Windows display scaling factors 125% + 175% are not applied correctly

[mixxxbot]

Reported by: mirh
Date: 2021-07-27T00:16:46Z
Status: Fix Released
Importance: Medium
Launchpad Issue: lp1938102
Attachments: [Screenshot from a 27" 2560x1440 monitor](https://bugs.launchpad.net/bugs/1938102/+attachment/5513914/+files/Screenshot from a 27" 2560x1440 monitor)

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At least on Windows it's pretty awfully small.

[mixxxbot]

Commented by: mirh
Date: 2021-07-27T00:16:46Z
Attachments: [Screenshot from a 27" 2560x1440 monitor](https://bugs.launchpad.net/mixxx/+bug/1938102/+attachment/5513914/+files/Screenshot from a 27" 2560x1440 monitor)

[mixxxbot]

Commented by: daschuer
Date: 2021-07-27T05:23:48Z

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There is work in progress to set an extra scale factor from the preferences #3960

In the meantime you can set the environment variable QT_SCALE_FACTOR
manually.

[mixxxbot]

Commented by: Be-ing
Date: 2021-07-27T07:39:59Z

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Mixxx uses the OS's scaling setting. What is the problem?

[mixxxbot]

Commented by: ronso0
Date: 2021-07-27T11:18:49Z

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A screenshot of a native windows app (Notepad?) would help us to compare the scaling.
Please post the entire screen with the app maximized.

[mixxxbot]

Commented by: mirh
Date: 2021-07-27T11:24:06Z

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You are absolutely right. I just tested 150% and 200% scaling and they work.
On the other hand, 125% and 175% are the same exact size of 100% and 150% respectively (save for the menu bar and the font size of the vertical folder list)

I just tested QT_SCALE_FACTOR=1.25 though, and that didn't have problems.

[mixxxbot]

Commented by: Be-ing
Date: 2021-07-27T11:28:38Z

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This is likely Qt trying to be too clever with rounding the scale factor...

[mixxxbot]

Commented by: ronso0
Date: 2021-07-27T11:57:11Z

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maybe QT_SCALE_FACTOR_ROUNDING_POLICY
https://bugreports.qt.io/browse/QTBUG-53022

[mixxxbot]

Commented by: mirh
Date: 2021-07-27T12:44:00Z

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You are spot on
https://bugreports.qt.io/browse/QTBUG-86344

EDIT: interestingly enough, while QT_SCALE_FACTOR_ROUNDING_POLICY=PassThrough managed to also do most of the trick, it neglected the size of the library fonts.

[mixxxbot]

Commented by: Holzhaus
Date: 2021-07-27T13:51:39Z

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We could use https://doc.qt.io/qt-5/qt.html#HighDpiScaleFactorRoundingPolicy-enum if we switched to Qt 5.14.

[mixxxbot]

Commented by: ronso0
Date: 2021-07-27T16:04:07Z

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isn't only Ubuntu requiring Qt 5.12? (in 2.3)
so #ifdef Qt <= 5.14 would fix it for Windows (macOS isn't affected IIRC)

@mirh
The library font can be set independently from the OS in Preferences > Library

I can't believe I can EDIT this comment..

[mixxxbot]

Commented by: mirh
Date: 2021-07-27T21:33:50Z

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I'm saying that forcing the scale factor still had an overall marginally better looking experience than the rounding policy.

Also, it is my understanding from the linked commits above that all platforms should be affected.. It's just that probably nobody has high hidpi expectations on linux /s

[mixxxbot]

Commented by: Be-ing
Date: 2021-07-29T02:09:45Z

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if we switched to Qt 5.14

We are already using Qt 5.15.2 on Windows. It is only macOS where we are stuck with Qt 5.12.

[mixxxbot]

Commented by: Be-ing
Date: 2021-07-29T02:12:42Z

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mirh, could you test setting the environment variable QT_SCALE_FACTOR_ROUNDING_POLICY=PassThrough before starting Mixxx from a command prompt? If this works well without odd looking artifacts we may consider setting the rounding policy to passthrough by default.
https://doc.qt.io/qt-5/qguiapplication.html#setHighDpiScaleFactorRoundingPolicy

[mixxxbot]

Commented by: ronso0
Date: 2021-07-29T10:06:46Z

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It is only macOS where we are stuck with Qt 5.12.

If we intend to fix this in a 2.3 point release it's not applicable to Ubuntu 20.04 builds because those are still using 5.12.8

[mixxxbot]

Commented by: Be-ing
Date: 2021-07-29T11:36:02Z

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That only affects Ubuntu LTS users. Other Linux distros are not stuck on Qt 5.12.

[mixxxbot]

Commented by: Holzhaus
Date: 2021-07-29T12:50:17Z

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I propose to add the fix inside a QT_VERSION_CHECK.

People using Ubuntu will have to live with the current scaling behavior, but it's actually a good thing. Stable distros are for users that don't want their system to change without a distro upgrade, so fixing the bug would be confusing and might break their workflows :D.

[mixxxbot]

Commented by: ronso0
Date: 2021-07-29T12:57:03Z

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I can't turn on the CPU fan with spacebar anymore :D

[mixxxbot]

Commented by: Be-ing
Date: 2021-07-29T13:17:13Z

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Yes, a QT_VERSION_CHECK is needed because Mixxx 2.3 still supports Qt 5.12.

[mixxxbot]

Commented by: Holzhaus
Date: 2021-07-29T13:49:25Z

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I can't turn on the CPU fan with spacebar anymore :D

Context: https://xkcd.com/1172/

[mixxxbot]

Commented by: daschuer
Date: 2021-07-30T23:14:28Z

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#4161

[mixxxbot]

Issue closed with status Fix Released.