mixed-reality

Tracking loss in Unity

When the device can’t locate itself in the world, the app experiences “tracking loss”. By default, Unity will pause the update loop and display a splash image to the user anytime tracking is lost. Once tracking is regained, the splash image goes away and the update loop continues.

As an alternative, the user can manually handle this transition by opting out of the setting. All content will seem to become body locked during tracking loss if nothing is done to handle it.

Default Handling

The update loop and all messages and events will stop for the duration of tracking loss by default. At that same time, an image will be displayed to the user. You can customize this image by going to Edit->Settings->Player, clicking Splash Image, and setting the Holographic Tracking Loss image.

Manual Handling

To manually handle tracking loss, you need to go to Edit > Project Settings > Player > Universal Windows Platform settings tab > Splash Image > Windows Holographic and uncheck “On Tracking Loss Pause and Show Image”. After which, you need to handle tracking changes with the APIs specified below.

Namespace: UnityEngine.XR.WSA
Type: WorldManager

World Manager exposes an event to detect tracking lost/gained (WorldManager.OnPositionalLocatorStateChanged) and a property to query the current state (WorldManager.state)
When the tracking state isn’t active, the camera won’t appear to translate in the virtual world even as the user translates. Objects will no longer correspond to any physical location and all will appear body locked.

When handling tracking changes on your own, you either need to poll for the state property each frame or handle the OnPositionalLocatorStateChanged event.

Polling

The most important state is PositionalLocatorState.Active, which means tracking is fully functional. Any other state will result in only rotational deltas to the main camera. For example:

void Update()
{
    switch (UnityEngine.XR.WSA.WorldManager.state)
    {
        case PositionalLocatorState.Active:
            // handle active
            break;
        case PositionalLocatorState.Activating:
        case PositionalLocatorState.Inhibited:
        case PositionalLocatorState.OrientationOnly:
        case PositionalLocatorState.Unavailable:
        default:
            // only rotational information is available
            break;
    }
}

Handling the OnPositionalLocatorStateChanged event

More conveniently, you can also subscribe to OnPositionalLocatorStateChanged to handle the transitions:

void Start()
{
    UnityEngine.XR.WSA.WorldManager.OnPositionalLocatorStateChanged += WorldManager_OnPositionalLocatorStateChanged;
}

private void WorldManager_OnPositionalLocatorStateChanged(PositionalLocatorState oldState, PositionalLocatorState newState)
{
    if (newState == PositionalLocatorState.Active)
    {
        // Handle becoming active
    }
    else
    {
        // Handle becoming rotational only
    }
}