Best way to think about ECS is a generic pattern to help make things data oriented. It’s not necessarily going to be optimal though. It’s SoA over the Entity ra

Best way to think about ECS is a generic pattern to help make things data oriented. It’s not necessarily going to be optimal though. It’s SoA over the Entity rather than individual struct members which might in a more tuned setup be more performant. This is also where ECS as a pattern falls down (from the simplistic ideas about them being performant) because keeping components in packed arrays is only one part of making them efficient. The biggest issue is making sure your entity data is best organised for the most common data access patterns. For example you can’t actually store data in big blocks of single component type but need to consider the shapes/archetypes (common sets of components) that make up an Entity. For each archetype we can store the components packed in arrays so that they can be iterated contiguously. That way Systems can visit all of the archetypes that contain the components they care about and iterate straight through them whilst minimising cache misses. This approach obviously falls down the more heterogeneous your Entities are. It also incurs a cost when a component is added or removed from an Entity so makes some common ECS patterns more expensive. There are other approaches with different trade offs. But this is also pretty academic for most games which don’t have the entity count or gameplay complexity to actually require this level of performance anxiety.