Hand

The Hand node represents a hand in the scene environment. The hand presence and visualization is of high importance when running immersive VR applications on devices such Oculus or OpenVR and even in AR experiences.

The hand node provides an important set of functionalities, such as:

• Support for different type of hands, device-related or generic.

• Automatic link from Oculus and OpenVR devices matrix to hand matrix.

• Free or position presets based finger management.

• Exposed hand and index finger matrix.

• Interaction with Rect2D nodes through ItemMonitor and Texture2D.

• Collision with CMeshes

Platform support

This node is fully supported on XR-Windows platform.

It is partially supported on XR-Portable Windows, XR-Portable iOS, XR-Portable Android, and XR-P WASM platforms.

Hand types

There are five supported types of hand, which can be specified by the handType field.

Each type (except off) must correspond to a specific geometry model (mwxTemplate field) with a specific naming convention.

Note: Users can provide custom geometry models for hands and devices, but they must reflect the joint and the geometry names used in the default models.

Hand position

When using a tracked device, such Oculus Touch or Vive controller, the hand is automatically linked to the device through the sensorMatrix field.

When using the hand in screen mode, the best option is to link the hand to the camera using the cameraSpace attribute. The position and orientation fields can be used to offset and to adapt placement to model-specific characteristics.

Finger posture

Each finger is managed through a set of four rotations (in radiants). The current hand posture is defined by an mvec4 field named fingersValues that consists of five rotation vectors from thumb to the little finger.

For the long fingers, the meaning of the four rotations are:

• Angle between first finger bone and the palm.

• Angle between middle finger bone and first finger bone.

• Angle between last finger bone and middle finger bone.

• Left-right finger abduction angle.

For the thumb, the meaning of the four rotations are:

• Angle between thumb and palm.

• Angle between middle finger bone and first finger bone.

• Angle between last finger bone and middle finger bone.

• Rotation of the thumb on its axes.

Managing finger posture

There are two ways to control the finger posture: by directly setting the posture angles or by using presets. You can mix both approaches and the last set posture set will take priority.

You can edit a preset by using the fingersValuesPresetDefintions dictionary to add new presets or modifying existing presets.

Fingers can react to a new posture in two ways: immediate or smooth, depending on the activation of the useFingersValuesFollower field.

When the follower is activated, posture values assigned to the fingersValuesFollower field are transfered to the fingersValues progressively with a delay based on the fingersValuesFollowerMul field value.

Interacting with ItemMonitor

As the position of the indexTerminalMatrix does not correspond to the index finger tip, but to its base where there is the joint with next bone, the indexFingerTipOffset and getIndexFingerTipMatrix have been added to be able to better map the finger tip position and improve interaction with ItemMonitors.

The offset is automatically added to the indexTerminalMatrix when the hand interacts with the monitor; however, it's also possible to get the resulting finger tip matrix using the sfunction field getIndexFingerTipMatrix.

Colliding with Cmeshes

The Hand node is able to manage different types of collision detection with collision meshes (Cmesh).

The mode is set by the enableCollisionWithCMesh field value with the following options: none, index, hand, and methacarpus.

The value none disables collision detection, while methacarpus and index can be applied only to left and right hand types.

While collision is happening, the collisionWithCMesh value is set to true and and the fully qualified collision mesh name is set in the collisionWithCMeshName field.

Code example

This is a code example for the Hand node.

<Hand name="test_hand_r" mwxTemplate="user\hand_r.mwx" mwxTemplateTag="HAND_NAME" handType="right" cameraSpace="true" position="0. -0.1 0.35" orientation="0 0 0" fingersValuesPreset="point"/>

Hand fields

These are the fields for Hand node. Only the node-specific fields are indicated, not fields obtained by inheritance.

Field inheritance: NodeBase > Hand