Scene Backend

A backend is the thing that actually loads a scene. There are two in the box — the Unity Scene Manager and Addressables — and ISceneBackend is what makes that choice a lookup rather than a branch.

You will not touch this to load a scene. It matters when you want to know how a scene gets loaded, or when you want to add a way of your own.

The interface

public interface ISceneBackend
{
  bool CanHandle(SceneRefKind kind);

  SceneBackendHandle Load(SceneRef sceneRef);
  SceneBackendHandle Unload(SceneBackendHandle handle);

  float GetProgress(SceneBackendHandle handle);
  bool IsDone(SceneBackendHandle handle);

  bool TryResolveScene(SceneBackendHandle handle, out Scene scene);
}

The addressable-or-not decision happens once per operation, when the resolved SceneRefKind is handed to the registry:

Kind	Backend
BuildIndex, Scene	StandardSceneBackend
Address, AssetReference	AddressablesSceneBackend
Key, None	Rejected — reaching selection with an unresolved key means the resolver was skipped

The one honest difference between them

TryResolveScene is the only method whose answer genuinely differs per backend, and it differs by returning false rather than by warning and handing back a default:

• AddressablesSceneBackend gets a SceneInstance back from Addressables, so it can name its own scene directly.
• StandardSceneBackend cannot. The Unity Scene Manager has no API that says "this AsyncOperation produced that Scene", so the honest answer is "no", and the scene is matched afterwards by the linker.

Returning false rather than a default Scene is what keeps that matching step explicit instead of silent.

Handles

SceneBackendHandle is a readonly struct — a value, not an object — carrying the backend that owns it, the SceneRef it came from, the Scene once known, and the underlying Unity operation.

Handles are ticked by the SceneOperationPump, a single player-loop pass over every live operation. That is what raises Progressed — and only when the value has actually moved past a small epsilon, so a bar bound to it does not churn every frame.

Writing your own backend

SceneBackendRegistry.Register puts yours ahead of the defaults — registration order decides precedence, and the last registered wins:

public class MyBackend : ISceneBackend
{
  public bool CanHandle(SceneRefKind kind) => kind == SceneRefKind.Address;
  // ...
}

SceneBackendRegistry.Register(new MyBackend());

info

This is the extension point for a different asset-delivery system — a custom bundle pipeline, or a storefront SDK that hands you scenes. Implement six methods, register the backend, and every existing call site keeps working.

atenção

The registry is static, so a registration made in the editor survives a disabled Domain Reload. Register from a [RuntimeInitializeOnLoadMethod] rather than from arbitrary code, and be aware that tests which register a backend need to reset it afterwards.