Do WPF applications normally scale correctly on high DPI screens out of the box (without further customisation of a manifest etc?). It was my understanding they did?
Two WPF applications I have written both appear blurry on my new laptop (running Windows 10) when viewed on the laptop screen. Normally the laptop has it's primary display set to be an external low-dpi monitor and the built-in laptop panel is scaling at 125%. However, the blurriness appears regardless of whether the low-dpi monitor is plugged in or not.
I thought it might have something to do with the way my two applications launch (via a main method, rather than the default code template that launches a primary window), but I've just fired up Visual Studio 2015 and generated a brand new WPF application with the project template (just a couple of radio buttons on a blank form) and it doesn't scale into high DPI on my system either.
It may also be worth mentioning that I have configured the "prefer external manifest" registry setting on my copy of windows to allow per-application disabling of high-dpi scaling with a manifest. (i.e. HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\SideBySide "PreferExternalManifest"=dword:00000001 ).
Any program that depends on PresentationCore is automatically DPI aware. It takes an attribute to explicitly disable that.
You are surely having a different problem, a WPF app does not automatically support per-monitor dpi-awareness. A feature available since Windows 8.1. Having the primary display on an external monitor makes that very likely, you probably gave it a different DPI setting and now windows on your laptop's screen are forced to use that same DPI setting unless they explicitly opt-in. Takes a fair amount of gritty work. Or consider to simply make your laptop's screen the primary display, it is easy to switch back-and-forth with the Display applet.