ComputeBuffer.GetData

Unity Engine
1

Simple question :

I need to use this function discussed here :
http://forum.unity3d.com/threads/148874-Compute-Shaders

ComputeBuffer.GetData

But I don’t know how to access to the returned data.
As it is a void function, it doesn’t return any value.

And I can’t access to any property of ComputeBuffer exept count and stride.

Any help ?

2

From the doc’s the definition function GetData (data : System.Array) : void doesn’t return a value but fills the source data array with the values.
You pass in an empty data array and it gets filled up. After the call is finished the array now contains the compute data.

NOTE: I have yet to actually test this in code and have no personal experience with DX11 compute shaders. The information provided above was gleaned solely from the Docs and might be in error.
YMMV

3

Ok thanks,

It seems like I’m a little bit confused.
I’m trying to compute an array ( fill with noise values ) via a compute shader ( or shader ) and to retrieve it on the cpu via ComputeBuffer.GetData.

But I’m stuck here. I was looking for a sample to start with but I can’t find anything.

4

Here is how I’m doing things :

c# code :

using UnityEngine;
using System.Collections;

public class ComputeShader_test : MonoBehaviour {
    public ComputeShader compute;
    public ComputeBuffer buffer;
    public int[] cols;
	
    void Start () {
	var mesh = GetComponent<MeshFilter>().mesh;
	int n = mesh.vertexCount;
        ///
	buffer = new ComputeBuffer (n, 16);
	///
	cols = new int[n];
        ///	
	for (int i = 0; i < n; ++i)
	     cols[i] = 0;		
	buffer.SetData (cols);	
        ///
	compute.SetBuffer(compute.FindKernel ("CSMain"),"bufColors", buffer);
        ///
        compute.Dispatch(0,4,4,1);
	///
	buffer.GetData(cols);
	Debug.Log (cols[0]);   
}

compute shader code :

// Each #kernel tells which function to compile; you can have many kernels
#pragma kernel CSMain

StructuredBuffer<int> bufColors;

[numthreads(8,8,1)]
void CSMain (uint3 id : SV_DispatchThreadID)
{
	bufColors[0] = 2;
}

I’m expecting cols[0] to return 2 as it is set in the compute shader. But it return the original value ( 0 ).

What am I missing to simply get back data from computebuffer ?

5

StructuredBuffer is a read only buffer.

Try RWStructuredBuffer instead.

6

That’s it !! You made my day !

Now I have a good starting point to play with compute shaders.

Many thanks smb02dunnal.

Cheers.

7

Sorry for reviving an old thread, but I have a similar problem with compute buffers. I use the exact same code as sepion, but instead of just having an int in a raw buffer, I use a struct which contains a single int with the default buffer type. Is there something special I must do to work with structs in compute buffers?

Thanks.

8

what do you mean by special?

9

Well, right now, I use computeShader.GetData() on an int array, like sepion did. However, my buffer contains a struct instead of a simple int. This struct contains a single “int” variable though.

So my question is, what should be the parameter of GetData() if my structuredBuffer contains a struct?

10

An array of structs

11

I’ll need to investigate this further. Nothing seems to work for me. If I put the exact same script as sepion, with a RWStructuredBuffer, it doesn’t work either, so I’m pretty confused here… Anyways, thanks for your help.

12

Please Can someone provide a little demonstration code of GetData… that works :stuck_out_tongue:

1401179--72688--$rrr.jpg same code as sepion in RWStructuredBuffer,
Shader error in ‘ComputeShader_test.compute’: l-value specifies const object at line 20

1401179--72689--$errr2.jpg
1401179--72689--$errr2.jpg1025×418 78 KB

13

Look at smb02dunnal answer.
replace “StructuredBuffer bufColors;” with RWStructuredBuffer bufColors;

but your error in the console do not deal with GetData issues.

14

error was thy .cs code missing a } at line 27/28