DX12 renderer does not support window transparency

[0x0ACB]

Tested versions

4.3

System information

Windows 11

Issue description

Looking at the code Godot currently creates the swapchain via:

res = context_driver->dxgi_factory_get()->CreateSwapChainForHwnd(command_queue->d3d_queue.Get(), surface->hwnd, &swap_chain_desc, nullptr, nullptr, swap_chain_1.GetAddressOf());

which returns DXGI_ERROR_INVALID_CALL and Godot then falls back to DXGI_ALPHA_MODE_IGNORE. Switching to DXGI_ALPHA_MODE_UNSPECIFIED successfully creates the swapchain but the background is still black.

It seems that godot is incorrectly creating the swapchain for transparency when using DX12. Accodring to DX12 validation layer output:

DXGI ERROR: IDXGIFactory::CreateSwapChain: Alpha blended swapchains must be created with CreateSwapChainForComposition, or CreateSwapChainForCoreWindow with the DXGI_SWAP_CHAIN_FLAG_FOREGROUND_LAYER flag. DXGI_SWAP_CHAIN_DESC{ SwapChainType = ..._HWND, BufferDesc = DXGI_MODE_DESC1{Width = 0, Height = 0, RefreshRate = DXGI_RATIONAL{ Numerator = 0, Denominator = 1 }, Format = R8G8B8A8_UNORM, ScanlineOrdering = ..._UNSPECIFIED, Scaling = ..._UNSPECIFIED, Stereo = FALSE }, SampleDesc = DXGI_SAMPLE_DESC{ Count = 1, Quality = 0 }, BufferUsage = 0x20, BufferCount = 3, OutputWindow = 0x00000000009F129A, Scaling = ..._NONE, Windowed = TRUE, SwapEffect = ..._FLIP_DISCARD, AlphaMode = ..._PREMULTIPLIED, Flags = 0x0 } [ MISCELLANEOUS ERROR #183: ]

Steps to reproduce

Minimal reproduction project (MRP)

[bruvzg]

CreateSwapChainForComposition and CreateSwapChainForCoreWindow seems to be for UWP windows only.

[alvinhochun]

CreateSwapChainForComposition can be used with DirectComposition.