4 ms·

I don’t know what ECS is. You should define the acronym…

anentropic 5y ago
Entity Component System commonly used in game programming
mrspeaker 5y ago
"Entity Component Systems" are common in game engine architecture, and there are a lot of variations on them - but they are a high-level architecture for making modular behavior in games. Generally they were thought of as "better than Object Oriented, because they very very heavily favor composition over inheritance." The idea is that everything in your game - like Players, NPCs, Bullets - are Entities. Entities are simply an ID. That's their only property. Nothing else. But there are Components - they have the data. For example, you might have a `PositionComponent` that has an `X Position` and `Y position` property. And maybe a `MassComponent` that has a property `Mass`. Somewhere in the framework (like a database table), a given Component will be related to a given Entity ID. The Entity therefore becomes a "bag of Components" through the relations. Finally there are Systems. They do stuff with the data. One system might be `GravitySystem`. It doesn't care directly about `Entity`s, but can query the relations. It might ask for anything that has BOTH a `PositionComponent` and a `MassComponent` (it doesn't know which Entity it is for - it only gets the Components). It takes any `PositionComponent`s it gets and applies gravity: `component.y += gravity`. The effect is that you can mix and match Components in weird and wonderful ways without having to hard-code behavior and rules for certain entities. You can obviously achieve this with other architectures too - but that's the primary goal of this one.
- thom 5y ago
  Correct me if I’m wrong, but isn’t one of the other motivations to store your data in CPU/memory management friendly ways? It’s not purely about developer ergonomics.
  - mrspeaker 5y ago
    I think originally it was primarily about developer ergonomics - here's the first thing I ever read about them in 2007 where they tested it on Tony Hawk Pro Skater (http://cowboyprogramming.com/2007/01/05/evolve-your-heirachy/ http://cowboyprogramming.com/2007/01/05/evolve-your-heirachy...). The CPU/memory management has been an on-going discussion ever since! Being able to process domains as flat arrays helps with cache misses - but there is a lot of other overhead, depending on how you designed everything. Making it performant was one of the big problems initially, and it seems like the `Component Graph System` this thread is about trying to answer "how do systems efficiently process components?"... But I don't really get how it answers that actually.
    - gmueckl 5y ago
      As far as I understand it this is about the ECS equivalent of an INNER JOIN, that is, some variation on "iterate over all entities that possess instances of component A and B". Iterating over single component types in a system is trivial if they are separated into pools by types. When you have a system requiring more than one component, it isn't that easy to do better than iterating over all entities and checking whether they possess each required component. You can decide to maintain back references from components to their entities, but this means that you incur that management overhead pretty much globally. This essay says that doing away with entities altogether and just keeping direct links between your components is better. And it probably is when it comes to handling related components. However, I believe (without having actually tried it) that this proposal has its own drawbacks. it's harder to thoroughly clean up all components that form a single entity. My suspicion is that it's easier to produce bugs like keeping e.g. a stray collision shape or sound source around while the other parts of an entity are removed. All you need for that to happen is an incomplete graph traversal.
      - Kinrany 5y ago
        I think CGS boils down to smart links between components, which may include SQL-like automatic checks: deleting components that refer to deleted components or components owned by the deleted component.
jcelerier 5y ago
there are two distinct definitions of ECS, the first one given in https://news.ycombinator.com/item?id=27856030 https://news.ycombinator.com/item?id=27856030 is the "(entity-component-system) architecture" where there are entities, components, and systems, as distinct objects in your software. The second is "(entity-component) system" or "entity-component architecture" where the behaviour goes inside components (for instance, Unity3D gameobjects with their components).
nodejs_rulez_1 5y ago
It's good old procedural programming. Systems (procedures) are mutating state (components) grouped by a common ID (entity).
- bordercases 5y ago
  You could do it functionally, i.e. the systems are all reducers on partial states of the world.
- leoc 5y ago
  I'm no expert on any of this but that doesn't seem right; is it? IIUC, most procedural programming is nearly as wedded to the "one entity, one master data structure, one address in memory" frame of mind as OO is. (And the same is true of most functional programming, come to that.)

