Changing entity order

[hfn92]

Hi, I have a case where I want to reorder some components after using sort while otherwise retaining the sorted order. Is this possible with the current api?

I was hoping to be able to something like this

  esc.sort<ToSort>([](auto& l, auto& r) { return l < r; });

  for (auto&& [e, order] : ecs.view<ForceOrderBefore>().each())
  {
    auto it = ecs.storage<ToSort>().find(order.entity);
    ecs.storage<ToSort>().move_to(it, e); // reinsert?
  }

  for (auto&& [e, order] : ecs.view<ForceOrderAfter>().each())
  {
    auto it = ecs.storage<ToSort>().find(order.entity);
    ecs.storage<ToSort>().move_to(it + 1, e);
  }

[skypjack]

Elements are stored in a paged vector. move_to isn't that easy to implement actually. 🙂
However, why not a single ForceOrder component with before and after members that you can use while sorting instead?
It looks much easier and even more efficient. 🤔

[skypjack]

How does the ForceOrderBefore enter the game then? I would expect something like a Renderable component with a z member instead.

[hfn92]

I would add that when creating the entity with its sub entities, each of which have their own components required for rendering.

[skypjack]

So, the parent entity has not the ForceOrderBefore and no z at all while the children have a ForceOrderBefore which is a sort of higher z if compared with that of the parent?

[hfn92]

The parent entity might have it's own graphical components. I'd just want an entity rendered in front of another despite it's z value being lower. The parent child relationship doesn't really matter for the renderer.

[skypjack]

I must admit that I don't get exactly all conditions and nuances of your approach.
In any case, from your last sentence you can just have a z and actual z value, the latter is also affected by ForceOrderBefore in a separate system. Then you can just sort it rather than trying the path of a post-sort fix of your order.
However, all solutions have the same problem imho. That is, you can have inconsistency in how ForceOrderBefore components are assigned to entities and this leads to errors no matter what.