entt VS ecs-faq

EnTT is a popular alternative to flecs for C++, which has different performance/memory characteristics.

https://pastebin.com/VPypiitk This is a very small experiment i did to learn the metaprogramming features. its an ECS library using the same model as entt (https://github.com/skypjack/entt). In 200 lines or so it does the equivalent of a few thousand lines of template heavy Cpp while compiling instantly and generating good debug code.

Some walkthrough:

Line 8 declares a SparseSet type as a fairly typical template. its just a struct with arrays of type T inside. Next lines implement getters/setters for this data structure

Line 46 Base_Registry things get interesting. This is a struct that holds a bunch of SparseSet of different types, and providers getters/setters for them by type. It uses code generation to do this. The initial #insert at the start of the class injects codegen that creates structure members from the type list the struct gets on its declaration. Note also how type-lists are a native structure in the lang, no need for variadics.

Line 99 i decide to do variadic style tail templates anyway for fun. I implement a function that takes a typelist and returns the tail, and the struct is created through recursion as one would do in cpp. Getters and setters for the View struct are also implemented through recursion

Line 143 has the for expansion. This is how you overload the for loop functionality to create custom iterators.

The rest of the code is just some basic test code that runs the thing.

Since we wanted a common game simulation that would be on both the server and the client we looked into a few libraries that would fit our ECS needs. It was decided we were going to write this common part of our game in C++, but rust was considered. C++ was a familiar language for us so naturally EnTT and flecs came up right away. I had used EnTT before, writing some small demo projects, so our choice was made based on familiarity. In order to integrate with Unity we created a small C interface to communicate between our simulation code and Unity’s C#. Here’s close to what it looked like. I removed some parts for brevity sake.

Are you sure you don't want to use a C++ package manager? Libtcod is on Vcpkg and with that setup you could add the fmt library or EnTT. fmt fixes C++'s string handling and EnTT fixes everything wrong with the entities of the previous tutorials.

There's also a performance question. While we can now use Blueprint nativization to convert Blueprints to C++ the result will be a fairly naive version, fast enough for most purposes but not if you're trying to push every bit of performance. This is where you're looking at making sure you're hitting things such as using the CPU cache as well as possible for an ECS system (Look at ENTT or Flecs if you want to see what they're about and why you'd want one), or a system needing to process massive amounts of data quickly such as the Voxel Plugin.

For a modern engine you’re probably best looking at Unity’s DOTS. You may also want to check out some of the different open source ECS libraries such as flecs and EnTT are two popular ones for C++, but there’s lots of them. Largely you’ll see lots of different approaches taken, all with their own pros and cons. Not all of them will be performant (some focus more on the design benefits) while others will be optimised for certain use cases. What you should prioritise will depend on your specific needs.

You can think of DynaMix as combining one of these libraries with an ECS like entt(https://github.com/skypjack/entt)

The Wikipedia article provides a broad overview, while this FAQ offers a more systematic exploration: https://github.com/SanderMertens/ecs-faq

Sparsey is an Entity Component System focused on flexibility, conciseness and providing features exclusive to its sparse set-based implementation.

For further reading, here is a great article about these different approaches within Rust specifically: https://csherratt.github.io/blog/posts/specs-and-legion/ and here is a great general resource for commonly-used terms and techniques in ECS development: https://github.com/SanderMertens/ecs-faq

Godot has a node based system (nodes can have child nodes linked to them, and there are different types of nodes for the type of functionality they represent). Another alternative could be a more OOP approach (utilising inheritance as the main means of extending functionality), not aware of any modern engines that take this approach anymore. It’s also worth noting that ECS implementations can differ wildly, this faq from the flecs creator has a good rundown on what some of different variants are.

You might wanna take a look at https://github.com/SanderMertens/ecs-faq, it lays this all out better than I can.

To find more about ECS, see the FAQ: https://github.com/SanderMertens/ecs-faq/blob/master/README.md

Using the relational model for app data in memory is really interesting.

Martin Fowler wrote about doing that as a way to get around the "object-relational mismatch" issue[1]. Richard Fabian describes "data-oriented design" as having a lot of overlap with the relational model[2]. ECSes becoming very popular in game engines are basically in-memory relational databases where "components" are "tables"[3].

[1]: https://martinfowler.com/bliki/OrmHate.html

[2]: https://dataorienteddesign.com/dodbook/

[3]: https://github.com/SanderMertens/ecs-faq#what-is-ecs

This is the ECS FAQ I'm currently using.

While Unity's DOTS/ECS is positioned as solving performance issues for large numbers of objects, there are a number of other advantages. See https://github.com/SanderMertens/ecs-faq for a more in-depth look. IMHO the reusability and extensibility ECS encourages is as valuable as any performance increase. Compared to the GameObject style, which encourages random state mutations and side-effects, ECS enforces a more functional style, which results in code that is easier to reason about and test.

thanks, i think a little more background on the ECS world will help you get the context, this is from the author of Flecs: https://github.com/SanderMertens/ecs-faq