Simple ECS.md

Description of a simple ECS

Requirements

• seperation between static and dynamic components

• dynamic components regulary change
• static components normally don't change

• static components can be shared between entities

• when changing a static component, it will change for all components, which share it

• iteration will only touch the important components
• the components are statically typed

Implementation details

Storage

• there is an array for each component type
• there is a single array, which contains the indices of the static components
• for each combination of components used in a system, there's an additional array

• it contains the set of indices of the components
• instead it may also just contain a single index to a data structure containing the component specific indices (less memory usage, additional indirection)

Add and remove entities

• when adding a new entity, all used components have to be specified
• depending on the specified components, a different function will be called
• the entities will only be added to the matching component combination arrays
• removing entites is much more difficult

• requires runtime function dispatch

Iterating over objects

• systems are just functions bound to a component combination

• they take one argument for each component (or instead a single tuple of references)
• they can take additional arguments
• only dynamic components are mutable

• when calling a system with some arguments, the additional arguemnts will be passed to every object afterwards

Change object type

• it has to be possible to remove components from or add components to a type
• therefore it has to be removed from or added to some component combination arrays
• this also requires runtime function dispatch

Optional optimizations

• it's possible to create multiple arrays for each dynamic component and copy them instead of changing them inplace