ecs.c

// We control two systems with two tags:
// - when Dirty, a system adds a Texture component to an entity
// - when Visible, a system renders the Texture component
//
// Visible is set on a base entity and inherited by the textured entity
  ...
  ecs_entity_t eOverlay = ecs_new_w_pair(world, EcsChildOf, ui->e);
  ecs_set_name(world, eOverlay, "debugOverlay");
  ecs_add(world, eOverlay, Visible);
  
  ecs_entity_t eTps = ecs_new_w_pair(world, EcsIsA, eOverlay);
  ecs_set_name(world, eTps, "tpsText");
  ecs_set(world, eTps, Texture, { NULL });
  ...
    

void
SdlImport(ecs_world_t* world)
{
  ECS_MODULE(world, Sdl);

  ECS_COMPONENT_DEFINE(world, Texture);

  ECS_IMPORT(world, Ui);  // for Visible tag
  
  // This is the system that fails to run after the system below 
  // removes Dirty from the entity
  ECS_SYSTEM_DEFINE(
      world,
      lm_sdl_sys_render_textures,
      0,
      [in] Texture,
      [in] Visible);
}



void
TtfImport(ecs_world_t* world)
{
  ECS_MODULE(world, Ttf);

  ECS_IMPORT(world, Sdl); // for Texture component

  ECS_TAG_DEFINE(world, Dirty);

  // This is the system that removes Dirty from the entity
  ECS_SYSTEM_DEFINE(
      world,
      lm_ttf_sys_bake_textures,
      0,
      [out] Texture,
      [EcsInOut] Dirty);
}



// Every frame, the first thing we do is add the Dirty tag
void
lm_ui_overlay_debug_update(ecs_world_t* world)
{
  ...
  ecs_add(world, eTps, Dirty);
}


// At this point, the types of the two entities are
// Base (eOverlay)                ui.Visible, (Identifier,Name), (ChildOf,ui)
// Descendant (eTps)  sdl.Texture, ttf.Dirty, (Identifier,Name), (IsA,ui.debugOverlay)



// Next we run the system that queries the Dirty tag, and removes it
ecs_run(world, ecs_id(lm_ttf_sys_bake_textures), ...

void
lm_ttf_sys_bake_textures(ecs_iter_t* it)
{
  Texture* textures = ecs_term(it, Texture, 1);

  for (size_t i = 0; i < it->count; ++i) {
    ecs_entity_t e = it->entities[i];

    textures[i].tex = ...

    // Everything works fine if we don't do this:
    ecs_remove(it->world, e, Dirty);

    log_debug("Baked %d", it->entities[i]);
  }
}


        
// At this point, the types of the two entities are
// Base (eOverlay)     ui.Visible, (Identifier,Name), (ChildOf,ui)
// Descendant (eTps)  sdl.Texture, (Identifier,Name), (IsA,ui.debugOverlay)

        

// Then we run the system that queries the Visible tag
ecs_run(world, ecs_id(lm_sdl_sys_render_textures), ...

void
lm_sdl_sys_render_textures(ecs_iter_t* it)
{
  Texture* textures   = ecs_term(it, Texture, 1);

  for (size_t i = 0; i < it->count; ++i) {
    log_debug("Rendered %d", it->entities[i]);
  }
}
        
        
// If we do not remove the Dirty tag then everything runs every frame:
Baked 553
Rendered 553
Baked 553
...
        
// If we do remove the Dirty tag then the second system stops running:
Baked 553
Baked 553
...