detect zoom in/out by 2 touches.

TouchZoom

using UnityEngine;
using System.Collections;

public class NewBehaviourScript : MonoBehaviour
{
    public int lastTouchCount;
    public float startTouchSpace;
    public float thisTouchSpace;

    public bool isControl;
    public bool isZoomIn;
    public float zoomValue;

    // Use this for initialization
    void Start()
    {

    }

    // Update is called once per frame
    void Update()
    {
        if (Input.touchCount == 2)
        {
            isControl = true;
            var t1 = Input.GetTouch(0);
            var t2 = Input.GetTouch(1);

            thisTouchSpace = (t1.position - t2.position).magnitude;

            if (Input.touchCount != lastTouchCount)
                startTouchSpace = thisTouchSpace;

            var zoomValue_t = thisTouchSpace - startTouchSpace;

            if (Mathf.Abs(zoomValue_t - zoomValue) > 3f)
            {
                zoomValue = zoomValue_t;
            }

            isZoomIn = zoomValue < 0f;
        }
        else
        {
            isControl = false;
        }
        lastTouchCount = Input.touchCount;
    }

    void OnGUI()
    {
        if (isControl)
        {
            GUILayout.Label(isZoomIn ? "zoom in" : "zoom out");
            GUILayout.Label("value:" + zoomValue);
        }
    }
}