Hey!

I am trying to get MSAA rendering to work in DX12, but I am having issues. My setup is like this:

I have a render target that I am rendering all my stuff into, it is generally used for UI and some parts of the game.

I have another separate render target, that I am rendering the shapes with MSAA to, mostly containing lines as they look very bad without anti aliasing. But when I call ResolveSubresource with destination being main render target and source being MSAA render target, my screen goes to black and I can only see the MSAA drawings, because this operation overwrites the render target's contents.

So I researched and found out I have to make a intermediate buffer to copy the msaa, then render it (blend??) to my main render target, but I can't figure out how to do this or find any examples, as the codes i found usually enable msaa for the whole render pipeline instead of only specific places, here is my current code:

	auto barrier = CD3DX12_RESOURCE_BARRIER::Transition(
		current_buffer.msaa_resource,
		D3D12_RESOURCE_STATE_RESOLVE_SOURCE,	// this is the initial state
		D3D12_RESOURCE_STATE_RENDER_TARGET);
	command_list->ResourceBarrier(1, &barrier);
	
	// clear msaa target
	constexpr FLOAT clear_color[4] = { 0.0f, 0.0f, 0.0f, 1.0f };
	command_list->ClearRenderTargetView(current_buffer.msaa_target, clear_color, 0, nullptr);
	
	// render to msaa target
	command_list->OMSetRenderTargets(1, &current_buffer.msaa_target, 
		FALSE, nullptr);

	// render shapes into msaa target
	// for example, render lines / circles or any other stuff you want with msaa.
	...
	
	// resolve msaa
	barrier = CD3DX12_RESOURCE_BARRIER::Transition(current_buffer.msaa_resource,
		D3D12_RESOURCE_STATE_RENDER_TARGET,
		D3D12_RESOURCE_STATE_RESOLVE_SOURCE);

	command_list->ResourceBarrier(1, &barrier);
	command_list->ResolveSubresource(current_buffer.msaa_intermediate_resource,
		0, current_buffer.msaa_resource, 0, rtv_format_);
		
	// now can render stuff without MSAA, original render target
	command_list->OMSetRenderTargets(1, &current_buffer.main_target, FALSE, nullptr);
	
	...
	
	// TODO HOW TO COPY current_buffer.msaa_intermediate_resource into current_buffer.main_target 	   without overwriting its contents?
	
	...
	
	// present

I was able to get this to work. For further reference, here is what I did:
0) clear the msaa render target
1) copy original render target to the msaa render target using CopyResource
2) draw to msaa target with msaa enabled pipeline
3) call ResolveSubresource and resolve the msaa to main render target
4) can now continue rendering more stuff into main render target without msaa as needed.