How to best structure entities?

help
1

I'm trying to set up an ECS for my game. I'm a bit lost as to how an indexing (instead of pointer) system works to look up entities.

In the following small sample (taken from creating ECS) , entities make use of various components as to not have it inside of itself. Therefore any entity can access any component they'd want.

struct PhysicsComponent { ... }
struct HumanoidItemsComponent { ... }
struct HealthComponent { ... }

type EntityIndex = usize;

struct Assets { ... }

struct GameState {
    assets: Assets,

    // All of these component vecs must be the same length, which is the current
    // number of entities.
    physics_components: Vec<Option<PhysicsComponent>>,
    humanoid_items_components: Vec<Option<HumanoidItemsComponent>>,
    health_components: Vec<Option<HealthComponent>>,
    player_components: Vec<Option<PlayerComponents>>,

    players: Vec<EntityIndex>,

    ...
}

Now, I can't figure out how the entities are stored; how do you loop over them? I can see there's an index, so an integer refers to an entity. But how do you make the int EntityIndex greater?
Do you use a function to set it; EntityIndex++?

However that is done, the players are a Vec of integers.
But how do you get the information out of the players Vec? It is just a number.

This is more of a problem for me with Enemies, since I won't be dealing with multiple players. But if I would have a Vec of enemy Indexes, the same would apply. I don't understand how you store the actual data of the Enemy and loop over it efficiently with this system.

2

If you want to loop over the indexes, skipping the ones that are None, you could do this:

for i in 0..state.physics_components.len() {
    if state.physics_components[i].is_none() { continue; }
    ...
}
3

Ay. But as I said, I don't even know how best to up the Index..

4

Since your index type is usize, you can do this:

let new_idx = old_idx + 1;

or

my_idx += 1;
5

Ok thanks, pretty simple.

So any idea how to get to the actual data?

6

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