Entity Component System commonly used in game programming

"Entity Component Systems" are common in game engine architecture, and there are a lot of variations on them - but they are a high-level architecture for making modular behavior in games. Generally they were thought of as "better than Object Oriented, because they very very heavily favor composition over inheritance." The idea is that everything in your game - like Players, NPCs, Bullets - are Entities. Entities are simply an ID. That's their only property. Nothing else. But there are Components - they have the data. For example, you might have a `PositionComponent` that has an `X Position` and `Y position` property. And maybe a `MassComponent` that has a property `Mass`. Somewhere in the framework (like a database table), a given Component will be related to a given Entity ID. The Entity therefore becomes a "bag of Components" through the relations. Finally there are Systems. They do stuff with the data. One system might be `GravitySystem`. It doesn't care directly about `Entity`s, but can query the relations. It might ask for anything that has BOTH a `PositionComponent` and a `MassComponent` (it doesn't know which Entity it is for - it only gets the Components). It takes any `PositionComponent`s it gets and applies gravity: `component.y += gravity`. The effect is that you can mix and match Components in weird and wonderful ways without having to hard-code behavior and rules for certain entities. You can obviously achieve this with other architectures too - but that's the primary goal of this one.

thom 5y ago
Correct me if I’m wrong, but isn’t one of the other motivations to store your data in CPU/memory management friendly ways? It’s not purely about developer ergonomics.
- mrspeaker 5y ago
  I think originally it was primarily about developer ergonomics - here's the first thing I ever read about them in 2007 where they tested it on Tony Hawk Pro Skater (http://cowboyprogramming.com/2007/01/05/evolve-your-heirachy/ http://cowboyprogramming.com/2007/01/05/evolve-your-heirachy...). The CPU/memory management has been an on-going discussion ever since! Being able to process domains as flat arrays helps with cache misses - but there is a lot of other overhead, depending on how you designed everything. Making it performant was one of the big problems initially, and it seems like the `Component Graph System` this thread is about trying to answer "how do systems efficiently process components?"... But I don't really get how it answers that actually.
  - gmueckl 5y ago
    As far as I understand it this is about the ECS equivalent of an INNER JOIN, that is, some variation on "iterate over all entities that possess instances of component A and B". Iterating over single component types in a system is trivial if they are separated into pools by types. When you have a system requiring more than one component, it isn't that easy to do better than iterating over all entities and checking whether they possess each required component. You can decide to maintain back references from components to their entities, but this means that you incur that management overhead pretty much globally. This essay says that doing away with entities altogether and just keeping direct links between your components is better. And it probably is when it comes to handling related components. However, I believe (without having actually tried it) that this proposal has its own drawbacks. it's harder to thoroughly clean up all components that form a single entity. My suspicion is that it's easier to produce bugs like keeping e.g. a stray collision shape or sound source around while the other parts of an entity are removed. All you need for that to happen is an incomplete graph traversal.
    - Kinrany 5y ago
      I think CGS boils down to smart links between components, which may include SQL-like automatic checks: deleting components that refer to deleted components or components owned by the deleted component.

jcelerier 5y ago

there are two distinct definitions of ECS, the first one given in https://news.ycombinator.com/item?id=27856030 https://news.ycombinator.com/item?id=27856030 is the "(entity-component-system) architecture" where there are entities, components, and systems, as distinct objects in your software. The second is "(entity-component) system" or "entity-component architecture" where the behaviour goes inside components (for instance, Unity3D gameobjects with their components).

nodejs_rulez_1 5y ago

It's good old procedural programming. Systems (procedures) are mutating state (components) grouped by a common ID (entity).

bordercases 5y ago
You could do it functionally, i.e. the systems are all reducers on partial states of the world.
leoc 5y ago
I'm no expert on any of this but that doesn't seem right; is it? IIUC, most procedural programming is nearly as wedded to the "one entity, one master data structure, one address in memory" frame of mind as OO is. (And the same is true of most functional programming, come to that.)