ComputeShader - Append Buffer Problem

Hi, I'm trying to use a compute shader with a "AppendStruturedBuffer" (hlsl) , but i only get a "Number overflow" when I try to get the size of my buffer.

When I get the size of my buffer, it's a huge negative value ( - 10e9 ) .

What did I do wrong here ?

Here is my C# code with the function to get the count of the append buffer

Code (CSharp):

1.  
2. public static Vector3[] KeyCam(Vector3 key, Vector3 cam, Vector3[] normal) {
3.             ComputeShader shader = (ComputeShader) Resources.Load("ComputeShader/Normal");
4.             int _kernel = shader.FindKernel("KeyCam");
5.  
6.             ComputeBuffer inputBuffer = new ComputeBuffer(normal.Length, sizeof(float) * 3);
7.             inputBuffer.SetData(normal);
8.             ComputeBuffer outputBuffer = new ComputeBuffer(normal.Length, sizeof(float) * 3, ComputeBufferType.Append);
9.  
10.             shader.SetBuffer(_kernel, "input", inputBuffer);
11.             shader.SetBuffer(_kernel, "output", outputBuffer);
12.             shader.SetVector("key", key);
13.             shader.SetVector("cam", cam);
14.  
15.             shader.Dispatch(_kernel, normal.Length/256, 1, 1);
16.             int c = GetAppendCount(outputBuffer);
17.             Debug.Log("Output Count : "+c + " Normal count : " + normal.Length);
18. //crash here : ofc it can't create a vector with negative size
19.             Vector3[] output = new Vector3[c];
20.             outputBuffer.GetData(output);
21.  
22.             inputBuffer.Dispose();
23.             outputBuffer.Dispose();
24.             return output;
25.         }
26.       //https://sites.google.com/site/aliadevlog/counting-buffers-in-directcompute
27.         private static int GetAppendCount(ComputeBuffer appendBuffer) {
28.             ComputeBuffer countBuffer = new ComputeBuffer(1, sizeof(int), ComputeBufferType.IndirectArguments);
29.             ComputeBuffer.CopyCount(appendBuffer, countBuffer, 0);
30.  
31.             Debug.Log("Copy buffer : " + countBuffer.count);
32.             int[] counter = new int[1] { 0 };
33.             countBuffer.GetData(counter);
34.             countBuffer.Dispose();
35.             return counter[0];
36.         }
37.     }

And here my simple ComputeShader

Code (CSharp):

1. StructuredBuffer<float3> input;
2. float3 key;
3. float3 cam;
4. AppendStructuredBuffer<float3> output;
5.  
6. [numthreads(256,1,1)]
7. void KeyCam(uint3 id : SV_DispatchThreadID) {
8.     if (dot(input[id.x], cam) >= 0.0)
9.         if (dot(input[id.x], key) <= 0.0)
10.             output.Append(input[id.x]);
11. }

Thanks

 

Did you ever find an answer?

 

This seems to work fine for me in Unity 2019.4. I had to make some changes documented below. First, the shader:

Code (CSharp):

1. AppendStructuredBuffer<float3> appendBuffer;
2.  
3.  
4. [numthreads(1024, 1, 1)]
5. void DoStuff(uint3 id : SV_DispatchThreadID)
6. {
7.     // .... deleted some irrelevant stuff ...
8.  
9.     if (id.x < 100) {
10.         appendBuffer.Append(float3(id.x, 66, 99));
11.     }
12.  
13.     //dataBuffer[id.x+1].val = dataBuffer[id.x].val + 1;
14. }

For the counting function, I had to change the countBuffer to type Raw because otherwise the first time this was called it was giving me a weird value if I used the type IndirectArgument.

Code (CSharp):

1. private static int GetAppendBufferCount(ComputeBuffer appendBuffer)
2.         {
3.             ComputeBuffer countBuffer = new ComputeBuffer(1, sizeof(int), ComputeBufferType.Raw);
4.             ComputeBuffer.CopyCount(appendBuffer, countBuffer, 0);
5.  
6.             // always size 1 -- Debug.Log("Copy buffer : " + countBuffer.count);
7.             int[] counter = new int[1] { 0 };
8.             countBuffer.GetData(counter);
9.             countBuffer.Dispose();
10.             return counter[0];
11.         }

Also, on initializing the buffer I called SetData() I'm not sure if needed, but importantly I also called SetCounterValue(0) to reset it (otherwise the GPU kept counting).

Code (CSharp):

1.  
2. // create the buffer
3. data = new Vector3[1024 * 1024];
4. appendBufferGPU = new ComputeBuffer(data.Length, sizeof(float) * 3, ComputeBufferType.Append);
5. appendBufferGPU.SetData(data);
6. appendBufferGPU.SetCounterValue(0);

The SetCounterValue() also needs to be manually reset before Dispatch.