DX12 example app crashes immediately after going into fullscreen

[0x90d]

Version/Branch of Dear ImGui:

Version: master
Branch: master

Back-end/Renderer/Compiler/OS

Back-ends: imgui_impl_d3d12.cpp
Compiler: VS 2019
Operating System: Win11

My Issue/Question:

DX12 example crashes (or freezes when its being debugged) as soon as you go fullscreen (ALT+RETURN). Tested in debug mode targeting x64. This issue might be related to a similar issue I've noticed in my own implementation. An investigation would be appreciated.

Screenshots/Video

It's hard to make a screenshot because once in fullscreen the application freezes up and I cannot alt+tab to another. The frozen example app stays in foreground. I think the crash occurs in ResizeSwapChain event. VS outputs this:

Exception thrown: read access violation.
**swapChain1** was nullptr.

Standalone, minimal, complete and verifiable example:
Download master branch or clone it, target x64 and launch DX12 example application. Hit ALT+RETURN.

[PathogenDavid]

Submitted a PR to fix this: #4347 #4348

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Basically this is happening because we're recreating the whole swap chain instead of just resizing it.

Creating a swap chain for a window that's already fullscreen isn't considered best practice in the first place, and we aren't even doing it correctly if we were trying to do it the legacy way. (Basically we're trying to create a swapchain for a window which was automatically transitioned into a fullscreen state.)

(Note that if you're modeling your own Direct3D app off of this sample, using DXGI's automatic fullscreen transitions or SetFullscreenState is not something I would consider to be modern best practice for Windows 10. It's good enough for samples though.)

[ocornut]

Fixed by #4348, thank you @PathogenDavid !