i < es.Count; i++)
{
    int e = es[i];
    // ...
}
```
> Although `EcsSpan` is an array reference, duplicate entities are not allowed.

### EcsGroup
Sparse Set based auxiliary collection for storing a set of entities with O(1) add/delete/check operations, etc.
``` c#
// Getting a new group. EcsWorld contains a pool of groups,
// a new one will be created or a free one reused.
EcsGroup group = EcsGroup.New(_world);
// Release the group.
group.Dispose();
```
``` c#
// Add entityID to the group.
group.Add(entityID);
// Check if entityID exists in the group.
group.Has(entityID);
// Remove entityID from the group.
group.Remove(entityID);
```
``` c#
// WhereToGroup query returns entities as a read-only group EcsReadonlyGroup.
EcsReadonlyGroup group = _world.WhereToGroup(out Aspect a);
// Iteration is possible using foreach and for loops.
foreach (var e in group) 
{ 
    // ...
}
for (int i = 0; i < group.Count; i++)
{
    int e = group[i];
    // ...
}
```
Groups implement the `ISet<int>` interface. Editing methods have two variants: one that writes the result to `groupA`, and another that returns a new group.       
                                
``` c#
// Union of groupA and groupB.
groupA.UnionWith(groupB);
EcsGroup newGroup = EcsGroup.Union(groupA, groupB);
```
``` c#
// Intersection of groupA and groupB.
groupA.IntersectWith(groupB);
EcsGroup newGroup = EcsGroup.Intersect(groupA, groupB);
```
``` c#
// Difference of groupA and groupB.
groupA.ExceptWith(groupB);
EcsGroup newGroup = EcsGroup.Except(groupA, groupB);
```
``` c#
// Symmetric difference of groupA and groupB.
groupA.SymmetricExceptWith(groupB);
EcsGroup newGroup = EcsGroup.SymmetricExcept(groupA, groupB);
```
``` c#
// Difference of all entities in world and groupA.
groupA.Inverse();
EcsGroup newGroup = EcsGroup.Inverse(groupA);
```

## ECS Root
A custom class that serves as the entry point for ECS. Its main purpose is to initialize systems, run them on each engine update, and release resources when no longer needed.
### Example for Unity
``` c#
using DCFApixels.DragonECS;
using UnityEngine;
public class EcsRoot : MonoBehaviour
{
    private EcsPipeline _pipeline;
    private EcsDefaultWorld _world;
    private void Start()
    {
        // Creating world for entities and components.
        _world = new EcsDefaultWorld();
        // Creating pipeline for systems.
        _pipeline = EcsPipeline.New()
            // Adding systems.
            // .Add(new SomeSystem1())
            // .Add(new SomeSystem2())
            // .Add(new SomeSystem3())

            // Injecting world into systems.
            .Inject(_world)
            // Other injections.
            // .Inject(SomeData)

            // Finalizing the pipeline construction.
            .Build();
        // Initialize the Pipeline and run IEcsPreInit.PreInit()
        // and IEcsInit.Init() on all added systems.
        _pipeline.Init();
    }
    private void Update()
    {
        // Invoking IEcsRun.Run() on all added systems.
        _pipeline.Run();
    }
    private void OnDestroy()
    {
        // Invoking IEcsDestroy.Destroy() on all added systems.
        _pipeline.Destroy();
        _pipeline = null;
        // Requires deleting worlds that will no longer be used.
        _world.Destroy();
        _world = null;
    }
}
```
### Generic example
``` c#
using DCFApixels.DragonECS;
public class EcsRoot
{
    private EcsPipeline _pipeline;
    private EcsDefaultWorld _world;
    // Engine initialization.
    public void Init()
    {
        // Creating world for entities and components.
        _world = new EcsDefaultWorld();
        // Creating pipeline for systems.
        _pipeline = EcsPipeline.New()
            // Adding systems.
            // .Add(new SomeSystem1())
            // .Add(new SomeSystem2())
            // .Add(new SomeSystem3())

            // Injecting world into systems.
            .Inject(_world)
            // Other injections.
            // .Inject(SomeData)

            // Finalizing the pipeline construction.
            .Build();
        // Initialize the Pipeline and run IEcsPreInit.PreInit()
        // and IEcsInit.Init() on all added systems.
        _pipeline.Init();
    }

    // Engine update loop.
    public void Update()
    {
        // Invoking IEcsRun.Run() on all added systems.
        _pipeline.Run();
    }

    // Engine cleanup.
    public void Destroy()
    {
        // Invoking IEcsDestroy.Destroy() on all added systems.
        _pipeline.Destroy();
        _pipeline = null;
        // Requires deleting worlds that will no longer be used.
        _world.Destroy();
        _world = null;
    }
}
```

</br>

# Debug
The framework provides tools for debugging and logging, independent of the environment. Many types have DebuggerProxy implementations for more informative display in IDEs.
## Meta Attributes
By default, meta-attributes have no use, but are used in integrations with engines to specify display in debugging tools and editors. And can also be used to generate automatic documentation.
``` c#
using DCFApixels.DragonECS;

// Specifies custom name for the type, defaults to the type name.
[MetaName("SomeComponent")]

// Used for grouping types.
[MetaGroup("Abilities", "Passive", ...)] // or [MetaGroup("Abilities/Passive/...")]

