Overlook.Ecs 1.0.0

Overlook ECS

Overlook ECS is a high-performance Entity Component System (ECS) designed for the Overlook Game Framework, built with C# and optimized for Unity development workflows.

Overview

Entity Component System (ECS) is an architectural pattern that emphasizes data-oriented design by separating data (Components) from identity (Entities) and behavior (Systems). This approach promotes:

• Improved Performance: By organizing data in a way that's cache-friendly (often through archetypes).
• Enhanced Code Reusability: Components and systems can be more modular and independent.
• Better Data Organization: Clear separation of concerns makes complex game states easier to manage.

Overlook.Ecs provides a robust implementation of these core principles.

Core Concepts in Overlook.Ecs

• World: The central container and manager for all ECS data. It holds entities, archetypes, and provides the primary API for interacting with the ECS (e.g., spawning entities, creating queries).
  • Each World is an isolated ECS environment.
• Entity: A lightweight struct that uniquely identifies a game object or logical element. It's essentially an ID (Identity) that groups a set of components.
  • Entity.None and Entity.Any are special static values.
• Component: Data structures (primarily struct for unmanaged components, but class for object components) that define the attributes or state of an entity. Examples: Position, Velocity, Health.
  • Unmanaged Components: struct components offer high performance due to direct memory layout within archetypes.
  • Object Components: class components allow for reference types and more complex behaviors, managed separately but still associated with entities.
  • Tagged Components (ITaggedComponent): A specialized mechanism for associating components with a "tag" type, allowing for more nuanced component relationships and querying (e.g., an Equipment component tagged with an EquippedByPlayer tag).
• Archetypes: An internal system that manages the unique combinations of component types. Entities with the exact same set of components belong to the same archetype. This is crucial for:
  • Efficient Storage: Components of the same type within an archetype are often stored contiguously in memory (Table, TableStorage).
  • Fast Querying: Queries can quickly identify matching archetypes and then iterate over their entities.
• StorageType: Represents the type of a component, used internally for managing storage and type information.

Key Features

• High-Performance Design:
  • Archetype-based component storage for cache efficiency.
  • Focus on unmanaged (struct) components for performance-critical data.
  • Object pooling (Overlook.Pool) is used internally (e.g., in EntityBuilder and Archetypes) to reduce allocations.
  • Uses Mask (or NativeBitArrayMask if OVERLOOK_ECS_USE_UNITY_COLLECTION is defined) for efficient component type matching in queries.
• Flexible Entity Management:
  • world.Spawn(): Creates a new entity.
  • world.Despawn(entity): Destroys an entity and its components.
  • Component Addition: world.AddComponent<T>(entity, data) for unmanaged, world.AddObjectComponent<T>(entity, data) for managed.
  • Component Removal: world.RemoveComponent<T>(entity), world.RemoveObjectComponent<T>(entity).
  • Component Access: world.GetComponent<T>(entity) (ref return for unmanaged), world.GetObjectComponent<T>(entity).
  • Checking for components: world.HasComponent<T>(entity).
• Powerful Querying System:
  • QueryBuilder: Fluent API to define which components an entity must have (Has<T>), must not have (Not<T>), or could have (Any<T>).
  • query.Build(world): Constructs a Query object.
  • Iterate over query results: foreach (var queryEntity in query) { ... }.
  • QueryEntity: Provides access to the Entity and its components within a query loop (e.g., queryEntity.Get<Position>()).
  • WhereQuery: Allows for additional filtering on query results using predicates.
• Entity Construction with EntityBuilder:
  • While World provides direct methods, EntityBuilder (and its extensions ValueComponentBuilder, ObjectComponentBuilder) offers a composable, fluent way to define an entity's components before instantiation.
  • EntityBuilder.Create().Add(new Position { ... }).Add(new Velocity { ... }).Build(world);
• Component Grouping (ComponentGroupAttribute):
  • An assembly-level attribute to define logical groupings of component types. This can be used for editor tooling or framework-level conventions.
• Tagged Components (TaggedComponent extensions):
  • Provides a way to create and query components that are "tagged" by another type, offering a form of component relationship or categorization.
  • Example: world.AddTaggedComponent(entity, myRenderer, typeof(PlayerViewTag));

Basic Usage Examples

using Overlook.Ecs;

