I'm working on a 3d grid based game, and I am trying to implement it using an ECS.
I have a position component which indicates the entity's position on the grid. It is comprised of 3 integers (for example [1,3,2]). Now lets imagine the user clicked on position [1,3,2]. I now want to efficiently retrieve all entities in position [1,3,2].
I can see only one way to achieve that using an ECS. I need to filter for all components that have a position component (this can be done in O(1)), then filter through all the position components to find only those positions that equal [1,3,2]. This is extremely inefficient, since I have a hundred thousand entities with a position component to loop through, but I only need a minuscule fraction of them.
It's important to note that I never need to loop through all the hundred thousand position components in a single frame in any other case. For all other systems, I filter entities that have both a position component as well as other components, so I end up only looping through a small fraction of positions in each frame. This means I cant just retrieve all the relevant entities as part of the loop that goes through all the positions, since I dont have such a loop.
Traditionally using OOP, I would have a dictionary from a position to a container that contains all the objects in that position, which would allow me to accomplish the above in O(1). This isn't correct design for an ECS though, from what I understand.
Am I misunderstanding something about Entity Systems? If anyone has any advice I would be glad to hear it.