Question Why is this Compute Shader not writing to a texture unless I set a render target?

Here is a simple example:

Code (CSharp):

1.  
2. private void InitializeSDFFromMask(CommandBuffer command)
3. {
4.     var volumeDepth = Mask.volumeDepth;
5.     var compute = volumeDepth > 1 ? settings.data.SDFComputeSPI : settings.data.SDFComputeMP;
6.  
7.     command.SetRandomWriteTarget(0, SDF.GetWriter());
8.     command.SetComputeTextureParam(compute, kernal_Initialize, compute_id_SDFOutput, SDF.GetWriter(), 0, RenderTextureSubElement.Color);
9.     command.DispatchCompute(compute, kernal_Initialize, SDF.GetWidth() / 8, SDF.GetHeight() / 8, volumeDepth);
10.  
11.     SDF.Swap();
12. }
13.  

If I remove 'command.SetRandomWriteTarget(0, SDF.GetWriter());' - the texture will not be written to. If it's there, the texture IS written to.

Here's a simplified version of the compute shader:

Code (CSharp):

1. [numthreads(8, 8, 1)]
2. void Initialize(int3 id : SV_DispatchThreadID)
3. {
4.     SDFOutput[id.xy] = 1.0;
5. }

SDF is just a Render Texture pair (wrapper class to swap between calls). Also, another strange thing is that I see it's inserting unnecessary Clear() draws in the middle of my compute dispatches. What is going on here?

 

Simple version: it's just a RW_TEXTURE2D<float4>. It's actually a custom macro setup to handle SPI/MP VR rendering based on defines, but in this example it is just a RWTexture<float4> (even when i trim it down to this directly to keep it simple, same result)

 

Alright so I managed to get it to work without any Clear()s. Instead of creating a RenderTexture and using that as a reference, I instead just added something like:

Code (CSharp):

1. MyCommandBuffer.GetTemporaryRT()

For some reason, doing it this way doesn't do a clear and doesn't require using SetRandomWriteTarget(). I don't know if there's some bug with URP/SRP/Unity somewhere in the CommandBuffer/RenderTexture/ComputeShader combo or what. I think there is, but this method works so I'll just be moving forward with it. Overall its a decent speedup, since it doesn't clear.

Here's a before/after pic of the frame debugger for reference.