low ms/frame when sharing/recording screen

[akosil]

Version/Branch of Dear ImGui:

v1.91.6 WIP , docking branch

Back-ends:

imgui_impl_dx11

Compiler, OS:

Windows 10

Full config/build information:

example_win32_directx11 build from v1.91.6 WIP - docking branch

Details:

high ms / frame (worse performance) when sharing screen on discord or recording screen with OBS

Screenshots/Video:

Minimal, Complete and Verifiable Example code:

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[ocornut]

You would need to investigate this on your own but it seems like a problem of your recording software, if not a feature (perhaps they are hijacking something to make vsync simulate 20 hz, is the 20 fps framerate stable?)
Maybe try with different examples/backends.

[akosil]

I will try to find the issue.
Another issue i found: When I undock a window and move it outside the main viewport, the main application experiences higher ms/frame (worse performance). Is this expected behavior, or could it be a bug?

[ocornut]

Is that also when recording?
What sort of ms/frame amount does it goes from and to ?

We create new windows and swapchains so there is a cost but normally it should be relatively negligible.
It’s related to your first question because our examples app are fully throttled using a vsync wait, and that may be affected by drivers and other sources.

[akosil]

2nd issue is without recording:
Application is running on main screen (240hz).
If I move out a window to main screen, with vsync on actually I get slightly higher FPS right now, but without vsync the performance drop is visible.
If I move out a window to second screen(60hz), I always get a way worse performance.
If I change the hz from 240 to 60, I get same performance drop wherever I undock the window.

ms/frame values without vsync:
normal, no undock: 3.284 ms / frame
undock from main screen to main screen: 5.912 ms / frame
undock from main screen to second screen: 9.253 ms / frame

I attached an image for reference:
With vsync

Without vsync

[ocornut]

Profiling would be needed, but unfortunately this can be due to so many things:

• drivers
• drivers settings related to vsync
• possibly swapchain swapeffect

One thing that may be worth trying

• change the SwapChain setup from

sd.SwapEffect = DXGI_SWAP_EFFECT_DISCARD;

to

sd.SwapEffect = DXGI_SWAP_EFFECT_FLIP_DISCARD;

And the other more modern FLIP modes.
For this to work:

• you need to ensure the project is built with Windows 10+ SDK (by default our vsproj are committed with SDK 8.1, need Visual Studio to upgrade them to SDK 10.
• need to change it in example_win32_directx11/main.cpp AND in backends/imgui_impl_win32.cpp's ImGui_ImplDX11_CreateWindow() function.

I would be curious to know if it makes a difference for you.
If it does it may be tempting to migrate committed examples to rely on SDK 10 + make backend inherit SwapEffect.