D12405: [WIP] Per-screen scale factors on X11 using QT_SCREEN_SCALE_FACTORS

[Fabian Vogt]

fvogt added a comment.


  I just tried that here and it works fine (Qt 5.15.1). Maybe there's something 
else in the environment which breaks it?

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D12405: [WIP] Per-screen scale factors on X11 using QT_SCREEN_SCALE_FACTORS

[Carlos Pita]

memeplex added a comment.


  
  
  > It should work. Are you sure the screen names are correct and match? You 
can run `QT_LOGGING_RULES=qt.qpa.screen.debug=true konsole` to get the ones 
`konsole` itself sees.
  
  The names are correct, otherwise I guess it wouldn't have worked in any case.
  
[test@carlos ~]$ QT_LOGGING_RULES=qt.qpa.screen.debug=true konsole
qt.qpa.screen: EDID data for output "eDP-1": identifier 'TIANMA XM ---', 
manufacturer 'Telxon Corporation',model '', serial 'TL139GDXP01--', physical 
size: 290.00x200.00
qt.qpa.screen: Output DP-1 is not connected
qt.qpa.screen: EDID data for output "DP-2": identifier '', manufacturer 
'Samsung Electric Company',model 'U28E590-', serial 'H4ZN800234-', physical 
size: 610.00x350.00
qt.qpa.screen: Output HDMI-1 is not connected
qt.qpa.screen: adding QXcbScreen(0x55d7568ef4e0, name="DP-2", 
geometry=3840x2160+0+0, availableGeometry=3840x2160+0+0, devicePixelRatio=1.0, 
logicalDpi=QPair(192.0,192.0), physicalSize=608.0x345.0mm, screenNumber=0, 
virtualSize=6840x2160 (6840.0x2160.0mm), orientation=Qt::LandscapeOrientation, 
depth=24, refreshRate=24.0, root=7de, windowManagerName="KWin") (Primary: true )
qt.qpa.screen: adding QXcbScreen(0x55d7568beb70, name="eDP-1", 
geometry=3000x2000+3840+0, availableGeometry=3000x2000+3840+0, 
devicePixelRatio=1.0, logicalDpi=QPair(192.0,192.0), 
physicalSize=293.0x196.0mm, screenNumber=0, virtualSize=6840x2160 
(6840.0x2160.0mm), orientation=Qt::LandscapeOrientation, depth=24, 
refreshRate=60.0, root=7de, windowManagerName="KWin") (Primary: false )
qt.qpa.screen: primary output is "DP-2"

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D12405: [WIP] Per-screen scale factors on X11 using QT_SCREEN_SCALE_FACTORS

[Fabian Vogt]

fvogt added a comment.


  In D12405#676733 , @memeplex wrote:
  
  > So I set QT_SCREEN_SCALE_FACTORS='eDP-1=2;DP-2=1.7;'. But consider:
  >
  > 1. QT_AUTO_SCREEN_SCALE_FACTOR=1 
QT_SCREEN_SCALE_FACTORS='eDP-1=2;DP-2=1.7;' konsole
  > 2. QT_AUTO_SCREEN_SCALE_FACTOR=0 
QT_SCREEN_SCALE_FACTORS='eDP-1=2;DP-2=1.7;' konsole
  >
  >   The first one correctly reduces the size of konsole (menubar, text inside 
the terminal emulator). The second one does nothing at all.
  >
  >   So since plasma seems to be deliveratelt setting 
QT_AUTO_SCREEN_SCALE_FACTOR=0, I don't see how this would possibly work.
  
  
  It should work. Are you sure the screen names are correct and match? You can 
run `QT_LOGGING_RULES=qt.qpa.screen.debug=true konsole` to get the ones 
`konsole` itself sees.

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D12405: [WIP] Per-screen scale factors on X11 using QT_SCREEN_SCALE_FACTORS

[Carlos Pita]

memeplex added a comment.


  I'm not testing the proposed patch per se, but if it's only about  setting 
QT_SCREEN_SCALE_FACTORS it doesn't work for me as I would have expected.
  
  I have two screens, my laptop requires 2x scale, the external monitor 
requires about 1.7x.
  
  So I set QT_SCREEN_SCALE_FACTORS='eDP-1=2;DP-2=1.7;'. But consider:
  
  1. QT_AUTO_SCREEN_SCALE_FACTOR=1 QT_SCREEN_SCALE_FACTORS='eDP-1=2;DP-2=1.7;' 
konsole
  
  2. QT_AUTO_SCREEN_SCALE_FACTOR=0 QT_SCREEN_SCALE_FACTORS='eDP-1=2;DP-2=1.7;' 
konsole
  
  The first one correctly reduces the size of konsole (menubar, text inside the 
terminal emulator). The second one does nothing at all.
  
