Graphics.DrawMeshInstancedIndirect - multiple submeshes

Hi,

I'm trying to get the DrawMeshInstancedIndirect work with multiple submeshes on a mesh (one call for each submesh index). I have succeeded with a single submesh mesh, but I'm having difficulty understanding the parameters for the argsbuffer (buffer with arguments) for the submeshes.

Here is the argsbuffer I'm trying to use for each submesh (where j is the submesh index)

Code (CSharp):

1.                  
2. uint[] args = new uint[5]
3. {
4.      mesh.GetIndexCount(j), // index count per instance
5.      (uint)instanceCount,
6.      mesh.GetIndexStart(j),   // start index location
7.      mesh.GetBaseVertex(j), // base vertex location
8.      0  // start instance location ???
9. }
10.  

The actual implementation is a bit too complex to post here, as I use a compute shader for visibility calculations, append to an append buffer and copycount the append buffer instance count to the args buffer. This works all fine when I use a single submesh mesh. For the multiple submesh version, I have corresponding append buffers, args buffers and materials (created in code) but I think I can't figure out the arguments for the argsbuffers. The result is only one of the submeshes being rendered no matter what I do.

Any help would be appreciated. (Shouting out to @richardkettlewell )

 

Ok, so I figured this out. If anyone is interested, the way args is constructed above is working as intended. The problem in my case was the way in which I set the append buffers for the materials.

 

If I may revive this thread, using Unity 5.6 when I use DrawMeshInstancedIndirect and use an argsOffset as one of the arguments to draw my submeshes, the performance tanks horribly. The profiler typically adds this overhead under GBuffer or ForwardObjectsToDepth, but the performance loss is several orders of magnitude.

In contrast, if I just make a seperate args buffer for every single submesh, and just change which buffer I pass to the DrawMeshInstancedIndirect and keep argsOffset to 0, then my performance is as we would expect from the function, aka phenomenal.

Has this bug been resolved in a newer version, and is there any insight into what the reason for this is?
It was reported here:
https://forum.unity.com/threads/drawmeshinstancedindirect-example-comments-and-questions.446080/
by XaneFeather, but he didnt elaborate much on it and he was ignored, but what he reports in terms of performance loss is exactly what I notice as well.

Also, if I may ask, what is the purpose of "int submeshIndex" in the draw call? I set this to the correct value (the index of my submesh, or 0 if I have no submeshes), and then for fun I changed the value and saw it had absolutely no impact, I can set it to any number thats within my submesh range and there is 0 visual impact. What does this actually do under the hood?

 

Well, I was aware of what the intent of the argument was, but it doesnt seem to actually do that. I took your own script you posted above, changed submeshIndexto a hard coded 0 in the draw call. Then issued drawcalls for any of the 4 submeshes of my tree, and they all worked. That is to say that the value of submeshIndexis having absolutely no noticeable impact on the draw call.

The selected submesh seems to only be described by the argsBuffer by changing the starting index of the triangle in the mesh as well as the number of indexes. Those 2 arguments are sufficient to describe the submesh you wish to draw call, so then what exactly is submeshIndex doing under the hood?

To clarify, I dont mean the submeshIndex in your script, I mean in the actual draw call functions:

public static void DrawMeshInstancedIndirect(Mesh mesh, int submeshIndex, Material material, Bounds bounds, ComputeBuffer bufferWithArgs, int argsOffset = 0,MaterialPropertyBlock properties = null, Rendering.ShadowCastingMode castShadows = ShadowCastingMode.On, bool receiveShadows = true, int layer = 0, Camera camera = null);

Feel free to try it out with your script, at the very least for me on unity 5.6 the int submeshIndex argument does nothing discernable.

 

I seem to be getting the same issue. I will probably try splitting my meshes with submeshes into multiple meshes with no submeshes to get it working...
The submesh index seems to work fine for

Graphics.DrawMeshInstanced

, but does not work at all for

Graphics.DrawMeshInstancedIndirect

 

I tried hard with Graphics.DrawMeshInstancedIndirect() function to renderer mesh with multiple submeshes.Can not get it work.Meshes work fine with standed shader,but will crack in DrawMeshInstancedIndirect().Vertices is deranged.Will this will fixed in next version?

 

Look at my code here, I am sure there is nothing wrong with this. At first I just use fbx files, and it have two materials.It does not work.Then I use two meshes and combine them with code below, I found somthing fun.The submesh0 works fine, but submesh1 was wrong. Look at the image, submesh0 is the cube, submesh1 is the sphere.



I also tried DrawMeshInstanced(), it also can't work well, but I can switch the index param make it work. With DrawMeshInstancedIndirect(), it works with the way in the image.I want submit a bug,but I don't know where can I do this.