// Sets the type color in RGB format, where each channel ranges from 0 to 255; defaults to white.
[MetaColor(MetaColor.Red)] // or [MetaColor(255, 0, 0)]
 
// Adds description to the type.
[MetaDescription("The quick brown fox jumps over the lazy dog")] 

// Adds a string unique identifier.
[MetaID("8D56F0949201D0C84465B7A6C586DCD6")] // Strings must be unique and cannot contain characters ,<> .

// Adds string tags to the type.
[MetaTags("Tag1", "Tag2", ...)]  // [MetaTags(MetaTags.HIDDEN))]  to hide in the editor 
public struct Component : IEcsComponent { /* ... */ }
```
Getting meta-information:
``` c#
TypeMeta typeMeta = someComponent.GetMeta();
// or
TypeMeta typeMeta = pool.ComponentType.ToMeta();

var name = typeMeta.Name; // [MetaName]
var group = typeMeta.Group; // [MetaGroup]
var color = typeMeta.Color; // [MetaColor]
var description = typeMeta.Description; // [MetaDescription]
var metaID = typeMeta.MetaID; // [MetaID]
var tags = typeMeta.Tags; // [MetaTags]
```
> To simplify generate unique MetaID values, use `MetaID.GenerateNewUniqueID()` or the [Browser Generator](https://dcfapixels.github.io/DragonECS-MetaID_Generator_Online/).

## EcsDebug
Provides methods for debugging and logging. Implemented as a static class that forwards calls to a Debug service. Debug services act as intermediaries between environment-specific debugging systems and EcsDebug, enabling portability.

By default, `DefaultDebugService` outputs logs to the console. To implement a custom service, inherit from `DebugService` and implement its abstract members.

``` c#
// Output log.
EcsDebug.Print("Message");

// Output log with tag.
EcsDebug.Print("Tag", "Message");

// Break execution.
EcsDebug.Break();

// Set another Debug Service.
EcsDebug.Set<OtherDebugService>();
```

## Profiling
``` c#
// Creating a marker named SomeMarker.
private static readonly EcsProfilerMarker _marker = new EcsProfilerMarker("SomeMarker");
```
``` c#
_marker.Begin();
// Code whose execution time is being measured.
_marker.End();

// or

using (_marker.Auto())
{
    // Code whose execution time is being measured.
}
```

</br>

# Define Symbols
+ `DRAGONECS_DISABLE_POOLS_EVENTS` - Disables reactive behavior in pools.
+ `DRAGONECS_ENABLE_DEBUG_SERVICE` - Enables EcsDebug functionality in release builds.
+ `DRAGONECS_STABILITY_MODE` - By default, many exception checks are skipped in release builds for performance. This define replaces checks with error-resilient code to increase stability at the cost of some performance.
+ `DRAGONECS_DISABLE_CATH_EXCEPTIONS` - Turns off the default exception handling behavior. By default, the framework will catch exceptions with the exception information output via EcsDebug and continue working.
+ `REFLECTION_DISABLED` - Restricts the framework's use of Reflection.
+ `DISABLE_DEBUG` - For environments where manual DEBUG disabling is not supported (e.g., Unity).

</br>

# Framework Extension Tools
Additional tools improve framework extensibility.

## Configs
Constructors of `EcsWorld` and `EcsPipeline` accept config containers implementing `IConfigContainer` or `IConfigContainerWriter`. These containers pass data and dependencies. The built-in container implementation is `ConfigContainer`. Сustom implementations are supported.

Example of using configs for EcsWorld:
``` c#
var configs = new ConfigContainer()
    .Set(new EcsWorldConfig(entitiesCapacity: 2000, poolsCapacity: 2000))
    .Set(new SomeDataA(/* ... */))
    .Set(new SomeDataB(/* ... */));
EcsDefaultWorld _world = new EcsDefaultWorld(configs);
// ...
var _someDataA = _world.Configs.Get<SomeDataA>();
var _someDataB = _world.Configs.Get<SomeDataB>();
```
Example of using configs for EcsPipeline:
``` c#
_pipeline = EcsPipeline.New() // similarly _pipeline = EcsPipeline.New(new ConfigContainer())
    .Configs.Set(new SomeDataA(/* ... */))
    .Configs.Set(new SomeDataB(/* ... */))
    // ...
    .BuildAndInit();
// ...
var _someDataA = _pipeline.Configs.Get<SomeDataA>();
var _someDataB = _pipeline.Configs.Get<SomeDataB>();
```

## World Components
World components attach additional data to worlds. World components are `struct` types. Access via `Get` is optimized and performs similarly to class field access.

Get component:
``` c#
ref WorldComponent component = ref _world.Get<WorldComponent>();
```
Component implementation:
``` c#
public struct WorldComponent
{
    // Data.
}
```
Or with lifecycle callbacks:
``` c#
public struct WorldComponent : IEcsWorldComponent<WorldComponent>
{
    // Data.

