AdiIRC

The windows anniversary update added a new <dpiAwareness> flag, I compiled a version using this at https://adiirc.com/build/AdiIRC64.exe, does that one work better for you?

I'm also on 1709. The issue arises specifically with the main display at 1920x1080 at 100% and a monitor at 3840 x 2160 at 250%. It's possible that having different resolutions might be part of the issue, but I don't have monitors with identical native resolutions to test that right now. It could also be that the relatively exaggerated numbers I'm working with make the bitmap scaling effect more apparent.

The build you submitted makes the text in Windows default widgets/graphics (eg a window's titlebar) look perfectly crisp and clear, but other text appears to still be blurry. This same behavior can be forced in the original build of 3.1 by changing its DPI compatibility setting to "System (Enhanced)". I've attached screenshots to hopefully illustrate the difference.

3.1 Beta, 1920x1080 at 100%:
https://i.imgur.com/5dVyTOQ.png

3.1 Beta, 3840x2160 at 250%:
https://i.imgur.com/dZIP0hp.png

3.1 Beta Special Build, 1920x1080 at 100%:
https://i.imgur.com/VgP8CwV.png

3.1 Beta Special Build, 3840x2160 at 250:
https://i.imgur.com/ocAmSxT.png

In this last picture, the "blurriness" in the rest of the picture not being present in the title bar is especially clear.

Oh, I see it now as well, the blur was not so obvious to me at first.

There are 3 options that controls how DPI scaling works in .NET. (4 actually)

I have tried enabling all combinations of them, but none of them seem to work satisfactory, either it blurs, or it renders at the main monitor DPI causing sharp but extremely small text, or it scales some controls which are using GDI, but not GDI+.

.NET 4.7 seems to have some fixes for this according to https://blogs.msdn.microsoft.com/dotnet/2017/04/05/announcing-the-net-framework-4-7/, unfortunately I can't make the switch to 4.7 just yet.

Using winforms, per-monitor DPI support was only actually added in 4.7 as well. Once 4.7 comes along, setting dpiAwareness to PerMonitorV2 will magically fix all the DPI issues per https://docs.microsoft.com/en-us/dotnet/framework/winforms/high-dpi-support-in-windows-forms but until then, you'll probably have to wontfix this one.

Thank you for all the help--on a personal note AdiIRC quickly became my client of choice a few weeks back and has served me well ever since, and I always appreciate a dev taking an interest in bug reports.

Your welcome and I'm glad you found AdiIRC useful :)

Gonna keep it open as a reminder to myself.