ZK_Framework/Assets/NewBehaviourScript.cs

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

public class NewBehaviourScript : MonoBehaviour
{
    private Vector3 start;

    // Start is called before the first frame update
    void Start()
    {
    }

    // Update is called once per frame
    void Update()
    {
        if (Input.GetMouseButtonDown(0))
        {
            this.start = Input.mousePosition;
        }

        if (Input.GetMouseButton(0))
        {
            var distance = Vector3.Distance(this.start, Input.mousePosition);
            var mousePosition = this.start - Input.mousePosition;
            Debug.Log(distance + " + " + mousePosition);
        }

        if (Input.GetMouseButtonUp(0))
        {
            this.start = Vector3.zero;
        }
    }
}