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Message-ID: <a8a9ce6d-5267-4944-afb2-e388d42350b6@mehconsulting.com>
Date: Sat, 27 Sep 2025 14:17:54 -0700
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Subject: XWin server is starting but creating a large black opaque rectangular
 area on the desktop
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To: cygwin AT cygwin DOT com
From: Mark Hansen via Cygwin <cygwin AT cygwin DOT com>
Reply-To: Mark Hansen <mark AT mehconsulting DOT com>
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Sender: "Cygwin" <cygwin-bounces~archive-cygwin=delorie DOT com AT cygwin DOT com>


I've been using cygwin with XWin server for decades. On one of my Windows 11 laptops, I'm
running into a problem where upon launching the XWin server, I see a large black filled-in
rectangle (opaque) which fills about 20% of the display. This rectangle has no decorations,
so there is no way to grab/resize/move/identify it. It doesn't allow me to see through it to
the desktop below.

I just updated the cygwin installation on this laptop using the setup-x86_64.exe, version 2.934
and the installation shows I got cygwin.dll version 3.4.10 (based on the cygcheck -s -v -r output).

I launch the X server using the following command:

    C:\Apps\cygwin\bin\run.exe --quote /usr/bin/bash.exe -l -c "cd; exec /usr/bin/startxwin -- -listen tcp -emulate3buttons"

This black rectangle issue is newly noticed as I just started trying to use a new large display
connected to the PC via a USB to HDMI adapter.

I've been noticing on my other Windows PC that from time to time, there is a region roughly the same
size where although I can see the desktop, I'm unable to click through to any of the shortcuts in
the region. I now think that region is the same rectangle - it's just that it's not black and opaque
on the other PC, and it doesn't do it all the time. When I notice this happening, I usually just stop
the X Server and restart it and it's fine.

On this problem laptop, each time I start the X Server, the black, opaque rectangle appears, but it
seems to only happen when I'm displaying to a second display via a USB - HDMI display adapter or
viewing the laptop via an RDP session. When I'm accessing the laptop native display directly, the
X Server seems to start just fine and there is no black rectangle.

I keep the XServer running through the use of the .startxwinrc file in my HOME directory. This
file includes a single line used to launch an executable "xnoexit.exe" application, which is basically
just a compiled C program that does a sleep forever which allows the X Server to keep running
until commanded to exit. I did replace that xnoexit.exe command with a simple /usr/bin/xload command
to make sure that wasn't the issue. When I did that, I saw the xload application launch, so I can
see the change worked, but the black rectangle still appeared while the X Server was running.

Is there any way to determine what is causing this? I really want to be able to use this laptop
while displaying via the USB -> HDMI adapter to the second display, as it's a much larger
display (3840x1600), which is much nicer to use than the laptop's native 1920x1080 display.


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