Object is not rotating from right direction

Question

im beginner to unity so im using this code to rotate object with mouse with max rotation of 35 degrees,it is working but it's only possible to rotate object if mouse is under of that object. here is my code:

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

public class rotObj : MonoBehaviour {
    //private float baseAngle = 0.0f;
    private float maxRotaion = 35f;
    void Update () {
        var dir = Camera.main.ScreenToWorldPoint (Input.mousePosition) - transform.position;
        var angle = Mathf.Atan2 (dir.y, dir.x) * Mathf.Rad2Deg;
        if (angle >= -maxRotaion && angle <= maxRotaion)
            transform.localRotation = Quaternion.AngleAxis (angle, Vector3.forward);
    }
}

as i think, localrotation is making that problem? how can i fix this without removing maximum rotation angle and will be able to rotate object not just from mouse under object, but from any position? my english grammar is very bad but i hope you will understand

Answer 1

The standard mathematical convention for the angles returned by atan2(y, x) is that they're measured counter-clockwise from the positive x-axis.

If I understand your problem correctly, you want to measure them from the positive y-axis instead, which you can do by rotating your coordinates 90 degrees clockwise (exchanging x & y and negating x):

var dir = Camera.main.ScreenToWorldPoint (Input.mousePosition) - transform.position;
var angle = Mathf.Atan2 (-dir.x, dir.y) * Mathf.Rad2Deg;

Or, for more flexibility, you could capture the direction your object is pointing at startup, and measure your angles from that direction. Then you can rotate your turret to any arbitrary angle and it will work, without needing different atan math for every combination:

Quaternion initialOrientation;

private void Start() {
    initialOrientation = transform.rotation;
}

void Update() {        
    var dir = Camera.main.ScreenToWorldPoint(Input.mousePosition + Vector3.forward) - transform.position;
    // Rotate the direction into our initial reference frame.
    dir = Quaternion.Inverse(initialOrientation) * dir;

    var angle = Mathf.Atan2(-dir.x, dir.y) * Mathf.Rad2Deg;
    angle = Mathf.Clamp(angle, -maxRotaion, maxRotaion);

    // Rotate the result back into worldspace.
    transform.rotation = initialOrientation * Quaternion.AngleAxis(angle, Vector3.forward);
}