SpectatorView.StateSynchronization.md

State synchronization

Pre-compilation

1. All of the assets in the unity project need to be assigned unique identifiers. This allows content in the user's application scene to be recreated/updated/destroyed dynamically in the spectator's application scene. This is done through calling Spectator View -> Update All Asset Caches in the Unity toolbar prior to compiling the application.

Note: Adding, updating and removing assets will require updating these asset caches as well as re-compiling each platform.

In application

1. On the user device, a StateSynchronizationBroadcaster is enabled, while on the spectator device a StateSynchronizationObserver is enabled.

   • These classes are responsible for delegating both network messages and network changes to the StateSynchronizationSceneManager, which drives scene state synchronization.
   • These classes are used to relay camera location, application time, and performance data from the user to spectator device.
   • These classes allow other components to register for custom network events and send network messages through the CommandService (Note: this allows Spatial Alignment components to use the same network connection).

2. In both the user and spectator application, ComponentBroadcasterServices register with the StateSynchronizationSceneManager.

   • ComponentBroadcasterServices specify ComponentBroadcaster types for in scene class types. This allows broadcasters to be created as new components are added to the user application scene.
   • ComponentBroadcasterServices also register for a specific id so that they can receive network messages and create ComponentObservers in the spectator scene.

3. When the StateSynchronizationBroadcaster observes that a StateSynchronizationObserver has connected, the user's scene is configured to be broadcasted. Configuring the user scene for broadcasting requires adding TransformBroadcasters to root game objects of content that is intended to be synchronized. This can be achieved through different manners:

   • GameObjectHierarchyBroadcaster items in the Unity scene will add a TransformBroadcaster to their associated game object.
   • If BroadcasterSettings.AutomaticallyBroadcastAllGameObjects is set to true, a TransformBroadcaster will be added to the root game object of every scene (This is DISABLED by default in SpectatorView).

4. On awake and for every related hierarchy change, the TransformBroadcaster will ensure that all of its children also have TransformBroadcasters. On creation, TransformBroadcasters also make sure that their associated game objects have ComponentBroadcasters created for all components with registered ComponentBroadcasterServices. This effectively sets up the classes needed for components in the user application to broadcast state information to spectator devices.

5. After each frame on the user device, the StateSynchronizationSceneManager will monitor network connection changes. It also determine if any ComponentBroadcasters have been destroyed. It then hands all of the known network connections to each ComponentBroadcaster so that state information can be sent to the spectator devices.

6. On the spectator device, the StateSynchronizationSceneManager will receive network messages to relay to the appropriate ComponentBroadcasterServices. These messages signal component creation, updates and destruction on the users device. This component state information also contains unique component ids that allow specific instances of ComponentBroadcasters on the user device to map 1:1 with specific instances of ComponentObservers on the spectator device. Through this state information, the spectator device's scene is updated to reflect content on the user's device.