Component of prefab uses prefab's scene in Load

[Dreikblack]

If i just use component with saved scene from Load() everything works.

But if i save entity as prefab, scene will expire. Most likely it's due scene in Load is Prefab's scene - scene->navmeshes is empty for prefab component in Load when real scene have it. Component and its prefab example

TestPrefab.zip

[Josh]

This is by design. The prefab has a temporary scene all entities are loaded into, which allows each component to retrieve the objects in that prefab.

What happens if you move the navmesh code into the first call to the Update() method? Something like this:

class component
{
	std::weak_ptr<Scene> scene;
}

void component::Update()
{
  auto scene = this->scene.lock();
  if (not scene)
  {
      scene = MyGame->scene;
      this->scene = scene;
      if (scene and not scene->navmeshes.empty())
      {
            //do some things here...
      }
  }
}

 

[Dreikblack]

3 hours ago, Josh said:

scene = MyGame->scene;

This is something that i can do in my game by using Singletones, but it's not proper option for components to share in Downloads or tutorials.

3 hours ago, Josh said:

component to retrieve the objects in that prefab.

Which should be possible via kids of root entity and normal scene anyway?

[Dreikblack]

And if it's needed internally can be normal scene be send to component Load() since it's called per instance anyway?

[Josh]

2 hours ago, Dreikblack said:

This is something that i can do in my game by using Singletones, but it's not proper option for components to share in Downloads or tutorials.

Which should be possible via kids of root entity and normal scene anyway?

Not exactly. Prefabs have a UUID for each entity, but since there can be multiple prefabs of the same file loaded, a new UUID is generated when the prefab gets added to the main scene. It's messy.

[Dreikblack]

Maybe something like std::list<std::weak_ptr<Scene>> scenes; can be added to World?

[Josh]

I am going to leave this open because I want to think about it more.

[Josh]

Okay, it appears the way you are using the prefab scene object is to add a created entity into the scene.

This seems like a bad approach to me. Is there some reason this must be done?

		auto targetPivotShared = CreatePivot(gameCamera->GetWorld());
		targetPivotShared->SetPickMode(PICK_NONE);
		targetPivotShared->SetPosition(targetPosition);
		targetPivotShared->SetRotation(0, gameCamera->GetRotation(true).y, gameCamera->GetRotation(true).z);
		gameCamera->SetParent(targetPivotShared); 
		sceneWeak.lock()->AddEntity(targetPivotShared);
		targetPivot = targetPivotShared;

 

[Dreikblack]

7 hours ago, Josh said:

This seems like a bad approach to me. Is there some reason this must be done?

It's most clear approach if anything for this case and just one of many uses of scene. Another often case is getting navemesh.

It's done to temporally save pivot until scene will be deleted. Camera have to be parented to this pivot so camera component can't have strong reference to the pivot to avoid circular references. The only another way to do it would be making extra component for a pivot which is already worse approach.

And no, it will not work if i will use pivot instead of camera and spawn camera with component because it would be require a LOT of extra stuff to make it work (pivot should be on the ground, so it could not be placed in the Editor like camera in air etc.).

[Josh]

The need to access the navmesh in order to create navigation agents is a good argument for some solution to be found for this.

Maybe the engine could replace all entity UUID values with the new ones in the loaded scene and pass the scene handle to the Load command.

[Josh]

I have made the change and I am compiling now. If everything works correctly, you may mark this issue solved.

[Josh]

FYI, this means that prefabs cannot contain navmeshes that can be accessed. I think this is the right choice.