awesome-uiwidgets/AwesomeUIWidgets/Assets/Scripts/RaycastableScene/DragRotate.cs

using System;
using UnityEngine;
using UnityEngine.EventSystems;
using UInput = UnityEngine.Input;

namespace UIWidgetsSample.RaycastableScene
{
    public class DragRotate : MonoBehaviour
    {
        Vector2? _lastPosition;

        public static Vector2 mousePosition
        {
            get
            {
                return new Vector2(UInput.mousePosition.x, UInput.mousePosition.y);
            }
        }

        void OnMouseDown()
        {
            if (EventSystem.current.IsPointerOverGameObject())
            {
                return;
            }
            
            _lastPosition = mousePosition;
        }

        private void OnMouseUp()
        {
            _lastPosition = null;
        }

        private void OnMouseDrag()
        {
            if (_lastPosition == null)
            {
                return;
            }
            Vector2 direction = mousePosition - _lastPosition.Value;
            _lastPosition = mousePosition;
            
            transform.Rotate(-direction.y, -direction.x, 0, Space.World);
        }
    }
}