[CrimsonCape]

Any idea why the example image in the OP link appears to be running at sub-optimal framerate?

What is the expected ECS overhead per frame (not including graphics interaction, i.e. code specifically in the ECS model)?

Since an ECS is typically a flattened scene graph, is there still a game loop? Wouldn't be necessary, correct? You only need to respond to the inputs...

[_cart]

I would say that the systems in the ECS _are_ the game loop. The ECS overhead per frame is kind of hard to measure / it depends on the scale of usage. To establish the scale of operations: Random single-entity ECS data accesses are a sparse array lookup to find the table the entity is in, and then an array lookup to find the component in the table. Iterating components in a query is roughly the same as iterating an array / is very cache friendly. Running individual systems is _slightly_ more expensive than a function call. Scheduling systems in parallel does introduce some overhead (which is currently higher than we'd like / we're working on optimizing it), but when you pay that cost you get the benefits of everything running in parallel.

[_cart]

That is a size-optimized webp / gif that isn't running at 60 fps. The game is butter smooth in practice: https://twitter.com/jarl_game

[james7132]

There is still a game loop that runs every tick. The engine wouldn't work so well if we only responded to inputs as they come in, event pub-sub style.

As for ECS overhead, I've made it one of my top priorities to eliminate it wherever possible since it underpins the entire engine. We're at the point where most optimizations are saving a few tens or low-hundreds of microseconds per frame in your average game/app (i.e. lowering context switch costs from parallel system execution). If you're pushing below 60 FPS in your app, chances are the performance issues are not coming from the ECS, but some other part of the engine, or the app's own code.

[SkiFire13]

> Since an ECS is typically a flattened scene graph, is there still a game loop? Wouldn't be necessary, correct? You only need to respond to the inputs...

How do you plan to have stuff moving then? You need to update their position every frame, so...