Unity Compute Shader Indexing Unequal Buffers

As the title already implies, I'm trying to index buffers which do not have the same size.

Imagine the following example:

Code (CSharp):

1. InputBuffer = new ComputeBuffer((int)(size * size), sizeof(float));
2. OutputBuffer = new ComputeBuffer((int)(size * size * 28), sizeof(int));

To index both, I thought I could just do:

Code (CSharp):

1. StructuredBuffer<float> input;
2. RWStructuredBuffer<int> output;
3.  
4. [numthreads( 16, 16, 1)]
5. void marching_squares (uint3 idx : SV_DispatchThreadID)
6. {
7.     uint iI = idx.x + idx.y * (size);
8.     uint iO = idx.x + idx.y * (size * 28);
9.  
10.     float v = input[iI];
11.  
12.     output[iO] = v;
13.     output[iO + 1] = 42;
14.     output[iO + 2] = 43;
15.     output[iO + 3] = 44;
16. }

For some reason I'm getting the following debug logs with this print function:

Code (CSharp):

1. for (uint i = 0; i < OutputBuffer.Length; i += 28)
2.             Debug.Log(string.Format("Idx={0}\tCse={1}\tOut1={2}\tOut2={3}\tOut3={4}",
3.             i, Buffer[i], Buffer[i + 1], Buffer[i + 2], Buffer[i + 3]));
4.  
5. Idx=0   Cse=0   Out1=42 Out2=43 Out3=44
6. Idx=28  Cse=44  Out1=44 Out2=44 Out3=44
7. Idx=56  Cse=44  Out1=44 Out2=44 Out3=44
8. Idx=84  Cse=44  Out1=44 Out2=44 Out3=44
9. Idx=112 Cse=44  Out1=44 Out2=43 Out3=44

It works only for the first 28 values. Why?

 

Did you ever figure this out? I'm trying to do something very similar.

 

If it is a 2D flattened array, you'd need something like this:

Code (CSharp):

1. iI = (id.y * size) + id.x;

where size is the width or resolution of your original 2D array