On Windows 11 GetWindowRgn doesn't seem to return the rounder corners region, just gives an ERROR.

Question

Hello,

I am the maintainer of Greenshot, a free & open source Windows screenshot application. (Found here: https://getgreenshot.org)

With Windows 11 there are now windows with rounded edges, similar to Windows 7.
I want to make it possible for Greenshot to capture a screenshot of the window without having pixels on it which do not belong to the window.

I was hoping to that I can use GetWindowRgn, like with Windows 7, which would return a Region specifying this, as described here:
https://learn.microsoft.com/en-us/windows/win32/api/winuser/nf-winuser-getwindowrgn

But for Windows 11 this doesn't work, it just returns ERROR, like there is no region.

Is this a shortcoming in Windows 11, or is there another way to see where the corners are?
I know already of DWMWA_WINDOW_CORNER_PREFERENCE as specified here: https://learn.microsoft.com/en-us/windows/win32/api/dwmapi/ne-dwmapi-dwmwindowattribute
but this doesn't help me with getting the corner information itself.

Any tips or ideas here?

Best wishes,
Robin

Answer 1

Hello,

Thank you for the quick answer!! That was really speedy!

For Windows 10 an ERROR result makes sense, there are no rounded corners so windows are always a rectangle and thus do not need a region.
No rounded corners made it easy on Windows 10 to create professional screenshots, but on Windows 11 a rectangle capture of a window with rounded corners where the parts (pixels) behind it are visible, is not what our users like.

This is why I took Windows 7 as an example for the region, all windows versions after that only had rectangle windows and thus no regions.
For backwards compatibility, this makes sense to compare, in Windows 7 there were regions when the window had corners.
Maybe you can ask around why this was removed?

I'll have a look at the example, but it's in cpp and I am a C# developer, and my Visual Studio complains about it being for VS 2017... Although I already looked at: https://learn.microsoft.com/en-us/windows/uwp/audio-video-camera/screen-capture and there was a weird UI, which breaks user experience. But I will check it out.

I also found that PrintWindow, with the undocumented flag "PW_RENDERFULLCONTENT" (value 2). gets me a screenshot of a window without corners (it looks like a Windows 10 window), see here: https://learn.microsoft.com/en-us/windows/win32/api/winuser/nf-winuser-printwindow
But somehow it has issues where there are black pixels left of the capture, I was thinking about creating a different issue for that.

I'm actually tracking my current experience here: https://github.com/greenshot/greenshot/issues/373

Best wishes,
Robin

Answer 2

Hello,

Welcome to Microsoft Q&A!

After testing, GetWindowRgn returns ERROR on Windows10 & Windows11. That could mean The specified window does not have a region.
You can refer to ScreenCaptureforHWND which can capture the rounder corners frame. But It seems the Window is rectangle even through It‘s corner rounded.

Thank you.

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