HiDPI doesn't appear to be handled by Cygwin/X11

[Hamish McIntyre-Bhatty]

On 17/07/2026 13:46, Jon Turney wrote:
> On 10/07/2026 15:39, Hamish McIntyre-Bhatty via Cygwin wrote:
>> Hi all,
>>
>> Apologies if this has already been reported, but I couldn't find 
>> anything about this exact issue. I've recently found that HiDPI 
>> screens with scaling don't appear to be handled well by Cygwin/X11 - 
>> windows render very small in this configuration. By contrast, if I 
>> use the VcxSrv server with the same Cygwin application it displays at 
>> the size you'd expect.
>>
>> I'd be happy to send screenshots or logs, or anything else I can send 
>> to help figure out why this is happening. I don't know much about X, 
>> other than that it's hard to maintain, so I appreciate this may not 
>> be an easy problem to fix.
>
> Interesting.
>
> The way this is supposed to work is (i) for windows owned by the X 
> server, we turn off all the scaling that Windows might do 
> automatically (so 1 pixel == 1 pixel), and (ii) advise X applications 
> of the real DPI so they (or, usually, the toolkit they use, qt, gtk, 
> etc.) can make appropriate scaling decisions.
>
> (Differences with VcxSrv might be because that's not marked dpiAware 
> and so let's Windows do scaling, or because it has some patches to do 
> more intelligent things...)
>
> It would be nice to know:
>
> * the DPI of your display
> * the dpi reported by xdpyinfo
> * the name of an application you see this problem with

Apologies for the very slow reply.

I don't actually know the DPI of my display, as it's a virtual machine 
in QEMU/KVM. I'm using the Red Hat QXL display adaptor at 2560x1600, 
150% scaling set in Windows.

xdpyinfo reports 144x144 DPI in my Windows VM, which is the same as what 
it says on my host OS (LMDE 7).

I see this problem with the wxPython demo, but also any Cygwin 
application I've tried that uses the X server. I first noticed it with 
my own wxPython-based application, but I sell that so I won't be 
providing links to it here.

Best,

Hamish