  So since plasma seems to be deliveratelt setting 
QT_AUTO_SCREEN_SCALE_FACTOR=0, I don't see how this would possibly work.

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D12405: [WIP] Per-screen scale factors on X11 using QT_SCREEN_SCALE_FACTORS

[Anthony Fieroni]

anthonyfieroni added a comment.


  I test, current situation, i don't think the parch is needed as is. 2 
monitors FullHD and 4K (HDMI) now KScreen does not allow different scale 
factor, to distinct monitor but you can changed config
  
[KScreen]
ScaleFactor=1
ScreenScaleFactors=eDP1=1;HDMI1=2;VIRTUAL1=1;
  
  That seems to work, but not well enough. When you move window from low res 
monitor to high res one window is scaled automatically, but it seems glitchy.

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D12405: [WIP] Per-screen scale factors on X11 using QT_SCREEN_SCALE_FACTORS

[Nathaniel Graham]

ngraham added a comment.


  Plasma now depends on Qt 5.14. Is there anything in there that would allow 
this to move forward?

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D12405: [WIP] Per-screen scale factors on X11 using QT_SCREEN_SCALE_FACTORS

[David Edmundson]

davidedmundson added a comment.


  There's some new env vars in Qt 5.14 to set a policy of what to do with DPI. 
Might be useful.

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D12405: [WIP] Per-screen scale factors on X11 using QT_SCREEN_SCALE_FACTORS

[Nathaniel Graham]

ngraham added a comment.


  Ok, thanks for the info. I'll excuse myself now since the technical 
discussion is way over my head. I just wanted to express support for the idea 
behind this patch.

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D12405: [WIP] Per-screen scale factors on X11 using QT_SCREEN_SCALE_FACTORS

[David Edmundson]

davidedmundson added a comment.


  The negative aspects of this patch are not related to whether Wayland exists.
  
  The negative aspects are that we have ui options that only affect a subset of 
applications, and merging this will make merging the patch to make plasma use 
Qt scaling a /lot/ harder. Possibly unfeasibly so.
  
  Also more importantly there's a big with font sizes in some setups to fix.

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D12405: [WIP] Per-screen scale factors on X11 using QT_SCREEN_SCALE_FACTORS

[Nathaniel Graham]

ngraham added a comment.


  We're past 5.14 and into 5.15 territory now. Does this deserve another look?
  
  My personal opinion is that it's not wise to under-invest in the X11 code 
while Wayland is still very much a work in progress. I get that it's 
frustrating to work on code that you know is going to be obsolete, but the time 
before that happens may be longer than we all think: we've been promising 
Wayland for years and it's still not at feature parity with X11, and on top of 
that there are many showstopping user-visible Wayland-specific bugs. I know for 
me personally it's unusable due to https://bugs.kde.org/show_bug.cgi?id=387156 
and https://bugs.kde.org/show_bug.cgi?id=387721 and 
https://bugs.kde.org/show_bug.cgi?id=384637 and 
https://bugreports.qt.io/browse/QTBUG-51640 and 
https://community.kde.org/Plasma/Wayland_Showstoppers#No_remote_support. I 
would love to use our Wayland session, but because of those issues, I just 
can't. I suspect a lot of users are in the same boat--many of them because of 
the NVIDIA situation. Realistically, most will not be running on Wayland until 
a distro makes it the default (like Fedora did with GNOME), which won't happen 
until there's feature parity with X11. In all likelihood, Wayland is not going 
to be a practical choice for a great many of our users for years. So it's not 
like X11-specific code is just totally worthless. That code is what most of our 
users rely on every day and would like to see improved.

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D12405: [WIP] Per-screen scale factors on X11 using QT_SCREEN_SCALE_FACTORS

[Fabian Vogt]

fvogt added inline comments.

INLINE COMMENTS

> gladhorn wrote in outputconfig.cpp:145
> Why not use QScopedPointer here?

I just moved the code from kcm/src/widget.cpp.

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D12405: [WIP] Per-screen scale factors on X11 using QT_SCREEN_SCALE_FACTORS

[Frederik Gladhorn]

gladhorn added inline comments.

INLINE COMMENTS

> outputconfig.cpp:145
> +connect(scaleDialogButton, ::released, [this] {
> +QPointer dialog = new ScalingConfig(mOutput, 
> this);
> +dialog->exec();

Why not use QScopedPointer here?

