Make a trail of triangles that follow the mouse

mouseTriangles.cs

// Draw a set of triangles that follow the mouse.
// This script should be attached to a GameObject that has a MeshRenderer (with Material).
// The script will create a MeshFilter and fill it with triangles.  On each frame, one triangle will be changed to appear at the mouse position.  It cycles through all the triangles, to create a tail of fixed length.
using System.Collections;
using System.Collections.Generic;
using UnityEngine;

public class mouseTriangles : MonoBehaviour {

  public int numTriangles=1;
  private int numVerts=3, curVert=0;
  private Vector3[] verts;
  private Mesh myMesh;

  void Start ()
    {
    gameObject.AddComponent<MeshFilter>();
    myMesh = GetComponent<MeshFilter>().mesh;
    numVerts = numTriangles * 3;
    verts = new Vector3[numVerts];
    for (int i=0; i < numVerts; i++)
        verts[i] = new Vector3(0f, 0f, 0f);
    myMesh.vertices = verts;
    int[] tris = new int[numVerts];
    for (int i=0; i < numVerts; i++)
        tris[i] = i;
    myMesh.triangles = tris;
    }
    
  void Update ()
    {
    verts[curVert] = Camera.main.ScreenToWorldPoint(new Vector3(Input.mousePosition.x+10, Input.mousePosition.y-5, Camera.main.nearClipPlane));
    verts[curVert+1] = Camera.main.ScreenToWorldPoint(new Vector3(Input.mousePosition.x-10, Input.mousePosition.y-5, Camera.main.nearClipPlane));
    verts[curVert+2] = Camera.main.ScreenToWorldPoint(new Vector3(Input.mousePosition.x, Input.mousePosition.y+5, Camera.main.nearClipPlane));
    curVert = (curVert+3) % numVerts;
    myMesh.vertices = verts;
    }
}