Win32+DX12: Vertical Offset After Connecting Another Display

[ChickenSandwhich]

Hey

We ran into a bug the other day that shows up when you connect another monitor to your PC after the application has already been started.

We were able to reproduce the problem with one of your example applications, too. win32 + directx12 on commit #534340c

So, this is what we did:

• start the custom application which uses ImGui first
• next plug in a second monitor
• observe how the content of the application window seems to flicker
• next observe how there's an offset in the rendering. The offset seems to be exactly as big as the titlebar (height)
• if the problem does not yet show up, unplug the second monitor, and now the problem should be visible

This problem is admittedly not extremely crucial. But in certain situations it causes some inconvenience for us.

Thank you

[ocornut]

Can you check if it happens with win32 + dx11 ? how about e.g. glfw + opengl3 ?

[ChickenSandwhich]

Oh yes, and sorry for not checking them right away.

So, I couldn't reproduce the issue with any of the two (win32+dx11, glfw+opengl3). And at first, I wasn't even able to reproduce again the issue with win32+dx12 ... That shocked me a bit.

But I didn't give up and was finally able to reproduce it with win32+dx12 (but not with the other two). Well, the ability to reproduce it depends on which monitor is selected as the primary one.

My setup is this:

• 2 x Dell 24" (identical model)
• and the third monitor (my plug in and out monitor) is a LG 27" 4K

So depending on which Dell is selected as the primary I do get the bug or not :-/

Note: it doesn't matter if I move the application window to the primary/secondary monitor first before plugging in the third monitor.

If you had any pointers for what I could do next - I was happy to try it. But don't worry too much about this bug. It's inconvenient and somewhat weird, but it's not a fatal game breaker ;)

On Wed, Jun 14, 2023 at 1:46 PM omar @.***> wrote:

Can you check if it happens with win32 + dx11 ? how about e.g. glfw + opengl3 ?

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[ocornut]

Assuming that's in master (but you didn't specify the branch and didn't fill issue template) everything related to this would be in example_win32_direct12/main.cpp and not imgui-core code, but fixing examples for edge case is always desirable.

[ChickenSandwhich]

Sounds great! Thanks so much for picking up that problem!

Version/Branch of Dear ImGui:

Version: 1.89.7 WIP (18963) Branch: master

Back-end/Renderer/Compiler/OS

Back-ends: imgui_impl_win32.cpp Compiler: MSVC Operating System: Windows

My Issue/Question:

Plugging in another monitor while the application is already running can result in a vertical and horizontal offset. In the end, it feels like the rendering result from ImGui was placed incorrectly in the window (shifted upwards and slightly to the left). More details in the previous posts.

Screenshots/Video

Nope

Standalone, minimal, complete and verifiable example:

example_win32_directx12 from the examples folder

[Demonese]

This may be a bug in Windows or the graphics card driver. I can't reproduce this problem, but I had a similar problem on another device.

After resizing the window, the content may be offset by the height of the title bar.

The solution is to use DirectComposition and create a swapchain through CreateSwapChainForComposition. This might help you.