Entity Component System

A lightweight C++ 20 Header only Entity Component System

Features

• Create entities with multiple components at once
• Multi component operations
• Fast, zero copy component queries
• Query filtering with With<T>() and Without<T>()
• Optional entity free query results with WithoutEntity()
• Safe structural changes during iteration with Stable()
• Capacity reservation with Reserve()
• Component add callbacks with OnAdd<T>()
• No external dependencies

How to use

#include <Ecs.hpp>

struct Position {
    float X = 0.0f;
    float Y = 0.0f;
};

struct Velocity {
    float X = 0.0f;
    float Y = 0.0f;
};

int main() {
    Ecs::Registry registry;

    Ecs::Entity entity = registry.Create();

    registry.Add<Position>(entity, 10.0f, 5.0f);
    registry.Add<Velocity>(entity, 1.0f, 0.0f);

    auto& position = registry.Get<Position>(entity);

    return 0;
}

Demo Preview

Component add callbacks

OnAdd<T>() follows the same naming as Add<T>() and lets a registry configure components as soon as they are attached:

class Scene {
public:
    void Setup() {
        m_Registry.OnAdd<Transform>()
            .Connect<&Scene::OnTransformAdded>(this);
    }

private:
    void OnTransformAdded(
        Ecs::Registry& registry,
        Ecs::Entity entity,
        Transform& transform)
    {
        transform.X = 10.0f;
    }

    Ecs::Registry m_Registry;
};

See Docs/ComponentEvents.md for event semantics and the planned lifecycle API.

Building with Premake

The ECS itself is header-only. Premake generates the project files for the library headers and tests:

premake5 vs2022

or run (defaults to the vs2022 Premake action):

Scripts\GenerateProjects.bat

You can pass another Premake action as the first argument when needed.

Generated Visual Studio/Premake output is written to Build/, Bin/, and Bin-Int/ and is ignored by Git.

The IndexSDK demo is optional and is only generated when a complete SDK exists in Thirdparty/IndexSDK-Dist-windows-x86_64:

premake5 vs2022 --with-demo