Question Ulong in Compute Shaders

Is there any way that works to send and receive 64 bit ints to and from a Compute Shader? I've been asking ChatGPT and got a bunch of ways that don't work.

 

@Maxeaman

Minimal Working Example:

Code (CSharp):

1. // Example of using 64-bit unsigned integers in Unity compute shader
2. // Requirements: Unity 2020.2.0a8 or later and active DX12 graphics API
3. using UnityEngine;
4.  
5. public class UnsignedInteger64 : MonoBehaviour
6. {
7.     [SerializeField] ComputeShader _ComputeShader;
8.  
9.     void Start()
10.     {
11.         if (_ComputeShader == null) return;
12.         ComputeBuffer reader = new ComputeBuffer(4, sizeof(ulong), ComputeBufferType.Default);
13.         reader.SetData(new ulong[] {172439890993963ul, 657367095657329ul, 277347196953998ul, 844613309877278ul});
14.         _ComputeShader.SetBuffer(0, "_Reader", reader);
15.         ComputeBuffer writer = new ComputeBuffer(2, sizeof(ulong), ComputeBufferType.Default);
16.         _ComputeShader.SetBuffer(0, "_Writer", writer);
17.         _ComputeShader.Dispatch(0, writer.count, 1, 1); // execute compute shader
18.         ulong[] result = new ulong[2];
19.         writer.GetData( result );
20.         Debug.Log( "172439890993963 + 657367095657329 = " + result[0].ToString()); //   829 806 986 651 292
21.         Debug.Log( "277347196953998 + 844613309877278 = " + result[1].ToString()); // 1 121 960 506 831 276
22.         reader.Release();
23.         writer.Release();
24.     }
25. }

Code (CSharp):

1. #pragma kernel CSMain
2. #pragma use_dxc
3.  
4. StructuredBuffer<uint64_t> _Reader;
5. RWStructuredBuffer<uint64_t> _Writer;
6.  
7. [numthreads(1,1,1)]
8. void CSMain (uint3 id : SV_DispatchThreadID)
9. {
10.     _Writer[id.x] = _Reader[id.x * 2] + _Reader[id.x * 2 + 1];
11. }

 

Maybe I don't have the right requirements? When I copy that exactly, I get that the answer = 0. How can I check? I'm using Unity 2021.3 and I have the latest version of DirectX (DirectX12, checked using dxdiag).

There is another possible problem though. In trying to figure this out before, it was suggested I use uint64_t, but that was undefined, so I made a #define for it, but it still didn't work, yet even after I removed the #define from my code, that type still showed up as green in my VB editor, and didn't specifically say there was an error. I tried your code in a new project, but could unity be remembering that previous definition somewhere?

Edit: I tried using #undef uint64_t and compiling and running it twice, then removed it and compiled and run it twice, and got the same results each time. I have checked that my GPU drivers are the correct versions as well.

 

"Active DX12 graphics API" it means that Unity uses DX12, to enable DX12 check this:

 

That was the missing piece! Thank you so much!!