High DPI zoom issue

[AndyL]

Paint.NET doesn't seem to be using the right DPI setting in a remote desktop connection to a Windows 10 box.

The PC is a laptop with a 4K display, with display scaling set to 225%. Paint.NET behaves as I'd expect when working directly on the laptop's screen.

When I connect to the laptop using a remote desktop session with scaling set to 175%, I get odd scaling behaviour. E.g. if I alt-printscreen another application, and then paste it into Paint.NET, the image is smaller than the original. If I set Paint.NET's zoom slider to 129% (= 225/175), the image then appears about the same size as the original (but fuzzy due to resizing effects).

It's as if Paint.NET is working from the "system" DPI scaling setting, rather than the setting of the current display.


Background: the most recent versions of the RDP protocol allow the client to specify desktop and device scale factors in the connection negotiation (reference: https://msdn.microsoft.com/en-us/library/cc240510.aspx) so that the session can be displayed using the preferred DPI of the client, instead of the server. I don't know if the standard Windows Remote Desktop Client supports this, but I think Microsoft's Remote Desktop Connection Manager application might. Personally I'm using xfreerdp on Linux with the /scale-desktop: option to send the scaling factor to the server.

I wonder if the same issue might also be reproducible on a machine with 2 monitors and different scaling set on each.