RotateMV

using UnityEngine;
using System.Collections;

public class DragRotateX : MonoBehaviour
{
    public Vector3 selectedAxis = Vector3.one;
    public float speed = 5;



    private Quaternion originalRotation;
    private float startAngle = 0;
    public Vector3 tempVector;

    public void Start()
    {
        originalRotation = this.transform.rotation;
    }
    public void Update()
    {
        if (Input.GetMouseButtonDown(0))
        {
           MouseDown();
        }

        //This block of code should be the last 2 things in your update
        if (Input.GetMouseButton(0))
        {
           MouseHeld();
           return;
        }
        transform.localEulerAngles = RotateAxisToNearestSide(transform.localEulerAngles, selectedAxis);
    }

   Vector3 RotateAxisToNearestSide(Vector3 eulerAngles, Vector3 selectedAxis)
    {
        Vector3 rounded = RoundToNearest90Degree(eulerAngles);
        Vector3 slerped = Vector3.Slerp(eulerAngles, rounded, Time.deltaTime * speed);
        return SetSelectedAxis(eulerAngles, slerped, selectedAxis);
    }

    Vector3 RoundToNearest90Degree(Vector3 eulerAngles)
    {
        for(int i = 0; i < 3; i++)
        {
            eulerAngles[i] = Mathf.Round(eulerAngles[i] / 90f) * 90f;
        }
        return eulerAngles;
    }

    Vector3 SetSelectedAxis(Vector3 original, Vector3 desired, Vector3 selectedAxis)
    {
        for(int i = 0; i < 3; i++)
        {
            if(selectedAxis[i] != 0)
            {
                selectedAxis[i] = desired[i];
            }else{
                selectedAxis[i] = original[i];
            }
        }

        return selectedAxis;
    }






    public void MouseDown()
    {
        originalRotation = this.transform.rotation;
        Vector3 screenPos = Camera.main.WorldToScreenPoint(transform.position);
        Vector3 vector = Input.mousePosition - screenPos;
        startAngle = Mathf.Atan2(vector.y, vector.x) * Mathf.Rad2Deg;
    }
    public void MouseHeld()
    {
        Vector3 screenPos = Camera.main.WorldToScreenPoint(transform.position);
        Vector3 vector = Input.mousePosition - screenPos;
        float angle = Mathf.Atan2(vector.y, vector.x) * Mathf.Rad2Deg;
        Quaternion newRotation = Quaternion.AngleAxis(angle - startAngle, this.transform.up);
        newRotation.z = 0;
        newRotation.eulerAngles = new Vector3(0, -newRotation.eulerAngles.y, 0);
        this.transform.rotation = originalRotation * (newRotation);
    }
}