How to use Graphics.DrawProcedural to render a quad over a scene?

I want to learn this so I could do some screen space particles in Unity. This is meant as a sort of "hello world" shader.

my current script is:

 using System.Collections;
 using System.Collections.Generic;
 using UnityEngine;
 using System.Runtime.InteropServices;

 public class ParticleFX : MonoBehaviour
 {

 public int particlecount = 4;
 private Material material;

 void Start()
 {
         material = new Material(Shader.Find("Hidden/CustomParticle"));
 }


 void OnRenderImage(RenderTexture source, RenderTexture destination)
 {

     material.SetPass(0);
     Graphics.DrawProcedural(MeshTopology.Quads, particlecount, 1);

 }

 void OnDestroy()
 {

 }
 }

And my shader looks like this:

 Shader "Hidden/CustomParticle"
 {
 SubShader
 {
     Pass
 {
     CGPROGRAM
 #pragma vertex vert
 #pragma fragment frag
 #include "UnityCG.cginc"
 #pragma target 3.5

     struct v2f {
     fixed4 color : TEXCOORD0;
     float4 pos : SV_POSITION;
 };

 v2f vert(
     uint vid : SV_VertexID // vertex ID, needs to be uint
 )
 {
     v2f o;
     o.pos = UnityObjectToClipPos(float3(vid>>1,vid&1,1));
     o.color = float4(1,0,0,1);
     return o;
 }

 fixed4 frag(v2f i) : SV_Target
 {
     return i.color;
 }
     ENDCG
   }
  }
 }

I expect to see a red quad cover my scene, but I don't. The core part is learning to use Graphics.DrawProcedural().