[unity technology accumulation] realize the mouse line drawing function &linerenderer

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

public class Painting : MonoBehaviour
{
    
    private LineRenderer lineRenderer;

    //  Record point 
    private Vector3 nowPos;

    //  Line width 
    public float lineWidth = 0.5f;

    //  Set the material 
    public Material material;

    private void Update()
    {
    
        //  When the mouse is pressed, the starting position switches 
        if (Input.GetMouseButtonDown(0))
        {
    
            //  Create an empty object and add components 
            GameObject obj = new GameObject();
            lineRenderer = obj.AddComponent<LineRenderer>();
            
            // Turn off automatic stitching 
            lineRenderer.loop = false;

            //  Set line width 
            lineRenderer.startWidth = lineWidth;
            lineRenderer.endWidth = lineWidth;

            //  Set the number of points to 0
            lineRenderer.positionCount = 0;

            //  Set line material 
            lineRenderer.material = material;

            //  Set the material to be affected by light 
            lineRenderer.generateLightingData = true;
        }

        //  When drawing, the mouse is pressed all the time 
        if (Input.GetMouseButton(0))
        {
    
            lineRenderer.positionCount += 1;

            //  Record the mouse position 
            nowPos = Input.mousePosition;
            
            //  Set the cross section to 10
            nowPos.z = 10;

            //  Set point 
            //  Mouse position viewport coordinates into world coordinates 
            lineRenderer.SetPosition(lineRenderer.positionCount
                - 1, Camera.main.ScreenToWorldPoint(nowPos));

        }
    }
}