https://bugs.kde.org/show_bug.cgi?id=442901
hkz85825...@gmail.com changed:
What |Removed |Added
----------------------------------------------------------------------------
Resolution|UPSTREAM |---
Status|RESOLVED |REOPENED
--- Comment #18 from hkz85825...@gmail.com ---
I don't think the issue has been fixed on GTK's side, I still have 400% scaled
text while using the latest version of GTK (4.6.7), and there doesn't seem to
be any code mentioning `GDK_DPI_SCALE` in GTK's repo. Perhaps your Xft.dpi has
been changed to 96 for some reason? That would make text on GTK 4 apps appear
correct, but GTK 3 apps would then have tiny text because of the
`GDK_DPI_SCALE=0.5` set by `startplasma-*.cpp`.
I went through some digging in the GTK codebase and fiddling in a VM running
GNOME 4 X11 set to 200% scale, here are my findings:
1. This is where GTK 3 used to read `GDK_DPI_SCALE`, and it hasn't come back
since GTK 4.
https://github.com/GNOME/gtk/blob/e670720d196bac1cef6f88313f6514cdd8c4a0c5/gdk/x11/xsettings-client.c#L495
2. This is where `GDK_SCALE` is read in both GTK 3 and 4. Note that the flag
`x11_screen->fixed_window_scale` will then be set to true.
https://github.com/GNOME/gtk/blob/d3ffc0c3bb72cddf57b564c0ac31c70f7bc8e504/gdk/x11/gdkscreen-x11.c#L892
3. GNOME doesn't set either of the environment variables `GDK_SCALE` or
`GDK_DPI_SCALE`, but instead provides the scaling information with GNOME
Settings Daemon, through an XSettings value `Gdk/WindowScalingFactor`, which is
set to 2. This code seems to be responsible for reading it, which is only run
when `x11_screen->fixed_window_size` is false, meaning the XSettings value is
ignored when `GDK_SCALE` is set, so far so good.
https://github.com/GNOME/gtk/blob/e670720d196bac1cef6f88313f6514cdd8c4a0c5/gdk/x11/xsettings-client.c#L506
4. GNOME also seems to set the Xrdb value Xft.dpi to 192, but doesn't have
giant text. The reason is probably the code here. GTK reads another XSettings
value `Gdk/UnscaledDPI` which is 98340, and overrides `Xft/DPI` which was
196608 on the client side.
https://github.com/GNOME/gtk/blob/e670720d196bac1cef6f88313f6514cdd8c4a0c5/gdk/x11/xsettings-client.c#L452
This is like having a GTK-specific override for the Xrdb value `Xft.dpi` to be
96. This works with both GTK 3 and 4. I think this is exactly what we want: We
want to have all other apps see Xft.dpi being 192, but GTK 3 and 4 to see 96,
so that we wouldn't need the defunct `GDK_DPI_SCALE` environment variable, it's
what GNOME does. The only caveat being, `Gdk/UnscaledDPI` is only used when
`x11_screen->fixed_window_scale` is false, i.e. when `GDK_SCALE` is not set.
But Plasma sets it.
xsettingsd is already used by KDE GTK Configurator, so I manually added
`Gdk/WindowScalingFactor 2` and `Gdk/UnscaledDPI 98340` to
`~/.config/xsettingsd/xsettingsd.conf`, sent SIGHUP to xsettingsd, then restart
a GTK 3 or 4 app while having `GDK_SCALE` and `GDK_DPI_SCALE` unset. I then
finally have correctly scaled text and UI for all of GTK 3, 4, Qt, GLFW!
There doesn't seem to be a way to unset a environment variable set by Plasma
through a script in `~/.config/plasma-workspace/env` though, so I can't find an
elegant workaround. Perhaps this should be made the default for Plasma, ditch
`GDK_SCALE` and `GDK_DPI_SCALE` from `startplasma-*.cpp`, and instead let KDE
GTK Configurator tell xsettingsd to provide the 2 aforementioned XSettings
values.
I've only explored things on X11, so I don't know about Wayland (probably more
complex with their different scales for each screen?).
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