https://github.com/seanmiddleditch/Simplecs

Simple Entity-Component-System library for C# with no dependencies on any game engine.

Pronounced "simplex."

This library is not the fastest nor most powerful. It's useful for simple cases. More sophisticated games or users may need to look elsewhere for a suitable library. The intended use cases are small demos, toys, and examples.

This library uses a naive approach based on sparse sets to implement O(1) component lookup. Iteration of a component table is cache-friendly, but iteration of a View over multiple components or using required/excluded components will incur non-cache- friendly memory access patterns.

The ECS concept of a "System" is actually not found in this library. A View can be used to implement a System, but the scheduling and logic execution is up to the library user. This library primarily implements a way of allocating Entity keys and storing Component instances associated via these keys, along with a View concept to iterate Entities with a matching set of Components.

A Component in Simplecs is any struct type that is Attached to an Entity. There are no other restrictions or requirements on Components.

This library does not attempt to provide any form of multi-threading, scheduling, advanced debugging, serialization, or reflection. These are all up to the library user. Feature additions that keep the library simple in nature may be considered in the future.

The World class is the main container that stores all entities and components.

var world = new World();

Component types must be struct types in Simplecs.

struct PositionComponent {
    public int x, y z;
}

Entities are identified by the Entity type, which is just an opaque handle. An entity can be constructed on a World using a builder interface, which can also be used to attach components.

var entity = world.CreateEntity()
    .Attach(new PositionComponent{x = 1, y = -2, z = 0})
    .Entity;

Components can also be attached and detached after creation.

world.Attach(entity, new NameComponent("Bob"));
world.Detach<PositionComponent>(entity);

Entities can be destroyed, which detaches all components. Unused entities should be destroyed to reclaim memory.

world.Destroy(entity);

Querying entities uses a View<> generic, which can be constructed via a builder on World like entities.

var view = world.CreateView().Select<PositionComponent, NameComponent>();

Views can be iterated to retrieve a list of entities and references to the selected components. Note that these references are fully mutable, which can be handy for some kinds of frequently-modified heavy components.

var view = world.CreateView().Select<PositionComponent, NameComponent>();
foreach (var row in view) {
    Console.WriteLine(row.Component2.Name);
}

A View can also be constructed with required components or excluded components. These components are used to find matching entities, but are not included in the iterated list of components like Select<> does. Excluded components are those which must not exist on an entity for it to match. Note that Select<> must be the final method in the builder chain.

// select all entities with a position, and which also
// have an actor component but do not have an AI component
//
var view = world.CreateView()
    .Require<ActorComponent>()
    .Exclude<AIComponent>()
    .Select<PositionComponent>();

// move all non-AI actors slightly to the right
//
foreach (var row in view) {
    row.Component.x += 1;
}

Additional support in the public interface exists to query which entities exist and to find all components on a given entity, which can be useful for tooling or serialization. Note that some of these interfaces necessitate boxing components which can be a significant performance penalty.

Written in 2019 by Sean Middleditch (https://seanmiddleditch.com).

To the extent possible under law, the author(s) have dedicated all copyright and related and neighboring rights to this software to the public domain worldwide. This software is distributed without any warranty.

You should have received a copy of the CC0 Public Domain Dedication along with this software. If not, see https://creativecommons.org/publicdomain/zero/1.0/.