CODEWITHSUNDEEP
c++windowsdialogdpihighdpi
jherron5225
jherron5225

Reputation: 31

DPI Scaling with windows-generated dialogues in C++?

I'm trying to properly DPI scale an application in C++ and I'm having trouble getting this to work with the File Picker window created from calling OPENFILENAMEW from commdlg.h.

I'm using three monitors: two with 1.0 dpi and one with 2.5 dpi. For me, the file picker only opens with 1.0 DPI regardless of what window my application is in. So when I drag the file picker to the 2.5 dpi monitor, the window is so small is hard to read. I can only get it to scale with 2.5 dpi when I disconnect the other monitors. I looked at the documentation for OPENFILENAMEW and there is a flag to allow the dialogue to resize manually but that's about it.

It has to register the dpi at some point to scale but I just can't find it. Does anyone know how to do this?

Upvotes: 1

Views: 1380

Answers (1)

jherron5225
jherron5225

Reputation: 31

Enabling per monitor DPI awareness in Manifest settings didn't solve this completely but it did lead me to the answer I was looking for! So the issue that persisted was that once the file-picker window was created, it kept it's DPI scale from its original window even after moving it to a window with different DPI.

Apparently the options in Manifest don't support this and neither does the SetProcessDpiAwareness function in the shellscaling api, which can be used to set that Manifest setting programmatically.

However, the SetProcessDpiAwarenessContext from winuser.h has one more option that the others don't: DPI_AWARENESS_CONTEXT_PER_MONITOR_AWARE_V2. This can only be used on windows machines with the Creators update (named Redstone 2) and you can check that to do DPI scaling right when you can, and wrong but as good as possible when you can't:

if (IsWindowsVersionOrGreater(HIBYTE(NTDDI_WIN10_RS2), LOBYTE(NTDDI_WIN10_RS2), 0)) {
      SetProcessDpiAwarenessContext(DPI_AWARENESS_CONTEXT_PER_MONITOR_AWARE_V2);
}
else {
      SetProcessDpiAwarenessContext(DPI_AWARENESS_CONTEXT_PER_MONITOR_AWARE);
}

And this works!

Upvotes: 2

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