D3D12 Use backbuffer surface as unordered access view (UAV)

Question

Im making a simple raytracer for a schoolproject were a compute shader is supposed to be used to shade a triangle or some other primitive. For this I'd like to write to a backbuffer-surface directly in the compute shader, to then present the results imideatly. I know for certain that this is possible in DX11 though i can't seem to get it to work in DX12.

I couldn't gather that much information about this, but i found this gamedev thread discussing the exact same problem I try to figure out and they seem to come to the conclusion which was my go to workaround: writing to an intermediate texture and then sampling in a pipeline. I can't fully accept that this would be impossible to achieve in dx12. Why would that feature be removed? Could it be that the queuing-systems removes some overhead that makes it unnecessary to have this feature?

Is there any way to achieve a raytracer without writing to a separate texture and then sampling in a pipeline or copy it onto the back-buffer? What are my best alternatives for achieving performance?

Answer 1

You will have to access the answer. They removed the capability to create an UAV the same way they removed the capability to use multisample surface in the swapchain.

The problem with authorizing UAV on the swapchain surface is that they would have to forfeit tracking of what is happening to it. DX12 rely on descriptor heaps that are 100% volatile at runtime for UAVs ( render targets are CPU side only and can be tracked ).

Microsoft need to track the swapchain surface status strongly in order to guarantee behavior with the desktop presentation and for that reason, they choose to deny the UAV binding.