EnTT: Gaming meets modern C++

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EnTT is a header-only, tiny and easy to use library for game programming and much more written in modern C++, mainly known for its innovative entity-component-system (ECS) model.
Among others, it's used in Minecraft by Mojang and the ArcGIS Runtime SDKs by Esri.
If you don't see your project in the list, please open an issue, submit a PR or add the #entt tag to your topics! :+1:


Do you want to keep up with changes or do you have a question that doesn't require you to open an issue?
Join the gitter channel and meet other users like you. The more we are, the better for everyone.

Wondering why your debug build is so slow on Windows or how to represent a hierarchy with components?
Check out the FAQ and the wiki if you have these or other doubts, your answers may already be there.

If you use EnTT and you want to say thanks or support the project, please consider becoming a sponsor.
You can help me make the difference. Many thanks to those who supported me and still support me today.

Table of Contents

Introduction

The entity-component-system (also known as ECS) is an architectural pattern used mostly in game development. For further details:

This project started off as a pure entity-component system. Over time the codebase has grown as more and more classes and functionalities were added.
Here is a brief, yet incomplete list of what it offers today:

  • Statically generated integer identifiers for types (assigned either at compile-time or at runtime).
  • A constexpr utility for human readable resource names.
  • A minimal configuration system built using the monostate pattern.
  • An incredibly fast entity-component system based on sparse sets, with its own pay for what you use policy to adjust performance and memory usage according to the users' requirements.
  • Views and groups to iterate entities and components and allow different access patterns, from perfect SoA to fully random.
  • A lot of facilities built on top of the entity-component system to help the users and avoid reinventing the wheel (dependencies, snapshot, actor class, support for reactive systems and so on).
  • The smallest and most basic implementation of a service locator ever seen.
  • A built-in, non-intrusive and macro-free runtime reflection system.
  • A cooperative scheduler for processes of any type.
  • All that is needed for resource management (cache, loaders, handles).
  • Delegates, signal handlers (with built-in support for collectors) and a tiny event dispatcher for immediate and delayed events to integrate in loops.
  • A general purpose event emitter as a CRTP idiom based class template.
  • And much more! Check out the wiki.

Consider this list a work in progress as well as the project. The whole API is fully documented in-code for those who are brave enough to read it.

Currently, EnTT is tested on Linux, Microsoft Windows and OSX. It has proven to work also on both Android and iOS.
Most likely it won't be problematic on other systems as well, but it hasn't been sufficiently tested so far.

Code Example

#include <entt/entt.hpp>
#include <cstdint>

struct position {
    float x;
    float y;
};

struct velocity {
    float dx;
    float dy;
};

void update(entt::registry &registry) {
    auto view = registry.view<position, velocity>();

    for(auto entity: view) {
        // gets only the components that are going to be used ...

        auto &vel = view.get<velocity>(entity);

        vel.dx = 0.;
        vel.dy = 0.;

        // ...
    }
}

void update(std::uint64_t dt, entt::registry &registry) {
    registry.view<position, velocity>().each([dt](auto &pos, auto &vel) {
        // gets all the components of the view at once ...

        pos.x += vel.dx * dt;
        pos.y += vel.dy * dt;

        // ...
    });
}

int main() {
    entt::registry registry;
    std::uint64_t dt = 16;

    for(auto i = 0; i < 10; ++i) {
        auto entity = registry.create();
        registry.emplace<position>(entity, i * 1.f, i * 1.f);
        if(i % 2 == 0) { registry.emplace<velocity>(entity, i * .1f, i * .1f); }
    }

    update(dt, registry);
    update(registry);

    // ...
}

Motivation

I started developing EnTT for the wrong reason: my goal was to design an entity-component system to beat another well known open source solution both in terms of performance and possibly memory usage.
In the end, I did it, but it wasn't very satisfying. Actually it wasn't satisfying at all. The fastest and nothing more, fairly little indeed. When I realized it, I tried hard to keep intact the great performance of EnTT and to add all the features I wanted to see in my own library at the same time.

Nowadays, EnTT is finally what I was looking for: still faster than its competitors, lower memory usage in the average case, a really good API and an amazing set of features. And even more, of course.

Performance

The proposed entity-component system is incredibly fast to iterate entities and components, this is a fact. Some compilers make a lot of optimizations because of how EnTT works, some others aren't that good. In general, if we consider real world cases, EnTT is somewhere between a bit and much faster than many of the other solutions around, although I couldn't check them all for obvious reasons.

If you are interested, you can compile the benchmark test in release mode (to enable compiler optimizations, otherwise it would make little sense) by setting the BUILD_BENCHMARK option of CMake to ON, then evaluate yourself whether you're satisfied with the results or not.

