ViveTouchpadScroll.cs

using System;
using System.Collections.Generic;
using UnityEngine;

[RequireComponent(typeof(SteamVR_TrackedObject))]
public class ViveTouchpadScroll : MonoBehaviour
{
    Vector2 scrollDelta = Vector2.zero;
    Vector2 lastTouchpadPosition = Vector2.zero;

    SteamVR_Controller.Device _controller;
    SteamVR_Controller.Device controller
    {
        get
        {
            if (_controller == null)
            {
                // Be careful if this index changes while the controller is cached
                var index = GetComponent<SteamVR_TrackedObject>().index;
                _controller = SteamVR_Controller.Input((int)index);
            }
            return _controller;
        }
    }

    void Update()
    {
        if (controller.GetTouchDown(EVRButtonId.k_EButton_SteamVR_Touchpad))
        {
            lastTouchpadPosition = GetTouchPosition();
        }

        if (controller.GetTouch(EVRButtonId.k_EButton_SteamVR_Touchpad))
        {
            var touchPosition = GetTouchPosition();

            float horizDelta = (touchPosition.x - lastTouchpadPosition.x) / Time.deltaTime;
            float vertDelta = (touchPosition.y - lastTouchpadPosition.y) / Time.deltaTime;

            scrollDelta = new Vector2(horizDelta, vertDelta);
            lastTouchpadPosition = touchPosition;
        }
        else
        {
            scrollDelta = Vector2.zero;
        }
    }

    Vector2 GetTouchPosition()
    {
        return controller.GetAxis(EVRButtonId.k_EButton_SteamVR_Touchpad);
    }

    public float GetHorizontalScrollDelta()
    {
        return scrollDelta.x;
    }

    public float GetVerticalScrollDelta()
    {
        return scrollDelta.y;
    }
}