    void IEcsWorldComponent<WorldComponent>.Init(ref WorldComponent component, EcsWorld world)
    {
        // Actions during component initialization. Called before the first return from EcsWorld.Get().
    }
    void IEcsWorldComponent<WorldComponent>.OnDestroy(ref WorldComponent component, EcsWorld world)
    {
        // Actions when EcsWorld.Destroy is called.
        // OnDestroy requires manual reset of the component if necessary.
        component = default;
    }
}
```

<details>
<summary>Example of use</summary>

The `IEcsWorldComponent<T>` interface events can be used to initialize component fields and release resources automatically.
``` c#
public struct WorldComponent : IEcsWorldComponent<WorldComponent>
{
    private SomeClass _object; // Object to be disposed.
    private SomeReusedClass _reusedObject; // Object to be reused.
    public SomeClass Object => _object;
    public SomeReusedClass ReusedObject => _reusedObject;
    void IEcsWorldComponent<WorldComponent>.Init(ref WorldComponent component, EcsWorld world)
    {
        if (component._reusedObject == null)
            component._reusedObject = new SomeReusedClass();
        component._object = new SomeClass();
        // After getting the component via EcsWorld.Get, _reusedObject and _object will be ready.
    }
    void IEcsWorldComponent<WorldComponent>.OnDestroy(ref WorldComponent component, EcsWorld world)
    {
        // Dispose and clear the reference so GC can collect it.
        component._object.Dispose();
        component._object = null;
        // Optionally reset the reused object.
        // component._reusedObject.Reset();
        // If full reset is needed, uncomment the line below.
        // component = default;
    }
}
```
</details>

> Components and configs can be used to create extensions in conjunction with extension methods.

</br>

# Projects powered by DragonECS
## With sources:

<table>
  <tr>
    <td align="center">
      <a href="https://github.com/DCFApixels/3D-Platformer-DragonECS-Demo">
        3D Platformer (Example)
        <img src="https://github.com/user-attachments/assets/6aba814d-a70b-432f-a905-84d1b6872581" />
      </a> 
    </td>
    <td align="center">
      <a href="https://github.com/DCFApixels/LD_56_Tiny_Aliens">
        Tiny Aliens (Ludum Dare 56)
        <img src="https://github.com/user-attachments/assets/1a8f06ed-c68d-483a-b880-c9faaf7e0b5f" alt="screenshot">
      </a>
    </td>
  </tr>
  
  <tr></tr>

  <tr>
    <td align="center">
      <a href="https://github.com/Evileptic/Arkanoid">
        Arkanoid
        <img src="https://github.com/user-attachments/assets/bbdb4a7f-2f59-4a3a-ab51-a3e4fe0ad35e" alt="screenshot">
      </a> 
    </td>
    <td align="center">
        _____________
        <img tabindex="-1" src="https://github.com/user-attachments/assets/3fa1ca6d-29f6-43e6-aafe-cc9648d20490" alt="screenshot">
    </td>
  </tr>
</table>

## Released games:

<table>
  <tr>
    <td align="center">
      <a href="https://dcfapixels.github.io/Project8.html">
        Crystal Siege
        <img src="https://github.com/user-attachments/assets/1aa60a50-2668-4919-aca9-d6d2b980c3dd">
      </a> 
    </td>
    <td align="center">
      <a href="https://play.google.com/store/apps/details?id=com.ZlodeyStudios.OrdersMatter">
        Order matters
        <img src="https://github.com/user-attachments/assets/c55b2647-9b6e-4145-98ff-c3d094600fa1">
      </a> 
    </td>
  </tr>

  <tr></tr>

  <tr>
    <td align="center">
      <a href="https://yandex.ru/games/app/206024?utm_source=game_popup_menu">
        Башенки Смерти
        <img src="https://github.com/user-attachments/assets/70fc55a0-c911-49f8-ba75-f503437f087f" alt="screenshot">
      </a> 
    </td>
    <td align="center">
        _____________
        <img tabindex="-1" src="https://github.com/user-attachments/assets/3fa1ca6d-29f6-43e6-aafe-cc9648d20490" alt="screenshot">
    </td>
  </tr>
</table>

</br>

 
# FAQ

## How to enable/disable systems?
Directly — not supported.

The need to enable or disable systems usually appears when the overall game state changes; this may also mean switching a group of systems. Conceptually this is a change of processes. Two solutions are recommended:

- For global process changes, create a new `EcsPipeline` and run the appropriate pipeline in the engine update loop.
- Split `IEcsRun` into multiple processes and run the desired process in the engine update loop. Create a new process interface, implement a runner for it, and obtain the runner via `EcsPipeline.GetRunner<T>()`.

## Recommendations list: [DragonECS-Vault](https://github.com/DCFApixels/DragonECS-Vault)
</br>

# Feedback
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