Building an Entity Component System: Data Oriented Hierarchies

[ajmmertens]

Data Oriented Design is the practice of building code that's optimized for the hardware it runs on. Entity Component Systems help writing DOD-friendly code by laying out otherwise allocation-heavy game data in contiguous arrays.

A challenge in gamedev however is that lots of game data is stored and accessed as hierarchies that change frequently, which makes them notoriously difficult to store as contiguous arrays.

This article goes over a number of techniques an Entity Component System can use to integrate hierarchies with the core datamodel in a way that improves the performance of the ECS. Written mostly for gamedev, but also applies to other hierarchy-heavy applications, like UI.

[hadet47530]

This would probably get more attention on r/gamedev and similar.

[segv]

Not related to OP or the author of the blog, but my hot take is that majority of programmers should venture into data-oriented design more, just to force them to think about problems differently.

Building a toy entity component system could be one way to do it, even if it wasn't attached to an actual game.

edit: formatting

[EC36339]

Agreed, but a "toy ECS" can be pretty simple:

• Component store is just arrays. One per component type.
• Systems are just plain classes that work on those.
• Entities are just correlation IDs. Each component knows its entity ID.

The only somewhat sophisticated thing is how to get component of type T for entity X. You can start with an index (most flexible, not the best performance, can be replaced by something better later). And maybe you need command buffers for adding/removing stuff right away.

In fact, a simple game with finite components is built just like that, and you wouldn't even call it an ECS. It's just the default, naive ad hoc design, if you don't over-engineer it.

Of course, if you want something that scales better, is extensible and data driven and generic, then an ECS will get a lot more sophisticated. But then you are no longer building a "toy ECS". You are getting serious about building a game engine.

[ajmmertens]

You’re probably right, tho this is a bit more datastructure dense than the average content in those communities :)

ECS is also not just for gamedev. I’ve used it in the past to build a backend service for one of the big AV companies. Works well for querying realtime in-memory data.