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D12405: [WIP] Per-screen scale factors on X11 using QT_SCREEN_SCALE_FACTORS

[Frederik Gladhorn]

gladhorn added a comment.


  I've been running with QT_SCREEN_SCALE_FACTORS set manually for at least half 
a year and it works for me. Except for suspending, so that seems to be a wide 
spread issue, maybe even in Qt. I'm strongly in favor of this, it is the only 
thing that works sensibly on xorg. Currently I haven't found a way to have one 
of the big browsers work with highdpi on wayland, so I'm stuck with X for the 
time being.

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D12405: [WIP] Per-screen scale factors on X11 using QT_SCREEN_SCALE_FACTORS

[Fabian Vogt]

fvogt added a comment.


  In D12405#257444 , @davidedmundson 
wrote:
  
  > The good:
  >
  > In one setup I was pleasantly surpised at how well it worked. Fonts did 
behave as expected. 
  >  Specatcle was able to capture all screens and individual rects correctly.
  >
  > The less good:
  >
  > When I switched round the primary monitor all through the GUI and rebooting 
I had a right mess. The @1x screen fonts were double the size, the @2x screen 
were 4x the size.
  >  In this setup spectacle had an issue with "current screen"  when it was on 
the non primary. I assume this problem: 
https://bugreports.qt.io/browse/QTBUG-64992  .
  
  
  That's possible - but unlikely: Except for the logical DPI difference the 
setups are identical.
  What happens with Xft.dpi: 96 and non-primary as 2x?
  
  > Possibly that's just a oneline fix wrt correct font DPI saving.
  
  Yup, that's the WIP part of this diff. Not sure how to do that though, as the 
code for this is in the frontend and not the (xrandr) backend.
  So if you unplug the primary monitor, newly started applications will behave 
strangely. But then again, this bug is in the current code as well:
  If you plug in a new monitor, the scale is 1 (never actually tried that).
  
  > Does this change make sense whilst Plasma is not using Qt scaling?
  
  It means that plasma uses the scale of the primary monitor (actually the font 
DPI, but that should be the same). So neither better nor worse than the current 
state.
  
  With Qt scaling, Plasma behaves as expected: Panels and menus scale depending 
on the monitor they're on. In exchange, some parts (like window tooltips) 
appear slightly misplaced.

INLINE COMMENTS

> davidedmundson wrote in outputconfig.cpp:143
> QPushButton*

Indeed, how did that build? Maybe the diff actually failed to build but I never 
noticed.

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D12405: [WIP] Per-screen scale factors on X11 using QT_SCREEN_SCALE_FACTORS

[David Edmundson]

davidedmundson added a comment.


  The good:
  
  In one setup I was pleasantly surpised at how well it worked. Fonts did 
behave as expected. 
  Specatcle was able to capture all screens and individual rects correctly.
  
  The less good:
  
  When I switched round the primary monitor all through the GUI and rebooting I 
had a right mess. The @1x screen fonts were double the size, the @2x screen 
were 4x the size.
  In this setup spectacle had an issue with "current screen"  when it was on 
the non primary. I assume this problem: 
https://bugreports.qt.io/browse/QTBUG-64992  .
  
  Possibly that's just a oneline fix wrt correct font DPI saving.
  
  Does this change make sense whilst Plasma is not using Qt scaling?

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D12405: [WIP] Per-screen scale factors on X11 using QT_SCREEN_SCALE_FACTORS

[Fabian Vogt]

fvogt updated this revision to Diff 33520.
fvogt added a comment.


  Fix build

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AFFECTED FILES
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  kcm/src/scalingconfig.cpp
  kcm/src/scalingconfig.h
  kcm/src/widget.cpp
  kcm/src/widget.h

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D12405: [WIP] Per-screen scale factors on X11 using QT_SCREEN_SCALE_FACTORS

[David Edmundson]

davidedmundson added inline comments.

INLINE COMMENTS

> outputconfig.cpp:143
> +} else {
> +QPushButton scaleDialogButton = new QPushButton(i18n("Scale 
> Display"), this);
> +connect(scaleDialogButton, ::released, [this] {

QPushButton*

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D12405: [WIP] Per-screen scale factors on X11 using QT_SCREEN_SCALE_FACTORS

[Fabian Vogt]

fvogt added a comment.


