How to write to Texture2DArray in compute shader? (getting UAV errors)

[Emerganz]

I am trying to create a simple compute shader that writes data to a texture array, but I keep getting UAV errors. I am new to compute shaders, so I may be missing something completely obvious.

I wish to be able to display the textures in the array on screen using a simple shader (currently one I created in ShaderGraph). I assumed I could use a Texture2DArray for this (and old forums posts seem to hint at this), but it seemingly doesn’t work.

The error I get is “Compute shader (Test): Property (data) at kernel index (0): Attempting to bind texture as UAV but the texture wasn’t created with the UAV usage flag set!”

I am using the somewhat unusual ‘RFloat’ textureformat, since my calculations will be in floating point buffers, but I don’t assume that’s related to the problem.

I made a very simple version of the shader to isolate the problem:

Shader:

#pragma kernel Test

RWTexture2DArray<float> data : register(u0); // Supposedly this initializes it for UAV?

float value;

[numthreads(8,8,1)]
void Test(uint3 id : SV_DispatchThreadID)
{
    data[uint3(id.x, id.y, 0)] = value;
}

Unity:

    private void TestCompute(int depth, RawImage image)
    {
        textureArray = new Texture2DArray(textureWidth, textureHeight, depth, TextureFormat.RFloat, false, true);

        int kernel = computeShader.FindKernel("Test");

        computeShader.SetTexture(kernel, "data", textureArray);
        computeShader.SetFloat("value", 0.2f);

        computeShader.Dispatch(kernel, textureWidth / 8, textureHeight / 8, 1);

        image.material = new Material(arrayMaterial);
        image.material.SetTexture("TextureArray", textureArray);
        image.material.SetInteger("ArrayIndex", 0);
    }

I don’t know if there’s a way to create a Texture2DArray that enables UAV or I need to use a different texture class in Unity (like RenderTexture). However if I do use a different texture class, then how do I access it in my shader? I would like to avoid copying the data (especially back to the CPU).

Old forum posts that hints that this is possible (but the linked example doesn’t use Texture2DArray):

How can I pass an array of textures to a Compute Shader?

In my compute shader, I've defined an array of textures: Texture2D _ColorTextures[22]; In my code, I've got an array of 22 RenderTextures (each created by a camera render). How can I pass this array to the compute shader? ComputeShader.SetTexture takes a string (or ID) of a single variable. One option I've seen mentioned is to use a Texture2DArray, but as far as I can tell, in Unity you can't create a Texture2DArray completely on the GPU, you have to transfer data to CPU and then back, whi…

Upload and write to RenderTexture as Texture2DArray in Compute shader !?

Ah, yes although you'll need RWTexture2DArray and uint3 (for indices). More here: https://msdn.microsoft.com/en-us/library/windows/desktop/ff471506(v=vs.85).aspx

The last of the post is the one that uses the “: register(u0)” bit when declaring the RWTexture2DArray, but I have no idea what it actually does. I know they also set “enableRandomWrite = true” on their RenderTexture, but there’s no such property on a Texture2DArray.

[Emerganz]

Ok it seems the solution is to use a RenderTexture formatted as a Tex2DArray and then just pretend that’s a Texture2DArray when assigning it to a Unity shader.

Here’s the code that works:

Compute:

#pragma kernel Test

RWTexture2DArray<float> data : register(u0); // Supposedly this initializes it for UAV

float value;

[numthreads(8,8,1)]
void Test(uint3 id : SV_DispatchThreadID)
{
    data[uint3(id.x, id.y, 4)] = value;
}

Unity:

    private void TestCompute(int depth, RawImage image)
    {
        RenderTexture texture = new RenderTexture(textureWidth, textureHeight, depth, RenderTextureFormat.RFloat, RenderTextureReadWrite.Default);

        texture.dimension = TextureDimension.Tex2DArray;
        texture.enableRandomWrite = true;
        texture.volumeDepth = depth;
        texture.Create();

        int kernel = computeShader.FindKernel("Test");

        computeShader.SetTexture(kernel, "data", texture);
        computeShader.SetFloat("value", 0.9f);

        computeShader.Dispatch(kernel, textureWidth / 8, textureHeight / 8, 1);

        image.material = new Material(arrayMaterial);
        image.material.SetTexture("_TextureArray", texture);
        image.material.SetInteger("_ArrayIndex", 4);
    }

ShaderGraph: