unity 3d 鼠标旋转物体脚本

using UnityEngine;
using System.Collections;

public class CubeRotate : MonoBehaviour
{

Vector3 StartPosition;
Vector3 previousPosition;
Vector3 offset;
Vector3 finalOffset;
Vector3 eulerAngle;

bool isSlide;
float angle;

void Start()
{

}

void Update()
{
if (Input.GetMouseButtonDown(0))
{
StartPosition = Input.mousePosition;
previousPosition = Input.mousePosition;
}
if (Input.GetMouseButton(0))
{
offset = Input.mousePosition - previousPosition;
previousPosition = Input.mousePosition;
transform.Rotate(Vector3.Cross(offset, Vector3.forward).normalized, offset.magnitude, Space.World);
}
if (Input.GetMouseButtonUp(0))
{
finalOffset = Input.mousePosition - StartPosition;
isSlide = true;
angle = finalOffset.magnitude;
}
if (isSlide)
{
transform.Rotate(Vector3.Cross(finalOffset, Vector3.forward).normalized, angle * 2 * Time.deltaTime, Space.World);
if (angle > 0)
{
angle -= 5;
}
else
{
angle = 0;
}
}
}
}