// Define your components
public struct Position // Assuming IComponentData or similar if you have one
{
    public float X, Y, Z;
}

public struct Velocity
{
    public float DX, DY, DZ;
}

public class EnemyAI // Example of a class component
{
    public float AggroRadius;
}

public struct IsPlayerTag { } // A simple unmanaged tag component

public class GameController
{
    private World _world;

    public void Initialize()
    {
        _world = new World();

        // === Entity Creation ===

        // Method 1: Direct with World API
        Entity playerEntity = _world.Spawn();
        _world.AddComponent(playerEntity, new Position { X = 0, Y = 1, Z = 0 });
        _world.AddComponent(playerEntity, new Velocity { DX = 1, DY = 0, DZ = 0 });
        _world.AddComponent<IsPlayerTag>(playerEntity); // Adding a tag

        Entity enemyEntity = _world.Spawn();
        _world.AddComponent(enemyEntity, new Position { X = 10, Y = 1, Z = 5 });
        _world.AddObjectComponent(enemyEntity, new EnemyAI { AggroRadius = 15f });

        // Method 2: Using EntityBuilder (conceptual, actual API from EntityBuilderExtensions)
        // Note: The direct EntityBuilder methods like Add<T>() are part of extensions.
        // The following is a more realistic use of how builders are chained.
        var builder = Overlook.Ecs.EntityBuilder.Create()
            .Add(new Position { X = 5, Y = 0, Z = 5 })
            .Add(new Velocity { DX = 0, DY = 0, DZ = -1 });
        Entity anotherEntity = builder.Build(_world);

        // === Querying Entities ===

        // Query for all entities with Position and Velocity
        var moveableEntitiesQuery = QueryBuilder.Create()
                                       .Has<Position>()
                                       .Has<Velocity>()
                                       .Build(_world);

        Console.WriteLine("Moveable Entities:");
        foreach (var queryEntity in moveableEntitiesQuery) // queryEntity is of type QueryEntity
        {
            ref var pos = ref queryEntity.Get<Position>(); // Get by ref for structs
            ref readonly var vel = ref queryEntity.Get<Velocity>(); // Can also get as readonly ref

            Console.WriteLine($"  Entity {queryEntity.Entity.Identity} at ({pos.X}, {pos.Y}, {pos.Z}) moving at ({vel.DX}, {vel.DY}, {vel.DZ})");

            // Modify component data directly
            pos.X += vel.DX * 0.1f; // Example: simple movement update
        }

        // Query for entities with the IsPlayerTag
        var playerQuery = QueryBuilder.Create().Has<IsPlayerTag>().Build(_world);
        foreach (var queryEntity in playerQuery)
        {
            if (_world.HasComponent<Position>(queryEntity.Entity)) // Check for other components
            {
                ref var playerPos = ref _world.GetComponent<Position>(queryEntity.Entity);
                Console.WriteLine($"Player {queryEntity.Entity.Identity} is at: ({playerPos.X}, {playerPos.Y}, {playerPos.Z})");
            }
        }

        // === Accessing/Modifying Components ===
        if (_world.IsAlive(playerEntity) && _world.HasComponent<Velocity>(playerEntity))
        {
            ref var playerVel = ref _world.GetComponent<Velocity>(playerEntity);
            playerVel.DX = 5f; // Change player velocity
            Console.WriteLine($"Updated player velocity X to {playerVel.DX}");
        }

        // === Despawning ===
        _world.Despawn(enemyEntity);
        Console.WriteLine($"Enemy {enemyEntity.Identity} despawned. IsAlive: {_world.IsAlive(enemyEntity)}");
    }

    public void Shutdown()
    {
        _world?.Dispose(); // Important to dispose the world to clean up resources
    }
}

Systems (Behavior)

Overlook.Ecs primarily provides the data container and manipulation APIs. The actual game logic (behavior) is typically implemented in Systems. Systems are classes or methods that:

1. Query the World for entities with specific combinations of components.
2. Iterate over these entities and update their components or perform other game logic.

This package focuses on the ECS core; you would build your systems on top of it.

Further Considerations

• Integration with Unity: While a general-purpose C# ECS, its design choices (like NativeBitArrayMask option) suggest an orientation towards Unity's performance-sensitive environment. Consider how this integrates with Unity's Job System and Burst Compiler for maximal performance if applicable.
• Error Handling and Debugging: The codebase includes Debug.Assert and conditional debug messages (OVERLOOK_ECS_DEBUG), which are helpful during development.

This README provides a foundational understanding of Overlook.Ecs. For more in-depth knowledge, refer to the source code and specific API documentation within the package.

Acknowledgments

• modified from RelEcs