在Unity中使用鼠标滚动或触摸进行缩放

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

public class ZoomBehaviour : MonoBehaviour
{
    float MouseZoomSpeed = 15.0f;
    float TouchZoomSpeed = 0.1f;
	float ZoomMinBound = 0.1f;
	float ZoomMaxBound = 179.9f;
    Camera cam;

    // Use this for initialization
    void Start()
    {
        cam = GetComponent<Camera>();
    }

    void Update()
    {
        if (Input.touchSupported)
        {
            // Pinch to zoom
            if (Input.touchCount == 2)
            {
				// get current touch positions
                Touch tZero = Input.GetTouch(0);
                Touch tOne = Input.GetTouch(1);
				// get touch position from the previous frame
				Vector2 tZeroPrevious = tZero.position - tZero.deltaPosition;
				Vector2 tOnePrevious = tOne.position - tOne.deltaPosition;

				float oldTouchDistance = Vector2.Distance (tZeroPrevious, tOnePrevious);
				float currentTouchDistance = Vector2.Distance (tZero.position, tOne.position);

				// get offset value
				float deltaDistance = oldTouchDistance - currentTouchDistance;
				Zoom (deltaDistance, TouchZoomSpeed);
            }
        }
        else
        {
            float scroll = Input.GetAxis("Mouse ScrollWheel");
            Zoom(scroll, MouseZoomSpeed);
        }
    }

    void Zoom(float deltaMagnitudeDiff, float speed)
    {
        cam.fieldOfView += deltaMagnitudeDiff * speed;
        // set min and max value of Clamp function upon your requirement
		cam.fieldOfView = Mathf.Clamp(cam.fieldOfView, ZoomMinBound, ZoomMaxBound);
    }
}