How to fix this multisampling error when creating a swapchain? - directx-11

Question

I'm getting an DXGI ERROR about multisampling when creating a swapchain and need some help after hours of trying to resolve this error.
I'm setting up a simple window for learning Direct3D 11. I have tried changing the SampleDesc.Count and SampleDesc.Quality in the DXGI_SWAP_CHAIN_DESC1 structure, but I still get the error.
// dxgiFactory is using interface IDXGIFactory7
// d3dDevice5 is using interface ID3D11Device5
ComPtr<IDXGISwapChain1> dxgiSwapChain1;
DXGI_SWAP_CHAIN_DESC1 desc;
desc.Width = 800;
desc.Height = 400;
desc.Format = DXGI_FORMAT_R8G8B8A8_UNORM;
desc.Stereo = FALSE;
desc.SampleDesc.Count = 0;
desc.SampleDesc.Quality = 0;
desc.BufferUsage = DXGI_USAGE_RENDER_TARGET_OUTPUT;
desc.BufferCount = 3;
desc.Scaling = DXGI_SCALING_STRETCH;
desc.SwapEffect = DXGI_SWAP_EFFECT_FLIP_DISCARD;
desc.AlphaMode = DXGI_ALPHA_MODE_STRAIGHT;
desc.Flags = 0;
hr = dxgiFactory->CreateSwapChainForHwnd(d3dDevice5.Get(), hWnd, &desc, nullptr, nullptr, &dxgiSwapChain1);
Debug output:
DXGI ERROR: IDXGIFactory::CreateSwapChain: Flip model swapchains (DXGI_SWAP_EFFECT_FLIP_SEQUENTIAL and DXGI_SWAP_EFFECT_FLIP_DISCARD) do not support multisampling.
How do I resolve this error?

Answer 1

TL;DR Either change your flip model to the older DXGI_SWAP_EFFECT_DISCARD or create an MSAA render target that you explicitly resolve.
Create your swap chain as one sample (i.e. no MSAA).
Create a render target texture that is using one or more samples (i.e. MSAA).
Create your render target view for your MSAA render target
Each frame, render to your MSAA render target, then ResolveSubresource to the swapchain backbuffer--or some other single-sample buffer--, then Present.
For a detailed code example, see GitHub.
You also can't create it as an DXGI_FORMAT_*_SRGB gamma-correcting swapchain with the new DXGI_SWAP_EFFECT_FLIP_* models. You can create a Render Target View that is DXGI_FORMAT_*_SRGB for a swapchain that is not sRGB to get the same effect. There's a little bit of a gotcha doing both MSAA and sRGB together with the new flip models that is fixed in Windows 10 Fall Creators Update (16299) or later.
If you were using DirectX 12, you don't have the option of using the older swap effects, so you have to implement the MSAA render target directly. Again, see GitHub.
In the 'pre-Directx 12 / Vulkan' days, DirectX made it easy to enable MSAA by doing a bunch of stuff behind the scenes for you. It would create a non-MSAA render target for display, give you back an MSAA render target for rendering, and do the resolve for you as part of the Present. It was easy, but it was also a bit wasteful.
With the new 'no magic' approach of DirectX 12, you have to do it explicitly in the application. In real games you want to do this anyhow because you usually do a lot of post-processing and want do the resolve well before Present or even do other kinds of resolve (FXAA, MLAA, SMAA). For example:
Render 3D scene to a floating-point MSAA render target
->
Resolve to a single-sample floating-point render target
->
Perform tone-mapping/color-grading/blur/bloom/etc.
->
Render UI/HUD
->
Perform HDR10 signal generation/gamma-correction/color-space warp
->
Present
As you can see from that flow, it's pretty silly to ever have the swapchain be MSAA except in toy examples or sample code.
To get a sense of just how much of a modern game is doing multiple passes of rendering, see this blog post
See DirectX Tool Kit for DX 11 and DX12
UPDATE: I covered this in detail in a recent blog post