Graphics.DrawMeshiInstancedIndirect Only Rendering 1 instance

I am trying to use append buffers to control a dynamic list of locations for spawning grass meshes (and later other type of foliage). I have had a lot of trouble trying to get the append buffers working.

I think I am on the right track with the code below, but only 1 mesh is being rendered at a time, flicking around which obviously isn't very helpful, but otherwise generally seeming to be following the sine wave threshold. I'm v new to shaders and have been trying to follow the Ned Makes Games and Acerola tutorials, and can see that this problem is solved when they do frustum culling, but I haven't yet been able to work out how to rework this for my purpose.

The code is adapted from this forum post: https://forum.unity.com/threads/app...er-how-to-transfer-to-geometry-shader.664927/

Code (CSharp):

1. using UnityEngine;
2.  
3. public class AppendBuffer : MonoBehaviour
4. {
5.     public Material material;
6.     public ComputeShader shader;
7.     public int size = 8;
8.  
9.     public Mesh grassMesh;
10.  
11.     ComputeBuffer meshTriangles;
12.     ComputeBuffer meshPositions;
13.  
14.     ComputeBuffer buffer, argBuffer;
15.     Bounds bounds;
16.  
17.     Vector3[] buf;
18.  
19.     void Start()
20.     {
21.         int[] triangles = grassMesh.triangles;
22.         meshTriangles = new ComputeBuffer(triangles.Length, sizeof(int));
23.         meshTriangles.SetData(triangles);
24.  
25.         Vector3[] positions = grassMesh.vertices;
26.         meshPositions = new ComputeBuffer(positions.Length, sizeof(float) * 3);
27.         meshPositions.SetData(positions);
28.  
29.         material.SetBuffer("Triangles", meshTriangles);
30.         material.SetBuffer("Positions", meshPositions);
31.  
32.         buffer = new ComputeBuffer(size * size * size, sizeof(float) * 3, ComputeBufferType.Append);
33.         argBuffer = new ComputeBuffer(1, 5*sizeof(int), ComputeBufferType.IndirectArguments);
34.         shader.SetBuffer(0, "buffer", buffer);
35.         shader.SetFloat("size", size);
36.         shader.SetFloat("time", Time.time);
37.         shader.Dispatch(0, size / 8, size / 8, size / 8);
38.         int[] args = new int[] { 0, 1, 0, 0, 0 };
39.         argBuffer.SetData(args);
40.         ComputeBuffer.CopyCount(buffer, argBuffer, 0);
41.         argBuffer.GetData(args);
42.         Debug.Log(args[0]+ "," + args[1]+ "," + args[2]+ "," + args[3]);
43.         bounds = new Bounds(Vector3.zero, new Vector3(-1000, 100, 1000));
44.     }
45.     void Update()
46.     {
47.  
48.         buffer.Release();
49.         argBuffer.Release();
50.  
51.         buffer = new ComputeBuffer(size * size * size, sizeof(float) * 3, ComputeBufferType.Append);
52.         buffer.SetCounterValue(0);
53.         argBuffer = new ComputeBuffer(1, 5*sizeof(int), ComputeBufferType.IndirectArguments);
54.  
55.         shader.SetBuffer(0, "buffer", buffer);
56.         shader.SetFloat("size", size);
57.         shader.SetFloat("time", Time.time);
58.  
59.         shader.Dispatch(0, size / 8, size / 8, size / 8);
60.         int[] args = new int[] { 0, 1, 0, 0, 0 };
61.         argBuffer.SetData(args);
62.         ComputeBuffer.CopyCount(buffer, argBuffer, 0);
63.         buf = new Vector3[buffer.count];
64.         buffer.GetData(buf);
65.         Debug.Log(buf[0] + ", " + buf[1]);
66.         argBuffer.GetData(args);
67.         Debug.Log(args[0] + "," + args[1] + "," + args[2] + "," + args[3]);
68.  
69.         material.SetPass(0);
70.         material.SetBuffer("buffer", buffer);
71.         //Graphics.DrawProceduralIndirect(material, bounds, MeshTopology.Triangles, argBuffer);
72.         Graphics.DrawMeshInstancedIndirect(grassMesh, 0, material, bounds, argBuffer);
73.     }
74.  
75.  
76.     void OnDestroy()
77.     {
78.         buffer.Release();
79.         argBuffer.Release();
80.     }
81. }
82.  

Code (CSharp):

1. // Upgrade NOTE: replaced 'mul(UNITY_MATRIX_MVP,*)' with 'UnityObjectToClipPos(*)'
2.  
3. Shader "AppendBuffer"
4. {
5.     SubShader
6.     {
7.         Cull Off
8.         Pass
9.         {
10.             CGPROGRAM
11.             #pragma vertex VSMain
12.             //#pragma geometry GSMain
13.             #pragma fragment PSMain
14.             #pragma target 5.0
15.  
16.             StructuredBuffer<float3> buffer;
17.             StructuredBuffer<int> Triangles;
18.             StructuredBuffer<float3> Positions;
19.  
20.             struct Structure
21.             {
22.                 float4 position : SV_Position;
23.                 uint id : custom;
24.             };
25.  
26.             Structure VSMain(uint id : SV_VertexID)
27.             {
28.                 Structure VS;
29.  
30.                 VS.position = UnityObjectToClipPos(float4(buffer[id], 1.0));
31.                 VS.id = id;
32.  
33.                 return VS;
34.             }
35.  
36.             float Sign(int x)
37.             {
38.                 return (x > 0) ? 1 : -1;
39.             }
40.  
41.  
42.             float4 PSMain(Structure PS) : SV_Target
43.             {
44.                
45.                 return float4(1.0, 0, 0, 1.0);
46.             }
47.  
48.             ENDCG
49.         }
50.     }
51. }
52.  

Code (CSharp):

1. #pragma kernel CSMain
2.  
3. AppendStructuredBuffer<float3> buffer;
4. float size;
5. uniform float time;
6.  
7. [numthreads(8, 8, 8)]
8. void CSMain(uint3 id : SV_DispatchThreadID)
9. {
10.     if (sin(id.x + id.z + time) > 0.5) {
11.         float3 center = float3(id.x, 0, id.z);
12.         buffer.Append(center);
13.     }
14.  
15. }
16.