https://bugs.kde.org/show_bug.cgi?id=391350
Bug ID: 391350
Summary: Shortcuts: Alt and Shift modifiers is not handled
correctly
Product: kwin
Version: 5.12.2
Platform: Neon Packages
OS: Linux
Status: UNCONFIRMED
Severity: normal
Priority: NOR
Component: input
Assignee: kwin-bugs-n...@kde.org
Reporter: v...@veqz.net
Target Milestone: ---
It seems the Alt+Shift modifiers do not work correctly together when using the
Tab key to walk through windows. I intiially assumed it was a hardware bug
(recently got a new laptop), but I have finally been able to get some details
of what is happening.
1.
I also have Alt+Shift set to walk through keyboard layouts. Alt+Shift+Tab is
never triggered because KWin has already triggered on Alt+Shift being pressed.
Disabling Alt+Shift to walk through keyboard layouts made Alt+Shift+Tab
function again.
The correct behaviour should be that Alt+Shift should only be triggerd when
those keys are released, and while just being pressed and held should function
as modifiers waiting for the next key to be pressed.
2.
A similar thing happens when cycling through tabs in applications.
2.1 Firefox
Ctrl+Tab will cycle through tabs, and works as it should. Ctrl+Shift+Tab
however, does not work. Holding Ctrl+Shift and hiting Tab appears to do
nothing. Continuing to hold Ctrl+Shift and hiting Tab again will bring the
focus to the address bar.
To correctly reverse cycle through tabs in Firefox, it is necessary to hold
Ctrl and hit Tab, to start the tab cycling process. By continuing to hold Ctrl
and now also holding Shift, it is possible to hit Tab to reverse cycle through
the tab list.
2.2 Kate
Holding Ctrl and hiting Tab will cycle through the open documents, as it
should. Holding Ctrl+Shift and hiting Tab, however, will start by cycling one
document forward, and then function as reverse cycling through documents.
3.
While experimenting with KWin's shortcut settings in System Settings, I noticed
a funny behaviour when trying to set a custom keyboard shortcut:
First pressing and holding Alt, and then pressing and holding Shift, will
display the shortcut as "Alt+Shift+...". A key combo like Alt+Shift+Tab can
then be set by hiting Tab.
However, by first pressing and holding Shift, and then pressing and holding
Alt, will display the shortcut as "Meta+Shift+..."! By hiting Tab it will
change to Alt+Shift+Tab again and work as before.
I don't know what is happening there, but I suspect there might be some bug in
the code which modifies Alt to appear as Meta. I'm including this here in case
it is related to the Alt+Shift bug. Utilising the Meta key in a combination
seems to make all three appear ("Meta+Alt+Shift+...").
4.
After looking through the bug tracker, I found several open, unconfirmed bugs
which I suspect are other symptoms of this bug:
- Alt + Shfit + <num> shortcut bug (2018)
https://bugs.kde.org/show_bug.cgi?id=391056
* kwin takes control over shortcut input and does not allow for "unshifting"
(2016) https://bugs.kde.org/show_bug.cgi?id=359206
- Keyboard layout switching ignores settings, sometimes it does not work at
all. (2016) https://bugs.kde.org/show_bug.cgi?id=370734
- Custom Alt+` shortcut brings up task switcher, but does not walk through
applications (2016) https://bugs.kde.org/show_bug.cgi?id=359141
- inconsistent behavior with alt+7 (2016)
https://bugs.kde.org/show_bug.cgi?id=365255
- Impossible to use AltGr as modifier (2016)
https://bugs.kde.org/show_bug.cgi?id=359146
- Remapping Num Lock with xmodmap breaks all Alt+* key shortcuts in KDE! O_OOO
(2015-2016) https://bugs.kde.org/show_bug.cgi?id=345816
- Shortcuts bound to F keys ignore state of ISO_Level3_Shift (2015)
https://bugs.kde.org/show_bug.cgi?id=357127
- Keyboard input shortcut keys do not work (2015)
https://bugs.kde.org/show_bug.cgi?id=348456
- Broken canvas input shortcut naming when pressing keys used to switch
keyboard layouts (2014-2017, Confirmed)
https://bugs.kde.org/show_bug.cgi?id=333431
- when connecting to a remote host, some modifier key (shift, or alt) is
permanently pressed (2014-2016) https://bugs.kde.org/show_bug.cgi?id=329951
- Ambigous shortcut detected with pressing Ctrl+Shift+w (2013-2017, Confirmed)
https://bugs.kde.org/show_bug.cgi?id=319172
- Keyboard shortcuts doesn't work if non-english keyboard layout is set before
english one (2012-2018, Confirmed) https://bugs.kde.org/show_bug.cgi?id=309193
- custom shortcuts: send keyboard input does not work for keys requiring AltGr
(2012-2018) https://bugs.kde.org/show_bug.cgi?id=295633
- Walk Through Windows (Reverse) does not work (2012-2017, Kde4+5)
https://bugs.kde.org/show_bug.cgi?id=294249
- Unsupported Key message when adding a custom Alt+Shift+<key> shortcut
(2012-2013) https://bugs.kde.org/show_bug.cgi?id=294245
- Alt-Tab menu cannot use Alt-Shift-Tab for going back through the list of
windows? (2008-2015, Fixed) https://bugs.kde.org/show_bug.cgi?id=174142
- some keyboard shortcuts don't work (2008, To be closed)
https://bugs.kde.org/show_bug.cgi?id=159063
5.
Technical info:
OS: KDE neon 5.12
Plasma: 5.12.2
Frameworks: 5.43
Qt: 5.10.0
Occurs on both X11 and Wayland
6.
Further thoughts:
The keyboard shortcut to walk through windows in reverse is listed as
"Alt+Shift+Backtab" in System Settings. Shouldn't this just be "Alt+Shift+Tab"?
Is there a translation between "Shift+Tab" and "Backtab" somewhere in the code?
After having read lots of these bug reports and the comments in them, I have a
hunch that there is a problem with how modifier keys are handled in the code.
Somehow there is some mixup between KeyPress, KeyRelease, and the different
modifier checks. Or a bug in Qt itself. There was a lot to go through though,
and I've never work with Qt, so I might very well have missed something as
well.
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