  > As for this patch. It needs Qt patches, so it's definitely not 5.13, 
possibly not even 5.14 material.
  > 
  > After 5.13.0 I'm willing to give this a fair test.
  >  If it indeed does work great, cool.
  
  That's a misunderstanding. The code here as-is works with Qt 5.6 and up.
  
  > However, I dont' want to merge something that replaces one set of bugs with 
a different set of bugs. The number of conflicting scaling approaches we have 
at once is becoming very difficult to manage.
  
  The mechanism is the same, it just uses more than one value for 
`QT_SCREEN_SCALE_FACTORS`.

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D12405: [WIP] Per-screen scale factors on X11 using QT_SCREEN_SCALE_FACTORS

[David Edmundson]

davidedmundson added a comment.


  As for this patch. It needs Qt patches, so it's definitely not 5.13, possibly 
not even 5.14 material.
  
  After 5.13.0 I'm willing to give this a fair test.
  If it indeed does work great, cool.
  
  However, I dont' want to merge something that replaces one set of bugs with a 
different set of bugs. The number of conflicting scaling approaches we have at 
once is becoming very difficult to manage.

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D12405: [WIP] Per-screen scale factors on X11 using QT_SCREEN_SCALE_FACTORS

[Fabian Vogt]

fvogt added a comment.


  > It is, for things that aren't Qt
  
  Yup. Just for Qt it's not required anymore.

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D12405: [WIP] Per-screen scale factors on X11 using QT_SCREEN_SCALE_FACTORS

[David Edmundson]

davidedmundson added a comment.


  > With https://bugreports.qt.io/browse/QTBUG-67928 fixed, the Xft.dpi setting 
code shouldn't be needed anymore either.
  
  It is, for things that aren't Qt

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D12405: [WIP] Per-screen scale factors on X11 using QT_SCREEN_SCALE_FACTORS

[Fabian Vogt]

fvogt added a comment.


  > -1 from here as well, it won't and it can't work reliably, it would be 
pretty much a false promise
  
  It does though.
  
  With https://bugreports.qt.io/browse/QTBUG-67928 fixed, the Xft.dpi setting 
code shouldn't be needed anymore either.

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D12405: [WIP] Per-screen scale factors on X11 using QT_SCREEN_SCALE_FACTORS

[Marco Martin]

mart added a comment.


  -1 from here as well, it won't and it can't work reliably, it would be pretty 
much a false promise

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D12405: [WIP] Per-screen scale factors on X11 using QT_SCREEN_SCALE_FACTORS

[Fabian Vogt]

fvogt added a comment.


  > I'm pointing out that I'm in general against any risky changes on X11. If 
users want to use this features: Wayland is there. KWin is feature frozen on 
X11 and I highly suggest to the Plasma community to decide the same at the 
sprint. We will have less maintenance issues due to it.
  
  Yes, but many can't or don't want to use Wayland.
  In fact, the machine where I tried this on last had to use the proprietary 
nvidia driver to work properly. The wayland session doesn't work, it just 
freezes (I'll try to have a look at that though).
  
  If I'm not mistaken scaling is currently broken on Wayland due to use of XCB 
as Qt's default platform.
  
  > I can promise you that this feature will create bug reports, it comes with 
a cost to add this on X11. While we have a almost finished Wayland solution 
which is hold back by among other developers still working on X11.
  
  Sure, but by setting the same scale on each screen you get the exact same 
behaviour as with the current state. I'd say that's as low risk as it can 
possibly be.

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D12405: [WIP] Per-screen scale factors on X11 using QT_SCREEN_SCALE_FACTORS

[Eike Hein]

hein added a comment.


  In principle I'm inclined to side with Martin here. At this point, I no 
longer want the extra burden/distraction of working on newly-introduced 
X11-related bugs. It's frustrating to spend manhours on code you know will be 
obsolete, and that delays getting work done to make it obsolete. I still have 
many scaling problems on Wayland that I think should be higher priority.
  
  I can't give a qualified assessment of the specific risk factor here though.

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D12405: [WIP] Per-screen scale factors on X11 using QT_SCREEN_SCALE_FACTORS

[Martin Flöser]

graesslin added a comment.


  I'm pointing out that I'm in general against any risky changes on X11. If 
users want to use this features: Wayland is there. KWin is feature frozen on 
X11 and I highly suggest to the Plasma community to decide the same at the 
sprint. We will have less maintenance issues due to it.
  
  I can promise you that this feature will create bug reports, it comes with a 
cost to add this on X11. While we have a almost finished Wayland solution which 
is hold back by among other developers still working on X11.

