Pinch zoom in windows 8 pc

hi,

everyone

i am working on simple orbit and zoom in/out using touch gesture. touch orbit is working excellent but pinch zoom in/out is the main prob.. i tried other scripts also but no success ..

one of the script i applied.

 using UnityEngine;
 using System.Collections;
 
 public class PinchZoom : MonoBehaviour {
 
 public float perspectiveZoomSpeed = .5f;
 public float orthoZoomSpeed = .5f;
 
 
 // Update is called once per frame
 void Update () 
 {
 if (Input.touchCount == 2) 
 {
 Touch touchZero = Input.GetTouch(0);
 Touch touchOne = Input.GetTouch(1);
 
 Vector2 touchZeroPrevPos = touchZero.position - touchZero.deltaPosition;
 Vector2 touchOnePrevPos = touchOne.position - touchOne.deltaPosition;
 
 float prevTouchDeltaMag = (touchZeroPrevPos - touchOnePrevPos).magnitude;
 float touchDeltaMag = (touchZero.position - touchOne.position).magnitude;
 
 float deltaMagnitudediff = prevTouchDeltaMag - touchDeltaMag;
 
 if(camera.isOrthoGraphic)
 {
 camera.orthographicSize += deltaMagnitudediff * orthoZoomSpeed;
 camera.orthographicSize = Mathf.Max(camera.orthographicSize , .1f);
 }
 else
 {
 
 camera.fieldOfView += deltaMagnitudediff * perspectiveZoomSpeed;
 camera.fieldOfView = Mathf.Clamp(camera.fieldOfView, .1f , 179.9f);
 }
 
 
 
 }
 
 }
 }

i found one demo for touch script i was planing to buy that plugin for my solution. but same prob occur in plugin's web player demo ...

here's the link of plugin's demo.

http://fingergestures.fatalfrog.com/features/online-demo

i tried in my windows 8 laptop and also on lenovo Horizon. same issue ..

plz guys tell me whats the prob i am facing.??

thanx