libgdx Ashley Entity System Creating a Sorted Entity System

Example

A simple EntitySystem that processes each entity of a given family in the order specified by a comparator and calls processEntity() for each entity every time the EntitySystem is updated. This is really just a convenience class as rendering systems tend to iterate over a list of entities in a sorted manner. Adding entities will cause the entity list to be resorted. Call forceSort() if you changed your sorting criteria. For more info, please see SortedIteratingSystem

In the below code example, the best usage for this the rendering of your sprites in a sorted order by zindex.

public class SpriteComponent implements Component {
     public TextureRegion region;
     public int z = 0;
}

public class Mapper {
     public static ComponentMapper<SpriteComponent> sprite = ComponentMapper.getFor(SpriteComponent.class);
}

public class RenderingSystem extends SortedIteratingSystem {

    public RenderingSystem () {
         super(Familly.all(SpriteComponent.class).get(), new ZComparator())
    }

    public void processEntity(Entity entity, float deltaTime) {
         if(checkZIndexHasChangeValue()) {
              forceSort();
         }
    }

    private static class ZComparator implements Comparator<Entity> {
        @Override
        public int compare(Entity entityA, Entity entityB) {
            return (int)Math.signum(Mapper.sprite.get(entityA).z - Mapper.sprite.get(entityB).z);
        }
    }

}