Code (CSharp):

1. using System.Collections;
2. using System.Collections.Generic;
3. using System.Runtime.InteropServices;
4. using Unity.Mathematics;
5. using UnityEngine;
6. using UnityEngine.Rendering;
7.  
8. public class SubMeshTest : MonoBehaviour {
9.     public Transform target;
10.     public Mesh mesh0;
11.     public Mesh mesh1;
12.  
13.     private Mesh combinedMesh;
14.  
15.     public Material mat0;
16.     public Material mat1;
17.  
18.     public Vector3 pos;
19.  
20.  
21.     private ComputeBuffer argsBuffer0;
22.     private ComputeBuffer argsBuffer1;
23.  
24.     private ComputeBuffer trsBuffer0;
25.     private ComputeBuffer trsBuffer1;
26.  
27.     uint[] args0 = new uint[5];
28.     uint[] args1 = new uint[5];
29.  
30.     Matrix4x4[] drawData0 = new Matrix4x4[1];
31.     Matrix4x4[] drawData1 = new Matrix4x4[1];
32.  
33.     bool inited = false;
34.     // Start is called before the first frame update
35.     void Start()
36.     {
37.         CombineInstance[] inses = new CombineInstance[2];
38.         CombineInstance CI0 = new CombineInstance() {
39.             mesh = mesh0,
40.             //subMeshIndex = 0,
41.             transform = target.localToWorldMatrix
42.         };
43.         CombineInstance CI1 = new CombineInstance() {
44.             mesh = mesh1,
45.             //subMeshIndex = 1,
46.             transform = target.localToWorldMatrix
47.  
48.         };
49.         inses[0] = CI0;
50.         inses[1] = CI1;
51.  
52.         combinedMesh = new Mesh();
53.         combinedMesh.CombineMeshes(inses, false);
54.         inited = true;
55.         UnityEngine.Debug.Log("Combined    " + combinedMesh.subMeshCount);
56.     }
57.  
58.     // Update is called once per frame
59.     void Update() {
60.         if (!inited) {
61.             return;
62.         }
63.  
64.         if (argsBuffer0 != null) {
65.             argsBuffer0.Release();
66.             argsBuffer0.Dispose();
67.         }
68.         if (argsBuffer1 != null) {
69.             argsBuffer1.Release();
70.             argsBuffer1.Dispose();
71.         }
72.  
73.         args0[0] = combinedMesh.GetIndexCount(0);
74.         args0[1] = 1;
75.         args1[0] = combinedMesh.GetIndexCount(1);
76.         args1[1] = 1;
77.         SubMeshDescriptor sub0 = combinedMesh.GetSubMesh(0);
78.         SubMeshDescriptor sub1 = combinedMesh.GetSubMesh(1);
79.        
80.         UnityEngine.Debug.Log($" indexCount:{combinedMesh.vertexCount}");
81.         UnityEngine.Debug.Log($"--A  indexStart:{sub0.indexStart} indexCount:{sub0.indexCount}");
82.         UnityEngine.Debug.Log($"--B  indexStart:{sub1.indexStart} indexCount:{sub1.indexCount}");
83.  
84.         drawData0[0] = Matrix4x4.Translate(pos) * Matrix4x4.Rotate(Quaternion.Euler(0, 0,0)) * Matrix4x4.TRS(-sub0.bounds.center + Vector3.up, Quaternion.identity, Vector3.one) ;
85.         drawData1[0] = Matrix4x4.Translate(pos) * Matrix4x4.Rotate(Quaternion.Euler(0, 0, 0)) * Matrix4x4.TRS(-sub1.bounds.center + Vector3.down, Quaternion.identity, Vector3.one) ;
86.  
87.  
88.  
89.         argsBuffer0 = new ComputeBuffer(5, Marshal.SizeOf(typeof(uint)), ComputeBufferType.IndirectArguments);
90.         argsBuffer1 = new ComputeBuffer(5, Marshal.SizeOf(typeof(uint)), ComputeBufferType.IndirectArguments);
91.  
92.         trsBuffer0 = new ComputeBuffer(1, Marshal.SizeOf(typeof(float4x4)));
93.         trsBuffer1 = new ComputeBuffer(1, Marshal.SizeOf(typeof(float4x4)));
94.  
95.         argsBuffer0.SetData(args0);
96.         argsBuffer1.SetData(args1);
97.  
98.         trsBuffer0.SetData(drawData0);
99.         trsBuffer1.SetData(drawData1);
100.  
101.         mat0.SetBuffer("classifyResult", trsBuffer0);
102.         mat1.SetBuffer("classifyResult", trsBuffer1);
103.  
104.         Graphics.DrawMeshInstancedIndirect(
105.             combinedMesh,
106.             0,
107.             mat0,
108.             new Bounds(Vector3.zero, new Vector3(2000000, 2000000, 2000000)),
109.             argsBuffer0);
110.  
111.         Graphics.DrawMeshInstancedIndirect(
112.             combinedMesh,
113.             1,
114.             mat1,
115.             new Bounds(Vector3.zero, new Vector3(2000000, 2000000, 2000000)),
116.             argsBuffer1);
117.     }
118. }
119.  

 

Thank you for reply,I fixed this by looking at others codes.There is something wrong with my codes.It's the argsBuffer data.
the right one is below:

Code (CSharp):

1.         args1[0] = combinedMesh.GetIndexCount(1);
2.         args1[1] = 1;
3.         args1[2] = combinedMesh.GetIndexStart(1);