Haptics.md

Haptics

The Logitech VR Ink is capable of providing high fidelity haptic feedback using its haptic engine. The haptic engine is compatible with the existing feedback designed for the HTC Vive Controller, and in addition it is possible to create custom feedback using the toolkit.

Implementation

This is an example implementation that allows you to simply trigger a haptic pulse on a button event. Ultimately you will need to implement the HapticAction in relevant places. For instance, the Toolkit also implements the HapticAction on the UIInteractable components and in the SnapInteraction.

You can find an implementation of haptics in the scene 8_Example_Haptics in the HapticsEngine GameObject.

Example Scene

In this scene we have implemented a simple Interaction that makes use of the HapticAction script. This action can be implemented anywhere else in the code where you want a haptic event to trigger. We will see in the following section how to implement a haptic action to create a ratchet feeling when interacting with a slider.

The HapticOnButton interaction is very simple and is made using only a trigger and an action.

If you press the specified button of the specified tracked drevice, you will trigger a haptic pulse with the designated amplitude, frequency and duration on another specified tracked device.

More Complex Haptic Actions

Let's have a look at the implementation of the haptic action in the case of a slider. This is an interesting one as you need to repeat the haptic pulse several time during the interaction to create a feeling of ratcheting.

In scene 4_Example_MenuInteracitons, you can play around with the slider and see that haptic pulses are periodically triggered as you change the value of the slider.

Let's have a look at the code:

//Dedicated inspector block to haptics
[Header("Haptics"), SerializeField]
private bool _enableHaptics = true;
[SerializeField, ShowIf("_enableHaptics")]
private HapticAction _vibrationOnActivation;
[Tooltip("The rate at which haptic ticks will occur, from every 0% - every 100%.")]
[SerializeField, Range(0, 100), ShowIf("_enableHaptics")]
private float _hapticTickRate;

When interacting, you want to trigger a haptic pulse when you first get in contact with slider either by touching the element or interacting with it at distance. In that case you can trigger the haptic pulse once:

//register the TriggerOnce() for when the user physically interact with UI
private void Awake()
{
    UIElement = _slider;
    OnPhysicalPressDown += () => _vibrationOnActivation.TriggerOnce();
}

//Override the OnButtonDownEvent call TriggerOnce() for the haptic action
protected override void OnButtonDownEvent()
{
    if (_enableHaptics)
    {
        if (_firstPress)
        {
            SetCurrentHapticTick();
            _firstPress = false;
        }
        _vibrationOnActivation.TriggerOnce();
    }
}

Now the haptic event can trigger when selecting the slider, but we need to implement that ratchet feeling. That is where the _hapticTickRate parameter comes into play. In our example the tick rate is set to 5, which means that for every 5% of the slider value we will trigger a haptic pulse. Check out the SetCurrentHapticTick method to see how we dynamically set the threshold that lets us trigger the haptic pulse at the right moment.

 private void SliderMove(Vector2 hitCoord)
{
    // Adjust received coordinate to slider direction.
    float normValue;
    switch (_slider.direction)
    {
        case Slider.Direction.BottomToTop:
            normValue = hitCoord.y;
            break;
        case Slider.Direction.LeftToRight:
            normValue = hitCoord.x;
            break;
        case Slider.Direction.RightToLeft:
            normValue = 1f - hitCoord.x;
            break;
        case Slider.Direction.TopToBottom:
            normValue = 1f - hitCoord.y;
            break;
        default:
            return;
    }

    // Update the slider value.
    _slider.value = _slider.minValue + normValue * (_slider.maxValue - _slider.minValue);

    if (_enableHaptics)
    {
        if (_slider.value >= _maxTickValue || _slider.value <= _minTickValue)
        {
            SetCurrentHapticTick();
            _vibrationOnActivation.TriggerOnce();
        }
    }
}