GL Commands within a system?

I want to convert this code to ECS:
https://docs.unity3d.com/ScriptReference/GL.LINES.html

Here's my quick attempt that doesn't work:

Spoiler: GLCommandsSystem.cs

Code (CSharp):

1. using Unity.Entities;
2. using UnityEngine;
3. using Unity.Rendering;
4.  
5.  
6. [AlwaysUpdateSystem]
7. [UpdateInGroup(typeof( PresentationSystemGroup ))]
8. [UpdateAfter(typeof(MatrixPreviousSystem))]
9. public class GLCommandsSystem : SystemBase
10. {
11.  
12.     // Draws a line from "startVertex" var to the curent mouse position.
13.     Material mat;
14.     Vector3 startVertex;
15.     Vector3 mousePos;
16.  
17.     protected override void OnCreate()
18.     {
19.         startVertex = Vector3.zero;
20.         mousePos = Vector3.one;
21.         mat = Resources.Load<Material>("Line"); // Default Sprite Renderer
22.     }
23.  
24.     protected override void OnUpdate()
25.     {
26.        
27.         mousePos = Input.mousePosition;
28.         // Press space to update startVertex
29.         if (Input.GetKeyDown(KeyCode.Space))
30.         {
31.             startVertex = new Vector3(mousePos.x / Screen.width, mousePos.y / Screen.height, 0);
32.         }
33.  
34.  
35.         if (!mat)
36.         {
37.             Debug.LogError("Please Assign a material on the inspector");
38.             return;
39.         }
40.         GL.PushMatrix();
41.         mat.SetPass(0);
42.         GL.LoadOrtho();
43.  
44.         GL.Begin(GL.LINES);
45.         GL.Color(Color.red);
46.         GL.Vertex(startVertex);
47.         GL.Vertex(new Vector3(mousePos.x / Screen.width, mousePos.y / Screen.height, 0));
48.         GL.End();
49.  
50.         GL.PopMatrix();
51.  
52.         Debug.Log("mouse: " + mousePos.ToString());
53.  
54.     }
55.    
56. }

I am using HDRP so maybe that's the issue?