# Singleton

## The Singleton

HPTK requires an instance of the HPTK component which will be publicly accessible from the static variable **HPTK.core**.

The following code exemplifies how to access this singleton in order to retrieve the AvatarView of the first registered avatar:

```
AvatarView avatar = HPTK.core.avatars[0];
```

You have more code examples [here](/hptk/master/examples.md).

![](/files/-MZgOoL8UCbHzSFypDUg)

## Variables

#### Tracked Camera

Represents the **Transform in your scene that will always match user's sight**.

This is **manually provided** as it's a platform-dependent variable. According to you platform this Transform will be found in the following GameObjects:

* **OVR:** OVRCameraRig > TrackingSpace > CenterEyeAnchor
* **UnityXR:** XRRig > Camera Offset > Main Camera

{% hint style="info" %}
If you use **DefaultSetup** prefabs this value is already set.
{% endhint %}

If **BodyModel.masterHeadFollowsCamera** is **enabled**, the master representation of BodyModel.head will be moved to match `HPTK.core.trackedCamera`. This application will be straight forward if `BodyModel.referenceTsf` or `BodyModel.replicatedTsf` are NULL, and it will be relative otherwise.

#### TrackingSpace

Represents the **Transform in your scene that will always match user's feet (floor)**.

If tracking space origin will be at **floor level (by default)**, this variable should refer to **tracking space origin**.

If tracking space origin will be at **eye leve**l, this variable should refer to some **Transform that always stays under camera at floor leve**l. This can be achieved through a custom Transform with a **Position Contraint** configured as show in the following image.

#### Default Conf Assets

Some HPTK modules require a **configuration asset (ScriptableObject)**. **If this reference is missing**, the Controller of the module will access `HPTK.core.defaultConfAssets` and **wil search in this list** for a configuration asset that matches the required type.

#### Controls Update Calls

If **enabled**, HPTK singleton will call, each frame, `AvatarController.ControllerUpdate()` for each registered avatar in the order of registration. Each `AvatarController.ControllerUpdate()` call will update each module registered in the avatar or any of its bodies or parts, always in order of registration. This is **useful if we are using some order-sensitive custom module** but this is not the case for any module included in the HPTK package or any of its current extensions.

If **disabled (recommended)**, each HPTKController will be updated by itself by calling its `ControllerUpdate()` method during its `Update()` method.

#### Input Data Providers

Similarly to *Default Conf Assets*, these Input Data Providers (IDPs) will be **accessed by Input modules that have no IDP already referenced**.

If you are **in PlayMode**, editor IDPs will be used. If you are **in build**, build IDPs will be used.

This way if **you can press Play in UnityEditor, a simulation of your player's movements will be played for debugging quicker**. Without any extra change, **if you build and play your app in your device, "build" IDPs will take control**.

**If you need to use build IDPs in editor** for instance to use hand tracking in Unity through Oculus Link, just **replace their references in the singleton**.

#### Layer to apply

**When an avatar is self-registered** in the singleton's list of avatars, this layer (layer "*HPTK"* by default) is **applied to each representations of the root bone of each of the bodies of the avatar and its children** gameobjects as well, recursively.

#### Events

* **OnAvatarEntered:** An avatar was registered and the ControllerStart() function of its Controller was called and completed.
* **OnAvatarExited:** An avatar is about to be removed from `HPTK.core.avatars`.


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