A pure system is a system that only cares about component presence, and thus would be more efficient to test entities against (since we can grab the entity's components, then only test against systems that care about said components).
Purity can be defined at two levels: has at least one component, has every component.
A pure system is a system that only cares about component presence, and thus would be more efficient to test entities against (since we can grab the entity's components, then only test against systems that care about said components).
Purity can be defined at two levels: has at least one component, has every component.