Honestly I got tired of updating the README file whenever there is an improvement.
There are already a lot of projects out there that use EnTT as a basis for comparison (this should already tell you a lot). Many of these benchmarks are completely wrong, many others are simply incomplete, good at omitting some information and using the wrong function to compare a given feature. Certainly there are also good ones but they age quickly if nobody updates them, especially when the library they are dealing with is actively developed.

The choice to use EnTT should be based on its carefully designed API, its set of features and the general performance, not because some single benchmark shows it to be the fastest tool available.

In the future I'll likely try to get even better performance while still adding new features, mainly for fun.
If you want to contribute and/or have suggestions, feel free to make a PR or open an issue to discuss your idea.

Build Instructions

Requirements

To be able to use EnTT, users must provide a full-featured compiler that supports at least C++17.
The requirements below are mandatory to compile the tests and to extract the documentation:

  • CMake version 3.7 or later.
  • Doxygen version 1.8 or later.

Alternatively, Bazel is also supported as a build system (credits to zaucy who offered to maintain it).
In the documentation below I'll still refer to CMake, this being the official build system of the library.

If you are looking for a C++14 version of EnTT, check out the git tag cpp14.

Library

EnTT is a header-only library. This means that including the entt.hpp header is enough to include the library as a whole and use it. For those who are interested only in the entity-component system, consider to include the sole entity/registry.hpp header instead.
It's a matter of adding the following line to the top of a file:

#include <entt/entt.hpp>

Use the line below to include only the entity-component system instead:

#include <entt/entity/registry.hpp>

Then pass the proper -I argument to the compiler to add the src directory to the include paths.

Documentation

The documentation is based on doxygen. To build it:

$ cd build
$ cmake .. -DBUILD_DOCS=ON
$ make

The API reference will be created in HTML format within the directory build/docs/html. To navigate it with your favorite browser:

$ cd build
$ your_favorite_browser docs/html/index.html

It's also available online for the latest version, that is the last stable tag.
Moreover, there exists a wiki dedicated to the project where users can find all related documentation pages.

Tests

To compile and run the tests, EnTT requires googletest.
cmake will download and compile the library before compiling anything else. In order to build the tests, set the CMake option BUILD_TESTING to ON.

To build the most basic set of tests:

  • $ cd build
  • $ cmake -DBUILD_TESTING=ON ..
  • $ make
  • $ make test

Note that benchmarks are not part of this set.

Packaging Tools

EnTT is available for some of the most known packaging tools. In particular:

  • Conan, the C/C++ Package Manager for Developers.

  • vcpkg, Microsoft VC++ Packaging Tool.
    You can download and install EnTT in just a few simple steps:

    $ git clone https://github.com/Microsoft/vcpkg.git
    $ cd vcpkg
    $ ./bootstrap-vcpkg.sh
    $ ./vcpkg integrate install
    $ vcpkg install entt
    

    The EnTT port in vcpkg is kept up to date by Microsoft team members and community contributors.
    If the version is out of date, please create an issue or pull request on the vcpkg repository.

  • Homebrew, the missing package manager for macOS.
    Available as a homebrew formula. Just type the following to install it:

    brew install skypjack/entt/entt
    

Consider this list a work in progress and help me to make it longer.

EnTT in Action

EnTT is widely used in private and commercial applications. I cannot even mention most of them because of some signatures I put on some documents time ago. Fortunately, there are also people who took the time to implement open source projects based on EnTT and did not hold back when it came to documenting them.

Here you can find an incomplete list of games, applications and articles that can be used as a reference.

If you know of other resources out there that are about EnTT, feel free to open an issue or a PR and I'll be glad to add them to the list.

Contributors

EnTT was written initially as a faster alternative to other well known and open source entity-component systems. Nowadays this library is moving its first steps. Much more will come in the future and hopefully I'm going to work on it for a long time.
Requests for features, PR, suggestions ad feedback are highly appreciated.

If you find you can help me and want to contribute to the project with your experience or you do want to get part of the project for some other reasons, feel free to contact me directly (you can find the mail in the profile).
I can't promise that each and every contribution will be accepted, but I can assure that I'll do my best to take them all seriously.

If you decide to participate, please see the guidelines for contributing before to create issues or pull requests.
Take also a look at the contributors list to know who has participated so far.

License

Code and documentation Copyright (c) 2017-2020 Michele Caini.
Logo Copyright (c) 2018-2020 Richard Caseres.

Code released under the MIT license. Documentation released under CC BY 4.0.
Logo released under CC BY-SA 4.0.

Support

If you want to support this project, you can offer me an espresso.
If you find that it's not enough, feel free to help me the way you prefer.






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