Compute shader synchronization

Hello !

I need your help today ! I begin to work with compute shader in a really simple use case :
I have a depth camera and I want to calculate the bounding box of an object near to the camera.

But I have too much pixel to process and I want to use GPGPU, compute shader and parallelization to compute this.

I currently have a problem, when I run my program, I have the same min and max coordinates. So I think that all my group and threads write in the same time to my StructuredBuffers.

Do you have an idea to how to do that ?

Thanks a lot !

PS : Sorry for my English, I'm French

Here is the code of my compute shader :

Code (HLSL Compute Shader):

1. #pragma kernel ComputeBoundingBox
2. //We define the size of a group in the x, y and z directions, z direction will just be one
3. #define thread_group_size_x 1024
4. #define thread_group_size_y 1
5. #define thread_group_size_z 1
6. //Size of the depthData frame
7. #define width 512;
8. #define height 424;
9.  
10. //DataBuffer = depthData of the camera
11. //minBuffer, maxBuffer, array of size 3 with min/max x, y and z
12. //mask = image area to process
13. RWStructuredBuffer<float> dataBuffer;
14. globallycoherent RWStructuredBuffer<float>minBuffer;
15. globallycoherent RWStructuredBuffer<float> maxBuffer;
16. RWStructuredBuffer<float> mask;
17.  
18.  
19. float xValue = 0, yValue = 0, zValue = 0;
20.  
21. [numthreads(thread_group_size_x, thread_group_size_y, thread_group_size_z)]
22. void ComputeBoundingBox(uint3 id : SV_DispatchThreadID)
23. {
24.     xValue = (id.x + 1) % width;
25.     yValue = (id.x + 1) / width;
26.     zValue = dataBuffer[id.x];
27.  
28.     if (mask[id.x] > 0.49)
29.     {
30.         if (zValue > 500 && zValue < 1500)
31.         {
32.             if (xValue < minBuffer[0])
33.                 minBuffer[0] = xValue;
34.             else if (xValue > maxBuffer[0])
35.                 maxBuffer[0] = xValue;
36.             if (yValue < minBuffer[1])
37.                 minBuffer[1] = yValue;
38.             else if (yValue > maxBuffer[1])
39.                 maxBuffer[1] = yValue;
40.             if (zValue < minBuffer[2])
41.                 minBuffer[2] = zValue;
42.             else if (zValue > maxBuffer[2])
43.                 maxBuffer[2] = zValue;
44.         }
45.     }
46. }