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D12405: [WIP] Per-screen scale factors on X11 using QT_SCREEN_SCALE_FACTORS

[Nathaniel Graham]

ngraham added a comment.


  +1 for not letting the perfect be the enemy of the good here. Multi-monitor 
support is a pain point for many of our users.

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D12405: [WIP] Per-screen scale factors on X11 using QT_SCREEN_SCALE_FACTORS

[Fabian Vogt]

fvogt added a comment.


  > So I wouldn't trust this thing in Qt to work due to the pain we have in 
KWin especially with these problems.
  
  Yes, it might not be perfect. It works well enough that not exposing this in 
the settings is a wasted opportunity though.
  I used this extensively for half a year with a 4k non-primary monitor, where 
the only other option is to meet halfway at 1.5x scale or move the screen so 
close that it's touching your nose.
  
  I doubt that users would expect this to work perfectly with any unusual 
configurations such as overlapping screens, but even then it's an improvement 
to the current situation.

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D12405: [WIP] Per-screen scale factors on X11 using QT_SCREEN_SCALE_FACTORS

[Martin Flöser]

graesslin added a comment.


  I also cannot imagine this to work due to the fact how X11 works. There is 
just no mapping from window to screen. No window can know on which screen it 
is. Not even KWin knows that as the window manager (screen is not a constant 
property, but evaluated every time it is accessed, it's based on the distance 
to closest screen). Especially for overlapping windows it's very difficult to 
try to get to which screen it belongs. It gets even more complicated when 
things like panning and overlapping screens get into it. So I wouldn't trust 
this thing in Qt to work due to the pain we have in KWin especially with these 
problems.

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D12405: [WIP] Per-screen scale factors on X11 using QT_SCREEN_SCALE_FACTORS

[Fabian Vogt]

fvogt added a comment.


  > Docs say QT_SCREEN_SCALE_FACTORS doesn't affect the logical DPI. which 
means you have a 1x scale on one screen 2x on another..they both have the same 
font size which will just be really wrong.
  
  Exactly that is not the case.
  
  Let me give you an example for broken font size: Screen "DP-0" has Scale 1 
and "DP-1" has scale 1. You set "Xft.dpi: 96". The result is 96 dpi font on 
DP-0 and 48 dpi font on DP-1.
  This can only happen if Qt scales the font DPI depending on the 
QT_SCREEN_SCALE_FACTORS values.
  
  Screenshot of a working setup: F5816419: image.png 


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D12405: [WIP] Per-screen scale factors on X11 using QT_SCREEN_SCALE_FACTORS

[David Edmundson]

davidedmundson added a comment.


  I can't imagine this working. It didn't when I've tried the same thing.
  Docs say QT_SCREEN_SCALE_FACTORS doesn't affect the logical DPI.  which means 
you have a 1x scale on one screen 2x on another..they both have the same font 
size which will just be really wrong.
  
  Also I bet spectacle's area selection is bust on at least one of the monitor 
variants. There's a whole lot of confusion (with no real right answer) as to 
what the size of a 1x monitor is in logical co-ordinates when your window is on 
the 2x screen and vice versa.

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D12405: [WIP] Per-screen scale factors on X11 using QT_SCREEN_SCALE_FACTORS

[Fabian Vogt]

fvogt created this revision.
fvogt added a reviewer: Plasma.
Restricted Application added a project: Plasma.
fvogt requested review of this revision.

REVISION SUMMARY
  Qt computes the scale factor relative to the primary screen. This means
  we can support per-screen DPI on X11 by setting QT_SCREEN_SCALE_FACTORS
  appropriately, while keeping Xft.dpi synced to the primary screen's DPI.
  This means applications which don't read QT_SCREEN_SCALE_FACTORS use the
  scale of the primary screen. This is a good compromise, especially for
  those who either need fractional scaling or can't use wayland for various
  reasons.
  
  WIP because this doesn't track changes of the primary screen and I'm not
  sure how to implement this the best way. The issue is that the
  QT_SCREEN_SCALE_FACTORS management is not done by the backend, but only by
  the KCM. Ideas welcome.

TEST PLAN
  VM with multihead QXL. I can now assign a per-screen scale in the KCM
  and after a relogin applications scale correctly based on the screen they're 
on.

REPOSITORY
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BRANCH
  perscreenxcb

REVISION DETAIL
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AFFECTED FILES
  kcm/src/outputconfig.cpp
  kcm/src/scalingconfig.cpp
  kcm/src/scalingconfig.h
  kcm/src/widget.cpp
  kcm/src/widget.h

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