Prevent blurriness when dpi changes

Question

When a user changes the system dpi (in Settings -> Display) a WPF Window becomes blurry. Closing the application and restarting it makes it clear again.

How can I get the Window clear again without closing it?

Recreate by creating a WPF app, adding a button and running it. Then change the dpi as mentioned above. Even changing it back again doesn't help.

@LeiYang Yes. Just create one, put a button on it, and change the system dpi. You'll see the text on the button become blurry. — ispiro, Jul 14 '21 at 12:59
i'm not very familiar with dpi. is there such setting? is it equal to the 'resolution(1920*1080)' list? — Lei Yang, Jul 14 '21 at 13:00
As a workaround you can monitor for DPI change and force UI reloading. See [this topic](https://stackoverflow.com/q/64355684/1997232). — Sinatr, Jul 14 '21 at 13:05
@Sinatr DpiChanged doesn't fire. Try it and see for yourself. Also, how would I be able to reload the UI - do you mean remove all elements from the Window and put them back there? Because if so, it doesn't work - the button returns blurry. — ispiro, Jul 14 '21 at 13:10
To reload UI try to close window and open it again. You need to customize [entry point](https://stackoverflow.com/q/6156550/1997232). If reloading UI is not enough, then just do [restart](https://stackoverflow.com/q/4773632/1997232). User don't change DPI often, right? — Sinatr, Jul 14 '21 at 13:15
@Sinatr `User don't change DPI often, right?` - _Some_ user is going to... I was hoping there would be some method I can call to "reload" the dpi. — ispiro, Jul 14 '21 at 13:41
Have you tried registering to SystemEvents.DisplaySettingsChanged in your MainWindow.xaml.cs, and then calling `this.UpdateLayout()`? — Tam Bui, Jul 14 '21 at 16:08
@Sinatr I have a PC with displays with different DPIs, whenever I drag a window from one screen to another that counts as a _DPI change_ as far as the application is concerned. That said, **just enable per-monitor DPI awareness** and WPF should handle it fine. — Dai, Aug 02 '21 at 20:48
@Dai, I expect wpf applications to be dpi aware [by defaut](https://stackoverflow.com/q/35865238/1997232). But it seems to be not ideal. Perhaps OP should post [mcve] so that you can reproduce the issue and try to find a better solution. I just suggest a workaround - to restart, that should help if everything was ok before DPI change. — Sinatr, Aug 03 '21 at 07:06
@Sinatr I’m guessing the OP’s project is an older WPF app running against something older than .NET Fx 4.7.2 and so per-monitor DPI awareness is disabled for back-compact purposes. The OP needs to test a _brand new_ blank WPF project targeting .NET Fx 4.8 or .NET 5. — Dai, Aug 03 '21 at 07:10
@Sinatr `minimal reproducible example` - I'm pretty sure anyone who's capable of answering this question is also capable of creating a WPF application and adding a button to it. — ispiro, Aug 03 '21 at 07:11
@Dai No. It's a the latest .net 4.8 with the latest Visual Studio version. With a brand new WPF project. Try it and see. — ispiro, Aug 03 '21 at 07:12
@ispiro “ I'm pretty sure anyone who's capable of answering this question is also capable of creating a WPF application and adding a button to it” - yes, and per-monitor DPI awareness works correctly for me. Something is wrong or broken with your computer. — Dai, Aug 03 '21 at 07:13
@Dai But your suggestion for per-monitor dpi awareness did work. Which I find strange since I'm only working on one monitor. Anyway, you can post that as an answer, because strange or not - it works. — ispiro, Aug 03 '21 at 07:13
@Dai See my previous comment. Per-monitor DPI awareness does, in fact, work. Thanks! — ispiro, Aug 03 '21 at 07:14
@ispiro How, **exactly** did you enable per-monitor DPI awareness? — Dai, Aug 03 '21 at 07:14
@Dai I said it _did_ work. Not that it didn't. And I used `PerMonitor`. — ispiro, Aug 03 '21 at 07:15
@ispiro You shouldn’t need to do that though. Unless, did your project already have a custom app.manifest? — Dai, Aug 03 '21 at 07:16
@Dai As I've said above, this is a completely new WPF project. VS -> New project -> etc. so yes, I needed to add an app.manifest file to it. And if you think per-monitor-etc. is by default - [you're not alone. And you are backed by a Microsoft blog post.](https://stackoverflow.com/a/39218709/939213) But unfortunately [still wrong](https://stackoverflow.com/questions/39217355/wpf-application-blurry-on-high-dpi-screen-on-windows-10#comment85923370_39218709). — ispiro, Aug 03 '21 at 07:20
@Dai Please feel free to post your answer. My answer is just there in case you don't. — ispiro, Aug 03 '21 at 07:24
@Dai Also, instead of me posting an answer myself, please feel free to post an answer to [my bountied question here](https://stackoverflow.com/q/68379924/939213) since you're the one who deserves that bounty. — ispiro, Aug 03 '21 at 07:43

ispiro · Accepted Answer · 2021-08-03T07:34:29.677

1

As Dai pointed out, adding per-monitor dpi-awareness fixes the issue.

Why, I'm not sure, since that's not supposed to affect a device using one monitor. But it works.

Since it seems that many think that per-monitor dpi-awareness is on by default, let me point out, as pointed out by Ben Voit, that it's not.

edited Aug 03 '21 at 07:34

answered Aug 03 '21 at 07:17

ispiro

26,556
38
136
291

Prevent blurriness when dpi changes

1 Answers1

Linked